ATOLL RESEARCH BULLETIN 
NO. 512 
THE AQUATIC ENVIRONMENT OF TWIN CAYS, BELIZE 
KLAUS R~JTZLER, IVAN GOODBODY, M. CRISTINA DIAZ, 
ILKA C. FELLER, AND IAN G. MACINTYRE 
ISSUED BY 
NATIONAL MUSEUM OF NATURAL HISTORY 
SMITHSONIAN INSTITUTION 
WASHINGTON, D.C., U.S.A. 
SEPTEMBER 2004 

THE AQUATIC ENVIRONMENT OF TWIN CAYS, BELIZE 
KLAUS RUTZLER', IVAN GOOD BODY^, M. CRISTINA DIAZ~,  
ILKA C. FELLER~, AND IAN G. MACINTYRE' 
ABSTRACT 
The rich fauna and flora of Twin Cays off southern Belize were explored and 
compared with coral and turtle-grass habitats of the surrounding Belize lagoon and the 
nearby barrier reef. Among the many subtidal habitats found in these cays, some 20 
stations were routinely sampled to study the composition of plankton and benthos, 
sediment and peat bottoms, and to investigate the parameters that determine distribution. 
The work also focused on distribution patterns, animal behavior, and community 
development over geological time scales. Each station is examined for its particular 
properties, including topography, substratum types, environmental parameters, and 
predominant organisms and communities, particularly the sessile benthos. 
INTRODUCTION 
Twin Cays off the southern coast of Belize are so named because a wide tidal 
channel splits the roughly oval mangrove island into two unequal parts. These islands are 
the closest mangrove development to Carrie Bow Cay and the Smithsonian's Carrie Bow 
Marine Field Station, less than 4 km to the northwest. They are among hundreds of 
mangrove cays perched on the leeward top of the Belize barrier reef platform (Plate la). 
We call this type of tidal forest "island mangrove," to distinguish it from "mainland 
mangroves," which fringe the continental shores, including the tidal mouths of freshwater 
rivers and creeks (Riitzler and Feller, 1996) and are awash by full-oceanic-salinity 
seawater. By contrast, mainland mangroves are subjected to a salinity gradient ranging 
from freshwater to fully oceanic, caused by coastal runoff. The absence of freshwater at 
Twin Cays' marine environment (except during periods of heavy rains), combined with 
Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, 
Washington, D.C. 20560-0163. 
Department of Life Sciences, University of the West Indies, P.O. Box 12, Kingston 7, Jamaica. 
Museo Marino de Margarita, Boca del Rio, Peninsula de Macanao, Nueva Esparta, Venezuela. 
Smithsonian Environmental Research Center, Smithsonian Institution, Edgewater, MD 21037 
Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, 
D.C. 20560-0125. 
the area's small tidal range accounts for the extensive and diverse development of marine 
habitats in these islands. 
Twin Cays (16" 49' 48" N, 88" 06' 1 I" W; at their center) are part of the Stann 
Creek District and are situated 15.5 km due 8 1" (ENE) of Sittee Point, the nearest 
mainland, and 20 km due 142" (SE) from Dangriga, the nearest town. The islands crown 
the N-S directed barrier-reef carbonate platform which at that location is 8 km wide and 
0-7 m (average 2.5 m) deep. To the west of Twin Cays, the platform extends for about 5 
km where its depth drops rapidly to about 20 m, the average for the trough-like main 
lagoon, including the Inner Channel that is a protected shipping lane for large vessels. 
The lagoon has a sediment bottom covered mainly by seagrass, Thalassia testudinum. 
About 2 km to the east of Twin Cays, the reef platform is delineated by the intertidal 
barrier-reef-crest. From there, the reef slopes rapidly, within a distance of 400 m, toward 
the continental dropoff (Riitzler and Macintyre, 1982). 
Barring unusual currents and storms, the lagoon water west of Twin Cays is 
influenced by mainland runoffs; the water east of the islands has open-ocean bluewater 
characteristics that are enhanced by a series of three 600 to 800 m wide and 5 to 8 m deep 
breaks through the barrier reef, South Water, Carrie Bow, and Curlew cuts. Within the 
perimeter of the cays, topography, water depth, extent and kind of vegetation, and 
seasonal and meteorological events determine habitat- and water quality parameters, 
including substratum composition and inclination, suspended and settled sediments, 
water level and flow velocity, temperature, salinity, turbidity, dissolved substances, and 
nutrients. 
In the following sections we summarize and illustrate the habitat characteristics of 
a number of tidal and subtidal locations throughout Twin Cays that served as sites for 
collecting, observation, illustration, and experimentation of sessile organisms for many 
researchers over the years since 1984 (see also, Calder, 1991a, b; Diaz et al., 2004; 
Goodbody, 2004a; Littler and Littler, 2000; Littler et al., 2004; Ott and Bright, 2004; 
Parrish and Ryan, 2004; Richardson, 2004; Winston, 2004; Wulff, 2004). 
STUDY AREA AND METHODS 
Twin Cays actually consist of four fully established mangrove islands. To identify 
the various topographic features, they were labeled by newly invented place names (no 
traditional local designations existed) suggested by participants of the Smithsonian 
Caribbean Coral Reef Ecosystems (CCRE) program (Fig. 1). The largest cay is East 
Island; it measures 52.1 ha in area, is 1400 m in maximum length, and 674 m at its widest 
point, just south of its center. East Island is nearly cut in half by the west-east oriented, 16 
to 58 m wide Lair Channel, separating a northern and southern portion. Both include in- 
shore ponds, lakes, and tidal mudflats. The northern section contains Candy's, East, and 
Hummingbird ponds and Aanderaa Flats; the southern part is distinguished by Hidden 
Lake and Boa Flats. West Island, the second largest cay and nearly a smaller mirror 
image of the former, extends over 21.5 ha and measures 895 x 377 m. It is separated from 
East Island by the s-shaped Main Channel which tapers from 136 m width at the south 
entrance into Twin Cays to 8 m at the northern exit. West Island includes the tidal West 
a Dredged & fllled oreor - 
Red mangrove lnnge 
Figure 1. Map of Twin Cays based on aerial photographs taken in 2002, with station numbers (grid 
coordinates used in this survey (map, M. K. Ryan). 
4 
J l 5  
1 j 1 
I 
. I 7  I 
8 
J 1 1 lo 
1 
Ill 
i 
i 
l2 
1 
113 
i I 
14 
15 
I 
Pond and Sinkhole Flats; its northward extension is formed by two islets, Big Dipper (0.5 
ha, 132 x 64 m) and Little Dipper (0.2 ha, 65 x 39 m). Several smaller islets, or, rather, 
isolated stands of mangrove trees, developed and vanished in different places over the 
past 20 years of our study, for instance, the one just outside Turtle Cove (Figs. 1, 7). 
The total shoreline of Twin Cays (excluding interior ponds, lakes, and mudflats) 
is 8.1 km long, more than half of that made up by the inshore mangrove fringe, the rest 
directly exposed to the open Belize lagoon. The tide is micro-tidal and of mixed 
semidiurnal type, with a mean range of 15 cm (Kjerve et al., 1982); maximum 
fluctuations have a range of 40 cm. Water surface temperature (lagoon at Carrie Bow 
Cay) averages 25" C in February, 30" C in August, with recorded extremes of 23.5"- 
3 1 So; air temperature minima and maxima differ only slightly, 22.5"-34.5" C (Koltes et 
al. 1998). Predominant wind direction during October through February is from the 
northwest, the rest of the year it is northeast to east. Monthly preciptation is lowest 
between March and May (0-25 rnrn), highest between June and November (100-480 
rnrn) (Riitzler and Ferraris, 1982; Koltes et al., 1998). Salinity in the open lagoon is fully 
oceanic, 35-36%0. Reactive silica content of interstitial water from sediments collected 
off Twin Cays (South Point) reaches 1.2-1.5 mg Si0211 (as compared with 0.3-0.4 mg 
around Carrie Bow Cay), with terrigenous particulate silica (87-92%) dominating the 
sediment fine fraction, 10.25 rnrn (0% at Carrie Bow) (Riitzler & Macintyre, 1978). 
Station numbers were assigned from an arbitrary grid (mesh-size ca. 135 m) 
superimposed on a 1985 version of a Twin Cays map (Fig. 1). Large-scale measurements 
and water-depth values outside Twin Cays were taken from nautical chart 28 167 (U. S. 
Defense Mapping Agency, HydrographicITopographic Center, Washington, DC; 1984 
edition). Topographic measurements at Twin Cays were based on a map from aerial and 
satellites images (Rodriguez and Feller, 2004). 
DESCRIPTION OF STATIONS 
These descriptions are presented in sequence from north to south and west to east. Station 
numbers are based on number-letter combinations from the aforementioned grid (Twin 
Cay locations are covered by the ranges 4-14 and E-M). Estimates of prevailing 
environmental conditions are expressed as follows: L=light exposure; C=current flow (+ 
is strong, & moderate, - low); T=temperature and S=salinity. These latter parameters are 
not mentioned if they are normal (close to open-lagoon water conditions) but are listed as 
"stressful range" (with measured range values where available) if they vary beyond the 
fluctuations of the open lagoon. 
Sta. 4 I, Little Dipper (Figs. 1,2; Plate 1 b) 
Location and Topography. South shore of the islet, facing Main Channel. 
Habitats. Mixture of free hanging roots and roots embedded in substratum. Sandy 
bottom with turtle grass (Thalassia testudinum). 
Depth. 1.5 m. 
Environmental Conditions. L: +; C: +. 
Sediment. Fine-grained sand. 
Communities. Algae (Caulerpa, Halimeda, Dictyota) and a modest number of 
sponges on roots (Lissodendorys cf. isodictyalis, Tedania ignis) and peat bank (Haliclona 
mucofibrosa). 
Sta. 
con 
Figure 2. Aerial view of Twin Cays looking southeast. Little Dipper (sta. 41), Big Dipper, and 
'Cuda Cut (5Ha) (left to right) are in the foreground, Cassiopea Cove (51) is seen directly 
behind Big Dipper; Batfish Point South (5Hb) is in the Main Channel, turning right after 
passing 'Cuda Cut (photo, D. Littler). 
Figure 3. Low-altitude aerial view of 'Cuda Cut and Batfish Point (background) (sta. 5Ha; 
photo, D. Littler). 
5 Ha, Batfish Point-'Cuda Cut (Figs. 1, 3 ,4;  Plates 1,2a) 
Location and Topography. The north coast of West Island, from its northeast 
ner (Batfish Point) to North Bay, opposite Big Dipper (the passage between the two 
Figure 6. Mangrove roots at Main Channel Northwest: a, root covered by sponges, purple Haliclona 
implexiformis (tubes) and orange Scopalina ruetzler (encrusting); 6, mangrove oysters, Isognomon alatus. 
Tedania, and Hyrtios; they alternate with clusters of mangrove oysters (Isognomon 
alatus) and alga-like fuzz of the bryozoan Zoobotryon verticillatum (Winston, 2004). 
Because a counter-current creates pockets of calm water, there are accumulations of 
light-green floats of cyanobacterial mats composed mainly of filamentous Lyngbya sp. 
Sta. 6 H, Turtle Cove and Turtle Pond (Figs. 1, 7; Plate 2e) 
Location and Topography. A deeply cut bay 30 m wide and 45 m long in the 
northwest shoreline of East Island. Its entrance from the Main Channel is partly blocked 
by a small mangrove patch that developed on a sandbank during the past 15 years (25 m 
diameter in 2003). About 100 m south of the entrance, sand deposits account for a very 
shallow shoreline covered by seagrass and lined by long hanging roots. The cove extends 
toward the northeast through a narrow, shallow channel (2-3 m wide, 3 1 m long), which 
ends in a deeper (2 m) pond, 16 x 12 m in diameters. Garbage dumping in Turtle Pond 
has interrupted research at this location for several years. 
Figure 5. Low-altitude aerial photograph of Northeast coast looking northwest (photo D. 
Littler). 
Sta. 6 G, Main Channel Northwest (Figs. l ,6 ,7 )  
Location and Topography. Western shore of the Main Channel, along the coast of 
West Island between the Dock and Batfish Point. 
Habitats. Steep and strongly eroded peat bank (1.5 m tall), with overhanging red- 
mangrove roots of low density protruding in 2-3 m distance from the bank. Thalassia 
seagrass sparsely covering the bottom of the channel which at this location is 55 m wide, 
1.5-2 m deep. 
Depth. 2-3 m. 
Environmental Conditions. L: +; C: + (wind-generated waterflow through the cuts 
to the open lagoon). 
Sediment. Abundance of fine sediments that tend to be resuspended by heavy boat 
traffic through the channel; it covers most substrata and ebibionts. 
Communities. Algal fuzz composed of calcareous red algae (Jania cf. adhaerens) 
and cyanobacteria (Lyngbya, Schizothrix spp.), fleshy green algae (Caulerpa verticillata) 
and red algae (Acanthophora spicifera), sponges (Lissodendoryx, Tedania, Scopalina 
ruetzleri, Haliclona implexiformis, H. manglaris, Spongia tubifera), and a few ascidians 
(Didemnum spp.) on the roots. Sponges are partly covered by rusty red cyanobacteria 
(Schizothrix spp.) and leafy greens (cf. Anodyomene). On the peat bank, one finds among 
other sponges the encrusting Clathria venosa; the sea urchin Lytechinus variegatus is 
abundant. Near the Dock there is an abundance of solitary ascidians (Phallusia nigra, 
Microcosmus exasperatus), which are rare elsewhere at Twin Cays. 
Swimming across the channel one encounters large mounds caused by burrowing 
crustaceans, and Cassiopea jellyfish among the turtlegrass. The opposite bank looks very 
much like its western counterpart but the roots are closer to shore, algae are more 
common than sponges, and there is more deposited fine sediment. Algae include 
cyanobacterial mats, Caulerpa, and Halimeda. Most sponges belong to Lissodendoryx, 
Islands; 'Cuda Cut, was named for its abundance of schooling barracudas). Outward 
(north) of North Bay, the water is very shallow (<0.5 m) because of sand deposits 
covered by turtle grass. 
Habitats. The southern shore of the passage has an intertidal peat bank protruding 
over a curved or nearly vertical peat wall, 3 m tall. The wall is recessed 1-3 m from the 
distal edge of the bank, thus creating an extensive cave habitat. Red mangrove is 
anchored on top of the bank, its roots protruding here and there from the otherwise 
smooth or somewhat pitted, compact peat; stilt roots hanging over edge of the bank. 
Depth. 3-4 m. 
Environmental Conditions. L: + to -; C: +. 
Sediment. Sand with mollusk fragments; very fine sand and soft, carbonate mud 
toward the center of the channels, extensively worked by crustacean burrowers. 
Communities. Peat banks are covered by tufts of algae and hydroids, coralline 
algae, calcified green alga (Halimeda), and a number of encrusting or cushion-shaped 
sponges (Scopalina ruetzleri, Spongia tubulosa) and ascidians (Diplosoma sp.) and 
populated by seaurchins (Lytechinus variegatus). Sea anemones (Condylactis gigantea, 
Bartholomea annulata) and sabellid polychaetes are anchored in fissures and depressions 
of the peat wall. The most common encrusting sponges on the dark cave wall and ceiling 
peat substrata are the orange Scopalina ruetzleri and the yellow Amorphinopsis sp. and 
Clathrina cf. coriacea. Other abundant species in this habitat are Chondrilla nucula, 
Clathria venosa, Mycale citrina, M. microsigmatosa, and Haliclona mucoJibrosa, and 
sheet-like forms of ascidians, including Diplosoma listerianum, D. glandulosum, 
Lissoclinum abdominale and Didemnum conchyliatum. Crisp white patches of sulfur- 
fixing bacteria (Beggiatoa) are conspicuous on the peat wall near the muddy bottom. 
Ascidians with a higher profile tend to be confined to hanging roots, as are fleshy macro- 
algae, and massive sponges such as Lissodendoryx cf. isodictyalis, Mycale laxissima (also 
large-growing and common on fully light-exposed peat walls), and Tedania. Many of the 
light-exposed sponges are covered (as observed in August 2004) by rusty-red veils of 
cyanobacteria (Schizotrix spp.). The sediment bottom near the banks is barren except for 
sporadic algae and seagrass but the Main Channel floor off Batfish Point is covered by 
stands of Thalassia seagrass, and Halimeda and Caulerpa algae interspersed with 
characteristic mounds and holes indicating the presence of burrowing decapods 
(Glypturus, Alpheus). Numerous specimens of the benthic jellyfish (Cassiopea 
xamancha) and of the starfish Oreaster reticulatus are also regularly encountered. Exiting 
north into and beyond North Bay one commonly encounters an encrusting black sponge 
(Artemisina melana) covering coral rubble and dead gorgonians. 
Sta. 5 Hb Batfish Point South (Figs. 1,2; Plate 2b,c) 
Location and Topography. Main Channel west, northeast shore of West Island 
just south of Batfish Point. 
Habitats. Intertidal, root-consolidated peat-bank with long adventitious red- 
mangrove roots covered mainly by sponges hanging in front of the bank. About 20 m 
toward the south, the peat bank decreases in height to about 0.5 m. 
Depth. 1-3.5 m. 
Environmental Conditions. L: + to -; C: + (wind-generated water flow through 
the cuts to the open lagoon). 
Sediment. Sand with mollusk fragments and Halimeda chips. 
Communities. Encrusting or low-growing algae, sponges, and ascidians on the 
bank, like at 'Cuda Cut (Sta. H 5A); ascidian numbers decrease with diminishing 
waterflow toward the south. Seagrass (Thalassia) appears where the current through the 
cuts slows and sediment accumulates on the bottom. Opposite across the channel (East 
Island), cool water entering through 'Cuda Cut stimulates a rich community of algae, 
sponges (Mycale microsigmatosa, Lissodendoryx, Tedania), and colonial ascidians 
(Didemnum spp., Botrylloides nigrum). 
Sta. 5 1, Cassiopea Cove (Figs. 1,2; Plate 2d) 
Location and Topography. North end of Main Channel, a small bay on East Cay, 
opposite Big Dipper islet. 
Habitats. Soft sedimentary bottom with Thalassia seagrass. Mangrove stilt-roots 
along the shore. 
Depth. 0.5-2 m. 
Environmental Conditions. L: +; C: +. 
Sediment. Fine-grained sand and carbonate mud. Median grain diameter of the 
sand fraction has a range of 94-268 pm, the mud fkaction (<63 pm) is 17-33% and the 
organic content 5.4-9.7% (Dworschak and Ott, 1993). The mud fraction tends to become 
resuspended during high winds, causing high turbidity. 
Communities. Large population of the benthic upside-down jellyfish Cassiopea 
xamancha. Sediment mounds and funnel-shaped holes among stands of algae (Penicillus, 
Halimeda) indicate the presence of burrowing decapods (Alpheus spp., Glypturus 
acanthochirus). Stilt or hanging prop roots are covered by algae and a few ascidians 
(Perophora) but much of the epifauna tends to become smothered by whitish flock from 
resuspended and resettling fine sediment. 
Sta. 5 K, East Island, Northeast Coast (Figs. 1,5)  
Location and Topography. Northernmost part of the highly exposed outer 
shoreline that faces northeast. 
Habitats. Mangrove fringe with Rhizophora stilt roots hanging freely, or (further 
to the southeast) firmly embedded in sandy substratum. About 30-40 m offshore, a 
shallow sandbank covered by turtle grass (Thalassia) parallels the coast and separates it 
from the extended turtle grass meadows of the lagoon. 
Depth. 0.5- 1 m 
Environmental Conditions. L: +; C: +. 
Sediment. Medium to coarse sand with ample Halimeda chips. 
Communities. Algal turf (bostrychietum) and a few ascidians (Didemnum) on 
roots; Halimeda algae and Thalassia seagrass covering the bottom. 
Figure 7. Habitats near the northern Main Channel: a, aerial photograph looking southeast (across Main 
Channel Northwest, 6G), onto Turtle Cove and Turtle Pond (6H, arrow), which are connected by Turtle 
Creek; Candy's Pond (61) is to the far left; b, underwater view of Turtle Creek (photo, M. Carpenter). 
Habitats. Dense bed of seagrass (Thalassia) at the entrance to the cove; otherwise 
muddy bottom. Ample free-hanging Rhizophora roots from overhanging trees that line 
cove, channel, and pond. (Roots at this location were measured to grow 0.2-0.4 mm per 
day.) 
Depth. 1-2 m. 
Environmental Conditions. L: -; C: -; T, S: stressful range (connection with 
nearby inshore Candy's Pond). 
Sediment. Fine, organics-rich mud. 
Communities. ~ntehidal parts of the roots are covered by algal fuzz and clusters of 
mangrove oysters (Isognomon alatus). Subtidal zones support brown cyanobacteria, algae 
(Ulva sp., Caulerpa racemosa), small sponges (Haliclona implexiformis, Biemna sp.) 
and, toward the tips of roots, an abundance of ascidians (Perophora regina, Didemnum 
conchyliatum, Eudistoma olivaceum) competing with serpulid worms and a few sponges 
(Haliclona curacaoensis). Owing to current patterns and the deposit of suspended 
sediments and other matter (such as loose seagrass leaves left from manatee feeding), 
roots on the south flank of the cove are less densely colonized by epibionts than the north 
side. Long-bladed Thalassia seagrass predominates the shallow bank just south of Turtle 
Pond where hanging mangrove roots have a poorly developed epibiont community with a 
few sponges and anemones. Patches of lower intertidal peat banks are covered by 
Halimeda algae. 
Sta. 6 I, Candy's Pond (Figs. 1,7; Plate 2f) 
Location and Topography. An inshore pond on East Island, 65 m from the Main 
Channel, accessible from Turtle Pond through a narrow, mangrove-overgrown canal, 1.5 
m wide, 0.5 m deep, and 45 m long. This is actually a double pond, two equal-sized 
lagoons of about 200 m2 area joined by a narrow neck of water. Only the northern pond is 
being considered here, which is elongate, 50 m long, and 8-30 m wide. 
Habitats. Rhizophora roots. Muddy bottom of decaying plant materials. 
Depth. 1-1.5 m. 
Environmental Conditions. L: +; C: -. T, S: stressful range; 34", 37%0 (highest 
values recorded, May, 1985). Strongly impacted by heavy rains and periods of 
evaporation over the surrounding swamp. 
Sediment. Very loose organic flock, up to 1 m deep. 
Communities. Abundance of ascidian Eudistoma olivaceum, known for its high 
stress tolerance, and Didemnum. Sponges are rare (mainly Haliclona implexiformis). 
Small sabellid polychaetes (Bispira melanostigma), hydroids (cf Myrionema), and a 
bryozoan (Bowerbankia, which always seems to grow near the water surface) are fairly 
common. The only fishes observed were mangrove snapper and small barracuda. 
Bacterial mats cover areas of the muddy bottom. 
Sta. 7 E, West Bay (Figs. 1, 2, 8; Plate 3c) 
Location and Topography. A recess of the outer (western, lagoon-ward) shoreline 
of West Island. The bay measures about 175 by 45 m, with a ragged shoreline. 
Habitats. Rhizophora mangrove lines the fringe, with stout roots firmly anchored 
in coarse sand along the shallow (0.5 m) coastal zone of West Island. The bay bottom is 
made up by a variety of coral rock rock, shell (bivalve, conch shells), and sand covered 
by calcareous and fleshy algae and patches of turtle grass. A barren sandy apron extends 
from close to shore several hundred meters outward into the lagoon at the southern part 
of the bay. 
Depth. 0.2-3.5 m. 
Environmental Conditions. L: +; C: +. 
Sediment. Poorly sorted but mainly coarse sand and gravel, patches of medium 
fine sand. 
Communities. The fauna and flora of West Bay are rich, possibly benefiting from 
nutrient input from the adjacent mangrove, lack of very fine sediments, and a moderate 
temperature-salinity regime. Mangrove roots support crustose coralline and Halimeda 
algae, algal turfs, and a reef-like fauna of a few sponges (Clathria venosa, Mycale laevis, 
Niphates sp.), coral (Porites porites and P. atroides, Millepora complanata), and serpulid 
worms. The bay floor is covered by a variety of algae (Halimeda, Penicillus, 
Rhipocephalus, Caulerpa), Thalassia and Halodule seagrass, clusters of bivalves and 
coral (Manicina areolata) with stands of octocoral, and numerous sea urchins (Lytechinus 
variegatus, Clypeaster rosaceus), and the occasional batfish (Ogcoephalus). Cushion- 
shaped and branching sponges occur on rock (e.g., Amphimedon viridis, A. compressa, 
Niphates erecta), ascidians are rather rare except for a few small patches on seagrass 
blades (didemnids, Ecteinascidia minuta) and a small burrowing form buried around 
Thalassia roots (Pyura munita). 
Sta. 7 G, Main Channel West, the Dock (Figs. 1,9)  
Location and Topography. West coast of Main Channel (central eastern shore of 
West Island). The Dock itself, a wooden structure, was built by CCRE Program 
participants to facilitate access to the swamps of West Island; its submerged pilings are 
fouled mainly by algae and sponges and are used as support for various experimental 
setups (settling frames, tide and temperature probes). 
Figure 8. Habitats at West Bay: a,  sieving sand samples in front of the mangrove fringe bordering the bay; 
b, Turtle grass surrounding sand patches with unattached solitary coral, Manicina; b, coral (Porites) and 
hydrocoral (Millepora) growing on Rhizophora stilt roots that are firmly embedded in sand. 
Habitats. Dense seagrass, Thalassia, comes up to the fringe where there is a low 
peat bank and roots are covered by sponges. Fallen trees and driftwood are stranded in 
places and entangled among the prop roots. 
Depth. 0.5-1 m. 
Environmental Conditions. L: *; C: *. 
Sediment. Carbonate mud with patches of HaIimeda chips. 
Communities. Fleshy and calcareous algae (Caulerpa, Halimeda, Jania), sponges 
(Lissodendoryx cf. isodictyalis, Chondrilla nucula, Clathria venosa, Tedania ignis, 
Clathrina cf. coriacea), and mangrove oysters (Isognomon) cover the roots. Juvenile 
fishes are common in protected areas where floating Sargassum seaweed is often trapped, 
particularly in spring. Thalassia seagrass covers the bottom. 
Figure 9. Main Channel West, the Dock: a, floating Sargassum seaweed entangled among Rhizophora 
roots (photo, M. Carpenter); b, tall Thalassia seagrass populated by epibionts (photo, L. M-Penland). 
Figure 10. View over 'Gator Creek near its entrance into East Pond. 
Sta. 8 I, 'Gator Creek (Figs. 1, 10; Plates 3d-f, 4a) 
Location and Topography. East Island, starting at the northern flank of the 
entrance to Lair Channel, and meandering north to East Pond. 
Habitats. Rhizophora mangrove roots, peat bank, mud bottom covered by 
decaying mangrove litter. 
Depth. 0.5 m (entrance) 1.5 -3 m. 
Environmental Conditions. L: -; C: +. T, S: stressful range, due to tidal drainage 
of water (heated-hypersaline, or cooled-brackish, depending on the weather) derived from 
the large, shallow East Pond. 
Sediment. Organic mud; patches of Halimeda chips. 
Communities. The Lair channel bottom slopes up to the creek's entrance where 
Thallassia seagrass becomes dense in 0.5 m depth and interspersed with some algae, 
mainly Caulerpa racemosa. Mollusk and polychaete egg cases crowd the muddy areas. 
Near the mouth of the creek along the north-shore of Lair Channel, there are clusters of 
mangrove oyster (Isognomon) on the roots, as well as ascidians Eudistoma olivaceum and 
Didemnum conchyliatum, the latter a hardy species tolerant of a wide range of 
environmental extreme (see Goodbody, 2004a) and often found on root tips and at the 
leaf bases of Thalassia seagrass. Algae (Caulerpa) and big sponges grow on the 
mangrove roots flanking the entrance (Tedania, Lissodendoryx). 
The channel is rich in cyanobacterial mats and tufts, algae (Halimeda, Caulerpa), 
sponges, hydroids, anemones (Aiptasia tagetes, Condylactis gigantea), and juvenile 
fishes hiding among the epibionts. Common sponges on mangrove roots and peat bank 
include Lissodendoryx, Biemna, Tedania, Tethya cf. actinia, Cinachyrella apion (mainly 
on peat walls), Dysidea etheria, Dysidea sp. (a large, undescribed bluish gray form also 
found in Hidden Creek), Haiiclona implexiformis, H. curacaoensis, H. manglaris, H. 
twincayensis, H. tubifera, H. magnzfica (on peat walls), and Chaiinula molitba. Sponges 
are also found loose among the mangrove litter of the channel floor (Lissodendoryx, 
Biemna), together with low-growing algae (Avrainvillea), or buried in organic sediment 
flock (H. magnifica). Bryozoans (Zoobotryon verticillatum, Amathia vidovici) and small 
colonies of ascidians (Eudistoma olivaceum) are co-occurring with sponges on roots and 
along the peat wall lining the creek. A conspicuous population of a telestinid gorgonian 
with brilliant white polyps (Carijoa riisei), and two color morphs of Tedanis ignis (red- 
orange and orange-red) with opposite color-morph Parazoanthus swiftii (orange-red and 
red orange) covering their surfaces were observed near the outer one-third distance into 
the creek in 1984. Four years later (1988), these organisms had disappeared, except for a 
few small colonies of the telestid, which reappeared in larger numbers by 1992 but were 
not noted during a survey in 2004. The Tedania;Parazoanthus population was never seen 
again since the original observation. 
Sta. 9 I Grouper Gardens (Figs. 1, 11; Plate 4) 
Location and Topography. A cluster of at least six interconnected ponds just 
south of the Lair Channel, which can be entered through a north-south-directed creek 
located 100 m to the east of the Main Channel. The Lair channel bottom outside Grouper 
Gardens is 2 m deep and sparsely covered by turtle grass. It slopes up to 0.5 m toward the 
Figure 11. Grouper Gardens, underwater view along a connecting channel between two 
ponds, with free-hanging, heavily colonized mangrove roots. 
creek where Thalassia becomes tall and dense. There are patches of Halimeda sand and 
healthy populations of this alga crowd the nearby Rhizophora roots. The creek at its 
entrance is relatively deep (3 m), but quickly shallows where it connects to the first pond 
(0.5 m). Most ponds and passages between them are 0.3 m or less deep and difficult to 
explore by swimming. 
Habitats. Vertical peat walls and overreaching hanging stilt roots, soft muddy 
bottom with seagrass and, particularly in the remote ponds, thick stands of seaweed 
(Avrainvillea). 
Depth. 0.1-3 m. 
Environmental Conditions. L: +; C :  *. 
Sediment. Fine sand with Halimeda chips; peat and detritic mud cover the 
bottoms of ponds and connecting canals. 
Communities. The mangrove roots outside the entrance to Grouper Gardens are 
covered mainly by Halimeda opuntia triloba. Just inside, the roots and peat walls are 
overgrown by sponges (Tedania, Lissodendoryx, Haliclona implexiformis, H. tubifera, 
Spongia tubulifera, Calyx podatypa, Geodia papyracea), more Halimeda algae, algal 
turfs (including intertidal bostrychietum), hydroids, anemones (Bartholomea annulata, 
Condylactis gigantea, Aiptasia tagetes), and a few colonies of the ascidian Eudistoma 
olivaceum. Extensive reddish veils covering epibions and streamer-like strands (up to 2 m 
long) formed by cyanobacteria (Lyngbya spp.) were noted during the month of August 
(2004).The astrophorid sponge Geodia papyracea there has periodically been overcome 
by stress-related disease involving its own cyanobacterial symbionts (Riitzler, 1988). The 
bottom is covered by stands of turtle grass, Thalassia, and patches of Halimeda and other 
algae. The encrusting orange ascidian Didemnum conchyliatum is common and often 
attached to seagrass blades. Short, 1 m deep tidal channels connect the ponds, which 
average 0.5 m in depth. Mangrove roots in the current flow here support clusters of 
mangrove oysters (Isognomon), a diverse population of sponges (Spongia tubulifera, 
Haliclona curacaoensis, H. manglaris, Biemna caribaea, Dysidea etheria, Clathrina cf. 
coriacea), hydroids, and algae (Caulerpa verticillata). The bottom of the shallow ponds 
consists mostly by stands of tall green algae (Avrainvillea longicaulis f. laxa) and 
supports populations of Cassiopea jellyfish and Tridachia nudibranchs. Some sponges 
(Haliclona spp., Lissodendoryx) that for some reason had lost their solid root substrate 
are surviving despite being buried in deep detritus. 
Sta. 9 J, Lair Channel (Figs. 1, 12; Plates 4a, 5a-c) 
Location and Topography. Second-largest channel (after the Main Channel, from 
where it originates) cutting west-east into East Island and blind-ending in a pond, known 
as The Lair. The channel is about 260 m long, widest at its mouth (56 m), and gradually 
narrows to 14 m (neck of the Lair channel), where it makes a sharp turn to the south and, 
after 40 m more, opens into a terminal pond, The Lair. Along the flanks of the Lair's 
neck are extensive peat-bank undercuts, dark cave-like features suggesting that the Lair 
was once connected to the open lagoon and that water run more briskly through the 
channel than now, eroding its banks. The undercuts occur along both the west and east 
banks of the Lair Channel neck, undercutting the root-peat bank horizontally to 0.5-3. 
Along the western shore the caves are deepest where the Lair neck first turns south, at the 
east bank they are best developed near the entrance point into The Lair proper, further 
supporting the idea that they were washed out by current rather than other mechanisms of 
erosion. Cave ceiling clearance at the entrance of undercuts is 0.4-1.4 m, tapering to 
0.3-0.8 m near the rear peat wall. 
Habitats. Fringe of hanging Rhizophora roots, particularly along the south (west) 
shore, muddy bottom with sparse seagrass and macrophytes restricted to shallow (<lm) 
areas and patches of coarse Halimeda-chip sand. Rhizophora-root reinforced peat 
undercuts and caves with sediment-free walls and ceiling and detritus-rich, pudding-like 
mud bottom. The center channel bottom is bare mud with Cassiopaea jellyfish, no 
seagrass. 
Depth. 0.8-1.9 m (fringe); to 2-3 m (channel bottom). 
Environmental Conditions. L: + to -; C: A- to -. T, S: stressful range, due to tidal 
drainage of water from surrounding shallow ponds and flats. Particularly affected are 
sessile communities (algae, sponges, ascidians) on shallow, bank-side roots because 
water flowing from the flats may differ by several degrees temperature and per-mille 
salinity from the channel ambient conditions (total range measured, 27"-36" C and 30- 
34%0 , in May 1985, February and April 1990, and April 1991). 
Sediment. Calcareous and detrital mud stabilized by mucuous components; 
patches of fine sand and Halimeda chips. Suspended fine sediments, mainly detritus, 
were observed to flow out of the creek at ebb tide (February, 1988). 
Communities. Thick sponge clusters on roots at both sides of the channel 
(Lissodendoryx, Tedania, Spongia tubulifera, Hyrtios proteus, Amorphinopsis sp., 
Biemna caribea, Haliclona curacaoensis, H. manglaris, H. implexiformis, Mycale spp.). 
Also, bunches of green algae (Halimeda, Caulerpa) and alga-like soft bryozoans 
(Zoobotryon), and ascidians (Perophora bermudensis) grow hanging into the water flow. 
The light-exposed peat banks are covered by algae (Halimeda, Caulerpa, 
Anodyamene), sponges (Lissodendoryx, Amorphinopsis, Biemna, Spongia obtusa), 
cyanobacterial webs (Lyngbya), and anemones (Aiptasia, Bartholomea). Colorful small to 
medium-large sponge crusts or cushions populate the dark cave- or overhang-ceilings of 
the Lair Channel neck where there is no competition from algae (yolk yellow Biemna and 
Amorphinopsis, red Tedania, greenish Haliclona manglaris, pink H. implexiformis, 
sulfiu--yellow Clathrina), along with the white calcareous tubes of serpulid polychaetes, 
patches of the soft filmy cream-colored ascidian Diplosoma, and bright-white 
accumulations of bacteria, Beggiatoa. 
Here and there, the mud bottom is covered by cyanobacterial mats (see Joye & 
Lee, 2004) but otherwise is bare except for jellyfish (Cassiopea), mollusk egg cases, and 
a few protruding sponge fistules (for instance Lissodendoryx); these sponges seem to 
have fallen off stilt roots that decayed after death of the tree or from borer's action 
(Kohlmeyer et al., 1995) and survive on and in the mud substratum. Turtle grass occurs 
only in small patches the shallow fringe areas and is often populated by anemones 
(A iptasia). 
Near drainage points of interior swamp water into the Lair Channel, large clusters 
of mangrove oyster, Isognomon, appear as well as dense populations of the ascidians 
Perophora spp., suggesting that nutrient-rich water and particulate matter become 
available; swarms of the mysid Mysidium columbiae are also seen concentrated near 
these drainage locations. Another ascidian common in this community is Distaplia 
corolla, which settles preferentially on the shaded side of free-hanging roots but was all 
but eliminated (at least to a depth of 0.3 m below low-tide level) during a massive 
mortality event in early 1986, possibly by unusually warm, hyposaline water draining off 
the swamp, or by exposure at a very low tide. 
Extensive microbial mats harboring a rich community of dinoflagellates, 
protozoans, and small invertebrates develop in protected (calm-water) locations and may 
become dislodged by the buoyancy of photosynthetic oxygen bubbles and float to the 
surface ("floating muck") until oxygen is consumed or dissipated and causes the mat to 
sink back to the bottom (Faust and Gulledge, 1996). Dense growth of Thalassia seagrass 
covers the light exposed parts of the channel bottom west of the Lair neck. The turtle 
grass blades are extensively colonized by different color morphs of the ascidian 
Diplosoma glandulosum. 
Sta. 9 K, The Lair (Figs. 1, 13; Plate 4a) 
Location and Topography. This terminal pond of Lair Channel is elongate and 
oriented parallel to the channel, but perpendicular to the orientation of the neck that make 
a sharp bend to the south before entering. It is 100 m long, 12 m wide at its west end, 45 
m at its east end. 
Habitats. Rhizophora mangrove roots along the margins. Soft, flocculent detritus 
bottom. 
Figure 12 (opposite). Lair Channel: a, view along the channel from one of its taller surrounding trees; b, 
cave-like peat undercut at the western flank of the channel's neck; c, seagrass along the shallow fringe 
populated by sea anemones (Aiptasia); d, algae-like bryozoans (Zoobotryon) on roots; e, detached sponges 
(Lissodendoryx) surviving partially buried in the detrital bottom of decomposed mangrove litter; a 
sediment-covered spherical sponge (Cinachyrella) is attached to the peat bank to the right. 

Figure 13. The Lair: a, detritus bottom in 2 m depth; the structure in the center is a square experimental 
frame with settlement plates that became partly buried after one year of exposure; 6, garbage dumped in 
May 1990 (photo, M. Carpenter). 
Depth. 2 my at center. 
Environmental Conditions. L: + to +; C: -. T, S: stressful range (see Lair Channel, 
above). A series of measurements during high and low tide (September 2003) were in the 
range of 30.5"-33" C temperature and 35.7-36.7%0. Nutrient levels measured in subtidal 
sites (0.5 m) are highest in the Lair, lowest in the Main Channel stations and locations in 
direct water exchange with the channel (Sponge Haven North, Sponge Haven South, 
Hidden Creek entrance). Comparative values (high: low, in January 2003, were: 
1.2: 0.2 pMol/l phosphate; 5.5: 1.4 pMoM ammonium; 0.4: 0.1 pMol/l nitrite, and 1.3: 
0.4 pMol/l nitrate. Garbage dumping prevented research for a number of years but was 
recently discontinued. 
Sediment: fine detritus, mainly from decomposed plant material. 
Communities. Not as rich as root communities observed elsewhere. Mangrove 
oysters (Isognomon) are common, as well as members of the ascidian family 
Perophoridae (see Goodbody, 2004a). A few sponges (Mycale microsigmatosa, 
Haliclona tubifera) and anemones (Aiptasia). Algae (Halimeda, Caulerpa) and 5 to 8 cm 
mucuous balls (polychae egg cases) populate the bottom. Cyanobacterial mats are 
abundant (see 9 J above). 
Sta. 10 G, Twin Bays (Figs. 1, 14; Plate 5d) 
Location and Topography. A shallow double bay just west of the southern tip of 
West Island. The outer bay (80 m long x 90 m wide) has a 60 m wide mouth that opens 
toward the southwest into the main lagoon, to the left (north of the Main Channel 
entrance. The triangular inner bay (60 x 20 m) is connected by a 10 m wide passage. 
Regrettably, by 1989 garbage dumping had made Twin Bays unsuitable for research and 
was excluded as a research site pending future developments. 
Habitats. A low (0.5 m) peat bank along the inner margin of the bays with 
overhanging red-mangrove roots that do not quite touch the bottom. Sandy bottom 
covered with sparse Thalassia seagrass, denser seagrass at the entrance. 
Depth. 0.2-1 m. 
Environmental Conditions. L: +; C: + (protected form prevailing north-east 
winds). 
Figure 14. Twin Bays are the first to the left (west) off the Main Channel entrance, viewed 
from the south (photo, M. Carpenter). 
Sediment. Fine calcareous sand and mud. 
Communities. Few sponges on the roots, some overgrown by a large population of 
an ascidian with two color morphs, Distaplia corolla (see Goodbody, 2004a). This 
species was (in 1984) particularly abundant at the western margin of the bank, close to 
the entrance to the inner bay. Other ascidians are the orange encrusting Didemnum 
conchyliatum, which is widespread and highly tolerant to environmental stress and often 
overgrows the root tips of mangrove, and the solitary Phallusia nigra and Microcosmus 
exasperatus, both characteristic of mildly eutrophic conditions (Goodbody, 2004b). On 
the bottom of the inner bay margin, specimens of the scyphozoan jellyfish Cassiopea 
frondosa and coral Manicina areolata were common. 
Sta. 10 H, Sponge Haven (Figs. 1, 15; Plate 5e) 
Location and Topography. Shallow, open bay near the southeast tip of West 
Island, facing the Main Channel. The opening is 65 m, directed eastward, recess is 25 m 
from the West Island shoreline, at that location. The shoreline is made up of a low (0.2- 
0.5 m) peat bank with numerous free-hanging and anchored roots in front; this feature 
extends around the point south of the bay, where the peat bank is even more eroded and 
recessed and roots hang free and clear of sediments. In the back of the bay there are 
accumulations of fine-sediment close in and under the roots; along the entrance 
Figure 15. Sponge Haven South, fringe seen from the Main Channel looking south toward the 
channel entrance. 
there is a shallow longitudinal bank supporting tall seagrass. The northern flank of 
Sponge Haven ("Sponge Haven North," see Diaz et al., 2004) is also exposed to fine 
sediment and to accumulations of detached seagrass leaves, floating cyanobacterial mats, 
and other debris. The coastline of the southern point ("Sponge Haven South," facing the 
Main Channel Entrance) has clean lagoon water prevailing along the fringe. 
Habitats. Hanging and anchored Rhizophora roots, peat bank with some 
undercuts; sandy and seagrass-covered bottom. 
Depth. 0.5-1 m. 
Environmental Conditions. L: + to *; C: + (clockwise water circulation, counter 
the predominant north-south flow in the Main Channel). Measurements taken during high 
and low tide (September 2003) ranged from 30.4" to 32.1" C in temperature and 35.2 to 
35.6%0 salinity. 
Sediment. Fine calcareous sand and mud. 
Communities. Highly diverse sponge fauna on roots, particularly along Sponge 
Haven South, including the very common Geodiapapyracea, Clathria venosa, Tedania 
ignis, Halichondria magniconulosa, H. manglaris, H. muciJibrosa, Calyx podatypa, 
Hyrtiosproteus, Spongia tubifera, and a few specimens of large Ircinia strobilina. 
Specimens of the sea urchin Echinometra lucunter abound along the bank. Many roots 
are covered by anemones (Aiptasia) and mangrove oysters (Isognomon) and, in clear 
water without much sediment loading, by Halimeda sp. Algae, the coral Porites, sabellid 
worms, and the ascidians Diplosoma listerianum and Distaplia corolla. The orange 
Scopalina ruetzleri encrusts large areas of the peat bank and undercuts. Red and green 
fleshy algae are common on hanging roots along with clumps of cyanobacteria (Lyngbya 
spp.). Extended patches of long-leaved Thalassia seagrass with a rich epifauna (hydroids, 
didemnids, stinging anemone Bunodeopsis antillensis) border the fringe and extend into 
the Main Channel; burrowing alpheid crustaceans abound in sand. 
Sta. 10 I, Main Channel Southeast (Figs. 1, 16) 
Figure 16. Main Channel Southeast, characteristic community of Halimeda algae with sea 
anemone Batholomea. 
Location and Topography. West coast of East Island, facing the Main Channel, 
across from Sponge Haven. It is a gently curved, shallow fringe with low but steep and 
eroded peat bank that is pitted and exposes old Rhizophora roots. 
Habitats. Peat bank, some mangrove stilt roots in shallow water, sand banks with 
Thalassia seagrass. 
Depth. 0.2-0.5 m. 
Environmental Conditions. L: +; C: +. A surface layer of brown swamp-water 
runoff was noted in places. 
Sediment. Fine calcareous sand. 
Communities. Halimeda occurs in dense patches on the peat, along with a few 
sponges (Mycale microsigmatosa, Haliclona tubifera) and sea urchins (Diadema 
antillarum). Shallow Rhizophora roots are covered by the bostrychietum algal 
community and other algae, anemones (Condylactis, Bartholomea), coral (Diploria 
strigosa), and sporadic ascidians (Microcosmus exasperatus). Extended beds of Thalassia 
with long and dense grass blades are populated by juvenile fishes and in places disturbed, 
indicating that manatees had grazed there. 
Sta. 11 G, Main Channel Entrance (Figs. 1, 14, 17; Plate 5f) 
Figure 17. Underwater images of habitats at Main Channel entrance: a, turtle grass alternating with sand 
mounds produced by the burrowing of shrimp Glypturus; b, large sponge (60 cm across) among turtle 
grass, Spheciospongia, is the reef-like center of a community of endobiotic invertebrates. 
Location and Topography. The funnel-shaped mouth of Main Channel that 
separates West and East islands and faces west, and some open-lagoon bottom just in 
front (west) of it. Width of the Channel mouth is about 110 m. 
Habitats. Mini-reefs composed of clusters of coral, sponge, algae, and octocoral 
and large loggerhead sponges (Spheciospongia vesparium) with associated epi- and 
endofauna. Firm sandy bottom with dense stands of Thalassia seagrass to the north (West 
Island), a bare sand apron along the southern shore (East Island). 
Depth. 0.5-3 m. 
Environmental Conditions. L: +; C: + (open lagoon conditions, but exposure 
modest because of orientation away from the predominant northeast winds). 
Sediment. Medium-grained sand-size fraction (267-426 pm median diameters), 
with mud-size (<63 pm) fraction 9-21%, organic content 3.9-4.6% (Dworschak and Ott, 
1993). 
Communities. The mini-patch reefs are formed by coral, Porites porites and P. 
astreoides (the latter often adorned by the colorful crowns of sessile polychaetes, 
Spirobranchus), and by sponges (Spheciospongia vesparium, Tectitethya crypta), bound 
together by algae, sponges (Lissodendoryx colombiensis, Clathria schoenus, A. erina, 
Hyrtios proteus, Aplysina fulva), and gorgonians. Associated with these reefs are seagrass 
(Thalassia, Halodule), several algae (Caulerpa, Halimeda, Rhipocephalus, Udotea), and 
anemones (Condylactis). Seagrass (Thalassia, Syringodium) growing between rubble 
and conch hides a number of sponges (Tedania ignis, Amphimedon compressa, Ircinia 
felix), sea urchins (Lytechinus), and, here and there, specimens of the bivalve Pinna 
carnea and large, erect leathery tubes occupied by the polychaete Eunice aphroditois. In 
sandy areas, small (<lo cm) mounds decorated with pieces of shell indicate the presence 
of a burrowing shrimp (Glypturus acanthochirus). Divers or swimmers in this area are 
regularly attacked by biting but otherwise harmless isopods, Rocinela signata. Along the 
east bank of the Entrance are shallow, anchored Rhizophora roots with Halimeda algae. 
Sta. 12 I, Hidden Creek (Figs. 1, 18; Plate 6) 
Location and Topography. The creek originates from deeply cut but shallow 
Boston Bay at the southern end of East Island. The mouth of the bay opens into the Main 
Channel. Hidden Creek starts at the opposite end and meanders first east, then south, and 
finally turning and running north, enters the large and shallow Hidden Lake. The creek is 
Figure 18. Hidden Creek and Lake: a, low-altitude aerial view of Hidden Creek looking west; Hidden Lake 
is to the right, Boston Bay to the back; in the background one can see the Main Channel with Twin Bays 
(left) and Sponge Haven (right); b, detail of the creek; c, entrance into the lake. 
a constant 3 4  m wide and 2-3 m deep (shallower toward its end), and about 20 m long. 
Hidden Lake covers an area of over 3 ha and is on average less than 0.5 deep (depth 
depending on tide). 
Habitats. Peat banks and undercuts, hanging Rhizophora roots, soft sandy bottom 
rich in detritus and covered by varying density of seagrass. The bottom of Boston Bay 
near the Creek's entrance is covered by turtle grass; the seafloor of Hidden Lake consists 
of soft detritus deposited on firm peat floor. 
Depth. 0.5-3 m. 
Environmental Conditions. L: + to -; C: + (with each tidal change). T, S: stressful 
range, due to tidal drainage of water from Hidden Lake that may be hot and hypersaline 
after a period of exposure to full sun, or cold and brackish after heavy rains. Water drains 
from nearby Boa Flats (in the south) into Boston Bay and Hidden Creek as well. During 
the cold season (January, February), the lake can approach the air temperature of a cold 
night, whereas the deeper lagoon acts as a buffer. Measurements by thermistor recorder 
just inside the Hidden Creek entrance show a combined maximum temperature range of 
18.5"-30" C (January 1990, February 1998) and 28"-37" C (August 1989, 1999). Salinity 
range at the same location measured by refractometer (April 1993, February 1998, 
August 1999) ranged from 22 to 38%0 (subsurface), depending on rainfall and direction 
and timing of tidal current flow. 
There were several observations of strong exposure to suspended sediments that 
may enter through tidal flow from either Hidden Lake or Boston Bay; some of these 
events may have been caused by boat traffic, a rare but not unusual occurrence. 
Sediment. Bottom samples taken at the entrance in 1.3 m depth, and 10 m into the 
creek (1.9 m) consisted of fine sand (70% less than 2 rnrn diameter), with larger 
Halimeda chips and shell fragments and a substantial amount (1 7% dry weight) of 
detritus (plant material). A similar sample taken near the mangrove fringe in Boston Bay, 
just outside the creek entrance, revealed mostly decaying plants (detritus) with a small 
amount (1 1 %) of carbonate chips and shell. Samples included just trace amounts of 
broken sponge spicules despite the close proximity of large sponge populations. 
Communities. Thalassia at the Boston Bay entrance is heavily overgrown by 
filamentous cyanobacteria (Lyngbya), anemones (Bunodeopsis), bryozoans (Zoobotryon), 
and ascidians (Didemnum). Algae, a great variety of sponges, sabellid polychaetes, and 
ophiuroids on the peat banks. Roots dominated by sponges and anemones (Aiptasia, 
Bartholomea, Condylactis), also Halimeda and Caulerpa algae, hydroids, ascidians, and 
clusters of mangrove oyster (Isognomon) in the intertidal. Common sponge species on the 
peat bank are Cinachyrella apion, Biemna caribea, Scopalina ruetzleri, Hyrtios proteus, 
and Clathrina. On the roots we find Spongia tubulosa. S. pertusa, Geodiapapyracea, 
very large specimens of Lissodendoryx, Scopalina, Biemna caribea, Mycale 
magniraphidifera, Tedania, Amorphinopsis sp., Halichondria cf. magniconulosa, 
Haliclona implexiformis, H curacaoensis, and Dysidea sp. Clusters of bivalve 
(Isognomon) shells in the lower intertidal zone offer additional substratum to small and 
encrusting sponges (e.g., Halisarca, Clathrina, Sycon), hydroids, and ascidians 
(Ecteinascidia minuta, Styela canopus). During the early 1980s, the green alga Halimeda 
was nearly as prominent as sponges but the population has since diminished. Some algae 
(Udotea, Halimeda, Caulerpa) are scattered over the bottom and sponges (Haliclona 
magnijka) and sabellid polychaetes are embedded in the soft sediment and attached to 
the bases of algae in protected side branches and near the entrance into Hidden Lake. 
Sponges that have fallen from broken or decayed mangrove roots are surviving partially 
buried in the muddy bottom (for instance, Lissodendoryx, Haliclona permollis) and 
Udotea algae were observed supporting small invertebrate settlers (e.g., the ascidian 
Botryllus tuberatus). Polychaete and mollusk egg cases are commonly encountered on the 
muddy bottom among decayed mangrove litter. 
Sta. 13 G, Crescent Bay (Figs. 1, 19) 
Figure 19. Aerial photograph of south Twin Cays looking toward the northwest; Crescent 
Bay (sta. 13G) is behind South Point (occupied by a ranger station of the South Water Cay 
Marine Reserve); in the center foreground is Southeast Coast (131). 
Location and Topography. A wide (>200 m), gently curved bay located at the 
southwest end of East Island, just south of the entrance to Main Channel and open toward 
the west; its southern limit is South Point. 
Habitats. Short Rhizophora roots along the margin with bostrychietum fuzz but 
no large invertebrates, anchored in sand. Sandy bottom with seagrass; a large, bare, near- 
shore sandy patch to the north. 
Depth. 0.2-2 m. 
Environmental Conditions. L: +; C:  + (fully exposed to west and southwest 
winds); water flow at ebb-tide from the adjacent Boa Flats may affect the organisms 
living close to the mangrove margin). 
Sediment. Fine to medium-grained calcareous sand, rich in Halimeda chips. 
Communities. Seagrass Thalassia and Halimeda algae, with solitary coral 
(Manicina areolata) and bivalves (Pinna carnea, Atrina sp.). Sandy bottom with traces 
(mounds) of burrowing shrimps. 
Sta. 13 I, East Island, Southeast Coast (Fig. 1, 19) 
Location and Topography. South exposed shore (open 1agoon)extending east 
from South Point. 
Habitats. Short, stout Rhizophora roots anchored in sand along the fringe. Sandy 
bottom with dense Thallassia seagrass and algae (Halimeda, Penicillus, Rhipocephalus), 
very similar to other peripheral sites such as 5 K, 13 G, but not as diverse as the more 
protected West Bay (7 E). 
Depth. 0.2-1.5 m. 
Environmental Conditions. L: +; C: + (fully exposed to southerly and south- 
easterly winds). 
Sediment. Fine to medium-sized calcareous sand; coarser Halimeda chips. 
Communities. Mangrove roots are populated mainly by bostrychietum and some 
encrusting hydrocoral (Millepora) but no large invertebrates. Turtlegrass and Halimeda 
algae, sponge clusters attached to dead shell, particularly Hyrtios proteus and 
Amphimedon erina. The only location in the Carrie Bow area where the symbiotic sponge 
(with filamentous cyanobacteria) Hyrtios violacea is common (Riitzler, 1990). 
DISCUSSION 
This account of subtidal localities in the Twin Cays mangrove concentrates on 
sessile fauna (sponges and ascidians, in particular) because these organisms are excellent 
indicators of long-term environmental conditions and community health. Algae too are 
highly diverse in mangroves (Norris & Bucher, 1982; Littler and Littler, 1997; Littler et 
al., 2004) but occur in different ecological niches and are more tolerant of environmental 
changes. Algae in fact are powerful competitors for the limited supply of substratum 
space and seem to flourish during the warmer summer months, overgrowing epifauna on 
stilt roots.The habitats described represent diverse topographic features that are unique to 
mangrove islands and are influenced by a wide range of environmental parameters, from 
near-oceanic quality of outer coasts to the life-restricting conditions of inshore ponds. 
Mangroves are forests composed of a diverse collection of salt-tolerant plants, but 
in the subtidal realm only one species has direct impact on the marine community: the red 
mangrove (Rhizophora mangle). Growth of these trees over thousands of years resulted 
in an accumulation of peat that is consolidated, eroded, and shaped by various physical 
and biological processes (Macintyre et al. 1995; McKee and Faulkner, 2000; Macintyre et 
al., 2004). 
Primary Substrata 
Availability of solid surfaces distant from sediment bottoms is the key to the 
existence of most sessile shallow-water invertebrates. In the mangrove, hard substrata are 
provided mainly by the stilt roots of Rhizophopra, many of which hang freely into the 
water if they are young and where the bottom is too deep to reach, for instance along 
deep-cut tidal creeks. Second in importance are the vertical surfaces of eroded peat banks 
lining canals and ranging from 0.2 m to nearly 3 m in height. Peat banks are eroded by 
past or present water currents that have also created deep undercuts and caves where they 
were forced to bend. Most of the Main Channel's west coast is lined by peat banks where 
the water flows fastest. High walls are found along 'Gator Creek (station 81), Grouper 
Gardens channel (91), and Hidden Creek (121). Cave-like undercuts occur at Batfish Point 
(5Ha) where currents from the open lagoon are the strongest. Undercut caves also occur 
at the neck of Lair Channel (9J), where water is quite stagnant but flow conditions may 
have been different in the past when there was a connection to the open lagoon. 
Under good conditions, mangrove adventitious roots grow several centimeters per 
year and therefore constantly provide new substrata for settlement. On the other hand, 
roots or entire trees may die, causing substrata to rot and leaving the entire epibiont 
community to sink into the muddy bottom. Most sessile invertebrates become smothered, 
but a few sponges (notably species of Haliclona, Lissodendoryx, and Ircinia) were 
observed buried in detritus and healthy for at least three years. Some developed fistulose 
structures, presumably for the increase of surface area to compensate for the restricted 
water and nutrient flow into the incurrent canal system of the sponge. 
Secondary Substrata 
Although Rhizophora roots and peat are the primary substrata for sessile 
mangrove organisms, secondary space becomes available as the community develops. 
One of the organism that provide new substrata are the bivalve Isognomon alatus, the 
mangrove oyster, a species that develops clusters of individuals, often near the water 
surface at the top of a hanging root. Although adjacent shells may be in close 
juxtaposition, two species of ascidians regularly make use of the shells as a settlement 
surface. These are the colony-forming Ecteinascidia minuta and the solitary species 
Styela canopus (Goodbody, 2004a). Other colonial ascidians, such as Diplosoma 
listerianum and Didemnum conchyliatum, and sponges (for instance, Biemna caribaea, 
Haliclona curacaoensis, H. manglaris, H. tubulifera, and Clathrina cf. coriacea), are 
more common on the outside of a bivalve cluster but still penetrate the intershell space. 
Sponges too provide biological surfaces for secondary settlement space, particularly 
Spongia tubulifera, which is always overgrown by other sponges and by algae, ascidians, 
hydroids and serpulid polychaetes. Other important members of the benthic community 
such as turtlegrass (Thalassia) and calcareous green algae (Halimeda) regularly provide 
secondary space, particularly for hydroids, Didemnum, anemones, such as the small but 
strongly stinging Bunodeopsis antilliensis, Aiptasia tagetes, and forarniniferans 
(Richardson, 2004). 
Tides 
One condition that determines the existence and structure of subtidal mangrove 
epifauna is tidal range. Twin Cays, like most parts of the Caribbean, has a small range 
(mean 20 cm), thus keeping habitats permanently submerged except for an upper, near- 
surface transition zone to the intertidal populated by species with some resistance to 
short-term exposure to dessication (Riitzler, 1995). In two recorded El Niiio years, tides 
of 30 cm below mean low during noon hours caused mass mortalities of all organisms in 
the uppermost subtital zone. 
Light 
Most organisms in this shallow-water ecosystem are adapted to strong 
illumination, but in some locations light, or the lack of it, determines the community 
structure. Photosynthetically active radiation determines most notably the distribution and 
density of seagrass, Thalassia, which is not found on deep channel bottoms with turbid 
water (for instance, part of Lair Channel, 9J; Lair, 9K). It is also sparse or missing in 
narrow creeks shaded by overhanging trees and flooded by (brown-colored) water high in 
tannin content as it returns from the swamp (Gator Creek, 81; Hidden Creek, 121) (Calem 
and Pierce, 1993). Algae and cyanobacteria are more tolerant and successfully compete 
with sessile animals for free space. Exceptions are peat overhangs and caves, and some 
recessed peat banks under a dense canopy, where light levels are very low. Sponges 
flourish under these conditions, without competing algae and (on cave ceilings) free of 
sediment. Although no unique cryptic species were found, the sponge diversity per area is 
highest in caves. One cream-colored ascidia (Diplosoma) was also found to be a common 
member of the cave community. 
Temperature 
Because much of the water in the mangrove occurs in shallow lakes and ponds, it 
is directly subjected to heating and cooling of the atmosphere. Tidal signature and timing 
strongly influences the temperature regime. Since the ponds are too shallow and muddy 
to support large populations of sessile animals, the effect of temperature change is mainly 
noticeable in the channels where water moves with each tidal cycle and is very hot when 
the ponds empty after noon hours of full sunshine in summer, very cold following a chilly 
night in winter. Swamp water also drains sideways into the channels, flowing across the 
peat banks and noticeable because of its tannin-brown color. The presence of large 
populations of filter feeders such as sponges and ascidians near the outflow of swamp 
water indicates high contents in nutrients (dissolved and particulate, mainly as 
bacterioplankton) overriding the limiting effects of temperature fluctuations. 
Measurements were taken on numerous occasions but unfortunately, long-term in situ 
recordings of temperature together with correlated parameters (tide, salinity, rainfall, 
dissolved organics) are still missing. 
Temperature changes in one tidal cycle during winter (January-March) can vary 
from 18" to 32" C (ocean mean temperature, 26" C); during summer (July-September), 
they fluctuate from 28" to 41 " C (ocean mean, 29" C). 
Salinity 
Normal seawater in the area has a salinity of 35-36%0. At Twin Cays, the range 
was measured after heavy overnight rains when ebb tide drained the swamp in the early 
morning. Samples along the main channel had lower salinity of 21%0 at the surface, 23%0 
at 50 cm depth. The same phenomenon has been recorded from the Port Royal, Jamaica, 
mangroves where it was demonstrated that if the low salinity water goes too deep it 
causes heavy mortality among sessile communities in which most organisms lack 
mechanisms for osmotic control (Goodbody 196 1). 
During some tidal exchanges after heavy rains, freshwater tends to form the top 
layer although it is colder by several degrees than the denser but warmer seawater. 
Intertidal and upper subtidal communities are strongly affected by this phenomenon, as 
reflected by extensive mortality after such conditions occurred repeatedly. 
Sediments 
Fine calcareous sand and mud, that is, rich in organics, make up the bottom of the 
Main and Lair channels and support stands of seagrass (Thalassia, Halodule) and algae 
(Halimeda, Penicillus, A vrainvillea), large populations of upside-down jelly fish 
(Cassiopea), and an ubiquitous burrowing crustacean endofauna that forms characteristic 
mounds, deposits from its tunneling activity (Dworschak and Ott, 1993). Despite the 
plant cover and consolidation by mucuous substances derived from bacteria, 
cyanobacterial mats, fecal pellets, and other sources, the sediment is easily disturbed and 
resuspended by storms, manatee feeding, and boat traffic. The wake of passing boats may 
also indirectly cause resuspension of sediments by moving thickly populated free- 
hanging roots with growth tips close to the bottom. Because most mangrove epibionts are 
filter-feeders with limited capability to clear themselves from sediment cover, these 
disturbances may result in burial and smothering. Sponges and ascidians are only 
successful in these mangroves because many of the hard substrata (mangrove roots, peat 
banks) have vertical orientation, keeping siltation to a minimum. Nevertheless, increased 
boat traffic through the channels in recent years may have contributed to a decline in 
populations, particularly of the rich sponge fauna in Sponge Haven (1 OH; Diaz et al., 
2004). Habitats with anchored roots and strong currents are mostly found along the 
perimeter of Twin Cays (stations 5 K, 7 E, 1 1 G, 13 G, 13 I). 
The bottoms of inshore ponds and creeks are equally soft but primarily made up 
by flock of fibrous, broken-down plant materials. As already mentioned above, some 
sponges are able to flourish being buried in this substratum. 
Water Flow 
Storms resuspend fine sediments but tidal and wind-generated currents help clear 
exposed substrata and bring nutrient- and bacteria-rich water from the interior of the 
swamp to the sessile benthos that is either filter or particle feeding. Water flow is most 
constant in the main channel because prevailing winds push water either from north or 
south and create conditions close to those of nearby coral reefs. Some narrow and long 
creeks connecting the outer lagoons to interior ponds ('Gator Creek 8 I; Hidden Creek, 12 
I) display the strongest currents within the system (20 crnlsec were measured) but depend 
on tidal signature and often combine the beneficial factor of strong flow, washing silt 
away from settlers, with less desirable poor (hot, cold, high or low salinity, tannin-rich) 
water quality. The wake of passing boats my indirectly cause resuspension of fine sand 
and mud by moving heavily populated free-hanging roots with growth tips near the 
bottom, thus affecting the epibionts both by wave action and by sedimentation. 
Biotic Factors 
Diversity and species composition are influenced not only by abiotic factors but 
also by differences in ecological interactions and recruitment history. Transplant 
experiments and new artificial substrata make it possible to highlight these parameters for 
sponge communities (Wulff, 2004; Ruetzler, in preparation). 
Algae and cyanobacteria affect invertebrate epibionts through space competition 
at settlement as well as in later stages of community development. During the winter 
months, large quantities of floating Sargassum seaweed enter the Main Channel from the 
north and prevailing winds push them against the western shore of the channel. Wave or 
boat wash causes the weed to move up and down along the roots in such a manner as to 
have an abrasive action damaging or destroying elements of the epibiont community, as 
was demonstrated by newly marked colonies of the ascidian Diplosoma glandulosum 
(July 1984), many of which were lost or damaged by the following February. 
A more serious threat to many epibionts, particularly filter-feeding sponges and 
ascidians, is the seemingly increasing presence of filamentous cyanobacteria, which tend 
to overgrow roots and everything settling on them. One common kind develops thick, 
hair-like filaments of tan, brown, to red color and covers substrata as entangled tufts or 
clumps, or forms strands that hang into the current like streamers, up to 15 cm wide and 2 
m long (for instance, in Grouper Gardens, 91; August 2004). The main species 
incorporated in these clusters are Lyngbya polychroa and Lyngbya sp. Dislodged strands 
may accumulate as thick masses forming bright green floats (bleached from full exposure 
to sun light) after they drifted into calm-water bays, such as the cove outside Turtle Pond. 
Another kind is commonly found as rust-red heavy drapes coating roots, sponges and 
other surfaces on mangrove roots and is composed mainly of Schizothrix tenerrima and 
Schizothrix sp. Their filaments are shorter and more fragile than Lyngbya and flake off 
and disperse easily. This phenomenon was already recorded in 1986 (May) when growths 
of this organism took over the lowest part of roots that were otherwise occupied by the 
ascidian Eudistoma olivaceum. Today, cyanobacterial accumulations seem ubiquitous 
throughout Twin Cays, at least during the summer months (July-September), and it 
remains to be investigated whether it is related to the increase of dissolved organic 
substances in the lagoon water. An ongoing project attempts to determine what 
environmental parameters (in particular, nutrient levels, temperature, current flow) 
stimulate growth of cyanobacteria and to what degree sponge and other sessile 
invertebrates are affected by microbial competitors and pathogens (Diaz et al., 2004). 
Shifts in community composition of physiologically sensitive epibionts such as sponges 
may be useful indicators of long-term environmental health. 
Pollution caused by human activities and rapidly increasing with economic 
development has particularly severe consequences in mangroves because as a tidal 
community they are affected by both terrestrial and aquatic stresses. Live trees make up 
the framework and principal components of the community and if lost they cannot be 
replaced in our life time, maybe never once the substratum buildup is washed away. 
Effects of clear-cutting are discussed in another contribution (Rodriguez and Feller, 
2004). Peat and hanging and anchored roots are the principal solid substratum for sessile 
organisms and hence the pillars of the rest of the marine community, as we have 
demonstrated after examining the effects of an oil spill in another Caribbean mangrove 
(Riitzler and Sterrer, 1970). 
Unfortunately, many people still believe that mangroves are areas of decay and 
therefore suitable dumping grounds for garbage. This notion has caused severe damage to 
the Twin Cays mangrove community, not to mention setbacks in ongoing research in 
places such as Turtle Pond (6H), The Lair (9K), and Twin Cays (10K). Repeatedly over 
the years, these secluded locations were apparently considered good hiding places and, 
unlike the more spectacular nearby coral reefs not affected by unsightly appearance, were 
subjected to excessive release of nutrients from kitchen waste and heavy metals from 
batteries, or the smothering action of large plastic bags. 
ACKNOWLEDGMENTS 
We thank Molly K. Ryan for the preparation of the map and for scanning and 
processing the digital images, Mike Carpenter assisting in fieldwork, and Vicky 
Macintyre for editorial revisions. Contribution number 701, Caribbean Coral Reef 
Ecosystems Program, Srnithsonian Institution. 
REFERENCES 
Calder, D.R. 
1991a. Associations between hydroid species assemblages and substrate types in the 
mangal Twin Cays, Belize. Canadian Journal of Zoology 69:2067-2075. 
1991b. Abundance and distribution of hydroids in a mangrove ecosystem at Twin 
Cays, Belize, Central America. Hydrobiologia 2 16/217:221-228. 
Calem, J.A., and J.W. Pierce 
1993. Distributional control of seagrasses by light availability, Twin Cays, Belize, 
Central America. Atoll Research Bulletin 387:l-13. 
Diaz, M.C., K.P. Smith, and K. Riitzler 
2004. Sponge species richness and abundance as indicators of mangrove epibenthic 
community health, Twin Cays, Belize. Atoll Research Bulletin 518: 1-18. 
Dworschak, P.C., and J.A. Ott 
1993, Decapod burrows in mangrove-channel and back-reef environments at the 
Atlantic barrier reef, Belize. Ichnos 2:277-290. 
Faust, M.A., and R.A. Gulledge 
1996. Population structure of phytoplankton and zooplankton associated with 
floating mangrove detritus in a mangrove island, Twin Cays, Belize. Journal 
of Experimental Marine Biology and Ecology 197: 159-1 75. 
Goodbody, I. 
1961. Mass mortality of a marine fauna following tropical rains. Ecology 42: 150- 
155. 
2004a. Diversity and distribution of ascidians (Tunicata) at Twin Cays, Belize. Atoll 
Research Bulletin 524: 1 - 19. 
2004b. The ascidian fauna of Port Royal, Jamaica, I: Harbor and mangrove dwelling 
species. Bulletin of Marine Science (in press). 
Hajdu, E., and K. Rutzler 
1998. Sponges, genus Mycale (Poecilosclerida: Demospongiae: Porifera), from a 
Caribbean mangrove and comments on subgeneric classification. Proceedings 
of the Biological Society of Washington 1 1 1 : 737-773. 
Joye, S.B., and R.Y. Lee 
2004. Benthic microbial mats: Important sources of fixed nitrogen and carbon to the 
Twin Cays, Belize, ecosystem. Atoll Research Bulletin 528: 1-24. 
Kohlmeyer, J., B. Bebout, & B. Volkrnann Kohlmeyer 
1995. Decomposition of mangrove wood by marine fungi and teredinids in Belize. 
Marine Ecology 16: 27-39. 
Koltes, K.H., J.J. Tschirky, and I.C. Feller 
1998. Carrie Bow Cay, Belize. In: Kjerfve B., ed., CARICOMP-Caribbean Coral 
Reej Seadrass and Mangrove Sites. UNESCO, Paris, pp. 79-94. 
Littler, D.S, and M.M. Littler 
2000. Caribbean reef plants. Off-Shore Graphic, Washington D.C. 
Littler, M.M., D.S. Littler, and B.L. Brooks 
2004. Extraordinary mound-building forms of Avrainvillea (Bryopsidales, 
Chlorophyta): Their experimental taxonopmy, comparative functional 
morphology and ecological strategies. Atoll Research Bulletin 515: 1-26. 
Macintyre, I.G., M.M. Littler, and D.S. Littler 
1995. Holocene history of Tobacco Range, Belize, Central America. Atoll Research 
Bulletin 430: 1-1 8. 
Macintyre, I.G., M.A. Toscano, R.G. Lighty, and G.B. Bond 
2004. Holocene history of the mangrove islands of Twin Cays, Belize, Central 
America Atoll Research Bulletin 5 10: 1- 16. 
McKee, K.L., and P.L. Faulkner 
1999. Mangrove peat analysis and reconstruction of vegetation history at the Pelican 
Cays, Belize. Atoll Research Bulletin 468:45-58. 
Ott, J., and M. Bright 
2004. Sessile ciliates with bacterial ectosymbionts from Twin Cays, Belize. Atoll 
Research Bulletin 5 16: 1-7. 
Parrish, M., and M.K. Ryan 
2004. Art in the SWAMP: Using field illustrations to prepare drawings of mangrove 
communities at Twin Cays, Belize. Atoll Research Bulletin 530:l-9. 
Richardson, S.L. 
2004. Seasonal variation in epiphytic Foraminifera biotas from Thalassia seagrass 
habitats, Twin Cays, Belize. Atoll Research Bulletin 517:l-39. 
Rodriguez, W., and I.C. Feller 
2004. Mangrove landscape characterization and change in Twin Cays, Belize, using 
aerial photography and Ikonos satellite data. Atoll Research Bulletin 5 13: 1-23. 
Rutzler, K. 
1988. Mangrove sponge disease induced by cyanobacterial symbionts: failure of a 
primitive immune system? Diseases of Aquatic organisms 5: 143-149. 
1990. Associations between Caribbean sponges and photosynthetic organisms. In: 
K. Rutzler (ed.), New Perspectives in Sponge Biology, Smithsonian Institution 
Press, Washington, D.C., pp. 455-466. 
1995. Low-tide exposure of sponges in a Caribbean mangrove community. Marine 
Ecology 16: 165-179. 
Riitzler, K., M.C. Diaz, R.W.M. van Soest, S. Zea, K.P. Smith, B. Alvarez, and J. Wulff 
2000. Diversity of Sponge Fauna in Mangrove Ponds, Pelican Cays, Belize. Atoll 
Research Bulletin 476:229-248. 
Riitzler, K., and C. Feller 
1988. Mangrove swamp communities. Oceanus 30(4): 16-24. 
1996. Caribbean mangrove swamps. Scientific American 274 (3):94-99. 
Rutzler, K., and J.D. Ferraris 
1982. Terrestrial environment and climate. In: K. Rutzler and I.G. Macintyre (eds.), 
The Atlantic Barrier Reef Ecosystem at Carrie Bow Cay, Belize 1: Structure 
and Communities, pp. 77-91. Smithsonian Contributions to the Marine 
Sciences 12. 
Rutzler, K., and I.G. Macintyre 
1978. Siliceous sponge spicules in coral reef sediments. Marine Biology 49: 47-159. 
1982. Habitat distribution and community structure of the barrier reef complex near 
Carrie Bow Cay. In: K. Rutzler and I.G. Macintyre (eds.), The Atlantic Barrier 
Reef Ecosystem at Carrie Bow Cay, Belize 1: Structure and Communities, 
pp. 9-45. Smithsonian Contributions to the Marine Sciences 12. 
Rutzler, K. and W. Stener 
1970. Oil pollution: Damage observed in tropical communities along the Atlantic 
seaboard of Panama. Bioscience 20:222-224. 
Weerdt, W. de, K. Riitzler, and K.P. Smith 
1991. The Chalinidae (Porifera) of Twin Cays, Belize, and adjacent Waters. 
Proceedings of the Biological Society of Washington 104: 189-205. 
Winston. J. E. 
2004. Bryozoans from Belize. Atoll Research Bulletin 523:l-14. 
Wulff, J. 
2004. How sponge species assemble on mangrove roots, Twin Cays, Belize. Atoll 
Research Bulletin 5 19: 1 - 10. 
PLATES 

Plate 1. Aerial views and habitats of northern Twin Cays: a, The archipelago looking 
southeast toward the barrier reef and some of its cays (left to right, South Water Cay, 
Carrie Bow Cay, and Curlew Bank; b, northern shore and channels; c, peat undercut and 
hanging roots at Batfish Point; d, peat wall with sponge; e, hanging root covered by fire 
sponge (Tedania ignis); J gray ascidian, Diplosoma glandulosum; g, orange sponge 
(Scopalina ruetzleri) on root. 

Plate 2. Sessile organisms and habitats of northern Twin Cays: a, Mycale laxissima, a 
sponge typical for the banks of 'Cuda Cut; b, Botrylloides nigrum, a common ascidian at 
Batfish Point; c, common encrusting sponge, Mycale microsigmatosa; d, filamentous 
cyanobacteria, Schizothrix spp., coating many sponges, such as Lissodendoryx; e, peat 
wall in the rear of an undercut showing patch of sulfur-fixing bacteria, Beggiatoa;J 
vertical view of mud bottom at Cassiopea Cove showing the upside-down jellyfish that 
gave the cove its name (yellowish-green disks), algae (fluffy green balls), Penicillus, and 
fine sand with openings of tunnels made by burrowing shrimps (Glypturus, Alpheus). 

Plate 3. Sessile invertebrates and views of habitats in ponds and bays of northern Twin 
Cays: a, ascidians, Perophora regina on a mangrove root at the type locality, Turtle 
Pond; b, typical loose organic-flock bottom in Turtle Pond, with decaying mangrove 
leaves and covered by a bacterial matt; c, West Bay, mini-reef cluster among turtlegrass 
consisting of green calcareous Halimeda algae and sponge (Clathria schoenus), visited 
by a sea urchin (Lytechinus); d, 'Gator Creek, the yellow sponge Cinachyrella apion, 
ornamented by porocalices (cups containing pores and oscula) and tiny buds, is typical 
for the peat wall lining the deep channel; e, mollusk egg case on the channel's soft 
bottom of mangrove 1itter;f; Haliclona magn@ca, a sponge with long oscular tubes is 
common on the peat bank and buried in detritus bottom of 'Gator Creek, its type locality. 

Plate 4. Lair Channel and associated biotopes: a, bird's eye view of Lair Channel, 
leading from the Main Channel eastward (right) through the channel's neck into The 
Lair; 'Gator Creek branches off at the channel's mouth, toward the north (top left); 
Grouper Gardens, a cluster of small ponds, is entered through a narrow passage cutting 
into the opposite (south) bank; b, calcified algae, Halimeda, and fire sponge, Tedania line 
the entrance to Grouper Gardens; c, bunches of mangrove oysters (Isognomon) grow on 
many roots along the canals connecting ponds and serve as a secondary substratum for 
small sponges, sea anemones, serpulid worms, and ascidians; d, in the back of Grouper 
Gardens entrance sponges, such as this Calyxpodatypa, may be threatened by thick 
layers of filamentous cyanobacteria (Lyngbya), which develop in masses during the 
summer months (July to September); e, the bottom of Grouper Gardens ponds is 
overgrown by tall Avrainvillea algae which provide shelter for invertebrates, such as this 
opisthobranch, Tridachia. 

Plate 5. Habitats of south Twin Cays locations: a, mangrove root at Lair Channel neck; 
the older root (right) is covered by the sponges Haliclona implexiformis (violet) and 
Biemna caribea (yellow); the sprout is overgrown by Clathria venosa (gray) and, on the 
new tip, turquoise H. manglaris; b, dark ceiling of peat cave covered by sponges, with 
mangrove root sprouting from above; sponges include H. implexiformis (pinkish violet), 
H. curacaoensis (light gray), H. manglaris (turquoise), Clathrina cf. coriacea (yellow); c, 
same habitat as b above, soft, cream colored ascidian crust, Diplosoma sp.; d, ascidian 
Distaplia corolla, a prominent colonizer of mangrove substrata at Twin Bays (sta. 1 OG); 
e, Sponge Haven fringe (sta. 1 OH) with researchers displaying a mangrove root heavily 
populated by sponges;J Main Channel entrance, mini-reef among Thalassia seagrass 
composed of fire sponge (Tedania ignis) agglutinating calcified algal (Halimeda) thalli. 

Plate 6. Hidden Creek habitats and common organisms: a, mangrove root hanging over 
peat-bank undercut overgrown by sponges, Chalinula molitba (purple), Lissodendoryx 
(greenish gray), and Tedania (orange red); b, seagrass Thalassia at Boston Bay entrance 
heavily overgrown by filamentous cyanobacteria, Lyngbya; c, turtlegrass blades covered 
by ascidian, Didemnum conchyliatum; d, corroded peat bank with partially exposed 
mangrove roots covered by sponge, Biemna caribea; e, anemones, Aiptasia tagetes on 
roots;J unidentified sabellid worms; g, Hidden Lake bottom with upside-down jellyfish, 
Cassiopea.