ATOLL RESEARCH BULLETIN NO. 369 CHAPTER 5 SPECIES COMPOSITION, DISTRIBUTION AND ABUNDANCE OF ALGAE AND SEAGRASSES OF THE SEYCHELLES ISLANDS BY A. A. KALUGINA-GUTNIK, L. P. PERESTENKO AND T. V. TITLYANOVA ISSUED BY NATIONAL MUSEUM OF NATURAL HISTORY SMITHSONIAN INSTITUTION WASHINGTON, D.C., U.S.A. June 1992 CHAPTER 5 SPEC= COMPOSITION, DISTRIBUTION AND ABUNDANCE OF ALGAE AND SEAGRASSES OF THE SEYCHELLES ISLANDS *** A.A. Kalugina-~utnik*, LP. ~erestenko** and T.V. Titlyanova INTRODUCTION Marine algae and seagrasses of the Republic of the Seychelles remain poorly studied. Macrophytic algae reported for the area (about 120 species) were collected between 1899-1990 by J. Stanley Gardiner during'the Sealark Expedition to the Indian Ocean (Gepp and Gepp 1909; 1911, Weber van Bosse 1913a, 1913b). Aleem (1984) reported 9 species of seagrasses and 22 algal species for the macrophyte communities of MahB, Latam, Aldabra, Comoro, Farquhar and Amirantes Islands. Subsequently, 5 seagrasses and 33 algal species were recorded (Titlyanova and Butorin 1987) for MahB and Wetivy Islands, half of these representing new records. There are no data on either algae or seagrasses for 12 of the Seychelles island groups. The present study of these island groups focused on: (1) macrophytic species composition; (2) distribution of algae and seagrasses at different depths for typical ecotopes; and (3) the structure of benthic plant communities (phytocoenoses), including determination of biomass for macroalgae and seagrasses. METHODS AND MATERIALS Studies were conducted at Wetivy Atoll, Desroches, African Banks, Providence, Farquhar Atoll, Aldabra Atoll, St. Joseph Atoll, Cosmoledo Atoll, Astove Atoll, MahB, Praslin and La Digue Islands. Quantitative and qualitative samples were collected using transects and square quadrats from the upper intertidal zone to a depth of 30-50 m, using a combination of snorkle and SCUBA diving techniques. In each intertidal horizon, four 25 x 25 cm quadrats were selected and sampled in representative habitats with vegetation coverage averaging 10-15%. In the subtidal zone, one 50 x 50 cm quadrat was harvested at each station. A total of 687 samples (479 quantitative harvest samples) were taken at 257 stations. Vegetation was described for 28 intertidal and 37 subtidal transects. About 4000 plant specimens were collected and duplicates are deposited in the herbaria of all three authors' institutions. Altogether, 327 algal species and 8 seagrass species were documented for the 12 island systems (Table 1). Intertidal zones were surveyed during periods of low water at which time type of substratum, bottom relief, vegetation coverage and the width of vegetation belts were determined. Laboratory Institute of South Seas Biology, USSR Academy of Sciences of the Ukraine, Sevastopol, USSR ** Botanical Institute, USSR Academy of Sciences, Leningrad, USSR *** Institute of Marine Biology, Far East Branch, USSR Academy of Sciences, Vladivostok, 690032, USSR processing included determination of the population density (individuals-m-2), wet biomass (gmm2), plant height and species composition. Macroalgae were identified using the following works: Bt#~rgesen (1914, 1915, 1916, 1917, 1918, 1919, 1920, 1940, 1941, 1942, 1943, 1944, 1945, 1946, 1948, 1949,1950,1951,1952,1953,1954,1957), Cordero (1977), Colinvaux (1968), Dawson (1954), Durairatham (1%1), Egerod (1975), Hartog (1970), Hillis (1959, 1980), Kraft (1986), Misra (1%6), Olsen-Stojkovich (1985), Pham-Hoang Ho (1967, 1969), Tanaka and Pham-Hoang Ho (1962), Taylor (1%0) and Valet (1%9). The structure of phytocoenosis (community associations) was analyzed with the use of the Shannon species diversity index (Wilhm 1%8), where: H - species diversity of a sample; Wi - biomass of the i-th species sampled (gm-2); W - total biomass of the sample (g.m-2) and s - number of species in the sample. At H = 0 - 0.8 the phytocoenosis structure was considered to be monodominant; at H = 0.9 - 1.5 - oligodominant and at H > 1.5 - polydominant. The Seychelles islands surveyed can be divided into three groups by their structure and the type of bottom vegetation. The first group includes: CC)etivy, Desroches, African Banks and Providence; the second: Farquhar, Aldabra, St. Joseph and D'Arros, Cosmoledo and Astove; and the third: Mahe, Praslin and La Digue. CtJetivy, Desroches, African Banks and Providence are calcareous and fringed with barrier reefs. Farquhar, Aldabra, St. Joseph and D'Arros, Cosmoledo and Astove are atolls with shallow sand lagoons and sand banks exposed at low waters. On their ocean sides, these atolls are fringed with a broad (250-1000 m) reef-flat, pre-slope platform and reef slope. The intertidal zone of these islands is mostly wide (100-1000 m), sloping and uniform in structure. The upper and the middle horizons of the intertidal zone consist of sand. The lower horizon is sandy with pits, or built of dead consolidated corals covered with sand. The subtidal zone has different relief and substrata: the upper reef edge is sandy. The reef edge is built of coral plates and blocks above a steep sandy slope covered with dead corals with live coral colonies. The upper intertidal horizon is usually devoid of vegetation; a wide belt of seagrasses spreads from the middle horizon of the intertidal zone down to depths of 15-20 m. Greater depths are occupied by Halimeda communities. CC)etivy is the most thoroughly studied island in the first group. Mahe, Praslin and La Digue, the third group, are high granitic islands with numerous inlets and are fringed by narrow reefs. Vegetation of the carbonate islands (groups 1 and 2) is dominated by seagrasses, and red and green algae. While on these granitic islands, brown algae (Phaeophyta), mostly Sargassum, predominate in plant communities along with seagrasses. RESULTS AND DISCUSSION Chtivy Island The benthic vegetation was surveyed along nearly the entire coastline (Fig. 1) and showed uneven distributional patterns. At the northern point of the island, the intertidal zone is narrow (5- 10 m in width), sandy and devoid of vegetation. Macrophytic growth begins at a depth of 2-3 m, a distance of 100-150 m from the shoreline. The southernmost intertidal zone is broad (500-1000 m in width) with numerous intertidal pools at low waters. Along the eastern and western coasts, the intertidal zone does not exceed 500 m in width. Settlements of Enteromorpha kylinii sometimes occur on individual coral blocks in the upper intertidal horizon. The middle horizon is occupied by the seagrasses Syringodium isoetifolium, Halodule uninervis and Thalassodendron ciliatum (Fig. 2, Table 2) characterizing the major associations (or phytocoenoses, characterized by dominant species). The species composition of these associations is limited, including among the dominant species, Jania adhamens, @pnea pannosa, Diciyosphaeria setchellii, BoaIlea composita and Halimeda gracilis. The lower intertidal horizon is dominated by Thalassodendron ciliatum. Halimeda gracilis, H. stuposa, H. micronesica, Dictyurus purpurascens and Laurencia sp. are subdominants in all associations dominated by T. ciliatum. Dense mats of Gelidiella acmosa, Laurencia parvipapillata, L. paniculata and Halimeda opuntia develop at the stem bases and on the rhizomes of T. ciliatum, while the stems are populated by the algal epiphytes Haloplegma dupereyi, Gelidiella myrioclada, Champia parvula, Ceramium fastigiatum, Lophosiphonia villum, Poiysiphonia sp. and Centrocmas apiculatum. Among the other organisms noted were Dictyosphaeria cavernosa, D. setchellii, Caulerpa sertularioides, Udotea argentea, U. orientalis, Laurencia obtusa, Dictyurus purpurascens, Jania ungulata and Valonia aegagropila. Scattered individuals of Lobophora variegata and lkrbinaria ornata occur on the reef edge. 'helve associations were distinguished in the intertidal zone (Table 2), ranging in structure from mono- to oligo-dominant (i.e., H = 0 - 0.8 and 0.9 - 1.6, respectively) with well developed plant coverages ranging from 70-100%. In the sublittoral zone, associations of Thalassodendron ciliatum - Halimeda dominate the sandy reef slope among coral debris (Fig. 2). Biomass of these two dominant species contributes 80-100% to the association (Fig. I), which includes almost all the species recorded for the lower intertidal horizon. In addition, Rhipilia tomentosa, Heterosiphonia sp., Lophocladia trichoclados, Grimhsia subcylindrica, Chlorodesmis comosa, Kh1l)menia sp., Coelarthm boergesenii, Tricleocarpa oblongata, Liagora divaricata and Botlyocladia skottsbergii were also found. The lower border of the association extends to a depth of 15-20 m with isolated specimens of T. ciliatum occuring to depths of 30-33 m. One of the most prominent species of subtidal coenoses is Halimeda opuntia. Off the southwestern border of the island, phytocoenoses of Halimeda appear at 1-m deep on the sand plateau and extend down to depths of 30-50 m and over vast areas. The biomass of Halimeda increases from 429 to 5078 gmv2 at depths between 1-5 m (Table 2; Fig. 1; Stations 15-20). Species composition of the phytocoenosis is limited, with the associated species being T. ciliatum, Lobophora variegata, Caulerpa cupressoides, Haloplegma duperreyi, Dictyurus pupurascens and Hetmosiphonia sp. At depths of 30-50 m, dominants wereAvrainvillea amadelpha f. submersa, Halimeda copiosa, Caulerpa sp., Dasya sp., Struvea elegans, Antithamnion sp., Chtysymenia pynYormis, Peyssonnelia sp. and Anadyomene wrightii. The associations are characterized by a monodominant structure with sparse and low-statured vegetation coverage (Table 2). The H index of species diversity ranges mainly from 0 to 0.7, but in some phytocoenoses it exceeds 1.0 (Table 2). The distributional pattern of common species of algae and seagrasses around Cetivy is shown in Figure 3. The lower intertidal horizon and the upper sublittoral horizon down to a de th of 7-10 m e2 (Fig. 4) show the greatest biomass of macrophytes (mean of 30% k 393 S.D. gnm- ). Ranking second in biomass (1597 k 272 g-m-2) are phytocoenoses at 10-20 m in depth along the eastern coast and in the lower intertidal zone of the southern end of the island. Closest to the shore, within the middle horizon of the intertidal zone, the mean biomass of macrophytes is 878 k 306 g-m-2. The lowest biomass (557 k 157 was found at greater depths. The total area of algal and seagrass growths around Coetivy Island is approximately 13,190 ha, with an estimated total standing stock of 1%,316 t wet weight. On average, 1 ha supports 15 t phytomass. Altogether, 113 plant species were found at Coetivy, 4 of which are seagrasses. The 109 algal species include 58 Rhodophyta, 46 Chlorophyta, 4 Phaeophyta and 1 Cyanophyta (Table 1). Desmhes Island The marine benthic vegetation of the island was studied in considerable detail (Figs. 5-7). The upper intertidal zone is similar to that of Coetivy Island. An association of Thalassia hemprichii with Potolithon gardineri forms in the middle horizon. The phytocoenosis is oligodominant in structure, vegetation coverage averages 80-100%. Population density and biomass do not exceed 1536 individuals-m-2 and 2471 respectively (Table 2). Among the associated species, Udotea orientalis, Caulerpa cupressoides, C. semlata, Dictyosphaeria cavernosa and Jania capillacea are common. In the lower intertidal horizon, Thalassodendron ciliatum forms three associations (characterized by their dominant species): Thalassodendron ciliatum + T. hemprichii - Halimeda micronesica, T. ciliatum - Halimeda opuntia and T. ciliatum alone. Biomass of T. ciliaturn accounts for 60-100% of the total biomass of the three phytocoenoses (Fig. 5). Population density and biomass are high, up to 2600 indi~idua1s.m.~ and 5095 g.m-2 (Table 2), respectively. The stalks of Thalassodendron ciliafum are densely overgrown with epiphytes. The most common associated species are Laurencia parvipapillata, L. papillosa, Dasya mollis, Dictyurus purpurascens, Smtvea anastomosans, Haloplegma duperreyi, Hypnea esperi, H. spinella, Gelidiella lubrica, G. myrioclada, Hetmsiphonia crispella, Jania capillacea, J. ungulata, Dictyosphaeria cavemosa, D. vmslyusii, Caulerpa semlata, C. cupressoides, Valonia aegagropila, V: fastigiata and Halimeda stuposa, with Laurencia, Jania and Halimeda forming mats. In terms of depth of habitat, community structure, species composition and the main quantitative characteristics, subtidal associations of Thalassodendron ciliatum-Halimeda at Desroches Island do not differ appreciably from corresponding associations at metivy Island (Table 2). In addition to species that were also common on CC)etivy Island, we found Neomeris bilimbata, Caulerpa mericana, Halymenia sp., Liagora pennata, Galaxaura maqinata, llkleocarpa oblongata, G. rudis, Haliptilon subulafum and Lomentaria mauritiana. In the depth range between 15-20 and 35-38 m, a steep cliff partly fringing the island is covered with sparse algal growths. Below the cliff, a Halimeda phytocoenosis extends to a depth of 50 m (Table 2), with high species diversity of associated algae, most of them being common in the upper subtidal and lower intertidal zones. Typical of these deep waters were Avrainvillea amadelpha f. submersa, Halimeda copiosa, H. tuna, Dudresnaya sp., Caloglossa sp., IIypoglossum sp. and Caulerpa mericana. Altogether, 132 plant species, including 3 seagrasses and 129 algal species (72 red algae, 50 green algae, 5 brown algae and 2 blue-green algae) were collected near Desroches Island. In general, the bottom vegetation of Desroches Island is characterized by relatively high quantitative indices (Fig. 8). The total area covered by benthic vegetation is about 711 ha and supports about 16,581 t wet plant biomass. African Banks The South Island's lower intertidal and upper subtidal zones (Figs. 9-11) are characterized by associations of Thalassia hemprichii + Thalassodendron ciliatum - Microdictyon montagnei. Thalassodendron ciliatum is responsible for 40-100% of the total biomass of all phytocoenoses (Fig. 9). In the subtidal zone, this association is replaced by the T. ciliafum association which extends along the slope of the reef down to a depth of 20-25 m. The population density and biomass in the T. ciliatum association is significantly lower than on Cetivy and Desroches Islands (Table 2). Common associated species were Halimeda micronesica, H. sfuposa, H. pacilis, H. macroloba, H. opuntia, Dictyosphaeria cavernosa, D. verluysii, Rhipilia tomentosa, Anadyomene plicata, Struvea anastomosans, Tricleocapa oblongata, Haloplegma duperreyi and Lobophora variegata. The deep- water association of Halimeda sp. (25-37 m) is characterized by a rich species diversity of associated algae similar to that near Desroches Island. Most characteristic were Halimeda stuposa, H. micronesica, Caulerpa cupressoides,Avrainvillea amadelpha f. submersa and Udotea orientalis. Several species were found only at the 37 m depth (Station 200): Halophila stipulacea, Caulerpa sp., Boergesenia forbesii, Boodleopsis pusilla, Anotrichium tenuis, Galaxaura rudis and Chrysymenia p r o m i s . Zjdemania gardinen', Halophila stipulacea and Anadyomene plicata were found only near South Island. Altogether, 84 plant species were collected near South Island: 3 seagrasses and 81 algae (47 red algae, 31 green algae, 3 brown algae and 3 blue-green algae). Providence Atoll The interdidal zone of the southern coast of Cerf Island (Fig. 12,13) is sandy, almost devoid of vegetation, with scattered coral debris covered by Enteromopha clathrata. The distribution of plant communities in the subtidal zone was typical of the other islands of this group. At a depth of 20-23 m, the Thalassodendron ciliafum association is replaced by communities dominated by Halimeda gracilis extending the down to 32 m (Table 2). Thalassodendron ciliafum associates include Microdictyon montagnei, Herposiphonia secunda f. tenella, Dictyurus purpurascens, Griffithsia subcylindrica and Cottoniella arcuata. The Halimeda communities included Halimeda micronesica, Micrdiciyon montagnei, Valonia fastigiata, Caulerpa brachypus, Tricleocapa oblongata, Galaxaura rudis and other minor species. Two seagrass species and 58 algal species (40 red algae, 16 green algae and 2 brown algae) were collected near Cerf Island. The intertidal vegetation of islands of the first and second groups is similar in structure and distribution. The upper, and sometimes mid-tidal horizons, are devoid of plant coverage. The middle and lower in ter t idal horizons suppor t associat ions of Thalassia hemprichii + Thalassdendron ciliafum. In the lower intertidal and subtidal horizons, this association is replaced by communities of T. ciliafum and green algae, which become more frequent in all phytocoenoses compared with those of the islands of the first group. Farquhar Atoll At Farquhar Atoll, Thalassia hemprichii + Thalassodendron ciliatum associations of North Island, South Island, Bird Island and the lagoon (Figs. 14-17) had moderate population densities and biomasses (Fig. 15, Table 2). Plant coverage near South Island ranges from 5 to 40% and 100% near North Island. Macrophyte associations include Boodlea struveoides, Valonia aegagropila, Cladophoropsis sundanensis, Diciyosphaeria cavemosa and D. verluysii. The green algae Cladophora socialis and B. sfruveoides form monodominant intertidal phytocoenoses. Boodlea sfruveoides, Caulerpa cupressoides and Valonia aegagropila are included as subdominant species in both the Thalassdendron ciliafum - B. struveoides and T. ciliatum - K aegagropila - C. cupressoides (Table 2) plant associations. The phytocoenoses also include Microdictyon okamurai, Dictyosphaeria cavernosa, Cladophoropsis sundanensis, Jania adhaerens, J. ungulata, Gelidiella pannosa, G. rnyrioclada, G. Iubrica, Lophosiphonia villum, Ceramium fastigiatum and Hypnea esperi. Haloplegma duperreyi, Liagora ceranoides, Laurencia papillosa, L. obfusa and Lobophora variegata are epiphytic on the stems of T. ciliafum at the reef edge. The subtidal zone vegetation is poorly developed on the reef slope, because abundant coral populations extend almost to the reef-front. The following phytocoenoses were distinguished at depths of 3-17 m: Caulerpa cupressoides + Boodlea struveoides, Halimeda opuntia + C. cupressoides and Thalassodendron ciliatum - Halimeda. With increasing depth these were replaced by phytocoenoses of M. okamurai + B. struveoides, Microdicfyon and Udotea + Caulerpa (Table 2). Plant coverage ranges from 5 to 90%, but more often 5-30%. The height of vegetative cover is not great (1-2, seldom more than 1 cm) and the biomass is small (261-520 g.m-2). Species richness of algae in the subtidal zone is low, and does not change with depth. Such species as M. okamurai, C, cupressoides, B. struveoides, H. opuntia and Struvea anastomosans, are widespread at 35 m. The epiphytes Haloplegma dupeweyi, Jania ungulata, Gelidiella myrioclada, G. lubrica, Gnmhsia subcylindiica, G. metcalfii, Heterosiphonia &pella and Lophocladia nichoclados inhabit the stems of T. ciliatum. Turbinaria omata and Lobophora variegata also occur but are rare. Sargassum ilicifolium was found between 1-4 m deep on a sunken vessel at the southwestern end of the atoll representing the only low island location where the genus occurred. Ulva rigzda, Boodlea struveoides, Dictyosphaena cavemosa, Struvea anastomosans, Cladophora laetevirens, Dictyopteris delicatula, Padina sp., Sphacelaria rigidula, Gelidium pusillum, Jania ungulata, Iiypnea espen and H pannosa occurred with the Sargassum. The vegetation of the lagoon is considerably richer than that of the outer reef slope. It is characterized by the Thalassodendron - Halimeda phytocoenosis (Figs. 14-17; Table 2). The central part of the lagoon is covered with sand and corals and is devoid of vegetation. In the southern region of the lagoon, sites with Thalassodendron ciliatum phytocoenoses are rare. The belt of Thalassia hemprichu + T. ciliatum, including species of Laurencia and Halimeda, runs along the northwestern reef edge. Northern and western parts of the lagoon are occupied by dense populations of T. ciliatum, which is responsible for 60-95% of the plant biomass. Halimeda opuntia, Caulerpa cupressoides and Microdicfyon okamurai are community subdominants. Halimeda gracilis, Caulerpa serrulata, C. peltata, C. racemosa, C. msricana, Valonia aegagropila, M l e a struveoides, Laurencia obtusa, L. papillosa, Iiypnea esperi, Jania ungulata, J. capillacea, Centroceras apiculatum, Ceramium fastigiatum and Gelidiella lubrica are of frequent occurrence. At Farquhar Atoll, an estimated 195,139 t of benthic phytomass occupies an area of 10,085 ha. Altogether near Farquhar Atoll, 2 seagrasses and 115 algal species (including 66 red, 39 green, 7 brown and 3 blue-green species) were found. Aldabra Atoll The structure of the Aldabra Atoll differs considerably from some of the other island groups, since its coasts are built primarily of dead consolidated corals and are steeply undercut and overhang the water. Surveys were conducted mostly on the western coast of the atoll near Bua Passage in the lagoon and on the outer part of the reef, as well as the southeastern parts of the atoll (Figs. 18-20). A polydominant association of Thalassodendron ciliatum - Thalassia hemprichu - Halimeda forms in the lower intertidal horizon (Table 2). Thalassodendron ciliatum is responsible for 40-90% of the community biomass, while T. hempnchii, Halimeda opuntia, Caulerpa cupressoides and Laurencia combine to contribute 60-10%. In addition to the above species, the phytocoenosis includes Laurencia, Hypnea and Jania species forming dense mats. The stems of T. ciliatum are overgrown with epiphytes, including Ulva rigida, Hypnea esperi, Dasya mollis, Dictyuruspurpurascens, Heterosiphonia sp., and occasionally Lobophora variegata and Synngodium isoetifolium are present. At the lower border of the intertidal zone, the association of Thalassodendron - Thalassia - Halimeda is replaced by a T. ciliatum association which forms a belt 400-500 m in width along the entire western coast. On the reef slope, T. ciliatum populations disappear at 10 m in depth on a sandy bottom with abundant dead coral debris. The most common associated species are Ulva rigida, Halimeda opuntia, H. tuna, H. gracilis, H. micronesica, Lobophora vanegata, Turbinaria ornata, Spyridia filamentosa, Acanthophora spicifera, Dasya mollis, Caloglossa adnata and species of Cmamium, M n e a and Gelidiella. Wurdemannia miniata, Gelidiella myrioclada and Ulva rigida grow on the stems of T. ciliatum. Depths to 12-35 m are occupied by simple monodominant phytocoenoses of Halimeda. These phytocoenoses include a considerable number of species similar to that of the T. ciliatum association. Additionally, Chlorodesmis comosa, Avrainvillea amadefpha f. submmsa, Acetabularia parvula, A. clavata, Boergesenia forbesii and Chondria polyrhiza occur here. The lagoon is connected with the ocean by the Bua Passage (depth of 5-6 m). The passage bottom is swept by strong currents and is hard and sandy with settlements of black gorgonians. Often the dead coral debris is populated by extensive growths of Thalassodendron ciliatum (Station 93). Thalassodendron leaves and stems are devoid of epiphytes, probably because of the strong current in the passage. Seagrass growths spread into the lagoon and occupy a zone 600-800 m from the shore where the depth decreases sharply. On shallow intertidal areas of the lagoon, vegetative coverage is composed of numerous assemblages, the most common of which is a phytocoenosis dominated by S ' i a jilamentosa. A phytocoenosis of Thalassia - Halimeda occupies the area near the coast along the northern part of the lagoon (Fig. 18; St. 90; Table 2). Opposite the passage, phytocoenoses of Turbinaria - Halimeda (St. 91) and Thalassodendron - Laurencia - Halimeda (St. 89) are present. Plant communities of the lagoon have oligo- to polydominant structures, mosaic patterns of the phytocoenoses and rich macrophyte compositions. Near Aldabra Atoll, 4 seagrass species and 119 algal species (i.e., 73 Rhodophyta, 40 Chlorophyta, 4 Phaeophyta, and 2 Cyanophyta) were collected. Cosmoledo Atoll The bottom vegetation of the reef slope and lagoons was surveyed at depths from 4 to 42 m near Wizard and Pagoda islands (Figs. 21,22). The vegetative coverage at 4-20 m depths is poorly developed and consists of separate groups with dominants consisting of species of Laurencia, Turbinaria, Galaraura, Caulerpa and Boodlea. Below 20 m, Halimeda, Microdic&w and Avrainvillea species predominate (Table 2). Thalassodendron ciliatum, Microdictyon and Avrainvillea species predominate (Table 2). Thalassodendron ciliatum phytocoenoses, common in the majority of the atolls surveyed, were not found in the subtidal zone. Most of the species found at this coastal site occur at all depths examined and do not reveal any definite regularity in vertical distribution. The following species were found rarely or for the first time: Neomeris vanbosseae, Caulepa webbiana, C. sp., Acetabularia pusilla, Mesophyllum mesomorphum, Hydrolithon breviclavium, Wrangelia argus, Cmamium huysmansii, Sphacelaria tribuloides and Phaeophila dendroides. The lagoon contains a rich vegetative cover. The vast sandy shallow water areas between the islands Wizard and Polit and the coastal zone of Wizard are occupied by an association dominated by Halodule uninervis. An association of Thalassia + Qnodocea is situated somewhat farther from the shore. An association dominated by Thalassodendron ciliatum - Laurencia was found between 0.4- 5.5 m in depth. The central and western parts of the lagoon are occupied by an association of T. ciliaturn - Halimeda opuntia (Table 2). The coenobionts Laurencia papillosa, Caulerpa racemosa, C. cupressoides, C. sp., Microdictpn okamurai and Chaetomorpha capillare are typical members of the association. The species composition of the lagoon algae is uniform and includes mostly green algae. In addition to the above mentioned species, Boergesenia forbesii, Dictyosphaeria cavernosa, NeomeTis annulata, Lobophora variegata and Haloplegma duperreyi were found here. Cosmoledo Atoll contained 4 seagrass species and 106 algal species, including 60 red, 42 green and 6 brown algae. St. Joseph Atoll The southern coast of D'Arros and Resourse islands and the eastern, northeastern and southern coasts of St. Joseph Island were surveyed. The distribution of seagrass communities over the intertidal zone of D'Arros and St. Joseph islands is typical of the other systems (Figs. 23-25; Table 2). A phytocoenosis dominated by Thalassodendron - Thalassia is replaced by a phytocoenosis of Cladophoropsis sundunensis+ Valonia fastgiata in the lower intertidal horizon near D'Arros island. The dominant species are all mat formers. Boodlea smtveoides, Dictyosphaeria verluysii, Microdictyon montagnei Jania capillacea and Gelidiella pannosa also occur here. The reef edge is exposed to a heavy wave action and is devoid of vegetation. Separate populations of Halimeda gracilis and Botryocladia skonsbergii occur at depths of 3-5 m. Deeper substrata are covered by crustose algae, such as Fosliella, Peyssonnelia and Neogonwlithon, and by corals. Resourse Island Two communities dominated by Thalassodendron - Microdictyon or Thalassodendron form in the lower intertidal and upper subtidal zones of Resourse island. Halimeda communities occupy depths of 7-37 m (Table 2). Thalassia hemprichii dominates the areas exposed to air at low waters. In the lagoon of St. Joseph Island, T. ciliatum tends to predominate with increasing depth. Microdictyon okamurai, M. montagnei, Boodlea struveoides, Dicfyosphaeria cavernosa, D. verluysii, Valonia fastigiata, Udotea orientalis, Halimeda stuposa, H. micronesica and H, opuntia dwell among the Thalassodendron. Caulerpa serrulata and C. cupressoides inhabit bottoms of sandy depressions. Phytocoenoses of T. ciliatum with typical species composition were found on parts of the northeastern coast of the subtidal zone of St. Joseph Island (Fig. 25). Halimeda communities with rich species composition of associated algae dominate on the reef slope. Cladophoropsis sundanensis, Boodlea struveoides and Valonia aegagropila form mats along the reef edge. Populations of Turbinaria omata, Lobophora variegata, Dictyosphaeria cavemosa, D. verluysii, Dictyuruspurpurascens, Rhipilia tomentosa and Udotea argentea occur at depths of 3-5 m. Deeper to 35-38 m, rubble and blocks are covered with dense low growing populations of numerous red algae such as Gelidiella myrioclada, Gelidium pusillum, Gelidiopsis scoparia, Poiysiphonia sp., Lophosiphonia villum, Herposiphonia secunda f. tenella, Heterosiphonia crispella, Ceramium fastgiatum, Centroceras apiculatum, M n e a spinella and Laurencia sp. The green algae Microdictyon okamurai, Struvea anastomosans, Caulerpa sp., Halimeda micronesica, H. stuposa, Valoniopsis pachynema and Valonia aegagropila are the most frequent, while Codium tomentosum, C. geppii, Cladophora laetevirens, Lophosiphonia reptabunda, Lomentaria mauritiana, L. hawaiiana, Chondria d q h y l l a , Jania decussatodichotoma and Halophila stipulacea occur less frequently. Anadyomene plicata, Scinaia and Gracilaria cylindrica are occasional and sparcely distributed. St. Joseph and D'Arros Islands contain 4 seagrasses and 120 algal species, including 69 Rhodophyta, 46 Chlorophyta, 4 Phaeophyta and 2 Cyanophyta. Astove Atoll As a rule, the intertidal zone of Astove Atoll is characterized by a mosaic structure of phytocoenoses and massive development of Laurencia. The intertidal and upper subtidal vegetative cover differs considerably from that of the other islands by its structure and species composition. There is a polydominant phytocoenosis of Thalassodendron ciliatum - Caulerpa sertularioides + Acanthopora spicifera formed on the vast silt-sand shallow area along the coast (Fig. 27; Table 2). In the lower horizon, this is replaced by a phytocoenosis formed by T. ciliatum and several Laurencia species, including L. decumbens (Fig. 26, Sts. 247-249; Table 2). Maximal quantitative development of macrophytes occurs a t the reef edge (Fig. 27), with associates consisting of Laurencia parvipapillata, L. cotymbosa, L. sp., Liagora sp., Hypnea spinella, Chaetomopha crassa, Halimeda opuntia, Dictyosphaeria cavernosa, D. verluysii, Valonia aegagropila and Boodlea struveoides. Two phytocoenoses can be distinguished on the subtidal reef slope. A phytocoenosis of Thalassodendron ciliatum - Halimeda hederacea - Laurencia sp. occurs from 0-3 m in depth. Deeper, coral populations appear, and between them oligodominant phytocoenoses of Halimeda copwsa + Caulerpa sp. are located on sandy areas containing dead coral debris (Table 2). Valonia aegagropila, Dictyosphaeria cavernosa, D, verluysii, Halimeda opuntia, H. m a , Awainvillea amadelpha f. submersa, Laurenciapatentisamea, L. cotymbosa and Gelidiella myrioclada are commonly associated species (Fig. 28). The distinctive feature of the subtidal vegetation of Astove Island is the development of massive populations of Caulerpa sp. at 20-50 m depths. The benthic vegetation of Astove Island was not examined fully due to time constraints, so only 3 seagrasses and 61 algal species (32 red, 27 green and 2 brown algae) were found. MahC and adjacent islands The northern, eastern and northeastern coasts of the island and three small islands just outside Victoria Harbor (Figs. 29-31) were studied. The intertidal zone of the northeastern coast is open to the sea and narrow (60-80 m), with a slight slope. A phytocoenosis of Cladophoropsis sundanensis + Centroceras clavulatum, along with the associated species Ulva rigzda, Cladophora socialis, Valonia aegagropila, Champiaparvula, Cladophorapatentiramea, Hypnea sp. and Jania sp., populate stone blocks in the middle intertidal horizon. An oligodominant association dominated by Sargassum- Gracilaria multifirrcata occupies the lower intertidal horizon spreading almost to the reef-flat edge (Fig. 30: Table 2). Gracilaria crassa develops in shallow water habitats, deeper it is replaced by populations of G. multifurcata, G. sp., Amphiroa foliacea, Gelidiella acerosa, Jania capillacea and Cheilosporum spectabile, forming mats. The species composition of the associated algae is rather rich with Gelidiopsis scoparia, Hypnea valentiae, Laurencia papillosa, Sargassum cristaefolium, S. microcystum, Colpomenia sinuosa, Dictyopteris delicatula, along with species of Padina, Dictyota, Turbinaria and Sphacelaria being found here. Sargassum cristaefolium and Turbinaria decuwens occur on the fringing reef-flat of the northeast and east coasts and dominate on stony reef slope sites lacking corals in the subtidal zone (Fig. 29; Table 2; Sts. 164-167) where Tricleocarpa oblongata is a subdominant. Associates include Hypnea valentiae, Ulva rigida, Caulerpa taxifolia, Cladophora patentiramea, Chlorodesmis comosa and Syringodium isoetifolium. Seagrass communities develop southwards into the harbor with m o d o c e a rotundata inhabiting a narrow band along the shore, which is then replaced by Thalassodendron ciliatum occupying the entire area exposed at low waters. Associations of Sargassum cristaefolium occupy the southeastern coast's lower intertidal and upper subtidal zones (Figs. 29-31; Table 2). In the intertidal zone, the lower level of the Sargassum phytocoenosis includes Gracilaria crassa, Cheilosporum spectabile, Jania longiartha, J. ungulata, Hypnea pannosa, H. nidulans, Laurencia parvipapillata, Amphiroa foliacea, Cladophoropsis sundanensis and Gelidiella acerosa, which form mats. Isolated populations of Dictyota indica, D. dichotoma, D. divaricata, Turbinaria omata, Padina sp. and Caulelpa racemosa occur as well. Sargassum phytocoenoses have mono- and oligodominant structures (H = 0-1, I), provide 100% cover and high biomass (Table 2). Minimal biomass was found in the upper intertidal zone while maximal biomass occurred near the reef edge (Fig, 30). The biomass of the various phytocoenoses decreases with depth. At 8-10 m deep, Sargassum phytocoenoses are replaced by those dominated by Halimeda, which are distributed around the island in a form of belt, as well as Sargassum spp. Seagrass phytocoenoses, including Thalassia hemprichii, Thalassodendron ciliatum, Halodule uninervis and Halophila ovalis, develop on shallow sites in the middle intertidal horizon where they attain maximal biomass. Sargassum phytocoenoses of the subtidal zone include species such as Turbinaria decumens, Lobophora variegata, Dictyota indica, Padina sp. and W l e o c a p a oblongata. St. Anne Island The association of Sargassum polycysntm + Turbinaria omata occupies the middle intertidal horizon of the south part of the island (Fig. 29), whereas in the lower horizon it is replaced by an association of Sargassum cristaefolium. The lower level of this association is made up of dense mats of Amphiroa foliacea and Gelidiella acerosa. Thalassia hemprichii and Halodule uninervis grow along this coast in small shallow bays, while Halophila ovalis occupies more silty sites. The lower border of the Sargassum phytocoenosis extends to a depth of 0.8-2 m. Coral populations occupy the bottom deeper. Cerf Island Sargassum microcystum and S. cristaefolium dominate the lower intertidal and upper subtidal zones. The main coenobiont of this community is firbinaria ornata. The lower level is formed by Amphiroa foliacea, Cheilospomm spectabile, Jania capillacea, Haliptilon subulantm, Gelidiella acerosa and Halimeda opuntia. Populations of Padina sp., Dictyota sp. and Qmodocea semlata occur rarely and near the shore. Dense mats of Gelidiopsis scoparia cover dead coral blocks among Sargassum spp. in the upper subtidal zone and Cladophoropsis membranacea grows on the sandy bottom among the blocks. Below 3-4 m in depth, Sargassum spp. communities are replaced by populations of coral. Anonyme Island The marine vegetation of the north side of Anonyme Island, situated at the south end of Victoria Harbor, was investigated. Monodominant continuous phytocoenoses of Sargassum micraysntm + S. cristaefolium occupy sandy-stony bottoms at 0.5-1.2 m in depth (Fig. 29; Sts. 169-173; Table 2). The species composition of these phytocoenoses is limited and includes such species as Hypnea nidulans, Jania capillacea, J. ungulata, Centroceras clavulatum, Leveillea jungermannioides, Sphacelaria rigidula, Gelidium pusillum, Chlorodesmis comosa, Acetabularia parvula, &yopsis pennata and Gelidiella acerosa. The north reef slope is exposed to wave action and consists of blocks with poorly developed vegetation (Fig. 12; Table 2; Sts. 173-175). Turbinaria ornata, Lobophora variegata, Dasya baillouviana and crustose algae occur rarely. Near MahC and its adjacent islands, 7 seagrasses and 173 algal species were collected, including 86 reds, 53 greens, 27 browns and 7 blue-greens. Praslln Island The marine vegetation of the eastern and central areas of Grande Anse Bay and the southern and southwestern coasts of Praslin were investigated to a depth of 40 m (Figs. 32-34). In the middle intertidal horizon of Grande Anse Bay, an association of Gelidiella acerosa is formed on separate rocky blocks, lower it is replaced by Gracilaria crassa associations. Sandy bottom sites between rocky blocks are overgrown by Sargassum ilicifolium. Phytocoenoses of the seagrasses Qmodocea serrulata + Syringodium isoetifolium + Thalassodendron ciliatum, S. isoetifolium and Halodule uninervis are situated in the nearshore sandy intertidal zone. C a u l q a serrulata predominates in the association of C. serrulata + S. isoetifolium and is responsible for 60-70% of the biomass. From the lower intertidal border, to 1-1.2 m deep, the T. ciliatum association inhabits sandy to stony substrata (Table 2; Fig. 34). The width of the T. ciliatum belt reaches 800-1000 m. Halimeda stuposa is typically found in this association. At shallow sites (0.3-0.5 m), the above seagrass belt is replaced by a phytocoenosis of Sargassum cristaefolium - Padina sp. The species composition of this association is reduced and includes Lobophora variegata, Dictyota indica and Chlorodesmis comosa. With increasing depth, populations of S.~taefolium - Padina sp. are replaced by multiple Sargassum assemblages that extend down to 8-10 m in depth. Maximal cover and biomass are found between depths of 1 to 3 m (Table 2). The species composition of Sargassum-dominated phytocoenoses is diverse and includes Caulerpa cupressoides, C. serrulata, C. racemosa, C. sertularioides, C. mexicana, C, taxifolia, C. ambigua, Dictyosphaeria cavernosa, Enteromorpha clathrata, Chlorodesmis cosmosa, Cladophoropsis sundanensis, Struvea anastomosans, Dictyopteris polypodiodes, Dictyota indica, D. friabilis, D. divaricata, Lobophora variegata, Turbinaria conoides, Sphacelaria rigidula, S. tribuloides, Centroceras clavulatum, C. apiculatum, Gelidiopsis scopariu, Gelidiella acerosa, Champia parvula, Tolypiocladia glomerulata and Wurdemannia miniata. Below 9 m, the bottom is sandy with large calcium carbonate blocks and coral colonies. Hard substrata are overgrown with crustose and small algae such as Gelidiella lubrica, Ceramium fastigiatum, Lophosiphonia villum, Gelidium pusillum and Champia parvula. Among the larger macroalgae, Lobophora variegata and Laurencia species are the most frequent. At the 40 m depth, Chlorodesmis comosa, Cladophora laetevirens, Halimeda sp., Cladophoropsis sundanensis, Dictyota divaricata, Champia salicomioides, Dasya sp., Antithamnion herminien and Chondria sp. are common. La Digue Island The eastern intertidal zone is exposed to strong wave action and is narrow and devoid of vegetation, whereas the western coast is more protected from wave effects. The upper and middle intertidal horizons consist of a sandy beach. Algae overgrow sandy-stony reef-flat habitats. The oligodominant association of Thalassdendron ciliatum - Hypnea pannosa occurs near the shoreline (Table 2; St. 180; Fig. 34) and includes Zhrbinaria omata, which deeper forms a 15-20 m wide belt. Sargassum turbinarioides dominates the middle of the reef-flat (Table 2). Distinctive phyto&oses develop at lower levels, consisting mainly of Hypnea nidulans and H. pannosa mats which provide up to 8-20% of the total biomass. Populations of Heterosiphonia sp. often occur along the edge of the reef-flat among the Sargassum phytocoenoses. In the subtidal zone, Sargassum phytocoenoses extend down to 8 m in depth. Deeper, down to 30-31 m, there is a belt of crustose algae with mats of small red algae and separate patches of Lobophora variegata and Laurencia sp. The species composition of algae in this region is similar to that of deep waters off Praslin Island. Phytocoenoses of granitic islands tend to have oligodominant structures, considerable biomass and limited species composition of associated species. Sargassum communities have monodominant structure, great biomass and rich species composition, which all become reduced with depth. Near Praslin and La Digue Islands, 6 seagrass and 136 algal species, including 72 red, 35 green, 22 brown and 7 blue-green species were recorded. CONCLUSIONS The benthic vegetation of the Seychelles Islands shows several common characteristics, presumably related to similar geomorphological features of the coastal zones and the tropical oceanic location of the islands: 1. Rich species composition of algae at every island. 2. Wide range of vertical distribution of most the macrophyte species. 3. Domination of red (4544.2%) and green (25.5-42.4%) algal species and poor development of brown algae (2.5-16.1%) in the floras of the low carbonate islands. 4. A great number of genera are common to all islands surveyed: green algae - Caulerpa, Halimeda, Microdictyon, Boodlea, Anadyomene, Cladophoropsis, Avrainvillea, Udotea, Acetabularia, Valonia, Diclyosphaeria and Struvea; brown algae - Lobophora, Thrbinaria and Dictyopteri~; red algae - Galaxaura, Gelidiella, Wurdemannia, Peyssonnelia, Jania, Melobesia, Hjpnea, Champia, Haloplegma, Anotrichium, Chondria, Centroceras, Dasya, Heterosiphonia, Lophocladia, Herposiphonia and Laurencia; and t h e seagrasses - Thalassia and Thalassodendron . 5. Thalassodendron ciliaturn and Thalassia hemprichii dominate the overall vegetative cover of soft bottoms. In the middle and lower intertidal horizons, seagrasses occur in the following sequence: Halophila ovalis - Halodule uninervis - Thalassia hemprichii - Cymodocea s m l a t a - C. rotundata - Syringodium isoetifolium - T. ciliatum. Thalassodendron ciliatum consistently forms a belt that dominates in the subtidal zone. 6. Thalassodendron ciliatum plays an important role in the stabilization of unconsolidated substrata in the coastal ecosystems of the atoll islands. 7. The benthic vegetation is characterized by relatively high standing stocks. In habitats with highly developed vegetative cover approaching loo%, the biomass reaches 2-4 kg.m-'. Maximal biomass was found w e r the depth range of 0.5-0.3 m, and averaged 4-8 kg-m-'. 8. Commercially exploitable stocks of macrophytes were found: mainly Thalassodendron ciliatum (biomass = 1-4 kg-m-') on atoll island sand and on the granitic islands, primarily species of Sargassum (biomass = 2-10 kgm-') and Gracilaria (biomass = 2-6 kg-m-'1. REFERENCES Aleem, kk 1984. Distribution and ecology of seagrass communities in the Western Indian Ocean. Deep-sea Res. 31(6-8):919-933. B$rgesen, E 1913. The marine algae of the Danish West Indies, Part I: Chlorophyceae. Dansk. Bot. Ark. l(4): 1-160, map. B$rgesen, F. 1914. 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(ed.), Biology of coral reefs: Photosynthesis of zooxanthellae, pp. 19-28. Far East Center, USSR Acad. Sci., Vladivostok. Valet, G. 1969. Contribution A l'dtude des Dasycladales: Revision systematique. Nova Hedwigia 17: 557-637. Weber van Bosse, A. 1913a. Marine algae, Rhodophyceae of the "Sealark" expedition, collected by J. Stanley Gardiner M.A. Trans. Linn. Soc. London, Ser.2, Bot. 7(1): 105-142, pls. 12-14. Weber van Bosse, A. 1913b. Liste des algues du Siboga. I.Myxophyceae, Chlorophyceae, Phaeophyceae. In: Weber, M.(ed.), Siboga Expeditie, monogr. # 59k.186. Wilhm T.L 1%8. Use of biomass units in Shannon's formula. Ecology, 49(1): 153-156. Table 1. Preliminary checklist of benthic marine algae and seagrasses collected near Seychelles Islands. M = Mahk, P = Praslin, Co = COetivy, F = Farquhar, D = Desroches, A = Aldabra, AB = African Banks, S = St. Joseph, Pd = Providence, Cs = Cosmoledo and As = Astove. Island C o F A D P M A B S P d C s A s Oscillatoriales Oscillatoriaceae 1. Oscillatoria margaritifera (Kutz.) Gom. 2. Oscillatoria miniata (Zanard.) Hauck 3. Lyngbya confervoides Ag. 4. Lyngbya majuscula (Dillw.) Ham. 5. Lyngbya martensiana Menegh. 6. Lyngbya sp. 7. Symploca hydnoides (Ham.) Kutz. Nostocales Rivulariaceae 8. Calothrir confervicola (Dillwyn) Ag. 9. Calothrir aeruginea (Kutz.) Thuret Nostocaceae 10. Calothrirparietina (Nlg. ex Kutz.) Thuret Nostocales 11. Homothamnium solutum Born. et Grunow Co Goniotrichales Goniotrichaceae 12. Chroodactylon omatum (C. Ag.) Basson (=Aster@ omata; Aster@ ramosa) 13. Stylonema akidii (Zanard.) Drew Bangiales Erythropeltidaceae 14. Etythrotrichia camea (Dillw.) J. Ag. 15. Eryhrocladia sp. Floridepphyceae Acrochaetiales Acrochaetiaceae 16. Acrochaetium occidentale B&g. 17. Acrochaetium robustum B@g. 18. Acrochaetium seriatum B@g. 19. Acrochaetium sp. 20. Chromastnrm crassipes (B&-g.) Papenf. (=Acrochaetium crassipes) P M A B P M P M A B F A D P M A B S F A ' M F M S P F A D M A B S F A D P M A B S Cs C o F A A B S Pd Cs M \ Island Taxon C o F A D P M A B S P d C s A s Nemaliales Liagoraceae 2 1. Liagora ceranoides Lam. F A S 22. Liagora divaricata Tseng Co 23. Liagora pinnata Haw. D 24. Liagora sp. 1 F 25. Liagora sp.2 Co 26. Liagora sp.3 Galaxauraceae 27. Scinaia complanata (Collins) Cotton S 28. Galuxaura marginata (Ell. et Sol.) Lam. D 29. Tricleocarpa oblongata C o F A P M Pd (Ell. et Sol.) Huisman et Borowitzka ( =Galaxaura oblongata) 30. Galaxaura mgosa (Ellis et Soland.) Lam. C o F A D P M Pd Cs ( = Galaxaura rudis) 31. Galaxaura sp. D Pd Gelidiales Gelidiaceae 32. Gelidium crinale f. colymbosa (Kutz.) M J. Feldm. et Hamel 33. Gelidium pusillum (Stackh.) Le Jolis C o F A D P M S Cs 34. Pterocladia caloglossoides (Howe) Dam. P Gelidiellaceae 35. Gelidiella acerosa (ForsskAl) P M Cs As J. Feldm. et Hamel 36. Gelidiella adnata Dam. C o F A P M Cs As 37. Gelidiella lubrica (Kutz.) J. Feldm. et Hamel Co F A D P M AB 38. Gelidiella myrioclada J. Feldm. et Hamel C o F A D P AB S Cs As 39. Gelidiella sanctamm J. Feldm. et Hamel Co 40. Gelidiellapannosa J. Feldm. et Hamel C o F A P M A B S (=Gelidiella tenuissima) Bonnemaisoniales Bonnemaisoniaceae 41. "Falkenbergia hillebrandii" .Co F D P M (N.B. - stage ofAsparagopsis) Corallinales Corallinaceae 42. Fosliella farinosa (Lam.) Howe 43. Neogoniolithon sp. 44. Pheophyllum confervicola (Kiitz.) Chamb. ( = Mefobesia minutufa) 45. Hydrolithon breviclavium (Fosl.) Fosl. 46. Porolithon gardinen' (Fosl.) Fosl. 47. Spongites reinboldii (W.V. Bosse et Fosl.) Penrose et Woelkerling Table 1. Continued. Island Taxon C o F A D P M A B S P d C s A s 48. Melobesia sp. 49. Mesophyllum mesomorphum (Fosl.) Adey 50. Sporolithon ptychoides Heydrich ( = Spongites erythraeum) 5 1. Spongites sporolithon 52. Lithophyllum kotschianum (Fosl.) 53. Cheilosporum spectabile Haw. 54. Haliptilon subulatum (Ell. et Sol.) Johan. 55. Jania adhaerens Lam. 56. Jania capillacea Haw. 57. Jania decussato-dichotoma (Yendo) Yendo 58. Jania longiartha Daws. 59. Jania ungulata (Yendo) Yendo f. brevior (Yendo) Yendo 60. Jania sp. 61. Amphiroa anastomosans W.V. Bosse 62. Amphiroa foliacea Lam. 63. Amphiroa ji-agilissima (L.) Lam. 64. Metagoniolithon stelligerum (Lam.) W.V. Bosse Cryptonemiales Peyssonneliaceae 65. Pqssonnelia dubyi Crouan 66. Pqssonnelia sp. 1 67. Pqssonnelia sp.2 Dumontiaceae 68. Dudresnaya sp. 69. Gibsmithia hawaiiensis Doty Halymeniaceae 70. Halymenia sp. Kallymeniaceae 71. Kallymenia sp. Gigartinales Gymnophlocaceae 72. Titanophora sp. 73. Portieria homemannii (Lyngbye) Silva Hypneaceae 74. Hypnea cenomyce J. Ag. 75. Hypnea cervicomis J. Ag. 76. Hypnea comuta (Kutz.) J. Ag. 77. Hypnea esperi Bory 78. Hypnea nidulans Setchell 79. Hypnea pannosa J. Ag. 80. Hypnea spinella (C. Ag.) Kutz. 81. Hypnea valentiae (Turn.) Mont. 82. Hypnea sp. M AB M M S M M M A B S S M M AB M S M M S Cs C o F A D P M S P d C s A s Pd Cs D P M P M P M C o F A D P M S Pd As P M A B Cs C o F A D P M As F A D P M S P d C s A s D P Cs As F A S As Table 1. Continued. Island Taxon C o F A D P M A B S P d C s A s Plocamiaceae 83. Plocamium sp. Caulacanthaceae 84. Caulacanthus sp. Wurdemanniaceae 85. Wurdemannia miniata (Sprengel) J. Feldm. et Hamel Phyllophoraceae 86. Gymnogongrus chnoosporoides Tan. et Pham-Hoang 87. Gymnogongrus Wgmaeus J. Ag. Gigartinaceae 88. Gigartina sp. Gracilariaceae 89. Gracilaria crassa Ham. 90. Gracilaria cylindrica B+rg. 91. Gracilaria multifircata B@g. 92. Gelidwpsis gracilis (Kiitz.) Vickers 93. Gelidiopsis scoparia (Mont. et Mill.) Schmitz 94. Gelidwpsis sp. 95. Ceratodictyon spongiosum Zanard. Rhodymeniales Rhodymeniaceae 96. Botyocladia s k o t t ~ b e ~ i (B4rg.) Levr. 97. Chrysymenia enteromorpha Ham. 98. Chrysymenia pyri~omis B@g. 99. Chrysymenia sp. 100. Coelarthrum boergesenii W.V. Bosse 101. Rhodymenia anastomosans W.V. Bosse 102. Rhodymenia sp. Lomentariaceae 103. Lomentaria corallicola Bq5rg. 104. Lomentaria mauritiana Bcprg. Champiaceae 105. Champia globulifea Bcprg. 106. Champia indica B&g. 107. Champiaparvula (C. Ag.) Ham. 108. Champia salicomoides Ham. 109. Champia viellardii Kiitz. 1 10. Champia sp. Ceramiales Ceramiaceae 11 1. Crouania attenuata (C. Ag.) J. Ag. 112. Antithamnion fherminieri Nasr. 113. Antithamnion sp. F D M S Pd As P F A P M A B S Cs As C o F A D P M A B S Cs As Pd Co AB S C o F A C o F A D AB S Pd D M D P D P M A B S Pd D M As C o F A D P M A B S P d C s A s D P M S Pd F A M D S A D AB S Pd Co D A D M A B S Cs Table 1. Continued. Island C o F A D P M A B S P d C s A s 114. Platythamnion sp. AB 115. Antithamnionella sp. F A D P M Pd Cs 116. Ceramium brevizonatum var. caraibicum Co H. Petersen et B&. 117. Ceramium fastigiatum (Wulf. ex Roth) Haw. Co F A D P AB S Cs f. flaccidum H. Petersen Co 118. Ceramium jimbriatum Setch. et Gardn. F A D P M 119. Ceramium gracillimum (Kiitz.) Zanard. C o F A D P M A B S Cs As 120. Ceramium huysmansii W.V. Bosse Cs 121. Ceramium mazatlanense Daws. C o F A D M S 122. Ceramium taylorii Daws. P M A B S Cs 123. Ceramium sp.1 A D 124. Ceramium sp.2 D P M S 125. Ceramium sp.3 M 126. Centroceras clavulatum (C. Ag.) Mont. F A D P M A B Pd Cs 127. Centroceras apiculatum Yam. C o F A D P AB S Cs 128. Spyndiajilamentosa (Wulf.) Haw. F A Cs 129. Wrangelia argus (Mont.) Mont. A M S Cs 130. Callithamnion byssoides Am. A D S 131. Aglaothamnion sp. M 132. Pleonosporium borreri (Smith) N2g. S 133. Haloplegma duperreyi Mont. C o F A D A B S Pd Cs 134. Grifithsia globulifera (Haw.) Kiitz. M 135. Grifithsia metcalfii Tseng C o F A D AB S 136. Grifithsia subcylindrica Okam. Co A D A B S Pd Cs 137. Anotrichium tenuis (C. Ag.) Nag. F D P M A B S Cs 138. Grifithsia weber-van-bosseae B@g. D S 139. Grifithsia sp. A 140. Gymnothamnion elegans P (Schousboe ex C. Ag.) J. Ag. Delesseriaceae 141. Caloglossa adnata (Zanard.) De Toni A D 142. Caloglossa leprieurii (Mont.) J. Ag. A 143. Caloglossa stipitata Post A Pd 144. Hypoglossum attenuatum Gardn. A D P S 145. Taeniomaperpusillum (J. Ag.) J. Ag. A 146. Cottoniella arcuata B#q. Pd Cs 147. Platysiphonia sp. D AB 148. Martensia sp. P S Dasyaceae 149. Dasya mollis Haw. C o F A D P AB S 150. Dasya baillouviana (Gmel.) Mont. Co A M Cs 151. Dasya sp.1 A D S 152. Dasya sp.2 M 153. Dasya sp.3 Cs Table 1. Continued. Island C o F A D P M A B S P d C s A s 154. Heterosiphonia crispella (C. Ag.) Wynne C o F A D P M A B S P d C s ( = Heterosiphonia wurdemannii) 155. Heterosiphonia sp.1 Co A D P S Cs As 156. Heterosiphonia sp.2 C o F A AB 157. Dictyuruspurpurascens Bo~y C o F A D P A B S P d C s A s Rhodomelaceae 158. Polysiphonia coacta Tseng Co F 159. Polysiphonia mollis J. Hook. et Haw. P M A B S 160. Polysiphonia ferulacea Suhr ex J. Ag. P 161. Polysiphonia scopulorum Haw. Co 162. Polysiphonia subtilissima Mont. F A D 163. Polysiphonia sp. C o F A D P M A B Cs 164. Truialia sp. Co F D S 165. Tolypiocladia glomerulata ( Ag.) Schmitz P M Cs 166. Lophocladia trichoclados (C. Ag.) Schmitz Co F A D P M AB S Pd As 167. Boshychia binderi Haw. M 168. Herposiphonia secunda (C. Ag.) Ambronn Co A f. tenella (Ag.) Wynne C o F A D P M A B S P d C s A s 169. Leveillea jungermannioides P M Pd Cs (Hering et Martens) Haw. 170. Lophosiphonia reptabunda (Suhr.) Kyl. Co F P S Cs 171. ~o~hosiphonia villum (J. Ag.) Setch. et Gardn. Co F A D P M AB S Cs 172. Lophosiphonia sp. Cs 173. Chondria dayphylla (Woodw.) C. Ag. A S 174. Chondria poiyrhiza Coll. et Hew. A 175. Chondria repens B+rg. Co F P M A B S P d C s 176. Chondria sp. F A Cs 177. Acanthophora spicifera (Vahl) B+rg. A M As 178. Laurencia articulata Tseng P 179. Laurencia corymbosa J. Ag. Pd Cs As 180. Laurencia decumbens Kiitz. F A D P S Cs As 181. Laurencia distichophylla J. Ag. A S 182. Laurencia obtusa (Huds.) Lam. Co F M 183. Laurenciapatentiramea (Montagne) Kiitz. Co F A M A B S Cs As 184. Laurencia par/ipapillata Tseng. C o F A D M S P d C s A s 185. Laurencia papillosa (Ag.) Grev. F A D P M S P d C s A s 186. Laurencia~gmaea W.V. Bosse A M 187. Laurencia sp.1 C o F A AB S As 188. Laurencia sp.2 M 189. Laurencia sp.3 A M 190. Laurencia sp.4 P 191. Laurencia sp.5 D P AB S Table 1. Continued. Island Taxon C o F A D P M A B S P d C s A s Ectocarpales Ectocarpaceae 192. Ectocarpus sp. M 193. Hincksia mitchelliae (Haw.) Silva D M 194. Hincksia breviarticulata (J. Ag.) Silva M 195. Streblonema sp. P Scytosiphonales Scytosiphonaceae 196. Colpomenia sinuosa P M (Mert. ex Roth) Derb. et Sol. 197. Hydroclathrus clathratus (C. Ag.) Howe M 198. Rosenvingea intricata (J. Ag.) B4rg. M Chnoosporaceae 199. Chnoospora minima (Hering) Papenf. M Sphacelariales Sphacelariaceae 200. Sphacelaria rigidula Kutz. F A P M A B Cs 201. Sphacelaria nibuloides Menegh. Co P M Cs Dictyotales Dictyotaceae 202. Dictyota bartayresii Lam. A D P 203. Dictyota ceylanica Kutz. P 204. Dictyota divaricata Lam. P 205. Dictyota friabilis Setch. A P 206. Dictyota indica Sond. ex Kiitz. P M 207. Dictyota patens J. Ag. M 208. Dictyota sp. M S 209. Dictyopteris delicatula Lam. Co F D P M S Pd 210. Dictyopterispolyposioides (DeCandalle) Lam. P M 211. Padina minor Yam. F 212. Padinapavonica (L.) Thivy P M 213. Padina sp. P 214. Lobophora variegata (Lam.) Womers. C o F A D P M A B S P d C s A s Fucales Cystoseiraceae 215. Hormophysa cuneiformis (Gmelin) Silva M Sargassaceae 216. Sargassum cristaefolium C. Ag. M 217. Sargassum ilicifolium (Turn.) C. Ag. M 218. Sargassum mcclurei Setch. P M 219. Sargassum microcystum J. Ag. P M 220. Sargassum piluliferum (Turner) C. Ag. P Table 1. Continued. Island Taxon C o F A D P M A B S P d C s A s 221. Sargassum polycystum C. Ag. M 222. Sargassum turbinarioides Grun. P M 223. Sargassum sp. P 224. Turbinaria conoides (J. Ag.) Kutz. A P M 225. Turbinaria decurrens Bory M AB 226. Turbinaria omata (Turn.) J. Ag. C o F A D P M S Cs As 227. Turbinaria sp. P Cs CHLOROPHYTA Phaeophilales Phaeophilaceae 228. Phaeophila dendroides (P. et H. Crouan) Batt. Dasycladales Dasycladaceae 229. Neomeris annulata Dickie 230. Neomeris bilimbata Koster 231. Neomeris vanbosseae Howe 232. Neomeris sp. Polyshysacaea 233. Polyphysa sp. 234. Acetabularia clavata Yam. 235. Acetabularia &gua Solms-hub. 236. Acetabulariaparvula Solms-hub. 237. Acetabulariapusilla (Howe) Collins 238. Acetabularia sp. Bryopsidales Caulerpaceae 239. Caulerpa brachypus Haw. 240. Caulerpa cupressoides (Vahl) Ag. 241. Caulerpa cupressoides var. mamillosa (Mont.) W.V. Bosse 242. Caulerpa fastigiata Mont. 243. Caulerpa mexicana Sond. ex Kutz. 244. Caulerpa microphysa (W.V. Bosse) J. Feldm. 245. Caulerpapeltata Lam. 246. Caulerpa racemosa (ForsskAl) J. Ag. var. macrophysa (Sond. ex Kutz.) W. Taylor var. occidentalis (J. Ag.) B@g. var. peltata (Lam.) Eubank 247. Caulerpa serrulata (ForsskAl) J. Ag. var. serrulata f. spiralis (W.V. Bosse) Gilbert 248. Caulerpa setularioides (Gmel.) Howe f. farlowii (W.V. Bosse) B@g. A D A D M M A D P M Cs A D P M Cs Cs F A D P A B S Pd Cs F D P Cs F F A D P S P M F A P M F P M F M Cs Cs P M F A D P M S Cs F S Cs P M A B S Cs Cs Table 1. Continued. Island Taxon C o F A D P M A B S P d C s A s 249. Caulerpa tarifolia (Vahl) C. Ag. C o F A P M S 250. Caulerpa ambigua Okam. P M S Cs 251. Caulerpa webbiana Mont. Cs 252. Caulerpa sp. 1 Co F 253. Caulerpa sp.2 A 254. Caulerpa sp.3 Co D P AB S Pd As Udoteaceae 255. Chlorodesmis comosa Haw. et Bail. C o F A D P M S Cs 256. Boodleopsis pusilla A D P AB (Collins) W. Taylor, Joly et Bernatowicz 257. Avrainvillea amadelpha f. submersa Gepp C o F A D M A B S P d C s As 258. Tydemania gardinen A et B. Gepp AB S 259. Rhipiliopsk reticulata (van den Hoek) Farghaly Co D Cs 260. Rhipilia tomentosa Kiitz. Co F D AB S Cs As 261. Udotea argentea Zanard. Co F D M A B S 262. Udoteaflabellum (Ell. et Sol.) Howe Co D 263. Udotea javensis (Mont.) A Gepp et E. Gepp D M 264. Udotea orientalis A Gepp et E. Gepp Co F D M A B S Pd Halimedaceae 265. Halimeda gracilis Haw. ex J. Ag. C o F A D M A B S P d C s A s 266. Halimeda copiosa Goreau et Graham Co A AB S Cs As 267. Halimeda macroloba Decne. F A D P M A B S 268. Halimeda micronesica Yam. C o F A D AB S Pd 269. Halimeda opuntia (L.) Lam. C o F A D P M A B S As 270. Halimeda stuposa W. Taylor C o F A D AB S Cs 271. Halimeda tuna (Ell. et Sol.) Lam. C o F A D A B S P d C s A s 272. Halimeda sp. A D P AB S Codiaceae 273. Codium formosanum Yam. M 274. Codium geppii O.C. Schmidt S 275. Codium tomentosum (Huds.) Stackh. M S 276. Codium sp. M Bryopsidaceae 277. Derbesia marina (Lyngb.) Solier F A M 278. Derbesia sp. P 279. Halicystis ovalis (Lyngb.) Aresch. M (N.B. - sporophyte stage of Derbesia marina) 280. Bryopsis pennata Lam. A D P M 281. Tnchosolen sp. S Siphonocladales Valoniaceae 282. Valonia aegagropila C. Ag. Co F D M A B S P d C s A s 283. Valonia fastigiata Ham. es J. Ag. D M A B S Pd 284. Valonia utriculari. (Roth) Ag. Co D S Cs f. crustacea Kuck. Cs Table 1. Continued. Island Taxon C o F A D P M A B S P d C s A s 285. Ventricaria ventricosa (J. Ag.) Olsen et West F A M Cs 286. Diclyosphaeria cavemosa (ForsskAl) B+rg. Co F A D P M AB S Pd Cs As 287. Diclyosphaenh versluysii W.V. Bosse C o F A D P M A B S Cs As 288. Valoniopsis pachynema (Mart.) B+rg. Co D AB S Cs As Siphonocladaceae 289. Boergesenia forbessii (Ham.) J. Feldm. A M AB Cs 290. Siphonocladus rigidus Howe Co D M Pd Cs As 291. Siphonocladus tropicus (P. et H. Crouan) J. Ag. D S 292. Cladophoropsis herpestica (Mont.) Howe P M 293. Cladophoropsis membranacea (Ag.) B4rg. M A B S Cs 294. Cladophoropsis modonensis (Kutz.) B+rg. P M 295. Cladophoropsis sundunensis Reinb. C o F A D P M A B S Cs Boodleaceae 296. Boodlea composita (Ham.) Brand Co D S 297. B d l e a siamensis Reinb. D 298. BoodIea struveoides Howe . C o F A D P M A B S P d C s A s 299. Boodlea sp. S 300. Struvea anastomosans (Ham.)Picc. et Grun. Co F A D P M AB S 301. Struvea elegans B4rg. F P Pd 302. Struvea sp. 1 Co D P 303. Struvea sp.2 Co Anadyomnaceae 304. Microdiclyon okamurae Setch. C o F A D M A B S P d C s As 305. Microdidyon montagnei Ham. Co S Pd Cs 306. Microdicyon sp. Co A S 307. Anadyomeneplicata C. Ag. AB 308. Anadyomene wrightii Ham. ex J.E. Gray C o F A D A B S P d C s A s Cladophoraceae 309. Cladophora vagabunda (L.) van den Hoek M 3 10. Cladophora laetevirens (Dillw.) Kutz. Co P M S Cs 31 1. Cladophora patentiramea (Mont.) Kutz. M S 312. Cladophora socialis Kutz. F M Cs 3 13. Cladophora sp. A M 314. Rhizoclonium implexum (Dillw.) Kutz. F M S (=Rhizoclonium kenten) 315. Chaetomorpha ligustica (Kutz.) B4rg. Co M Cs As 316. Chaetomorpha crassa (C. Ag.) Kutz. Co F M As Chaetophorales Ulvellaceae 317. Entocladia sp. F 318. Phaeophila dendroides (P. and H. Crouan) Batt. P Cs Ulvales Ulvaceae 3 19. Enteromorpha clathrata (Roth) Grev. Co A D P M A B Cs 320. Enteromorphajlexuosa (Wulf.) J. Ag. D Table 1. Continued. Island C o F A D P M A B S P d C s A s 321. Enteromorpha intestinalis (L.) Link ex Nees D P 322. Enteromorpha hylinii Bliding C o F A D 323. Enteromorpha linza (L.) J . Ag. P 324. Enteromorpha ralfsii Harv. A 325. Enteromorpha sp. D 326. Ulva rigida C. Ag. C o F A SPERMATOPHYTA Potamogetonaceae 1. Halodule uninervis (Forsskal) Aschers. P 2. Cymodocea rotundata Ehrenb. P and Hemprich ex Aschers. 3. Cymodocea semlata (R. Br.) P Aschers. et Magnus 4. Syringodium isoetifolium (Aschers.) Dandy Co A P 5. Thalassodendron ciliatum (Forsskal) den Hartog Co F A D P Hydrocharitaceae 6. Thalassia hemprichii (Ehrenb.) Aschers. C o F A D 7. Halophila ovalis (R. Br.) Hooker f. hawaiiana (Doty et Stone) den Hartog D 8. Halophila stipulacea (Forsskal) Aschers. M M A B S P d C s As M A B S P d C s As S M AB S Table 2. Quantitative characteristic of bottom vegetation of the Seychelles Islands (12 January - 12 March, 1989). In zone heading, "rnih" = middle intertidal horizon, "lih" = lower intertidal horizon. "s" = sand, "st" = stones, "c" = corals, "cd" = coral debris and "Hs" = Halimeda sand. Depth in # of Biomass, % Growth Coast Station m, zone Substrate species.m-' in g.m-2 cover height Association H N-W N-W N-W N-W N-W N-W S S S S S N N-E W W W W W W W W W W E E E E E E N-E N-E N-E N-E N-E 1 mih s, &,st 2 mih s, cd 3 mih s, cd 4 mih s,cd 5 lih S, cd, 6 lih S, cd, 7 mih s, cd, 8 mih s, cd, 9 lih S, cd, 10 mih s,cd 11 mih s, cd, 12 1-2 s, cd, 13 1 S, cd, 14 8 S, cd, 15 1.5 s, cd 16 2.5 s, cd 17 3.5 s, cd 18 3.5 s, cd 19 4.0 s, cd 20 4.5 s, cd 21 3.0 s, cd 22 4.5 s, cd 23 5-6 S, cd 24 mih s, cd 25 mih s, cd 26 lih S, cd 27 2 s, C O e t i v y I s l a n d 5 - Enteromorpha kylinii 100 15 Thalassia hemprichii 100 10 Halodule uninervis +Thalassia hemprichii 70 6 Halodule uninervis + Thalassia hemprichii 80 15 Thalassodendron -Halimeda +Hypnea 100 20 Thalassodendron-Halimeda -Dictyurus 90 20 Thalassodendron 100 15 Thalassia-Caulerpa 100 10 Halimeda+Dictyuius +Lawencia 90 15 Thalassia + Thalassodendron 90 20 Halimeda + Thalassodendron ciliarum-Laurencia 90 25 Thalassodendron-Halimeda 100 25 Thalassodendron-Halimeda 50 30 Thalassodendron-Caulerpa 10 Halemeda 10 Halemeda 20 (Tha1assodendron)-Halemeda 10 Halemeda 10 Halemeda 10 Halemeda 21 Thalassodendron ciliatum 22 Thalassodendron-Halimeda 25 Thalassodendron 80 12 Thalassiu 100 25 Thalassodendron- Thalassia 100 25 Thalassodendron-Dictyuius 100 20 Thalassodendron-Halimeda -Dictyurus 80 20 Thalassodendron-Halimeda 30 12 (Thalassodendron) -Caulelpa -Halimeda 100 18 (Tha1assodendron)-Caulerpa- -Halimeda 95 10 Halimeda +Boodles +Microdictycon 50 23 Thalassodendron-Halimeda Thalassodendron-Halimeda 10 27 Thalassodendron-Halimeda Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate ~ ~ e c i e s . m - ~ in g.m-2 cover height Association H N-E N-E N-E N-E S S S W W W W W W w . W W W S S S S S S S N N N N-E N-E N-E Lagoon Lagoon Lagoon Lagoon Lagoon Lagoon Lagoon Lagoon 35 mih 36 mih 37 lih 38 32 39 5 40 10 41 12 42 mih 43 mih 44 mih 45 lih 46 3 47 3 48 6 49 7 50 17 51 1.5 52 mih 53 lih 54 lih 55 lih 56 6 57 15 58 25 59 mih 60 lih 61 lih 62 6-7 63 12h 64 22 65 3 66 7 67 9 68 2.5 69 8 70 12 71 3 72 1.2 Lagoon 73 1.0 F a r q u h a r Thalassia Thalassodendron + Thalassia Thalassodendron-Dictyurus Avrainvillea-Halimeda Thalassodendron Thalassodendron (Thalassodendron) -Halimeda -Microdictyon Thalassia +Halodule Syringodium + Thalassodendron Halodule + Thalassia Thalassodendron Thalassodendron Thalassodendron Thalassodendron Thalassodendron Thalassodendron-Dictyurus Thalassodendron I s l a n d 15 Thalassodendron + Thalassia 13 Thalassodendron 1-2 Boodlea 15 (Thalassodendron) -Caulerpa -Bodlea 3 Caulerpa 1-2 Microdictyon + Boodlea 1-2 Microdictyon 8 Thalassodendron-Boodlea 1-2 Boodlea struveoides 1-2 Microdictyon + Boodlea 2 Caulerpa + Boodlea 2 Caulerpa 2-5 Udotea +Caulerpa 2 Caulerpa cupressoides 2 Caulerpa cupressoides 2 Halimeda opuntia + Caulerpa cupressoides 28 Thalassodendron - - - - 35 Thalassodendron-Halimeda 24 Thalassodendron-Halimeda 28 Thalassodendron-Caulerpa Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate species.m-2 in g.m-2 cover height Association Lagoon Lagoon Lagoon Lagoon Lagoon Lagoon Lagoon N N 74 8 75 10 76 12 77 6 78 3-4 79 2 80 1 81 mih 82 lih 0 - - 0 - - 0 - - 1 - Heterosiphonia 100 30 Thalassadendron-Halimeda 100 126 Thalassadendron-Thalassia 100 20 Thalassadendron-Caulerpa 100 14 Thalassadendron-Caulerpa 100 12 Thalassadendron- Valonia + Microdictyon 100 12 Thalassadendron-Valonia 100 50 Sargassum ilicifolium 70 25 Thalassodendron 83 lih 84 4 85 1 A l d a b r a I s l a n d E E E Lagoon 86 12 87 25 88 12 89 lih s, cd s, cd Halimeda s S, cd 518 60 10 Halimeda 20 10 Halimeda 30 lOHalimeda 70 18 (Thalassadendron) -Lawencia +Halimeda 70 12 Thalassia +Lawencia 80 25 Thalassia +Halimeda 80 17 Thalassia +Halimeda 100 24 Thalassia 100 24 Thalassadendron 100 15 Thalassadendron + Thalassia -Halimeda 100 17 Thalassadendron + Thalassia -Halimeda 100 20 Thalassadendron +Halimeda Lagoon Lagoon Lagoon Lagoon W W 90 lih 91 lih 92 mih 93 5 94 1 95 lih s, cd 376 s, cd 284 s, cd 584 s,cd 960 s, black c 1004 s, black c 960 96 lih s, black c 768 97 lih s, black c - D e s r o c h e s I s l a n d N-W 98 mih 662 80 20 Thalassodendron + Thalassia -Halimeda 2400 100 30 Thalassadendron-Halimeda -Haloplegma 3864 100 42 Thalassadendron 70 40 Thalassadendron 2164 100 42 Thalassadendron 1572 50 25 Thalassadendron-Halimeda + Udotea 1700 25 10 Halimeda N-W 99 mih N-W N-W N-W N-W 100 lih 101 2 102 6 103 12 N-W Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate species-m-2 in g-m-2 cover height Association H N-W N-W N-W N-W N-W S-E S-E W W W W S S S S S S S S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S S S S S S S S-W S-W S-W S-W S-W S-E 105 30 106 mih 107 mih 108 lih 109 lih 110 13 111 30 112 2 113 7 114 8 115 12 116 mih 117 mih 118 lih 119 lih 120 5-6 121 20 122 35-38 123 50 124 1.5-3 125 6 126 15 127 16-30 128 42 129 30 130 13 131 20 132 50 133 mih 134 lih 135 lih 136 1.2 137 1.5-3 138 9 139 20 140 mih 141 lih 142 lih 143 lih 144 0.5 20 Thalassodendron-Halimeda 20 Thalassia + Thalassodendron 1.34 -Halimeda 20 Thalassia + Thalassodendron 1.60 -Halimeda 30 Thalassodendron- Thalassia -Halirneda 40 Thalassodendron 40 Thalassodendron-Halimeda 10 Halimeda 38 Thalassodendron 0 10 Halimeda 0 40 Thalassodendron 0 10 Halimeda 6 Thalassia + Thalassodendron 1.30 -Udotea 6 Thalassodendron- Thalassia-Udotea 1.62 15 Thalassodendron - Thalassia 1.24 25 Thalassodendron-Halimeda 1.57 + Dicwrus 33 Thalassodendron 0 10 Halimeda 0 10 Halimeda 0 10 Halimeda 30 Thalassodendron 0.23 30 Thalassodendron 0.14 Halimeda 0.13 10 Halimeda 0 5 Caulepa +Halimeda 10 Caulerpa + Halimeda 30 Thalassodendron -Halimeda 10 Halimeda 10 Halimeda +Caule?pa 20 Cymodocea + Thalassodendron 1.33 +syringodium 30 Thalassodendron 0 40 Thalassodendron 0 60 Sargassum 0 60 Sargassum 0.16 40 Sargassum 0.21 3 Hjtpnea, Laurencia 16 Syringodium +Qmodocea 1.20 + Thalassia 30 Synngodium + Cymodocea 0.30 30 C)modxea-Syringodium 0.76 S, cd 1112 3776 40 50 Sargassum cnktaefoium-~adina sp. 0.80 s. cd 656 5858 80 60 Sat~assum -Turbinaria Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate ~ ~ e c i e s - m - ~ in g-m-2 cover height Association S-E S-E S-E S-E S-E W W W W E E E E E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E N-E 146 17 147 20 148 5 149 8 150 8 151 lih 152 lih 153 0.5 154 mih 155 mih 156 lih 157 0.5 158 mih 159 mih 160 mih 161 mih 162 lih 163 lih 164 3-6 165 15-16 166 3-7 167 13-14 168 0.5 169 0.5 170 0.5 171 0.5 172 0.2 173 2-11 174 15 s 1 30 Thalassodendron-Dictyota s 0.5 - Chlorodesmis cd 128 1480 50 50 Sargassum 0 cd % 840 60 60 Sargassum 0 cd 5 - Chlorodesmis M a h e ( C e r f ) S, cd 948 4465 80 20 Sargassum S, cd 332 5700 100 30 Sargassum Jania +Gelidella cd 376 5600 100 30 Sargassum s 111 13% 70 10 Qmodocea M a h e ( S a i n t A n n e ) I s l a n d s 600 3304 70 30 Sargassum posIycystum Turbinaria omata S, cd 708 6500 100 20 Sargassum cristaefolium cd 268 5292 100 30 Sargassum-Turbinaria rock 8 2935 40 20 Garcilaria crassa silty s 624 342 40 10 Qmodocea +Halodule M a h e I s l a n d 80 30 (Sargassum)-Gracilaria 90 30 (Sargassum)-Gracilaria 100 30 Sargassum 100 30 Sargassum 30 10 Turbinaria decurrens - Chlorodesmis 30 40 Sargassum 20 30 Sargassum A n o n y m e I s l a n d rock 720 7480 80 30 Sargassum cd 456 6340 100 40 Sargassum cd 517 6933 100 20 Sargassum cd 152 3320 100 20 Sargassum cd 112 2900 100 20 Sargassum cd 0 - crustose algae cd 1 - Lobophora + Dasya Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate speciesm-2 in g.m'2 cover height Association H S-E S-E S-E S-E N-W N-W N-W N-E N-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E S-E N-W S-E S S S S S S S S 176 0.4 s, cd 284 177 0.5 s, cd 500 178 0.5 s, cd 116 179 0.5 s, cd 525 180 lih s, cd 992 181 lih s, cd 500 182 lih s, cd 316 183 31 s 184 22 s, rock - 185 30 s 186 10-15 cd M a h C I s l a n d 30 Sargassum -Amphiroa -Caule~a - 30 Sargassum 0.42 30 Sargassum-Amphiroa 0.84 15 Sargassum 0.11 20 Thalassodendron-Hypnea 1.50 18 Turbinaria omata-Hypnea pannosa 1.10 30 Sargassum turbinarioides-Hypnea 0.27 single Champia pawula single Dictyota bartayresii +Hypnea - Diciyota + Gracilaria cylindrica - - crustose algae A f r i c a n B a n k s 32 Thalassodendron 0 30 Thalassodendron 0.29 27 Thalassodendron 0.3 1 26 Thalassodendron 0.15 - Thalassodendron - Thalassodendron - Thalassodendron - Thalassodendron 42 Thalassodendron 0 18 Thalassodendron 0 20 Thalassodendron -Valonia-Thalassia 1.63 25 Thalassodendron-Thalassia 1.50 -Microdictyon 25 Thalassodendron 0.12 8 Dasya +Halimeda 0.90 - Halimeda S a i n t J o s e p h I s l a n d s ( D ' A r r o s , R e s s o u r c e ) 201 mih s,cd 202 mih s, cd 203 lih cd 204 lih cd 205 30 cd 206 16 cd 207 3-5 cd 208 1 cd 50 10 Thalassia hemprichii 0 50 1 1 Thalassodendron-Thalassia 1.22 -Diciyosphaeria 50 10 Thalassodendron-Thalassia 0.94 30 - Cladophoropsis + Valonia 0.66 1-5 - Halimeda 20 - Thalassodendron Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate species.rn-' in gm-' cover height Association H S S S S S S S S S S E N-E N-E S S S S S W W S-W S-W Lagoon Lagoon Lagoon Lagoon Lagoon Lagoon E E E N E S E Lagoon 209 37 210 23 211 37 212 0.5 213 lih 214 lih 215 0.3 216 25 217 18 218 7-8 219 10-12 220 1.-1.5 221 5-6 222 20 223 30 224 1.5 225 13 226 23 227 1.5 228 23 229 32 230 3-6 231 0.4 232 0.4 233 0.4 234 0.4 235 0.2 236 0.1 237 4-5 238 10 239 20 240 mih 241 40 242 10 243 42 244 1.0 Lagoon 245 0.5 - Halimeda - Halimeda - Halimeda 30 Thalassodendron 20 Thalassodendron-Microdictyon 30 Thalassodendron 30 Thalassodendron - Crustose algae - Halimeda - Halimeda - Thalassodendron- Udotea 40 Thalassodendron 10 Halimeda - Boodlea struveoides - Halimeda +Caulerpa P r o v i d e n c e A t o l l Thalassodendron 0 Thalassodendron 0.11 Thalassodendron 0.27 Thalassodendron-Microdictyon - Thalassodendron-Microdictyon - Halimeda Thalassodendron C o s m o l e d o I s l a n d s 20 Thalassodendron-Halimeda +Lawencia 25 Thalassodendron-Halimeda 35 Thalassodendron-Halimeda 30 Thalassodendron-Laurencia 10 Thalassia +Cymodocea Jania 6 Halodule uniervis - Laurencia-Caulerpa - Caulerpa - Awainvilleaamadelpha-Halimeda - Caulerpa +Halimeda + Boodlea - Halimeda +Microdictyon - Turbinaria +Galaxaura + Halimeda - Halimeda 20 Thalassodendron-Halimeda 20 Thalassodendron-Halimeda Table 2. Continued. Depth in # of Biomass, % Growth Coast Station m, zone Substrate ~ ~ e c i e s - m - ~ in g.m-2 cover height Association H S 246 lih S 247 lih S 248 lih S 249 lih Lagoon 250 0.3 S 251 1.5 S '- 252 5 S 253 30 S-W 254 50 S 255 50 S 256 5-40 A s t o v e I s l a n d (Thalassia) +Caulerpa +Amphiyou 2.12 Thalassodendron-Laurencia 2.53 + Thalassia Thalassodendron-Laurencia 1.34 + Thalassia Thalassodendron-Laurencia 1.46 Thalassia-Caulerpa +Acanthophora - Halimeda + Caulerpa sp. Halimeda + Caulerpa sp. Halimeda + Caulerpa sp. 1.02 Caulerpa sp. +Halimeda copiosa - Caulerpa sp. +Halimeda copiosa - Avrainvillea +Halimeda + Caulerpa sp. Figure 1. Location of stations and species ratios in phytocoenoses of Cdetivy Island. 1 - Thalassodendron ciliatum, 2 - Caulerpa cupressoides, 3 - Halimeda species, 4 - Microdiclyon okamurai, 5 - Halodule uninervis, 6 - Thalassia hemprichii, 7 - Gelidiella myrioclada, 8 - syringodium isoetifolium, 9 - Jania adhaerens, 10 - Hypnea pannosa, 11 - Dictyurus pupurascens, 12 - Laurencia species, 13 - other minor species. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at COetivy Island. 1 - Enteromoqha, 2 - Thalassia hempnchii, 3 - Halodule uninervis, 4 - Porolithon gardineri, 5 - Thalassodendron ciliaturn, 6 - Laurencia species, 7 - Dictyuruspurpurascens, 8 - Halimeda species, 9 - Caulerpa species, 10 - Avrainvillea amadelpha, 11 - Boodlea struveoides. Figure3. Horizontal distribution of algal and seagrass species of COetivy Island. 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Syringodium isoetifolium, 4 - Halodule uninervis, 5 - Dictyuruspurpurascens, 6 - Jania adhaerens, 7 - crustose species, * - Turbinaria omata, 9 - Lobophora variegata, 10 - Caulerpa species, 11 - Halimeda species, 12 - Avrainvillea amadelpha f. submersa. Figure 4. Distribution of macrophyte biomass at COetivy Island (in g.m'2): 1 - 30962393; 2 - 15972306; 3 - 8782306; 4 - 5572 157. Figure 5. Location of stations and species ratios in phytocoenoses at Desroches Island. 1 - Thalassia, 3 - Halimeda, 4 - Udotea, 5 - Haloplgema, 6 - Dictyurus, 7 - other minor species. Figure 6. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at Desroches Island. 1 - Thalassia hemprichii, 2 - Thalassodendron ciliatum, 3 - Halirneda species, 4 - Jania adhawens, 5 - Dictyurus purpurascenr, 6 - Dasya mollis, 7 - Microdicqon okamurai, 8 - Rhipilia tomentosa, 9 - lbrbinaria omata, 10 - 7Yicleocarpa oblongata. Figure 7. Horizontal distribution of algal and seagrass species at Desroches Island. 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Halimeda, 4 - Turbinaria omata, 5 - Jania species, 6 - Dasya mollis, 7 - Galaxaura species, 8 - Udotea argentea, 9 - Dictyuruspulpurascens, 10 - Caulerpa species. Figure 8. Distibution of macrophyte biomass at Desroches Island (in g.m-2): 1 - 3158k680; 2 - 1241 2462. Figure 9. Location of stations and species ratios in phytocoenoses at African Banks (South Island). 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Dasya mollis, 4 - Valonia fastigiata, 5 - Microdictyon okamurai, 6 - Halimeda species, 7 - other minor species. Figure 10. Vertical distribution of dominant species, biomass and percent cover of algae and segrasses at African Banks. 1 - Thalassodendron ciliaturn, 2 - Boodlea stnrveoides, 3 - Halimeda species, 4 - Tricleocaipa oblongata, 5 - Haloplegma duperreyi, 6 - Microdictyon okamurai, 7 - Turbinaria oblongata, 8 - Caulerpa species, 9 - Avrainvillea arnadelpha, 10 - Rhipilia tomentosa, 11 - Lobophora variegata, 12 - Udotea argentea. Figure 11. Horizontal distr ibution o f algal and seagrass species o f African Banks. 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Tricleocarpa oblongata, 4 - Avrainvillea amadelpha, 5 - Boodlea struveoides, 6 - Halimeda species, 7 - Lobophora variegata, 8 - Valonia fastigiata, 9 - Dictyurus purpurascens , 10 - Caulerpa species, 11 - Dasya mollis, 12 - Laurencia species, 13 - Turbinaria omata, 14 - Dictyosphaena species, 15 - Porolithon gardinen, 16 - Udotea argentea, 17 - Rhipilia tomentosa. Figure 12. Location of stations and species ratios of phytocoenoses at Providence Island. 1 - Thalassodendron ciliaturn, 2 - other species. Figure 13. Horizontal distribution o f algal and seagrass species at Providence Island. 1 - Thalassodendron ciliatum, 2 - Halimeda species, 3 - Caulerpa species, 4 - Laurencia species, 5 - Dictyurus purpurascens, 6 - Tricleocarpa oblongata, 7 - Microdictyon montagnei, 8 - Avrainvillea amadelpha, 9 - Jania species, 10 - Valonia fastigiata 11 - Lobophora variegata, 12 - Dictyosphaeria cavernosa, 13 - Hatoptegma duperreyi, 14 - Boodlea struveoides, 15 - Porolithon gardineri. Figure 14. Location of stations and species ratios in phytocoenoses at Farquhar Atoll. 1 - Thalassodendron ciliatum, 2 - Sargassum ilicifolium, 3 - Valonia aegagropila, 4 - Microdictyofl okumurai, 5 - Cauletpa cupressoides, 6 - Boodlea struveoides, 7 - Thalassia hemprichii, 8 - Halimeda opuntia, 9 - Udotea, 10 - Dictyosphaeria cavemosa, 11 - other minor species. DISTANCE, m Qi-f ; P-2 ; Pb-5 ; Q-4 ; *5 ; 7-6; Q7 Figure 15. Vertical distributon of dominant species, biomass and percent cover of algae and seagrasses at Farquhar Atoll. 1 - Thalassia hemprichii, 2 - Thalassodendron ciliatum, 3 - Caulerpa cupressoides, 4 - Halimeda opuntia, 5 - Porolithon gardinen, 6 - Udotea, 7 - Awainvillea arnadelpha. Figure 16. Horizontal distribution o f algal and seagrass species at Farquhar Atol l . 1- Thalassodendron ciliatum, 2 - Udotea, 3 - Halimeda species, 4 - Valonia aegagropila, 5 - Caulerpa cupressoides, 6 - Microdictyon okamurai, 7 - Boodlea smtveoides, 8 - crustose species, 9 - Turbinaria omata, 10 - Liagora ceranoides, 11 - Sargassum ilicifolium, 12 - Laurencia species, 13 - Haloplegma duperreyi, 14 - Thalassia hemprichii. Figure 17. Distribution of macrophyte biomass at Farquhar Atoll (in g.m2-2): 1 - 25081-994; 2 - 2880, 3 - 12092300, 4 - 303294. LAGOON Figure 18. Location of stations and species ratios in phytocoenoses at Aldabra Atoll. 1 - Thalassodendron ciliaturn, 2 - Thalassia hemprichii, 3 - Halimeda opuntia, 4 - Turbinaria ornata, 5 - Laurencia species, 6 - other minor species. Figure 19. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at Aldabra Atoll. 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Halimeda species, 4 - Avrainvillea amadelpha, 5 - Laurencia species, Dictyurus puqnmscem. Figure20. Horizontal distribution o f algal and seagrass species at Aldabra Atol l . 1 - Thalassodendron ciliaturn, 2 - Thalassia hemprichii, 3 - Halimeda opuntia, 4 - Ulva rigida, 5 - Enteromolpha kylinii, 6 - Avrainvillea amadelpha, 7 - Turbinaria omata, 8 - Dictyurus pulpurascens, 9 - Dasya species, 10 - Laurencia species, 11 - S'iafi lamentosa. Figure 21. Location of stations and species ratios in phytocoenoses at Cosmoledo Atoll. 1 - Thalassodendron ciliatum, 2 - Halimeda opuntia, 3 - Laurencia papillosa, 4 - Thalassia hemprichii, 5 - m o d o c e a semlata, 6 - Jania species, 7 - Halodule uninervis, 8 - other minor species. Figure 22. Horizontal distribution of algal and seagrasses at Cosmoledo Atoll. 1 - Thalassodendron ciliatum, 2 - Halimeda opuntia, 3 - Laurencia species, 4 - Thalassia hemprichii, 5 - Qmodocea senulata, 6 - Jania species, 7 - Halodule uninervis, 8 - Lobophora variegata, 9 - Microdictyon okamurai, 10 - Caulerpa species, 11 - Dictyosphaeria cavernosa, 12 - Avrainvillea amadelpha, 13 - Hypnea species, 14 - Tricleocarpa oblongata, 15 - Turbinaria ornata, 16 - Valonia fastigiata 17 - Boodlea struveoides, 18 - Porolithon gardineri, 19 - Rhipilia tomentosa, 20 - Valonia aegagropila. Figure23 Location of stations and species ratios in phytocoenoses at St. Joseph Atoll. 1 - Thalassodendron ciliaturn, 2 - Thalassia hemprichii, 3 - Dictyosphaeria species, 4 - Cladophoropsh suntianensis, 5 - Valonia species, 6 - Mkrdkiyon species, 7 - other minor species. Figure 24. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at St. Joseph Atoll. 1 - Thalassodendron ciliaturn, 2 - Thalassia hemprichii, 3 - Boodlea struveoides, 4 - Cladophoropsis sundunensis, 5 - Laurencia species, 6 - Valonia fastigiata 7 - Dictyosphaeria species, 8 - Halimeda species. Figure 25. Horizontal distribution o f a l g a l and seagrass species at St . Joseph Atoll. 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Halimeda species, 4 - Boodlea shuveoides, 5 - Microdictyon montagnei, 6 - Valonia fastigiata 7 - Valonia um'cular& 8 - Valonia aegagropila, 9 - Dictyosphaeria species, 10 - Rhipilia tomentosa, 11 - Udotea argentea, 12 - Udotea orientalis, 13 - Codium species, 14 - Cladophoropsi3 sundanensis, 15 - Caulerpa species, 16 - Lobophora variegata, 17 - Turbinaria omata, 18 - Laurencia species, 19 - Dictyuruspurpurascens, 20 - Dasya mollis, 21 - Sporolithon sporolithon, 22 - Jania species, 23 - crustose species. LAGOON Figure26. Location of stations and species ratios in phytocoenoses at Astove Island. 1 - Thalassodendron ciliatum, 2 - Thalassia hemprichii, 3 - Caulerpa species, 4 - Laurencia species, 5 -Arpphiroa, 6 - Halirneda species, 7 - other minor species. Figure 27. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at Astove Island. 1 - Caulerpa species, 2 - Thalassia hemprichii, 3 - Thalassodendron ciliatum, 4 - Halimeda species, 5 - Laurencia species, 6 - iagora species. Figure 28. Horizontal distribution o f algal and seagrass species at Astove Island. 1- Thalassia hemprichii, 2 - Thalassodendron ciliatum, 3 - Halodule uninervis, 4 - Halimeda species, 5 - Caulerpa species, 6 - Dictyosphaeria species, 7 - Rhipilia tomentosa, 8 - Valonia aegagropila, 9 - Awainvillea amadelpha, 10 - Turbinaria omata, 11 - Lobophora variegata, 12 - Laurencia Species, 13 - Dictyuruspurpurascens, 14 - Hpnea spinella, 15 - Galaxaura species, 16 - Heterosiphonia species, 17 - Jania species, 18 - Liagora species, 19 - S ' i a jilamentosa. Figure 29. Location of stations and species ratios in phytocoenoses at Mahe Island. 1 - Sargassum species, 2 - Amphiroa foliacea, 3 - Gelidiella acerosa, 4 - Turbinaria decurrencs, 5 - Gracilaria species, 6 - Caulerpa racemosa, 7 - other minor species. Figure 30. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at MahC Island. 1 - Halirneda, 2 - Padina species, 3 - Turbinaria species, 4 - Sargassum species, 5 - Gracilaria species, 6 - Amphiroa foliacea, 7 - Laurencia species, 8 - Tricleocalpa oblongata. Figure 31. Horizontal distribution of algal and seagrass species at Mahe Island. 1 - Thalassodendron ciliatum, 2 - qmodocea serrulata, 3 - Halimeda species, 4 - Caulerpa racemosa, 5 - Ulva rigida, 6 - Dictyota species, 7 - Turbinaria species, 8 - Padina species, 9 - Lobophora vanegata, 10 - Sargassum species, 11 - Gracilaria species, 12 - Amphiroa foliacea, 13 - Hypnea species, 14 - Gelidiella acerosa, 15 - Tricleocarpa oblongata, 16 - Laurencia species, 17 - Halodule uninervis. Figure 32. Location of stations and species ratios in phytocoenoses at Praslin and La Digue Islands. 1 - Sargasmm species, 2 - Cyrnodocea serrulata, 3 - synitgodium isoetifolium, 4 - Thalassia hemprichii, 5 - Turbinaria species, 7 - M n e a pannosa, 8 - Padina species. Figure 33. Vertical distribution of dominant species, biomass and percent cover of algae and seagrasses at Praslin Island. 1 - Thalassodendron ciliaturn, 2 - Thalassia hemprichii, 3 - Synngodium iroetifolium, 4 - Caulerpa serrulata, 5 - Halimeda species, 6 -Padha species, 7 - Lobophora variegata, 8 - Turbinaria species, 9 - Sargassum species, 10 - Hypnea species, 11 - Laurencia species. Figure 34. Horizontal distribution o f species o f algae and seagrasses at Praslin and La Digue Islands. 1 - Halodule uninervis, 2 - Thalassia hemprichii, 3 - Syringodium isoetifolium, 4 - Thalassodendron ciliatum, 5 - Cymodocea senulata, 6 - Halophila ovalis, 7 - Halimeda m,acroloba, 8 - Dictyosphaeria cavernosa, 9 - Caulerpo species, 10 - Lobophora variegata, 11 - Turbinaria species, 12 - Dicryota species, 13 - Dicryopteris polypodioides, 14 - Turbinaria species, 15 - Sargassum species, 16 - Laurenczh species, 17 - Hpnea species, 18 - Heterosiphonia species, 19 - Gracilaria crarso, 20 - crustose species.