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At least 73 records · Page 4Linked to original sources

USGS2018

Quantifying salinity and season effects on eastern oyster clearance and oxygen consumption rates

There are few data on Crassostrea virginica physiological rates across the range of salinities and temperatures to which they are regularly exposed, and this limits the applicability of growth and production models using these data. The objectives of this study were to quantify, in winter (17 °C) and summer (27 °C), the clearance and oxygen consumption rates of C. virginica from Louisiana across a range of salinities typical of the region (3, 6, 9, 15 and 25). Salinity and season (temperature and reproduction) affected C. virginica physiology differently; salinity impacted clearance rates with reduced feeding rates at low salinities, while season had a strong effect on respiration rates. Highest clearance rates were found at salinities of 9–25, with reductions ranging from 50 to 80 and 90 to 95% at salinities of 6 and 3, respectively. Oxygen consumption rates in summer were four times higher than in winter. Oxygen consumption rates were within a narrow range and similar among salinities in winter, but varied greatly among individuals and salinities in summer. This likely reflected varying stages of gonad development. Valve movements measured at the five salinities indicated oysters were open 50–60% of the time in the 6–25 salinity range and ~ 30% at a salinity of 3. Reduced opening periods, concomitant with narrower valve gap amplitudes, are in accord with the limited feeding at the lowest salinity (3). These data indicate the need for increased focus on experimental determination of optimal ranges and thresholds to better quantify oyster population responses to environmental changes.

Marine Biology↗

USGS2018

Measuring carbon and nitrogen bioassimilation, burial, and denitrification contributions of oyster reefs in Gulf coast estuaries

The eastern oyster ( Crassostrea virginica ) and the reefs they create provide significant ecosystem services. This study measured their possible role in nutrient mitigation through bioassimilation, burial, and oyster-mediated sediment denitrification in near-shore shallow water (< 1 m water depth) and deep-water (> 1 m water depth) oyster reefs in Louisiana. Nitrogen (N) and carbon (C) in shell and tissue differed by oyster reproductive status, size, and habitat type. Changes in tissue percent N and C post-spawning combined with significant reductions in tissue dry weight from the release of gametes, resulted in 20 and 46% reductions in tissue N and C load (mg), respectively, for a 100-mm oyster. Oyster reefs did not enhance burial rates, with burial range rates estimated at 1.4–2.6 g N m −2 year −1 , and 26.9–43.8 g C m −2 year −1 . Closed-system ex situ incubations indicated net denitrification in all habitat types studied, with the highest rates exceeding 600 µmol N m −2 h −1 during the summer, but no enhancement attributable to oyster reefs specifically. Within the highly productive, organic-rich wetland complex systems of coastal Louisiana, oyster reefs were not associated with enhanced denitrification, likely due to the organic-rich setting, and redundant supplies of organic nitrogen and carbon from adjacent marshes. Context remains critical in determining ecosystem provision of habitats, and efforts to extrapolate and predict nitrogen removal across locations necessitates consideration of local conditions. Considering the large extent of reefs and oyster production across coastal Louisiana, oyster habitats may still contribute to N and C mitigation, but their unique contribution likely comes from bioassimilation, and removal of the oysters from the system.

Louisiana↗

USGS2019

Migration routes, foraging behavior, and site fidelity of loggerhead sea turtles (Caretta caretta) satellite tracked from a globally important rookery

The Archie Carr National Wildlife Refuge, Florida, USA (27.946°N, − 80.494°W) represents one of the largest loggerhead turtle ( Caretta caretta ) nesting sites in the Western Hemisphere. Surprisingly, little work has been conducted to determine females’ post-nesting migratory behavior and characteristics of their foraging areas. Between 2008 and 2017, satellite telemetry was used to trace the locations and movements of 45 post-nesting loggerhead turtles. A switching state-space model was employed to estimate the behavioral state of each location. Internesting, migrating and foraging activity periods were determined for 38 loggerheads based on the SSSM. Seven environmental variables were extracted from remote sensing imagery for each location to compare values among behaviors. Core primary foraging areas ranged in size from 5.89 to 4572.80 km 2 . Four foraging types (primary, secondary, seasonal, and loops) were observed. Most turtles resided at a primary foraging area year round. A few individuals conducted foraging loops away from a primary foraging area. Both seasonal and loop movements were associated with changes in sea surface temperature as turtles moved to avoid temperatures that could cause cold-stunning or mortality. Turtle size and nesting beach offshore currents may play a role in foraging area selection, and date of departure from the nesting beach may be linked to foraging destination. By making the connection among oceanic features, foraging areas, and the influence of environmental variables on these areas, it is possible to identify and characterize critically important feeding areas and migration corridors for loggerheads nesting on the east coast of Florida.

Marine Biology↗

USGS2021

Lipidomics reveals specific lipid molecules associated with cold stress syndrome in the Florida manatee (Trichechus manatus latirostris)

Cold stress syndrome (CSS) in the Florida manatee ( Trichechus manatus latirostris) results in perturbations to many physiological pathways, often leading to further illness or death. In this study, we applied a non-targeted lipidomics approach with ultra-high performance liquid chromatography and high-resolution tandem mass spectrometry to characterize changes related to CSS in the lipidomic profiles of manatee plasma. Lipidomic analyses were conducted on healthy manatee (control) and cold-exposed manatee plasma samples with varying concentrations of Serum Amyloid A (SAA), an acute-phase protein that is associated with inflammatory disease. Control manatees ( n = 10) were compared to all manatees exposed to cold temperatures ( n = 17), and a subset of those manatees with SAA values > 120 μg/mL ( n = 9). Increased SAA values were associated with higher levels of various acylcarnitine lipids, while several triacylglycerols and oxidized triacylglycerols were significantly lower in manatees with cold exposure. These identified lipids are critical molecules involved in the maintenance of energy homeostasis and could potentially be examined in conjunction with current physical parameters to characterize cold stress. The ability to detect such differences highlights the addition of lipidomics as a valuable tool in understanding cold stress and potentially other illnesses in manatees. Further investigation into the function of the altered lipids could greatly increase our understanding of lipid metabolism in physiologically stressed manatees as well as other marine mammals and inform future management recovery strategies.

Marine Biology↗

USGS2021

Role of ingesta particle size in the green turtle grazing strategy, ontogenetic diet shifts, and responses to seagrass declines

Populations of the green turtle ( Chelonia mydas ), a mega-herbivore that consumes seagrasses, are recovering worldwide. Understanding green turtle adaptations to herbivory and responses to changes in seagrass availability will be critical to interpreting plant–herbivore interactions as green turtle populations continue to rebound. Ingesta particle size and diet composition of two green turtle foraging aggregations (Bermuda, 32.3° N, 64.8° W; U.S. Virgin Islands [USVI], 17.8° N, 64.6° W) in the Northwest Atlantic (NWA) were evaluated to assess the prevalence of herbivory across foraging sites and life stages, determine if there is an optimum ingesta particle size, and evaluate green turtle responses to changes in seagrass availability. Both aggregations were herbivorous (> 90% seagrass/algae) across size classes (straight carapace length, SCL). Ingesta particle size (mean ± SD) did not differ between Bermuda (2.6 ± 1.4 cm) and the USVI (2.3 ± 1.2 cm). Of seagrass leaves ingested, 20–30% were 1.7 cm in length, indicating a potential optimum for maximizing digestion rates. Turtle size (SCL) had a significant effect on particle size in Bermuda ( p = 0.01, R 2 = 0.16) (35.1 ± 9.9 cm SCL) but not in the USVI aggregation, which was comprised of larger turtles (49.0 ± 6.1 cm SCL). In Bermuda, there was no apparent response to the declines in seagrass availability. Ingesta particle size and volume of seagrass leaves did not decline from 2015 to 2019, nor was there an increase in volume of seagrass roots and rhizomes. These results indicate herbivory is prevalent across size classes at two NWA foraging sites and ingesta particle size has important implications for optimizing the green turtle grazing strategy and facilitating ontogenetic diet shifts to herbivory in juveniles. Ingesta particle size is a valuable tool for assessing green turtle responses to seagrass declines that should be interpreted within the context of population demographics.

Marine Biology↗

USGS2023

Isotopic niche partitioning in a multi-species assemblage

Multi-species assemblages can help identify key resources in their habitat by evaluating how they are partitioning their resources. Here we used the isotopic niche of loggerhead, Kemp’s ridley, and green sea turtles to assess their ecological niche within a Gulf of Mexico bay. Additionally, we assessed temporal and size-class variation in their diets by comparing the δ 13 C and δ 15 N values over various capture years and size classes. Based on the isotopic niche overlap results, interspecific competition occurs among loggerhead, Kemp’s ridley, and smaller green turtles. Green turtle and Kemp’s ridley diet varied by size class, while Kemp’s ridley diet also varied temporally. The three species partition resources by selecting different preferred diet items, although some overlap in diet, including between the herbivorous (green) and carnivorous (Kemp’s ridley, loggerhead) species, appears to occur. The high quality of this habitat may allow species co-existence and population recovery despite the possible use of shared resources.

Florida↗

USGS2024

Carotenoid skin ornaments as flexible indicators of male foraging behavior in a marine predator: Variation among Mexican colonies of brown booby (Sula leucogaster)

Carotenoid-dependent ornaments can reflect animals’ diet and foraging behaviors. However, this association should be spatially flexible and variable among populations to account for geographic variation in optimal foraging behaviors. We tested this hypothesis using populations of a marine predator (the brown booby, Sula leucogaster ) that forage across a gradient in ocean depth in and near the Gulf of California. Specifically, we quantified green chroma for two skin traits (foot and gular color) and their relationship to foraging location and diet of males, as measured via global positioning system tracking and stable carbon isotope analysis of blood plasma. Our three focal colonies varied in which foraging attributes were linked to carotenoid-rich ornaments. For gular skin, our data showed a shift from a benthic prey-green skin association in the shallow waters in the north to a pelagic prey-green skin association in the deepest waters to the south. Mean foraging trip duration and distance of foraging site from coast also predicted skin coloration in some colonies. Finally, brown booby colonies varied in which trait (foot versus gular skin color) was associated with foraging metrics. Overall, our results indicate that male ornaments reflect quality of diet and foraging–information that may help females select mates who are adapted to local foraging conditions and therefore, are likely to provide better parental care. More broadly, our results stress that diet-dependent ornaments are closely linked to animals’ environments and that we cannot assume ornaments or ornament signal content are ubiquitous within species, even when ornaments appear similar among populations.

Marine Biology↗

USGS2024

In-situ valve opening response of eastern oysters to estuarine conditions

High-frequency recordings of valve opening behavior (VOB) in bivalves are often used to detect changes in environmental conditions. However, generally a single variable such as temperature or the presence of toxicants in the water is the focus. A description of routine VOB under non-stressful conditions is also important for interpreting responses to environmental changes. Here we present the first detailed quantitative investigation of the in-situ VOB of eastern oysters ( Crassostrea virginica ) to environmental variables typically not considered stressful. The VOB of eight individuals was monitored for seven weeks in a Louisiana estuary. We examined the relationships between VOB metrics (variance in mean % max opening among oysters, the probability of an oyster being closed, and the rate of valve closure), and temperature, salinity, chlorophyll-a (chl-a) concentration, the rate of change in those environmental variables, and the rate of change in water depth. Relationships were analyzed through statistical models including rates of change over 0, 0.25, 1-, 6-, 12-, and 24-hours. All the responses were best explained by the 12-hour time step model. The interaction effect between salinity and the rate of change of salinity had the greatest impact on variance in oysters’ behavior. Oysters closed faster at higher salinities and were more likely to be closed at lower chl-a concentrations. Significant interactions were found between many environmental variables, indicating a high level of complexity of oyster behavior in the natural environment. This study contributes to a better understanding of the impact of environmental conditions on oyster behavior and can help inform predictive tools for restoration initiatives and fisheries practices.

Louisiana↗

USGS2024

Wide-ranging migration of post-nesting hawksbill sea turtles (Eretmochelys imbricata) from the Caribbean island of Nevis

Little is known about the post-nesting migration and foraging areas of hawksbill turtles ( Eretmochelys imbricata ) nesting on St. Kitts and Nevis, an important nesting site for hawksbills in the eastern Caribbean. To elucidate internesting, migration and foraging patterns of hawksbills from Nevis, we satellite tagged 28 post-nesting turtles between 2006 and 2022. Internesting, migrating and foraging activity periods were determined using a switching state–space model to estimate the behavioral state of the turtle’s locations. Twenty-five turtles (83–2,171 tracking days) established a foraging area, migrating between 5.3 and 2,799.5 km from the nesting beach. Twenty-one turtles were tracked during internesting movements with internesting areas ranging between 1.9 and 28.2 km 2 . Nearly half of the internesting centroids were located closer to a different beach than the beach where the turtle was originally encountered nesting. Hawksbills crossed through 29 different Exclusive Economic Zones (EEZs), including zones with legal sea turtle fisheries or traditional subsistence use. Core foraging areas (KDE 50%) ranged between 3.8 and 69.0 km 2 . Nearly a third of foraging centroids were within a Marine Protected Area (MPA), while nearly a quarter were within a legal sea turtle fishery EEZ. Hawksbills nesting on Nevis disperse to local, regional, and Caribbean wide foraging grounds, emphasizing the necessity of cooperative efforts to protect turtles and their habitats to ensure support of the recovery of hawksbill turtles throughout the wider Caribbean.

Caribbean, Nevis↗

USGS2025

Spawning and larval development of the mesophotic octocoral Swiftia exserta in aquaria

The 2010 Deepwater Horizon oil spill injured mesophotic and deep-sea environments over a vast area. In order to restore mesophotic and deep-sea coral species impacted by the spill, information on fundamental ecosystem processes such as reproduction is needed. During expeditions in 2021 and 2022, fragments of the mesophotic octocoral Swiftia exserta were collected from the northern Gulf of Mexico and transported to aquaria at federal facilities in South Carolina, Florida, and Texas. In fall of 2021 and 2022, several of these fragments spawned in captivity, providing an opportunity to learn about their reproduction and inform future restoration activities. Broadcast spawning occurred on 19 and 20 October, 2021, and on 20 days from 29 September to 7 November, 2022. These spawning events permitted detailed observations of spawning behavior and timing, and yielded over 2,400 oocytes. Individual spawns were preceded by a distinctive “spawning posture” in the polyps, lasting between five minutes and two hours, and may have been cued by light. Swiftia exserta larvae settled and developed at comparable rates to other broadcast spawning octocorals, becoming swimming planulae by three days post spawn (dps) and starting to settle by 14 dps. These observations represent the first such records for S. exserta and, more broadly, for any mesophotic coral in the Gulf of Mexico, providing important insights for the restoration of these species. This investigation lays the foundation for future work to explore the influences of seasonal environmental variables, such as light and temperature, on spawning and reproductive seasonality in this species.

Marine Biology↗

USGS2025

Regional differentiation in somatic growth and maturation attributes for loggerhead sea turtles (Caretta caretta) in the Northwest Atlantic

The ages and sizes at which organisms mature have significant implications for lifetime reproductive success. For species at risk of extinction, such as sea turtles, these attributes can ultimately impact probability of population persistence. Within the Northwest Atlantic Ocean, the broader loggerhead sea turtle ( Caretta caretta ) population comprises management units both along the US Gulf of America (formerly Gulf of Mexico) and Atlantic coasts. Although age, growth, and maturation have been more intensively studied along the US Atlantic, data specific to the Gulf of America have remained sparse. To address this data gap, we conducted skeletal growth mark analysis (skeletochronology) for 123 humerus bones collected from loggerheads found dead in the US Gulf of America from 1998 to 2021. We compared resulting age, growth, and maturation data with information from studies of US Atlantic coast loggerheads for similar size and year ranges, using the exact same skeletochronology methods, as well as with Gulf of America mark-recapture growth data. Results indicate that Gulf of America loggerheads exhibit significantly faster juvenile somatic growth. In addition, sizes at maturation were substantially smaller, corresponding with mean estimates of age at maturation 7.5 to 15 years earlier than US Atlantic counterparts. Finally, the maximum observed Gulf of America adult age estimate was 42.5 years, considerably less than the highest US Atlantic estimate of 77.0 years. These detailed data offer insights into regional variability in somatic growth dynamics and characteristics associated with maturation, which in turn can impact relative reproductive contributions and, ultimately, population trajectories.

Marine Biology↗

USGS2025

Satellite tracking reveals heavy use of local MPAs by green turtles (Chelonia mydas) nesting in southeast Florida, USA

Florida hosts a regionally important nesting aggregation of green turtles ( Chelonia mydas ) in the North Atlantic, yet internesting and post-nesting movements for this rookery remain poorly understood. Here, we used satellite telemetry to track 23 green turtles nesting on southeast Florida beaches from 2017 to 2021 to investigate their spatial ecology and use of marine protected areas (MPAs) during internesting, migration, and foraging. Marine protected areas are widely used in marine conservation and can be powerful tools for managing species and protecting biodiversity. During internesting, turtles used nearshore, unprotected coastal waters adjacent to the study site. After the nesting season, turtles migrated 24.1 to 203.5 km to previously identified foraging grounds, including areas within Biscayne National Park and Florida Keys National Marine Sanctuary, as well as a high-use but unprotected area off Cape Sable, Florida. Throughout the internesting and foraging periods, turtles exhibited little spatial overlap of core-use areas, suggesting limited space-use sharing even in high-density regions. This study provides the first satellite telemetry dataset for green turtles from southeast Florida and reveals their strong reliance on a relatively small MPA network along southwest Florida. Our findings underscore how these MPAs can support conservation efforts for Florida’s overall green turtle nesting population, while further emphasizing the potential benefits of expanded protections in key areas to safeguard regionally important green turtle habitat.

Florida↗

USGS2025

Energetic value of Arctic forage-sized fish with implications for a nearshore seabird predator

Arctic cod ( Boreogadus saida , also called polar cod) are considered the single most important Arctic forage fish due to their high abundance and nutritional quality. Because Arctic cod are strongly ice associated and prefer colder waters, their frequency in coastal waters has declined with warming, decreasing availability to nearshore predators. To consider the nutritional quality of alternative prey, we measured energy density and estimated whole-body energy of forage-size (39–200 mm) fishes collected during summers 2021–2023 ( n = 274). The fishes sampled included 16 potential prey species from Foggy Island Bay (70.3°N, 147.5°W, near Prudhoe Bay) and Lion Bay (70.2°N, 146.4°W, near Flaxman Island), northern Alaska. Dry weight energy densities ranged from 16.2 to 27.5 kJ g -1 (mean ± SD = 22.0 ± 1.73 kJ g -1 , n = 274) across individuals. Of common species, Arctic cod had the highest mean energy density (24.3 ± 1.1 kJ g -1 , n = 25) and fourhorn sculpin ( Myoxocephalus quadricornis ) had the lowest (19.7 ± 0.8 kJ g -1 , n = 20). To account for size differences among prey species, whole-body energy of typical fish sizes available to predators were modeled using whole-body energy to length relationships and length distributions. Juvenile salmonids (e.g., ciscoes and whitefishes) provided the most energy per individual and were four-fold greater than smaller-bodied Arctic cod. Predators that consume juvenile ciscoes and whitefishes may be more resilient to declines in Arctic cod availability than predators with smaller gapes.

Alaska↗

USGS2026

Accounting for emigration reveals high survival and bimodal size at departure from a loggerhead sea turtle (Caretta caretta) foraging area

The life history of hard-shelled sea turtles includes several ontogenetic shifts in habitat use and these complex permanent emigration patterns can impact estimates of stage-specific population rates, including survival. We developed several multistate mark recapture models to estimate survival of adult and juvenile loggerhead turtles from a coastal bay in the northern Gulf of America (also commonly referred to as the Gulf of Mexico) while, in some cases, accounting for permanent emigration and transient individuals. Our mark-recapture dataset consisted of 228 individual turtles with 37 total recaptures from 2011 to 2024. Of the models we fit, those that incorporated emigration produced higher estimates for annual survival than models that did not, and higher estimates than what is commonly seen in the literature for loggerheads. All models suggested a major permanent emigration pulse at the typical size of sexual maturity (70 cm straight carapace length) and another major pulse at > 90 cm. This bimodal pattern of departure may reflect differences in size at sexual maturity among loggerheads, possible genetic variability within the assemblage, or both. To assess the models’ ability to effectively recover true parameter values, we developed a simulation study of 50 randomly generated independent data sets under our specified models of similar sample size to our study dataset. Simulation results suggested that models that accounted for permanent emigration and transient individuals produced relatively unbiased estimates of survival, while models that did not often underestimated survival rates. Mark-recapture studies that may exhibit emigration and suffer from low recapture rates would benefit from auxiliary data collection such as acoustic telemetry detections to better estimate true rates of emigration and survival. Obtaining unbiased estimates of true survival by accounting for processes like emigration can support effective conservation of endangered long-lived species like loggerheads.

Florida↗

USGS2026

Variable pH habitats could help prepare stone crabs for coastal acidification

Coastal acidification is being exacerbated by terrestrial organic inputs, especially after high precipitation events. Florida’s rainy season coincides with stone crab ( Menippe mercenaria) reproduction, and pH extremes could limit future harvests by reducing reproductive output. Populations that experience pH variability can serve as “natural laboratories” for estimating the tolerance of a species to coastal acidification. Here, we conducted a series of experiments to determine if ovigerous stone crabs conditioned in more variable pH habitats (seagrass) would result in faster embryonic development, greater hatching success, and higher larval survival relative to crabs conditioned in habitats with lower pH variability (sandy habitats). After field conditioning, crabs were transported to the laboratory and randomly acclimated to either a control pH (pH = ~ 7.90) or a reduced pH condition (pH = ~ 7.60) until larval release. The rate of embryo development was slower in the laboratory reduced pH treatment, however, there were no observable field condition effects on embryo development rate. Crabs conditioned in the more pH variable seagrass habitat did have greater hatching success and higher larval survival than crabs in less pH variable sandy habitats; however, larval survival was low across all treatments. These results suggest that the pH variability experienced in seagrass habitats during brooding may serve as a mechanism for stone crabs to acclimatize to extremes in seawater pH.

Marine Biology↗

USGS2001

Association of Syscenus infelix (Crustacea: Isopoda: Aegidae) with benthopelagic rattail fishes, Nezumia spp. (Macrouridae), along the western North Atlantic continental slope

During submersible surveys along the continental slope (summers of 1991 and 1992, 184-847 m) between False Cape, Virginia, and Cape Hatteras, North Carolina, USA, we observed the aegid isopod, Syscenus infelix Harger, attached to the macrourid Nezumia bairdii (Goode and Bean). This is the first report of S. infelix attached to fishes in the western North Atlantic. The association of this blind isopod with its host appears species specific. The large, conspicuous isopod always attached to a fish in the same location, the dorsal midline, immediately behind the first dorsal fin. Attachment appears to be long term, with the isopod forming a characteristic scar consisting of a distinct discolored oval depression with seven small, dark impressions that coalesce as the fish grows. Only one S. infelix was found on each host fish. The isopod occurred on 23.7% of N. bairdii observed from submersible on the middle continental slope off Virginia and North Carolina, compared with 16.6% of 1236 museum specimens of the same species (based on inspection for scars) collected at latitudes 26??-64??N. Prevalence of the fish-isopod association was not correlated with depth or latitude. We also found identical scars on preserved specimens of N. aequalis (2.6% of 660 specimens), N. sclerorhynchus (1.2% of 86 specimens), and N. suilla (14.3% of 7 specimens), mostly from areas outside the range of N. bairdii. No scars were found on museum specimens of N. atlantica (n = 27), N. cyrano (n = 57), or N. longebarbata (n = 7). The low incidence of isopod attachment on these species suggests that N. bairdii is the preferred host. Infestation by the isopod appears to result in erosion of host fish scales and tissue. We propose that S. infelix is an obligate associate of its host fish and should be considered parasitic.

Marine Biology↗

USGS1997

Assimilation efficiencies and turnover rates of trace elements in marine bivalves: A comparison of oysters, clams and mussels

Assimilation efficiencies (AEs) and physiological turnover-rate constants ( k ) of six trace elements (Ag, Am, Cd, Co, Se, Zn) in four marine bivalves ( Crassostrea virginica Gmelin, Macoma balthica Linnaeus, Mercenaria mercenaria Linnaeus, and Mytilus edulis Linnaeus) were measured in radiotracer-depuration experiments. Egestion rates of unassimilated elements were highest during the first 24 h of depuration and declined thereafter. Significant egestion of unassimilated Co, however, continued for up to 5 d in Macoma balthica , Mercenaria mercenaria and Mytilus edulis . With the exception of the extremely low values for 110 m Ag, 109 Cd, and 65 Zn in C. virginica , physiological turnover-rate constants ( k ) showed no general pattern of variation among elements, bivalve species or food types, and were relatively invariant. Values from  ≤0.001 to 0.1 d −1 were observed, but excluding those for Co, most values were  ≤0.04 d −1 . In all four species, the AEs of Ag, Am, and Co were generally lower than those of Cd, Se, and Zn. The AEs of Ag, Cd, Se, and Zn in these bivalves are directly related to the proportion of each element in the cytoplasmic fraction of ingested phytoplankton, indicating that >80% of elements in a prey alga's cytoplasm was assimilated. C. virginica , Macoma balthica , and Mercenaria mercenaria assimilated &sim;36% of the Ag and Cd associated with the non-cytoplasmic (membrane/organelle) fraction of ingested cells in addition to the cytoplasmic fraction. The ratio of AE: k , which is proportional to the consumer–prey trace-element bioaccumulation factor (concentration in consumer:concentration in prey) was generally greater for Cd, Se, and Zn than for Ag, Am, and Co. This ratio was lowest in Mytilus edulis , suggesting that this bivalve, the most widely employed organism in global biomonitoring, is relatively inefficient at accumulating important elements such as Ag, Cd, and Zn from ingested phytoplankton.

Marine Biology↗

USGS1998

Sulfur contents and sulfur-isotope compositions of thiotrophic symbioses in bivalve molluscs and vestimentiferan worms

Total sulfur (S(TOT)), elemental sulfur (S??) and sulfur-isotope compositions (??34S) of marine animals were analyzed to determine whether these chemical characteristics could help distinguish animals with a sulfur-based, thiotrophic nutrition from animals whose nutrition is based on methanotrophy or on more normal consumption of phytoplankton-derived organic matter. The presence of S??was almost entirely confined to the symbiont-containing tissues of thiotrophs, but was sometimes undetectable in thiotrophic species where sulfide availability was probably low. When S??contents were subtracted, the remaining tissue-sulfur concentrations were similar for all nutritional groups. ??34S values were typically lower for thiotrophs than for other groups, although there was overlap in methanotroph and thiotroph values at some sites. Field evidence supported the existence of small to moderate (1 to 10???)34S fractionations in the uptake of sulfides and metabolism of thiosulfate. In general, a total sulfur content of >3% dry weight, the presence of elemental sulfur, and ??34S values less than + 5??? can be used to infer a thiotrophic mode of nutrition.

Marine Biology↗