Distribution of Microborers within Planted Substrates along a Barrier Reef ‘Transect, Carrie Bow Cay, Belize Jeffrey A. May, lan G. Macintyre, — and Ronald D. Perkins stood, microborings were not present in the sec- ABSTRACT ond subsurface station, in fore-reef sand at a A diverse assemblage of endolithic microorgan- depth of 24 m. isms was identified in a series of carbonate sub- strate stations planted along a transect across the barrier reef near Carrie Bow Cay, Belize. ‘These tropical endoliths at the sediment-water interface Introduction include the cyanophytes, Hyella tenuior Bornet and Flahault, Mastigocoleus testarum Lagerheim, and Endoliths are microorganisms (generally less Plectonema terebrans Bornet and Flahault, the chlo- than | pm to 100 pm in diameter) that penetrate rophytes, Ostreobium brabanttum Weber Van-Bosse calcareous substrates by chemical and/or me- and Phaeophila englert Reinke, the rhodophyte Por- phyra sp. (Conchocelis-phase), and various fungi. chanical means and that leave post-mortem mi- This assemblage was subdivided into an upper croscopic networks. They are distinguished from photic zone assemblage dominated by Mastigoco- “epiliths,’ > which live only on a substrate’s sur- leus, Hyella, Phaeophila, and Ostreobium species, and face, and from “‘chasmoliths,’” b w) hich adhere to a lower photic zone assemblage dominated by surfaces of fissures or cavities within the substrate Porphyra sp. (Golubic et al., 1975). Endoliths include cyano- Subsurface endolithic activity detected at the shallow lagoon station included filamentous irreg- phytes, chlorophytes, rhodophytes, fungi, and ular polygonal networks, irregular flattened possibly bacteria and sponges. masses, and regular crenulate discoids, which dif- The most diverse and ecologically important fered from and were less diverse than the assem- microborers occur in the marine setting; their blage at the sediment-waiter interface. Affinities boring patterns—size, mode of branching, spatial of these subsurface microborings are unknown but they resemble endolithic traces and organic arrangement, and growth directions—are taxo- scars variously attributed to fungi, bacteria, and nomically characteristic (Golubic, 1972). The ma- Actinomycetes. The regular discoids and irregular rine endoliths have been subdivided on the basis masses occurred only in association with the fila- of bathymetric and regional assemblage distri- mentous form, and therefore may be related re- butions, which are controlled by geographic, cli- productive bodies. For reasons not fully under- matic, photic, and environmental factors (Perkins and Halsey, 1971; Perkins, 1972; Rooney and Jeffrey A .May ,Departmen to fGeology ,Rice University ,Box 1892, Houston ,Texas 77001 .Ian G .Macintyre ,Departmen to fPaleo- Perkins, 1972; Golubic et al., 1975; Green, 1975 biology N, ationa Ml useum o Nf atura Hl istory S,mithsonia nInstitu- Various studies of ancient and modern forms tion ,Washington ,D.C .20560 .Ronald D .Perkins ,Departmen tof have indicated that endoliths may be used to Geology ,Duke University ,Box 6665 ,College Station ,Durham, INCH 27708. interpret paleoclimatic conditions and to recon- 93 94 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES struct depositional environments (for example, Methods see Swinchatt, 1965; Gatrall and Golubic, 1970; Perkins and Tsentas, 1976). As well, microboring This study examined two types of carbonate organisms have been used to establish the posi- substrates planted at and below the sediment- tions of relict shorelines (Perkins and Halsey, water interface along a reef transect of Carrie 1971; Edwards and Perkins, 1974) and to detect Bow Cay (Figure 62): (1) crushed, fresh inner sediment transport (Rooney and Perkins, 1972). shell parts of the queen conch, Strombus gigas Microborers modify both lithified and unlithi- Linnaeus, and (2) cleaved calcite rhombohedra. fied carbonate coasts (Purdy and Kornicker, Samples of each type were retained as controls. 1958; Hodgkin, 1970; Schneider, 1976), in the Fragments from | to 10 mm in size were attached colonization of shifting upper sublittoral sub- to 15 cm’ plexiglass plates (one type per plate) strates—where they create finer carbonate sedi- and 40 cm long polyvinyl! chloride (PVC) pipes ments, preferentially remove certain components, (types mixed) by a thin film of epoxy resin. and initiate micrite rind formation (Bathurst, Fourteen substrate-covered plexiglass plates were 1966; Golubic, 1969; Alexandersson, 1972; Roo- mounted on short lengths of protruding PVC ney and Perkins, 1972; Perkins and ‘T’sentas, pipe to maintain the samples above shifting sub- 1976)—and in their alteration of the deep-sea strata (Figure 63). These plates were placed in sedimentary record (Zeff and Perkins, 1979). En- pairs at seven locations extending from the la- dolithic algae not only dissolve carbonates, but goonal Thalassia zone (depth 1.2 m) to the fore- also induce precipitation of calcium carbonate reef slope (depth 27.4 m). One subsurface pipe within shallow marine corals (Schroeder and station (consisting of one pipe) was inserted into Ginsburg, 1971; Schroeder, 1972a, b; Scherer, the sea floor in the Thalassia zone (Figure 64) and 1974). Furthermore, their biologically related another into the Halimeda-rich sand of the fore- physico-chemical processes may influence low- reef sand trough (depth 24 m). Exposure time of temperature sedimentary mineralization within substrates ranged from 21 to 24 months. boring networks (Taylor, 1971; Kobluk and Risk, After being harvested, the planted substrates E TODN were preserved in 4 percent formaldehyde in 0.1 Recently, planted substrates have been used to M phosphate neutral buffer. Fragments intended identify modern microboring assemblages and to for light microscopic study were carefully scraped establish rates of infestation (Golubic, 1969; to remove epilithic organisms, then dissolved with LeCampion-Alsumard, 1975; Perkins and Tsen- 5 percent EDTA solution (van Reine and van tas, 1976). The present investigation examined den Hoek, 1966) at a pH of 6. Although the three- and identified endoliths within planted substrates dimensional configuration of the microborers is in order to determine the distributional patterns lost because of their collapse, organic structure of these organisms at the sediment-water interface and color are not damaged by this slow-dissolving along a reef transect. Two stations planted below solution. Extracted tissues were then mounted on the sediment surface allowed a cursory examina- glass slides. tion of subsurface microboring activity. Scanning electron microscopic (SEM) analysis ACKNOWLEDGMENTS.— The authors thank M. was based on the casting-embedding technique of R. Carpenter (Smithsonian Institution) and Golubic et al. (1970). An alcohol dehydration R. G. Zingmark (University of South Carolina) series was followed by an infiltration series using for field assistance, and G. W. Lynts and R. B. Durcupan ACM Araldite Base Embedding Searles (Duke University) for helpful comments Agent. After polymerization within plastic hold- on the manuscript. Support for part of this re- ers, the substrate fragments were exposed by search was provided by National Science Foun- means of a rotary grinding tool, then etched with dation Grant OCE74-12555 AOl to Duke Uni- 3 percent hydrochloric acid. This technique re- versity. vealed plastic casts of the microboring networks, NUMBER 12 99 Lagoon Back Reef freee Inner Fore Reef Outer Fore Reef uhe aRlu- bble Patch Ree fZon e |Rubble & Pavemen tZ Soanne Cdres tHigh Spur & Groo &ve Zone Low Spur & Gro Ionvne eZone Ree frae ee asics 5 DEETH Zo AnNe D... 1° | 1100 12 Z0o0ne 1300 7 1400 500 Slope [600 meters O SLFOUBCSATTRIOANT eEe 4 1.5m 24.4mM 12.2mM 27.4mF stanton. tft tt ft ft it LY vw SOO 1// 2 1/2 Th If 10 | | | # > 10] | 2|0 | | | “a ae . 20| | I L30 meters | | | 30, : I | | ; [es I 1 | | || | | | | | l | | | p7t7-y) SS | Y eG SHE . 2Y co CT WONa EMA ~P LTYEECRTEOBNRANS Y W yY, Y, Y YYW | ! | | 1 | ! Ze W|A WA SA Vin WY MASTIGOCOLE |US WA TESTARU YM Yj T 0 F: || I I =| = ) | I Hl * HYELLA TENUIOR | | || || ALGAE 2 oe |VL I | i] PHAE OENPHGILLEARI iN | | || | Y U/ | | | Za ! OSTREOB IBURMABANT I|UM| l | | | I| cr 2 | PORPH YSRPA.(CONCHOCE LZIZS) | | Demme, SPO RS ATIARNLUGCTURES FUNGI FORM ABSN DC (Funga flilament sfound in a lsl ubstrate station s)FORM A Ficure 62.—Idealized cross section of Carrie Bow Cay transect showing locations of substrate stations planted at sediment-water interface and the distribution of endoliths collected from these plates (hatched squares = great abundance; hatched rectangles = presence observed). which retained the original spatial relationships consisted of Hyella tenuor Bornet and Flahault, of the endoliths and their three-dimensional con- Mastigocoleus testarum Lagerheim, and Plectonema figurations. The mounted plastic blocks were terebrans Bornet and Flahault. Green algal micro- scanned with an International Scientific Instru- borers, likewise abundant, included Ostreobium bra- ments Super II electron microscope after vacuum banttum Weber Van-Bosse and Phaeophila engleri shadowing with gold-palladium alloy. Casts of Reinke. Red algae were much less abundant and boring networks were correlated with the endo- were represented only by the Conchocelis-stage of _ liths isolated by acid dissolution. Porphyra sp. Fungal forms were found in almost all samples. Results Plectonema terebrans was the most common cy- anophyte at all stations. Diagnostic are its ENDOLITHS AT THE SEDIMENT-WATER_ INTER- smooth, elongate, thread-like filaments 2 to 4 wm FACE.—Blue-green algae were ubiquitous and in diameter, which may run along the interior 96 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES Figure 63.—Patch reef zone substrate station, Carrie Bow Cay, showing location of plates abov eth esediment-wate rinterface. surface of the substrate or may form dense, inter- woven meshworks (Figure 65a,6). Also ubiquitous was Mastigocoleus testarum, which is composed of sharply curved to elongate filaments 5 to 8 wm in diameter that have numerous short lateral branches and heterocysts (Figure 65c,d). The mor- phology of M. testarum penetrating inorganic sub- strates 1s much more affected by the rhombo- hedral microstructure than is the morphology of P. terebrans; this observation corresponds with findings of LeCampion-Alsumard (1975). Hyella tenuior, which is less common, appears as a cluster of slender, elongate, relatively straight to bent filaments 5 to 8 wm in diameter (Figure 662,6). These filaments grow subperpendicular to the surface of the substrate. Figure 65.—Scanning electron and transmitted light pho- tomicrograph so ef ndolithi calgae a :P, lectonem aterebran sform- ing a typica ldense network of filaments ,acid-etched mollusk fragment, Thalassia zone (note the smooth, elongate, fine nature of the plastic casts); b, P. terebrans isolated by disso- lution o fa mollusk fragment ,reef-crest zone ;c ,characteristic Ficure 64.— Thalassia-zone subsurface substrate station ,Car- heterocys tdevelopmen to fMastigocoleu stestarum shown on rie Bow Cay, showing a closeup of the buried substrate- plastic casts ,acid-etched mollusk fragment ,Thalassia zone; covered 40 cm long PVC pipe. Note that only the protective d ,M .testarum isolated by dissolution of a mollusk fragment, collar and a small portion of the pipe protrude above the Thalassia zone (note the heterocyst development marked by sediment-wa tinerterface. arrows). (Scale = 50 wm for a, d; 40 wm for 6; 25 pm for c.) NUMBER 12 oF, PAe. >é-LSAOT heap 98 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES ff Vtipj Wy, WW NUMBER 12 99 Phaeophila engleri was the most abundant and sides, so that these spore cases appear positioned widespread chlorophyte. This species is charac- along filaments (Figure 694). The irregular hy- terized by rectilinear branching and pronounced phae of less than | wm diameter become branched bulbous or irregularly ovoid, 15 to 20 pm swell- and fused, and form interconnected networks. ings at points of branching or along the irregular Fungal form C has 5 to 15 um globose to discoid 5 to 10 wm filaments (Figure 66c,d). The largest | sporangial bodies with indented ends that appear boring species detected, Ostreobsum brabantium has “doughnut-shaped” (Figure 68c). These bodies digitate growths of single or bilobate branches occur alone or in clusters directly upon the surface (Figure 67a,b). Single plants up to 1 mm in length of endolithic algae; connective hyphae are lack- radiate into the substrate; individual branches of ing. 40 to 60 wm may enlarge up to 120 um before ENDOLITHS BELOW THE SEDIMENT- WATER INTER- bifurcation. The Conchocelis-stage of the rhodo- FACE.—In contrast to the diverse assemblage of phyte Porphyra sp. is characterized by rectilinear microorganisms boring into the substrates branching of long and fine, 2 to 3 ym filaments planted at the sediment-water interface, only a running along slightly beneath the substrate sur- few endolithic forms were found below the sur- face (Figure 67c,d). face. These boring organisms were present only Extremely fine filaments from less than 1 up to in the molluscan fragments planted within the 4 pm in diameter occur in a wide variety of forms, lagoonal Thalassia zone. Classification is problem- from non-branched to extensively branched and atic as these forms have not previously been fused, sparse to massive networks (Figure 68a,)). described. No microboring activity was recorded These filaments probably represent fungal hy- at the subsurface station in the fore-reef sand- phae. The hyphae appear to be directed towards trough zone. algae and can be observed penetrating these or- An extremely irregular, polygonal network of ganisms, presumably in the act of feeding (Figure variable and intermittent filaments 5 to 7 ym in 685). Three different types of structures observed diameter (Figure 70a,5) commonly crosses the with the scanning electron microscope were at- regular and parallel lines representing remnants tributed to fungal spore cases. Form A has 5 to of the organic matrix that separated the inorganic 15 pm ovoid to pyriform reproductive bodies, crystals of the gastropod shell. This network of from the bases of which radiate long and thread- variously spaced filaments bores just below the like, i to 2 um hyphae (Figure 69a): These hyphae surface of the molluscan substrates. The filaments are typically unbranched and connect spore cases. are curvilinear, have a twisted appearance, and Form B has 8 to 20 pm, globose to oblong fruiting branch sideways. This form is recurrent in ap- bodies with connective hyphae attached at their proximately 10 percent of the molluscan frag- ments throughout the pipe planted in the Yhal- FiGuRE 66.—Scanning electron and transmitted light pho- lasta zone, and was not found in the control tomicrographs of endolithic algae: a, elongate casts of the samples or in samples from the sediment-water blue-green alga Hyella tenuior directed away from the sub- interface. Possibilities for taxonomic assignment strate surface ,some branching near their bases ,plastic cast include marine fungi (Phycomycetes, Ascomy- within an acid-etched calcite rhomb, Thalassta zone (very little control is exerted by the substrate microstructure); ), cetes, and Deuteromycetes) and filamentous bac- filaments o fH .tenuzo rdisplaying elongate ,somewha trectan- teria (Actinomycetes). gular cells ,isolated by dissolution o fthe molluscan substrate, Another group occurs as regular patches or Thalassia zone; ¢, green alga Phaeophila engleri exhibiting regular crenulate discs associated only with the characteristic ovoid swelling at points of branching and irregular polygonal networks described above rectangular branching pattern ,plastic cas to fetched mollusk (Figure 70c,d). These may be reproductive struc- fragment T, halassia zone ;d P, .engler di emonstrating probable sporangia (arrows) and swellings at branching points, fila- tures or separate endolithic forms; they rang¢ ments isolated by dissolution of a molluscan substrate ,7hal- from 125 to 200 um in diameter and average 2 assia zone. (Scale = 50 pm for a; 25 wm for 6, c; 40 wm for d.) pum in thickness. Although they may be remnants 100 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES b Peeeagk.s ts eal NUMBER 12 101 FicurE 68.—Scanning electron photomicrographs of endolithic fungi: a, little-branched, thin plastic casts believed to be funga lhyphae ,intertwined with the larger blue-green alga Plectonema terebrans, etched mollusk fragment, Thalassia zone; 6, network of fine fungal borings covering and possibly feeding (arrows) upon the underlying alga, plastic casts within an etched mollusk substrate, Thalassia zone. (Scale = 5 um for a; 25 um for 0.) of the organic matrix, no analogous structures Discussion were found in any control sample or in any sample infested at the sediment-water interface. ENDOLITHS AT THE SEDIMENT-WATER INTER- FACE.— The bathymetric distribution of Belizean FiGuRE 67.—Scanning electron and transmitted light pho- endoliths was compared with similar tropical mi- tomicrographs of endolithic algae ;a ,large ,radiating growth croboring assemblages recovered from artificial form of the green alga Ostreobium brabantium ,plastic cast substrate stations planted in reefs off St. Croix within an acid-etched mollusk fragment ,Thalassia zone (note and Jamaica (Green, 1975; Perkins and Tsentas, both the single and bilobate branches ,background forms are 1976). The distribution of autotrophic endolithic algae and fungi); 6, O. brabantium filaments isolated by dis- solution of a molluscan substrate, patch-reef zone; c, char- organisms is related to light penetration in the acteristic rectilinea rpattern o fthe Conchocelis-stage o fthe red sea—both the intensity of illumination and spec- alga Porphyra sp., plastic cast, enhanced on a microscale by tral composition (Golubic et al., 1975). Although boring within a calcite rhomb, fore-reef slope zone (larger endolithic organisms cannot be assigned to abso- forms are an unidentified alga with strong microstructural lute depths—owing to variations in water clarity, contro lupon its boring pattern) ;d ,Conchocelis-stage of Por- currents, and other environmental factors—Per- phyra sp. displaying fine filaments in the typical rectilinear pattern, isolated by dissolution of a molluscan substrate, kins and Tsentas (1976) pointed out that “clear- fore-reef slope zone. (Scale = 200 um for a; 100 wm for 6; 25 water” assemblages might be used to estimate lum fo rc ,d.) maximum depths for endolithic algae. Their di- 102 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES Ficure 69.—Scanning electron photomi- crographs of endolithic fungi: a, form A, characterized by ovoid to pyriform repro- ductive bodies ,distributive unbranched casts of hyphae radiate from the base of the fruiting bodies just below the surface of the substrate, plastic cast of an etched calcite rhomb, fore-reef slope; 6, repro- ductive bodies of fungal form B laterally connected by hyphae, etched mollusk fragment T, halassia zone (these bodie sare typically globose to oblong ,note twisted or irregular appearance of the hyphal casts) ;c ,“doughnut-shaped” o rindented sporangial bodies of fungal form C, plas- tic cast in an etched mollusk substrate, Thalassia zone (note that these occur in close proximity to the outer substrate sur- face or to algal borings). (Scale = 10 um for a,b; 25) imi tone) NUMBER 12 103 vision of such assemblages into an upper photic shaped” bodies, respectively, were found only in zone of Mastigocoleus, Hyella, Phaeophila, and Os- the shallow reef-crest, patch-reef, and Thalassia treobium species, and a lower zone dominated by zones off Belize. Porphyra sp. in its Conchocelis-phase parallels, to ENDOLITHS BELOW THE SEDIMENT- WATER INTER- some extent, the zonation found in the present FACE.—Fungi may be as important as bacteria in study (Figure 62). breaking down organic matter into a nutrient Ostreobium brabanttum was observed only in the source for other organisms. Marine fungi may be shallowest (1.2 and 1.5 m) sites of the Thalassia as versatile and potent in their feeding activity as -and patch-reef zones off Belize. In St. Croix, their terrestrial and fresh-water counterparts, and although present to 30 m, O. brabantium was pre- are probably able to attack the entire spectrum dominant in depths less than 15 m (Perkins and of plant and animal detritus (Johnson and Spar- Tsentas, 1976). Also, only the three shallowest row, 1961). Endolithic fungi in living and dead sites off Belize contained Ayella tenuior, which was shells at the sediment-water interface produce found down to 45 m in Jamaica (Green, 1975). intertwined, anastomosing, and branched net- Four species of algae occurred at all depths works, and are able to use the energy contained along the Carrie Bow Cay transect. Phaeophila in organic conchiolin and chitin matrix and to engler. was most abundant from 1.2 m to the 7.6 parasitize algal microborers (Kohlmeyer, 1969; m spur and groove zone of the inner fore reef; Calvaliere and Alberte, 1970; Green, 1975; Zeff similarly, this species is very common in the and Perkins, 1979). shallower zones of St. Croix and Jamaica. Mastu- Although marine fungi are generally believed gocoleus testar'um was most abundant in the upper to be restricted to the aerobic surface layers of 12 m of the Belize sites, as was the case in St. bottom sediments, the Thraustochytriacea and Croix. Off Belize, however, it decreased slightly Chyritidiaceae commonly occur well below the in the reef-crest and Thalassia zones. Plectonema sediment surface (Clokie, 1970; Bremer, 1976: terebrans was ubiquitous off Belize as well as Ja- Johnson, 1976). The similarity between irregular maica and St. Croix, except that in Belize it was polygonal networks observed in this study and less abundant in the Thalassia and reef-crest microborings attributed to fungi leaves little zones. Patchily distributed below 1.5 m, Porphyra doubt that these polygonal networks are of fungal sp. was most common in depths of 12 to 27 m, origin. the deepest zone examined off Belize. This pat- The associated irregular masses and crenulate tern has also been reported from the Australian discoids may be the reproductive bodies of these Barrier Reef (Rooney and Perkins, 1972), the boring fungi. Kohlmeyer (1969) described irreg- Puerto Rico shelf (Perkins, 1972), and Woods ular black peritheca and conidia 100 to 125 um Hole, Massachusetts (Golubic et al., 1975), as in diameter as fruiting bodies for endolithic ma- well as Jamaica and St. Croix (Green, 1975; rine Ascomycetes and Deuteromycetes. Alterna- Perkins and Tsentas, 1976). tively, these masses may be separate endolithic Although thin filaments believed to be fungal fungal colonies, similar to irregular patches and hyphae were present at all depths, the distribu- to crenulate rosettes attributed to fungal colonies tion of different sporangial structures was depth attacking spores, pollen, and other organic micro- dependent. Fungal form A, with pyriform to fossils (Elsik, 1971). ovoid bodies, from which basal hyphae radiate, In addition, two other groups of organisms, the was found only in the sample from 27 m on the bacteria and Actinomycetes, could produce en- fore-reef slope. Similarly, Perkins and Tsentas dolithic scars resembling these forms. Similai (1976) found a reticulate fungal form at 30 m in scars on modern and ancient spores and pollen St. Croix. Forms B and C with laterally arranged have also been attributed to bacteria and Acti- globose spore cases and isolated “doughnut- nomycetes (Moore, 1963; Elsik, 1966, 1971; Hav- 104 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 7es > NUMBER 12 105 inga, 1971). Both groups are abundant at all PALEOECOLOGIC AND GEOLOGIC SIGNIFICANCE.— levels within bottom sediments (ZoBell and Fel- Endoliths and their borings found in carbonate tham, 1942) and at all depths sampled in lakes sediments that are exposed on the sea floor may and the ocean (ZoBell and Rittenberg, 1938; provide valuable information for the study of Weyland, 1969; Willoughby, 1976). Boring by paleoecological conditions of carbonate sedi- bacteria and Actinomycetes into carbonate sub-. ments. The microborers and their distributional strates has not yet been investigated. patterns at the sediment-water interface of Belize The heterotrophic or chemoautotrophic mode closely resemble those of assemblages previously necessitated by endolithic life within buried sed- examined in St. Croix, Jamaica, and Florida iments may explain the occurrence of these forms (Perkins and Tsentas, 1976). It thus becomes only in the molluscan shell fragments planted in possible to identify endoliths typical of a tropical the Thalassta zone. The lack of endoliths within shallow marine setting and to establish their oc- inorganic calcite rhombs planted below the sedi- currence in upper photic and lower photic zones. ment-water interface may indicate parasitic or Microborings commonly are preserved within an- saprophytic requirements of these organisms. Bor- cient carbonates (Hessland, 1949; Gatrall and ing might be an effort to obtain nutrients from Golubic, 1970; Golubic et al, 1975), but they have the organic matrix of the molluscan substrates. not been examined in relation to recent zonations No reasons are known for the lack of these endo- for the interpretation of paleoenvironmental con- liths in the deeper fore-reef sand-trough zone of ditions. Carrie Bow Cay. Although both this environment and the Thalassia zone consist of a carbonate sand Conclusions bottom, the latter may contain more interstitial detrital organic matter or may be a more reducing Carbonate substrates, both conch shell frag- environment. The availability of nutrients may ments and cleaved calcite, planted just at the control the distribution of these endoliths and sediment-water interface in various depths along therefore may explain the paucity of these forms the reef transect off Carrie Bow Cay, Belize, within coarse sediments lacking necessary nutri- contained a diverse assemblage of microboring ent sources. Eh conditions within sediments may forms. The blue-green alga Hyella tenuior and the also be a controlling factor. Endolithic boring in green alga Ostreobium brabantium were restricted to this case may not be an “active” search for or- the shallowest sample sites of the upper photic ganic matrices in carbonate substrates, but a zone, which is also characterized by the abundant “passive” result of metabolic reaction or a form blue-green alga Mastigocoleus testarum and the of protection from interstitial grazers. green alga Phaeophila engler: and very little of the Conchocelis-stage of the red alga Porphyra sp. The Figure 70.—Scanning electron and transmitted light pho- lower photic zone, below approximately 12 m, Is tomicrographs o funidentified microborings collected in sub- characterized by abundant Porphyra sp. and con- surface station in the Thalassia zone: a, irregular polygonal siderably less M. testarum and P. englert. The blue- network of varying intermittent borings, plastic cast within green alga Plectonema terebrans was abundant at all an etched mollusk fragment, 20 cm below the sediment- water interface; b, irregular polygonal endolithic network depths examined. Hyphae of fungal endoliths within molluscan substrate, collected 35 cm below the sedi- were present at all sample sites, although different ment-wate rinterface ;c ,irregular ,flattened aggregates asso- sporangial forms were bathymetrically restricted. ciated with a polygonal network, these patches might be This study of algal endoliths supports previous related reproductive bodies o rseparate colonia lforms ,plastic findings of a distinct tropical assemblage th cast of acid-etched molluscan substrate ;d ,crenulate discoid may provide a basis for paleoecological studi associated with a polygonal network, this also might be a separate organism or related reproductive body ,plastic cast ancient assemblages. of an etched mollusk fragment, 5 cm below the sediment- Below the sediment-water interface off Belize, water interface. (Scale = 50 um for a, c, d; 25 um for 0.) endoliths infested only the molluscan (conch 106 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES fragments in the Thalassta-zone station and were tened amorphous masses, and (3) regular crenu- not present in material buried in a deeper fore- late discoids. These microborers have unknown reef sand-trough station. Restriction of infestation taxonomic affinities but they closely resemble to the molluscan shell fragments suggests that endolithic traces and scars attributed to fungi, these subsurface endoliths require organic matri- bacteria, and Actinomycetes. Further studies are ces as nutrient sources. Three types of endoliths needed to explain the origin and geological im- occur below the sediment-water interface: (1) portance of these possible environmental indica- irregular filamentous networks, (2) irregular flat- tors and post-depositional carbonate degraders. Literature Cited Alexandersso nT,. Golubic S, 1972. 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Geologica lSociety of clastic Bacteria in the Sea .Journa lof Bacteriology, Americ aB,ulletin 8,3:1139-1150. 35:275-287. May, Jeffrey A., Macintyre, Ian G., and Perkins, Ronald D. 1982. "Distribution of Microborers within Planted Substrates along a Barrier Reef Transect, Carrie Bow Cay, Belize." The Atlantic Barrier Reef Ecosystem at Carrie Bow Cay, Belize 12, 93–107. View This Item Online: https://www.biodiversitylibrary.org/item/131277 Permalink: https://www.biodiversitylibrary.org/partpdf/387313 Holding Institution Smithsonian Libraries and Archives Sponsored by Biodiversity Heritage Library Copyright & Reuse Copyright Status: In Copyright. Digitized with the permission of the rights holder License: http://creativecommons.org/licenses/by-nc-sa/3.0/ Rights: https://www.biodiversitylibrary.org/permissions/ This document was created from content at the Biodiversity Heritage Library, the world's largest open access digital library for biodiversity literature and archives. 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