Eastern Florida Research Articles

Mercury in livers of wading birds (ciconiiformes) in southern Florida

Mercury was measured in livers from 144 wading birds representing seven species collected from four different areas in southern Flordia, including the Everglades National Park. Significant differences in hepatic mercury concentrations were identified between birds collected from different geographic locations, birds of different ages, dietary factors, and relative amounts of body fat. Birds collected from an area encompassing the central Everglades and eastern Florida Bay had significantly greater concentrations of hepatic mercury than did birds from other collection areas. Livers from fledgling and young adult birds contained approximately three times the concentration of mercury as livers from nestling birds. Bird species whose prey base consists of larger fish were found to have approximately four times the hepatic concentration of mercury as did those species which consume smaller fish or crustaceans. Birds with minimal to moderate amounts of body fat had two to three times the concentration of hepatic mercury as birds with relatively abundant body fat reserves. Four great blue herons collected from the central Everglades contained liver mercury at concentrations typically associated with overt neurologic signs (⩾30 μg/g). Between 30% and 80% of potential breeding-age birds collected from this area contained hepatic mercury at concentrations associated with reproductive impairment in ducks and pheasants. These data suggest that declining numbers of nesting ciconiiform birds in Florida may be due, in part, to mecury contamination of their food supply.

Genetic subdivision and morphological variation in a freshwater snail species complex formerly referred to as Viviparus georgianus (Lea)

Genetic and morphological variation was studied in a brooding (ovoviviparous) and morphologically variable freshwater snail [Viviparus georgianus (Lea)] species complex in southern Georgia and Florida. Eleven populations were clustered into three genetically isolated, allopatric groups characterized by 7 to 14 diagnostic loci out of the 38 loci examined. These allopatric groups were identified as V. georgianus (in eastern and southern Florida), V. limi (in the Ochlockonee River) and V. goodrichi (in the Florida panhandle). Nei's standard genetic distances between the species were large (0.23-0.52) compared to intraspecific distances (0.00-0.06). Hierarchical F-statistics for differentiation among sites within drainage systems (FSD) for V. goodrichi and V. georgianus were large (0.519 and 0.387, respectively). The FDT values (differentiation among drainage systems within the total area sampled) were negative or close to zero, so most of the intraspecific genetic differentiation was due to differences among populations within drianage systems, rather than to differences among systems. Canonical discriminant analysis of nine shell morphological measurements separated all three species with little overlap. Principal components analysis of the shell morphology revealed intraspecific variation among sites possibly due to environmental effects. This study demonstrates the marked genetic and morphological variation among and within drainage systems in freshwater prosobranchs.

Improved chronologic resolution of the Hawthorn and the Alum Bluff Groups in northern Florida: Implications for Miocene chronostratigraphy

Several geochronologic methods are used to constrain the ages of the early to middle Miocene Hawthorn and Alum Bluff Groups in the eastern Florida panhandle. The Dogtown Member of the upper Torreya Formation (Hawthorn Group) in northern Gadsden County contains an early Barstovian land-mammal fauna, has 87 Sr/ 86 Sr age estimates between 14.7 ± 1.5 and 16.6 ± 1.0 Ma, is of reversed magnetic polarity, and probably correlates with Chron C5B-R. These results constrain the age of the Dogtown Member in the study area to between about 15.3 and 15.9 Ma, significantly younger than previously recognized for the upper Torreya Formation. A second fossil locality from the Dogtown Member occurs in the same lithostratigraphic interval but is older, based on vertebrate biochronology. This indicates that the Dogtown Member is time transgressive, that is, younger to the north. Early Hemingfordian land-mammal faunas and an invertebrate fauna correlative with planktonic foraminiferal zones upper N5 and N6 are known from the lower Torreya Formation. One mollusc sample from the Seaboard locality produced a 87 Sr/ 86 Sr age estimate of 18.4 ± 1.0 Ma, consistent with the biochronology. The revised age of the Torreya Formation is late early to early middle Miocene, between about 19 and 15.3 Ma. The Chipola Formation has been interpreted to be late early or middle Miocene (N7 and N8) in age and younger than the Torreya Formation, based on the superposition of the Chipola over the Torreya at the only known stratigraphic contact and apparent biochronologic differences. Four samples from the Chipola Formation at Alum Bluff yield 87 Sr/ 86 Sr age estimates between 18.3 and 18.9 (±1.0) Ma (early Miocene), much older than previous interpretations. A small land-mammal fauna from an overlying unit supports the older age for the Chipola Formation. The discrepancy in ages is probably due to poor biostratigraphic correlation rather than erroneous 87 Sr/ 86 Sr ages. The lithostratigraphic relationship between the Chipola and the Torreya Formations is poorly known from cores only; chronostratigraphic evidence indicates that the Chipola and Torreya Formations overlap in age and may interdigitate, possibly representing transitional marine and nearshore/shelf facies.

Seasonal Distributions and Abundances of Loggerhead and Leatherback Sea Turtles in Waters of the Northeastern United States

Seasonal distributions and abundances of loggerhead (Caretta caretta) and leath- erback (Dermochelys coriacea) sea turtles in continental shelf waters off the coast of the northeastern United States were derived from more than three years of aerial and shipboard surveys. There were 3460 sea turtle sightings, including 2841 loggerheads, 128 leatherbacks, and 491 unidentified. Relative abundance patterns, corrected for uneven distribution of survey effort, demonstrated an extensive area of loggerhead distribution from near Long Island, New York, along the mid-shelf to near Cape Hatteras, North Carolina. Areas of high relative abundance of leatherbacks were more scattered, with clusters south of Long Island and in the central and eastern Gulf of Maine. Loggerheads occurred significantly farther south (x = 38?20' N) than leatherbacks (x = 40005' N), and in significantly warmer waters (mean surface temperatures of 22.2 C and 20.4 C, respectively). The two species did not differ significantly in water depth or bottom slope at sighting; the modal depth interval for both was 21-40 m. Patterns of distribution and concentration of sea turtles differed greatly from nearly all species of marine mammals, suggesting little overlap in resource utilization. Both relative and absolute density estimates were much higher for loggerheads. Overall mean relative densities were 21.6 loggerheads per 1000 km of survey track, and 6.85 leatherbacks per 1000 km. Absolute density estimates, derived from 454 special aerial surveys, ranged from 1.64 x 10-3 to 5.10 x 10-1 loggerheads km-2 and 2.09 x 10-3 to 2.16 x 10-2 leatherbacks km-2. The maximum densities for both species were higher than values reported for the Gulf of Mexico and off the eastern Florida shore. Total study area populations during the summer were estimated at 2200-11,000 loggerheads and 100-900 leatherbacks. These estimates are minimal because they are based on observations of turtles at the surface, and may represent much greater abundances. The patterns of relative abundance derived from this analysis could be used as a basis for the designation of critical sea turtle habitat off the northeastern U.S.

New early Barstovian (middle Miocene) vertebrates from the upper Torreya Formation, eastern Florida panhandle

ABSTRACT A new vertebrate fauna has been recovered from the Dogtown Member of the Torreya Formation, Hawthorn Group (early to middle Miocene), northern Gadsden County, Florida. Fossils were recovered from four fuller's earth clay mines. This new fauna, called the Willacoochee Creek Fauna (WCF), contains at least 68 vertebrate taxa, including 29 mammals, from marine, freshwater, and terrestrial environments. The WCF is restricted to the early Barstovian land-mammal age based on the presence of Copemys, Perognathus, Rakomeryx, and Ticholeptus, and the overlapping chronologic ranges of 8 other mammals. Lanthanotherium, Perognathus, and a squalodont whale are reported from the southeastern U.S. for the first time. Biochronological range extensions into the early Barstovian are proposed for Lanthanotherium, Anchitherium clarencei and “Merychippus” primus. The WCF is the first well documented early Barstovian fauna in the southeastern U.S., thus filling a large gap in the temporal distribution of vertebrate fau...

Acoustic tomography in the Straits of Florida

Variability of the Florida Current has been monitored via acoustic tomography. A reciprocal tomography experiment was conducted in the eastern half of the Florida Straits during mid‐October and November, 1983. A triangular array of transceivers, with leg separations of approximately 45 km, was deployed at 27°N. The presence of a surface mixed layer in the region allowed for the ducted propagation of acoustic energy in the surface layer. A deeper layer was sampled by an unresolved group of refracted, bottom‐reflected ray arrivals. Incorporating the complete set of arrivals, we are able to obtain depth‐dependent estimates of the temperature field, current velocity, and relative vorticity. The oceanography of the region has been shown to be dominated by the lateral shifting of the surface and subsurface core of the Florida Current. The influx of westward flowing water through the Northwest Providence Channel at 26°N also appears as a large‐scale signal in the eastern Florida Straits. Low‐frequency fluctuations of temperature, current velocity, and vorticity occur at periods ranging from several days to nearly 2 weeks, and are intimately related to meandering of the Florida Current system.

Sediment Distribution of the Prairie Terrace in the Florida Parishes, Louisiana

ABSTRACT The Pleistocene-aged Prairie Terrace is an east-west trending deposit of wide lateral extent that crops out in the southern portion of the Florida Parishes, southeastern Louisiana. It is characterized by low topographic relief and low surface gradient. Meandering streams dominate the drainage pattern; quartz sand is the primary component in channel deposits. Deposition of the terrace material occurred primarily during the Sangamon Interglacial period, when sea level stood higher than at present and sediment was being transported by the north-south trending streams and bayous in the area. The clay mineral suite found throughout the study area is a mixture of smectite, kaolinite, and illite. An alteration zone of hydroxy-interlayered vermiculite (HIV) is present in St. Tammany Parish. The alteration zone represents an intermediate stage in the weathering process, where smectite is being chemically altered to kaolinite. The weathering process appears to occur preferentially in terraces of fluvial origin rather than in marine facies. This is the first recognized occurrence of HIV in late Pleistocene sediment in the eastern Florida Parishes.

Ultrastructure of sperm development and mature sperm morphology in three species of commensal bivalves (Mollusca: Galeommatoidea).

Ultrastructural features of the ovotestes, spermatogenesis, and the mature sperm are described for three galeommatid bivalves, Divariscintilla yoyo, Divariscintilla troglodytes, and Scintilla sp., from stomatopod burrows in eastern Florida. All three species yielded similar results except with respect to mature sperm dimensions. The ovotestis contains three types of somatic cells within the testicular portion: flattened myoepithelial cells defining the outer acinal wall; underlying pleomorphic follicle cells containing abundant glycogen deposits; and scattered, amoeboid cells containing lysosomal-like inclusions which are closely associated with developing sperm. Early spermatogenesis is typical of that reported from other bivalves. In contrast, the late stages of spermiogenesis involve the migration and gradual rotation of the acrosomal vesicle, resulting in a mature acrosome tilted about 70° from the long axis of the cell. The mature sperm possesses an elongated, slightly curved nucleus; a subterminal, concave acrosome with a nipple-like central projection; five spherical mitochondria and two centnoles in the middlepiece; and a long flagellum. The rotational asymmetry and the presence of perimitochondrial glycogen deposits in these sperm are unusual in the Bivalvia and may be associated with fertilization specializations and larval brooding common among galeommatoideans.

Cathodoluminescent bimineralic ooids from the Pleistocene of the Florida continental shelf

ABSTRACTA bored and encrusted late Pleistocene ooid grainstone was recovered from the seafloor at a depth of approximately 40 m on the outer continental shelf of eastern Florida. Ooid cortices are dominantly bimineralic, generally consisting of inner layers of radial magnesian calcite and outer layers of tangential aragonite. Ooid nuclei are dominantly rounded cryptocrystalline grains, although quartz grains and a variety of skeletal grains also occur as nuclei. Ooids are partially cemented by blocky calcite, and interparticle porosity is partially filled by micrite.Radial cortex layers are composed of brightly cathodoluminescent magnesian calcite having a composition of approximately 12 mol% MgCO3 and 1000 ppm strontium. The iron and manganese concentrations in radial cortex layers are generally in the range of 500–1000 ppm and 100–250 ppm, respectively. Tangential cortex layers are composed of noncathodoluminescent aragonite containing approximately 11 500 ppm strontium and less than 0.5 mol% MgCO3. Iron concentrations in tangential cortex layers are generally in the range of 150–400 ppm, and manganese concentrations are generally below the detection limit of 100 ppm. Echinoderm skeletal fragments, which are present as accessory grains, are composed of brightly cathodoluminescent magnesian calcite. Some ooid nuclei and the thin outer edges of some blocky calcite cement are cathodoluminescent; micrite matrix and the bulk of blocky calcite cement are noncathodoluminescent. Ooids do not exhibit textural evidence of recrystallization.The ooid grainstone underwent an episode of meteoric diagenesis. but ooid cortices were not affected by the event. We propose a previously unrecognized process by which the magnesian calcite cortex layers underwent diagenetic alteration in oxygen‐depleted seawater. During this diagenesis, magnesium was lost and manganese was incorporated without apparent textural alteration and without mineralogical stabilization. Thus, we Suggest that cathodoluminescence may result from diagenetic alteration on the sea‐floor.

Helminths of the Florida Manatee, Trichechus manatus latirostris, with a Discussion and Summary of the Parasites of Sirenians

We examined 215 Florida manatees (Trichechus manatus latirostris) at necropsy to determine the helminth fauna. Six species were identified: Heterocheilus tunicatus (Nematoda: Ascaridoidea); Anoplocephala sp. (Cestoda: Cyclophyllidea); and 4 species of trematodes, Cochleotrema cochleotrema (Digenea: Opisthotrematidae), Chiorchis fabaceus (Digenea: Paramphistomatidae), Nudacotyle undicola (Digenea: Nudacotylidae), and Moniligerum blairi (Digenea: Opisthotrematidae). Seventy-three percent of the manatees examined were infected with at least 1 species of helminth. The mean number of species of helminths per infected manatee was 1.9 with a range of 1-4. Fifty-nine manatees were helminth-free; 30 of these were calves. No associations were found between the intensity of helminth infections and host sex, age class, season, and geographic location of recovery, or cause of death. Differences in parasite prevalence between age classes were highly significant for Chiorchis, Cochleotrema, and Heterocheilus, due to a low number of infected calves. A higher prevalence of Cochleotrema was found in manatees recovered from eastern Florida, and Heterocheilus was evident in significantly more manatees from western and souther Florida. Comparisons in the parasite fauna are made among Florida manatees and other sirenian populations, and a brief review of sirenian parasites is included.

Cathodoluminescent Bimineralic Ooids from Pleistocene of Florida Continental Shelf: ABSTRACT

A bored and encrusted late Pleistocene ooid grainstone was recovered from the sea floor at a depth of approximately 40 m on the continental shelf of eastern Florida. Ooid cortices are dominantly bimineralic, consisting generally of inner layers of radial magnesian calcite and outer layers of tangential aragonite. The transition from radial to tangential cortex layers occurs at an approximate diameter of 0.30 to 0.35 mm. Ooid nuclei are predominantly rounded cryptocrystalline grains, although quartz grains and a variety of skeletal grains also occur as nuclei. Ooids were partially cemented by blocky calcite, followed by partial infilling of interparticle porosity by micrite and subsequently by sparse acicular cement. The radial cortex layers and some ooid nuclei are brightly cathodoluminescent, whereas the tangential cortex layers, micrite matrix, acicular cement, and the bulk of blocky calcite cement are nonluminescent. Some blocky calcite cement has a thin outer cathodoluminescent zone. Electron microprobe analyses indicate that radial layers contain approximately 10 mole % MgCO/sub 3/ and tangential layers generally contain 10,000 to 11,000 ppm strontium. The manganese content of radial layers ranges as high as 250 ppm, whereas the manganese content of tangential layers is generally below the detection limit of approximately 100 ppm.more » Iron content varies over a wide range. Scanning electron microscope analysis indicates no microdolomites. They assume manganese is the principal cathodoluminescent activator. Although there is some uncertainty concerning the partition coefficient for manganese into magnesian calcite and the influence of kinetic effects at varying rates of precipitation is poorly understood, they favor the interpretation that these cathodoluminescent magnesian calcite cortex layers have undergone diagenetic alteration in sea water of the Florida continental shelf.« less

Fabia felderi Species Novum, a New Pinnotherid Crab from the Central Eastern Coast of Florida (Crustacea: Decapoda: Brachyura)

Fabia felderi, a new species of pinnotherid crab collected from oculinid coral rubble in 80 m of water off the central eastern Florida coast, is described and illustrated from the unique holotypic male. The crab shows morphological similarities to some Pinnotheres species, as well as to two eastern Pacific species in the genus Fabia. All share a more or less subcircular carapace, a produced frontal region rimmed with a heavy fringe of hair, well developed setae along all pereopodal borders, and a generally similar positioning of the palp on the merus of maxilliped 3.

Reproduction by great white herons Ardea herodias in Florida Bay as an indicator of habitat quality

Reproduction parameters of great white herons Ardea herodias were used to evaluate the habitat quality of eastern Florida Bay. Clutch size and productivity of the herons during three breeding seasons were compared with similar data from 1923 which predated suspected human alteration of the Florida Bay ecosystem. In addition, since about 15% of the great white herons nesting in eastern Florida Bay supplemented their diet with food obtained from people, it was possible to evaluate the impact of food availability on reproduction. Herons that fed naturally in Florida Bay (unsupplemented) had significantly smaller clutches and produced significantly fewer fledglings than those of 1923. Herons that received supplemental food had reproductive parameters similar to those of 1923. We interpret these data as indicating that habitat quality is currently reduced from 1923 levels. These results support the prediction that wading bird reproduction can be sensitive to habitat quality and that these species should be useful as biological indicators for monitoring habitat quality.

LARVAL AND EARLY POSTLARVAL DEVELOPMENT OF LEPIDOPA BENEDICTI SCHMITT, 1935 (ANOMURA: ALBUNEIDAE) REARED IN THE LABORATORY

The complete larval development of an Atlantic Lepidopa from a known parental female is described for the first time. The ovigerous L. benedicti was collected at Horn Island, Mississippi (Gulf of Mexico). The larval development consisted of 4 zoeal stages, and one megalopal stage which was reached 14-17 days after hatching, at 25?C and 26%0 salinity. Zoeae of L. benedicti are very similar to those of other known Atlantic Lepidopa; there are differences among the corresponding zoeal stages in abdominal spination, and in zoeae II and III, differences in setation of the antennule and exopods of maxillipeds 1 and 2. The megalopa of L. benedicti is compared with other known megalopae of Lepidopa, 1 from the Atlantic and 2 from the Pacific. All megalopae are separable using setation of the antennular ventral flagellum, and the megalopa of L. benedicti can also be separated from the other Atlantic species by segmentation of the antennular dorsal flagellum. The development of selected adult key characters of L. benedicti (carapace frontal margin, eyeshape and pigmentation, posterior dorsal carapace groove, and pereiopod 2 dactylus shape) is illustrated and described through crab 4. In crab 4, all selected characters became diagnostic except for the pereiopod 2 dactylus which has not yet attained adult shape. Abele and Efford (1971) and Efford (1971) recognized 17 species of sand crabs, genus Lepidopa, from both coasts of the Americas and adjacent islands, including six species from the western Atlantic. Lepidopa benedicti Schmitt, 1935, and L. websteri Benedict, 1903, are the only western Atlantic species known from the nearshore waters of the southeastern United States (Efford, 1971). In the Gulf of Mexico, these species are sympatric at least from Grand Isle, Louisiana, to Petit Bois Island, Mississippi (Efford, 1971; Felder, 1973). In the Atlantic, L. benedicti is reported only as far north as central eastern Florida (Gore and Van Dover, 1980) and L. websteri only as far south as Sapelo Island, Georgia (Kurata, 1970; Williams, 1984). The four other western Atlantic species, L. dexterae Abele and Efford, 1971, L. distincta Gomes, 1968, L. richmondi Benedict, 1903, and L. venusta Stimpson, 1860, are known as adults only from the Caribbean coast of Panama, the eastern Antilles, and the eastern coast of South America (Abele and Efford, 1971; Efford, 1971; Gore and Van Dover, 1980). Information on the larval development of species of Lepidopa is scanty. Johnson and Lewis (1942) described zoea I, and Knight (1970) the entire zoeal series and megalopa from laboratory-hatched eggs of females attributed to L. myops Stimpson, 1860. Based on Efford's (1971) revision of Lepidopa, Johnson and Lewis (1942) and Knight (1970) actually described developmental stages of L. californica Efford, 1971 (Sandifer and Van Engle, 1972). Knight (1970) also described four zoeal stages of an unidentified species, and Sanchez and Aguilar (1975) described the entire zoeal development and the megalopa of L. chilensis Lenz, 1902, from laboratory-reared larvae. In the Atlantic, Kurata (1970) partially described zoea I of L. websteri hatched in the laboratory, and three other zoeal stages and the megalopa (from plankton samples) that he assumed were L. websteri. Sandifer and Van Engle (1972) described zoeae I-III of putative L. websteri from plankton samples taken in Virginia waters. At that time L. websteri was not known as an

Calcium Carbonate Production by Epibionts on Thalassia in Florida Bay

ABSTRACT Annual production of lime mud by two genera of red algae and one genus of serpulid worms was estimated for an area of modern lime mud accumulation in Eastern Florida Bay. The red algae Melobesia membranacea and Fosliella farinosa and the serpulid worm Spirobis sp. live as epibionts on the leaves of Thalassia testudinum, the extensive marine grass. The lime mud produced by the epibionts was estimated by quantifying 1) the life span of Thalassia; 2) the abundance of Thalassia; and 3) the average amount of epibiont calcium carbonate per blade. The estimate also accounts for both aerial variations in standing crop and seasonal variations in growth rate of Thalassia. The estimated annual production of epibiont carbonate is 118 ± 44 g/m2/yr, over six times more than the estimated production by the green alga Penicillus capitatus from the same area (Stockman et at. 1967). This leads to the conclusion that the epibionts on Thalassia produce significant amounts of lime mud in Florida Bay. This result is close to the published estimate for epibiont production in Jamaica of 180 g/m2/yr (Land 1970), but it is significantly less than a published estimate for epibiont production in Barbados (Patriquin 1972). Turtle grass has been around since the late Cretaceous (Eva 1980), and algae most likely has had a longer history. Therefore, epibionts may have been significant contributors since the late Cretaceous.

Variation in the Southeastern Pocket Gopher, Geomys pinetis, Along the St. Johns River in Florida

Colonies of pocket gophers (Geomys pinetis pinetis) in the St. Johns River basin of eastern peninsular Florida occur in uplands which generally correspond to islands emergent from the Pamlico Sea of the latest Sangamonian interglacial. The uplands presently occupied by G. pinetis are isolated by intervening unsuitable habitats and by the St. Johns River. Cranial morphometrics were used to evaluate the pattern of geographic variation among populations of modern G. pinetis in the St. Johns River basin and to examine the influence of the river as a dispersal barrier. Significant variation was found among samples on the E side, the W side, and on opposite sides of the St. Johns River. Results are interpreted in light of historical biogeography of the Quaternary Period; the distribution of pocket gophers in peninsular Florida has been significantly affected by changes in eustatic sea level.

Mechanisms of Deposition of a Carbonate Mud Spit: Ramshorn Spit, Eastern Florida Bay: ABSTRACT

The turtle grass (Thalassia testudinum) community has a significant influence on sedimentation in Florida Bay, but the roles other processes may play in the buildup of mud bank and spit sediments are poorly understood. Samples from cores taken from Ramshorn Spit and Ramshorn Shoal were classified into 4 basic types on the basis of particle size distribution, organic content, and faunal assemblages. In order of increasing volumetric importance they are: (1) very thin, discontinuous shelly packstones, representing overbank or storm deposits; (2) thin, continuous basal shelly packstones, the initial marine deposit on the Pleistocene bedrock surface; (3) muddy wackestones, of variable thickness, deposited in the presence of a seagrass community; (4) very thick, faintly lamina ed fine mudstones, with very sparse fauna, representing weak current-transported sediments settling out of suspension. Discriminant function analysis confirms the classifications and shows that these sediment layers are indeed correlatable between cores. Interpretation of the core logs from Ramshorn Spit indicates a definite change in stratigraphy southwestward from the spit and bank junction to the tip of the spit itself. The different sediment layers show a small but significant inclination to the southwest. Throughout its depositional history, Ramshorn Spit seems to have been actively accreting outward into the surrounding lake by means of a current-transported fine mud fraction. After settling out at the growing tip of the spit, the sediments are subsequently stabilized at some later time by a turtle-grass cover. End_of_Article - Last_Page 266------------

NEW ENDOLITHIC CYANOPHYTES FROM THE NORTH ATLANTIC OCEAN. III. HYELLA PYXIS LUKAS & HOFFMAN SP. NOV.1

ABSTRACTA new species of marine endolithic cyanophyte, Hyella pyxis Lukas and Hoffman (Order: Pleurocapsales), differs from other species of Hyella in its cell and filament dimensions, the manner in which its branches are initiated and the presence of gloeocapsin in the sheaths of colonies from the intertidal zone. Hyella pyxis colonies consist of a small cluster of coccoid cells located at the substrate surface and long, conspicuously branched filaments composed of cells that are longer than they are wide. Branches are initiated by the reorientation of the distal end of a filament cell or by the elongation of a filament cell, usually at one of its distal corners. Chromatic adaptation was not observed perhaps accounting for the relatively shallow depth limit of this species. Hyella pyxis was found within mollusk shells from the continental margin of eastern Florida to a depth of 50 m and carbonate rocks in the intertidal zone on Bermuda.

13C/12C ratios and the trophic importance of algae in Florida Syringodium filiforme seagrass meadows

Over 380 stable carbon isotope (δ13C) analyses made during 1981–82 showed that Syringodium filiforme Kutz seagrass meadows in the Indian River lagoon of eastern Florida have food webs based on algal rather than seagrass carbon. Seagrasses averaging approximately-8‰ were isotopically distinct from algae epiphytic on seagrass blades (X=-19.3‰) and particulate organic matter in the water column X=-21.6‰. δ13C values of most fauna ranged between-16 and-22‰, as would be expected if food web carbon were derived solely from algal sources. These results counter the idea that seagrass detritus is the dominant carbon source in seagrass ecosystems. Two factors that may contribute to the low apparent importance of seagrass in the study area are high algal productivities that equal or exceed S. filiforme productivity and the high rates of seagrass leaf export from meadows.

The Distribution and Abundance of Marine Turtles in the Gulf of Mexico and Nearby Atlantic Waters

Aerial surveys of marine waters up to 222 km from shore in the Gulf of Mexico and nearby Atlantic Ocean suggest that marine turtles are largely distributed in waters less than 100 m in depth. The loggerhead turtle (Caretta caretta) was observed nearly 50 times as often in waters off eastern and western Florida as in the western Gulf of Mexico. Loggerheads were present year- round but the frequency of sightings in the winter months was lower than at other seasons. Green turtles (Chelonia mydas) were infrequently observed but were most conspicuous in waters off eastern Florida. Kemp's ridleys (Lepidochelys kempi) were most frequently sighted off southwest- ern Florida and rarely observed in the western Gulf of Mexico. Leatherback turtles (Dermochelys coriacea) were more conspicuous on the continental shelf than in adjacent deeper waters. A con- centration of leatherback and loggerhead turtles occurred west of the Gulf Stream Current in August 1980, near Brevard County, Florida. Studies of marine turtles have fo-