Three Decades of Horseshoe Crab Rearing: A Review of Conditions for Captive Growth and Survival

Threats to wild horseshoe crab populations and growing interest in their use for research, education and biomedical applications have prompted demand for improved techniques to rear and maintain crabs in captivity. Although numerous laboratory studies have been conducted to determine growth and survival of horseshoe crabs under various conditions, these data have not been compiled and summarized to inform culture practices. We surveyed the literature and analysed the range of available techniques to identify and define a consistent set of conditions for maximum growth and survival of horseshoe crabs in culture. We considered three age classes; embryo, juvenile and adult, and included all extant species (Limulus polyphemus, Carcinoscorpius rotundicauda, Tachypleus gigas and Tachypleus tridentatus). We discovered relatively few published studies that clearly related husbandry conditions to growth and survival. Comparison among studies was complicated by inconsistent data collection and reporting techniques. Most published sources reported data for younger age classes, and more studies considered L. polyphemus than Asian species. The most commonly reported variables (temperature, salinity, enclosure maintenance and diet composition) showed size dependent and in some cases species-specific effects on growth and survival that will be important in guiding culture efforts. We suggest that future studies give additional consideration to substrate type, water flow, dissolved oxygen concentrations, diet quality and the quantity and frequency of feeding. If laboratory-reared stocks are to be used for propagation and restoration activities, future studies will benefit from closing these data gaps and promoting international data sharing

Bivalve-Enhanced Nitrogen Removal From Coastal Estuaries

Interest in use of bivalves to remediate estuarine eutrophication has increased in recent years. High variation among data sets, substantial focus on particle removal, and insufficient links to anthropogenic nitrogen (N) sources encouraged this empirical examination of N removal by bivalves from estuaries receiving different N loads. We determined the capacity of the oyster Crassostrea virginica to remove N by comparing N assimilated into tissues with anthropogenic N from land or available in phytoplankton. Oyster growth yielded 0.2–0.4 g N in tissues and depended on estuary-specific conditions. d15N values confirmed that N in oyster tissues derived from local anthropogenic sources. At representative restoration and aquaculture conditions (≤400 oysters m–2 at 0.5%–1.0% of estuary area), estimated N removal was ≤15% of land derived loads and \u3c1% of phytoplankton N. N removal via biogeochemical processes was negligible during grow-out, but became important after oysters attained harvestable size. This study explicitly demonstrates that oysters assimilated land derived N, but suggests that bivalve bioremediation consider trade-offs between intensity of planting, ecological effects, and available space

Use of settlement patterns and geochemical tagging to test population connectivity of eastern oysters Crassostrea virginica

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gancel, H. N., Carmichael, R. H., Du, J., & Park, K. Use of settlement patterns and geochemical tagging to test population connectivity of eastern oysters Crassostrea virginica. Marine Ecology Progress Series, 673, (2021): 85–105, https://doi.org/10.3354/meps13796.Freshwater-dominated estuaries experience large fluctuations in their physical and chemical environments which may influence larval dispersal, settlement, and connectivity of populations with pelagic larval stages. We used settlement patterns and natural tagging along with numerical hydrodynamic model results to assess settlement and connectivity among oysters across the freshwater-dominated Mobile Bay-eastern Mississippi Sound (MB-EMS) system. Specifically, we (1) tested how freshwater inputs and associated environmental attributes influenced settlement patterns during high and low discharge conditions in 2014 and 2016, respectively, and (2) analyzed trace element (TE) ratios incorporated into multiple shell types (larval and settled shell of spat and adult shells) to determine if shells collected in situ incorporate temporally stable site-specific signatures. We also assessed if TE ratios compared between adult (TE natal signature proxy) and larval shells could infer connectivity. Larval settlement was 4× higher during low discharge than during high discharge when oyster larvae only settled in higher salinity regions (EMS). Spat and adult shells incorporated site-specific TE ratios that varied from weeks to months. Connectivity results (May-June 2016 only) suggest that EMS is an important larval source to EMS and lower MB. While we were able to infer probable connectivity patterns using adult and larval shells, more study is needed to assess the utility of adult shells as proxies for natal-location TE signatures. Results provide a baseline for measuring future larval connectivity and adult distribution changes in the MB-EMS system. Biological and geochemical data demonstrate the potential to identify environmental attributes that spatiotemporally mediate settlement and connectivity in dynamic systems.This work was funded by the Mississippi−Alabama Sea Grant Consortium (project number #R/ SFA-03) and the Food and Drug Administration and MESC/ Dauphin Island Sea Lab Collaboration (award numbers: 5U19FD005923-04 and 5U19FD004277-04)

A New Sighting Network Adds to 20 Years of Historical Data on Fringe West Indian Manatee (Trichechus manatus) Populations in Alabama Waters

Recent findings suggest increased use of fringe habitats by the endangered West Indian manatee. To begin collecting fundamental data on population dynamics and ecology of fringe manatees in the northern Gulf of Mexico, we established the Mobile Manatees Sighting Network (MMSN), the first formal network to receive and track manatee sightings in Alabama waters. Comparison of MMSN data with compiled historical data indicated that West Indian manatees are regular seasonal visitors to Alabama waters. Historical (1985–2006) and newly collected data shared consistent distributions, seasonal patterns of abundance in sighting number, and group size frequencies. These data indicate that MMSN was as effective at capturing data as two decades of historical sighting reports and suggest consistent long-term patterns in habitat preference and seasonal movements of manatees in Alabama waters. A nearly fourfold increase in number of manatee sightings, with inception of the MMSN, made evident the success of community outreach efforts but also betrayed the potential influence of observers on data quality. The MMSN maintains a 24-hr toll-free phone line, website with interactive online sighting form, and E-mail address to receive citizen sighting reports and provide supporting educational materials. Our data demonstrate that this type of monitoring for manatees in fringe habitat is feasible, effective, and essential to guide local management and recovery efforts of this endangered species

Were Multiple Stressors a \u27Perfect Storm\u27 for Northern Gulf of Mexico Bottlenose Dolphins (Tursiops truncatus) in 2011?

An unusual number of near term and neonatal bottlenose dolphin (Tursiops truncatus) mortalities occurred in the northern Gulf of Mexico (nGOM) in 2011, during the first calving season after two well documented environmental perturbations; sustained cold weather in 2010 and the Deepwater Horizon oil spill (DWHOS). Preceding the stranding event, large volumes of cold freshwater entered the nGOM due to unusually large snowmelt on the adjacent watershed, providing a third potential stressor. We consider the possibility that this extreme cold and freshwater event contributed to the pattern of perinatal dolphin strandings along the nGOM coast. During the 4-month period starting January 2011, 186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003-2010) washed ashore from Louisiana to western Florida. Comparison of the frequency distribution of strandings to flow rates and water temperature at a monitoring buoy outside Mobile Bay, Alabama (the 4th largest freshwater drainage in the U. S.) and along the nGOM coast showed that dolphin strandings peaked in Julian weeks 5, 8, and 12 (February and March), following water temperature minima by 2-3 weeks. If dolphin condition was already poor due to depleted food resources, bacterial infection, or other factors, it is plausible that the spring freshet contributed to the timing and location of the unique stranding event in early 2011. These data provide strong observational evidence to assess links between the timing of the DWHOS, other local environmental stressors, and mortality of a top local predator. Targeted analyses of tissues from stranded dolphins will be essential to define a cause of death, and our findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns during and after an unusual mortality event

Effects of Lipid Extraction on δ13C and δ15N Values and Use of Lipid-Correction Models Across Tissues, Taxa and Trophic Groups

1. Lipid-rich animal tissues have low δ13C values, which can lead to inaccurate ecological inferences. Chemical lipid extraction (LE) or correction models account for this depletion, but the need for LE or correction is tissue- and species-specific. Also, LE can alter δ15N values, increasing labour and costs because bulk samples must be analysed for δ15N values separately. 2. We studied the effects of LE on δ13C and δ15N values in liver, muscle and skin of common bottlenose dolphins Tursiops truncatus and West Indian manatees Trichechus manatus, two ecologically important species that occupy different trophic levels. We fit lipid-correction models to each species. We also performed a meta-analysis to more broadly determine the effects of LE across taxa, tissues and trophic groups (carnivores, omnivores and herbivores) and to fit lipid-correction models to different taxonomic and trophic groups. 3. Lipid extraction increased the δ13C values in dolphin tissues but had little effect on manatee tissues and no effect on the δ15N values in either species. A mass balance lipid-correction model best fit the data from all dolphin tissues, and a linear model best fit data for manatee liver while null models best fit data from manatee muscle and skin. Across 128 terrestrial and aquatic species, the effects of LE varied among tissues and were lower for herbivores compared to carnivores. The best-fitting lipid-correction models varied among tissue, taxa and trophic groups. Finally, the δ15N values from muscle and liver were affected by LE. 4. Our results strengthen the growing body of evidence that the need for LE is tissue- and species-specific, without a reliable C:N ratio predictive threshold. The prediction errors of lipid-correction models generally decreased with taxonomic and trophic specificity. The smaller effects of LE in herbivores may be due to differences in diet composition or the physiology of lipid synthesis in members of this trophic group. These results suggest that researchers should use the most species-, tissue- and trophic group-specific information on LE available and, if not available, perform LE on a subset of samples prior to analysis to determine effects

Addition of Passive Acoustic Telemetry Mitigates Lost Data From Satellite-Tracked Manatees

Satellite-tracked manatees routinely lose satellite tags or tag functionality, resulting in the loss of valuable data on migration and habitat use patterns. Fortunately, some movement data from these animals remain salvageable because manatees typically retain a peduncle belt containing an acoustic transmitter that can be detected with a submersible hydrophone. We deployed an array of moored datalogging hydrophones at key locations in our study area to detect manatee belt-embedded acoustic transmitters, a technique not typically used to track manatees. Our array was successful in detecting five tagged manatees, and concurrently detected compatible acoustic tags of other estuarine fauna (e.g. Bull Sharks) tagged by local researchers. Moored datalogging hydrophones, therefore, provided a method to mitigate the loss of satellite tags from estuarine megafauna, and enhanced collaborative opportunities with researchers who tagged other species using compatible equipment

Seasonal and Spatial Effects of Wastewater Effluent on Growth, Survival, and Accumulation of Microbial Contaminants by Oysters in Mobile Bay, Alabama

We measured seasonal effects of wastewater treatment plant (WTP) effluent on growth, survival, and accumulation of microbes in oysters near a major WTP in Mobile Bay, AL. Despite higher nutrients near the WTP, seasonal conditions rather than distance affected chlorophyll a concentration and oyster growth. In summer and fall, when oyster growth was higher, δ15N‰ in oysters near the WTP changed through time to reflect δ15N‰ in effluent (approx. −4‰). Microbial indicators (male-specific coliphage, fecal coliforms) were highest in oysters near the WTP in all seasons and correlated with δ15N‰ in fall and summer. Increased riverine discharge and slower acquisition of δ15N‰ likely confounded correlations in winter/spring. Although we did not detect gross ecological effects of wastewater exposure for oysters, data indicated waste water derived particles entered the local food web and accumulated in oysters. These data highlight the importance of using multiple indicators of wastewater exposure and considering both seasonal and spatial effects when defining wastewater influence on a system or species