Crassostrea Virginica Research Articles

Assessment of Dermo Perkinsus marinus in the “Southern Oyster” from a High‐Salinity Environment

The prevalence and intensity of dermo Perkinsus marinus were examined in the eastern oyster Crassostrea virginica “southern oyster” population within the high salinity (35‰ or greater) waters of South Texas' lower Laguna Madre (LLM). During 2017, 192 oysters from four collection sites (approximately 111 km2 study area) were examined via culture for the presence of Perkinsus hypnospores. Additionally, dermo DNA was detected in oysters by PCR. The number of oysters infected (prevalence = 0.36), as well as the intensity of infection, were consistent within three of the four collection sites but varied between sites, suggesting that environmental differences influence P. marinus infection in the LLM. All sites showed an upward trend in the number of oysters infected as oyster size increased, yet the highest infection intensities were not found predominately in the larger oysters. Although the warm, high‐salinity waters might be expected to be ideal for dermo infection, the relative number and intensity of infections were low for most sites, suggesting that dermo in the LLM may not pose a significant threat to commercial oyster culture and that the southern oyster may be uniquely suited for developing a strain of oysters suitable for offshore culture in the Gulf of Mexico.

Demography of Oysters Pre‐ and Postcollapse in Apalachicola Bay, Florida, Using Stage‐Based Counts

AbstractThe collapse of oyster populations and the fisheries they support has been a worldwide phenomenon, but studies of oyster demography in situ prior to and after the collapse have been rare. We used time series of stage‐based counts of eastern oysters Crassostrea virginica in Apalachicola Bay, Florida, to help understand how abundance and demographic rates may have changed in the decade after the 2012 collapse relative to the period before the collapse. We relied on a Bayesian hierarchical model in which the latent stage structure of the oyster population (i.e., densities of spat, sublegal oysters, and legal oysters) was governed by a system process and where the count data represented summaries of that latent structure. Count data were sufficient to conduct this on two large oyster bars that had some of the highest precollapse oyster densities. We also examined nine other bars with less data for any temporal trends in postcollapse abundance that might be associated with recent restoration efforts. Among the 11 bars examined, oyster densities were often increasing prior to the collapse and were very low, without detectable trends, afterward. Based on our demographic analyses, mortality rates of Apalachicola Bay oysters in the decade after the collapse generally exceeded (often greatly so) those during the precollapse period for all oyster stages. On the other hand, spat settlement rates apparently were increasing prior to the collapse and remained high during the postcollapse period. Simulations of postcollapse demography suggest that without improved survival rates, further declines of the oyster population can be expected. We discuss these findings in light of ongoing restoration and management efforts and suggest ways in which rapid transitions to undesirable socio‐ecological regimes might be avoided in the future.

Use of a Bayesian network as a decision support tool for watershed management: a case study in a highly managed river-dominated estuary

Decision making in water resource management has many dimensions including water supply, flood protection, and meeting ecological needs, therefore, is complex, full of uncertainties, and often contentious due to competing needs and distrust among stakeholders. It benefits from robust tools for supporting the decision-making process and for communicating with stakeholders. This paper presents a Bayesian network (BN) modeling framework for analyzing various management interventions regulating freshwater discharges to an estuary. This BN was constructed using empirical data from 98months of monitoring the Caloosahatchee River Estuary in south Florida during the period 2008-2021 as a case study to illustrate the potential advantages of the BN approach. Results from three different management scenarios and their implications on down-estuary conditions as they affected eastern oysters (Crassostrea virginica) and seagrass (Halodule wrightii) are presented and discussed. Finally, the directions for future applications of the BN modeling framework to support management in similar systems are offered.

Energetic budget of diploid and triploid eastern oysters during a summer die-off.

Triploid oysters are widely used in off-bottom aquaculture of eastern oysters, Crassostrea virginica. However, farmers of the Gulf of Mexico (GoM) and Atlantic coast estuaries have observed unresolved, late-spring die-offs of triploid oysters, threatening the sustainability of triploid aquaculture. To investigate this, the physiological processes underlying oyster growth (e.g., feeding, respiration) and mortality of one-year-old diploid and triploid oysters were compared in early summer following an uptick in mortality. It was predicted that higher triploid mortality was the result of energetic imbalances (increased metabolic demands and decreased feeding behavior). Oyster clearance rates, percentage of time valves were open, absorption efficiency, oxygen consumption rates (basal and routine), ammonia excretion rate were measured in the laboratory and scope for growth was calculated. In addition, their condition index, gametogenic stage, Perkinsus marinus infection level, and mortality were measured. Mortality of triploids in the laboratory was greater than for diploids, mirroring mortality observed in a related field study. The physiological parameters measured, however, could not explain triploid mortality. Scope for growth, condition index, and clearance rates of triploids were greater than for diploids, suggesting sufficient energy reserves, while all other measurements where similar between the ploidies. It remains to be determined whether mortality could be caused from disruption of energy homeostasis at the cellular level.

Evaluating a short vs. long-term progeny test and investigating physiology associated with survival in extreme low salinity for the eastern oyster Crassostrea virginica

Low salinity negatively affects growth and survival in the eastern oyster, which decreases productivity of aquaculture operations along the mid-Atlantic and Gulf Coasts of the United States. With heavy rainfall events predicted to become more frequent, coastal aquaculture operations face increased risk of prolonged exposure to extreme low salinity conditions. While recent experimental work has determined that survival in extreme low salinity (< 3) is a moderately heritable trait in the eastern oyster, further experimental challenges were conducted to investigate the importance of challenge duration and temperature on the survival phenotype and estimation of its genetic parameters to hone the experimental challenge for potential incorporation into a breeding program. Growth (shell height) and algal removal were also assessed to investigate physiological phenotypes associated with differential survival in extreme low salinity. A subset of individuals from 51 half-sibling families were exposed to one of two experimental challenges: a short-term low salinity (2.5) challenge at constant temperature (27 °C) for 2 months, or a long-term low salinity (2.5) challenge where temperature was adjusted daily to match local ambient conditions for 6-months. Differential mortality was observed across families for both the short-term and long-term low salinity challenges, and narrow-sense heritability estimates were similar for both challenges (short-term h2 = 0.35, long-term h2 = 0.4). Strong phenotypic (rS = 0.89) and genetic (rG = 0.81) correlations for family mortality were found between challenges. Algal clearance metrics over a 24-h clearance experiment differed among families (p < 0.001), but were only weakly associated with family survival in the long-term low salinity exposure (range p = 0.08–0.23, R2 = 5–10%). Growth was negligible during the long-term challenge. However, after being returned to ambient salinities (13), there was no difference in growth rate, wet weight gain, or mortality between oysters from families with low or high survival in the long-term exposure (p > 0.05), indicating that low salinity tolerant oysters can recover following low salinity events. This work shows that a short-term (2 month) low salinity (2.5) challenge at a constant temperature captures the same patterns of family mortality as a 6-month, temperature fluctuating challenge. Additionally, measuring individual oyster clearance rate and the parameters derived from the algal removal curves provide additional insight into the physiological status of oysters under extreme low salinity stress.

MOLECULAR CHARACTERIZATION OF SPOROCYSTS AND CERCARIAE (DIGENEA: BUCEPHALIDAE) INFECTING THE EASTERN OYSTER CRASSOSTREA VIRGINICA FROM VIRGINIA.

The identity of a larval bucephalid infecting the eastern oyster, Crassostrea virginica (Gmelin, 1791), from a tidal river in Virginia is investigated using ribosomal deoxyribonucleic acid (rDNA). The internal transcribed spacer (ITS1, 5.8S, ITS2) region and a portion of the 28S rDNA were isolated from genomic DNA from sporocysts containing cercariae and compared with sequences from GenBank and from our previous collections of possibly related bucephalids. The studied larval bucephalid was 100% identical at the ITS1, 5.8S, and partial 28S rDNA sequences with Prosorhynchoides paralichthydis (Corkum, 1961) Curran and Overstreet, 2009; however, it differed from P. paralichthydis by 6 bases plus 3 deletions in the ITS2 region. This level of variation at the ITS2 region has been demonstrated among some Indo-Pacific species of Prosorhynchoides Dollfus, 1929, suggesting that the larval bucephalid represents an unidentified or innominate species of Prosorhynchoides that is closely related to P. paralichthydis.

Development and evaluation of a formulation of probiont Phaeobacter inhibens S4 for the management of vibriosis in bivalve hatcheries

AbstractLarval eastern oysters (Crassostrea virginica) grown in shellfish hatcheries are susceptible to bacterial diseases, particularly vibriosis. Probiotics are microbes that confer health benefits to the host and have been identified as promising tools to manage diseases in aquaculture. The marine bacterium Phaeobacter inhibens S4 (S4) protects larval eastern oysters against challenge with the bacterial pathogen Vibrio coralliilyticus RE22 (RE22). A concentrated liquid formulation of probiont S4 that maintained high cell viability after long‐term storage was developed for commercial use in shellfish hatcheries. The safety and efficacy of the formulation were tested in six different trials in two hatcheries. The S4 formulation was added to C. virginica larvae culture tanks daily at 104 colony forming units (CFU)/mL from Day 1 post fertilisation until Day 6, 12 or 14, depending on the trial. Treatment of larvae in the hatchery with the S4 formulation did not significantly affect the survival and growth of the larvae. Formulated probiont S4 treatment in the hatchery led to a significant increase in relative percent survival (RPS) when larvae were subsequently challenged with the pathogen RE22 (105 CFU/mL) for 24 h in a laboratory challenge as compared to probiotic‐untreated RE22‐challenged larvae (RPS increase of 46%–74%, p &lt; 0.05). These results suggest that this novel S4 formulation is a safe, easy‐to‐use and effective tool in preventing larval losses due to vibriosis in hatcheries.

Eastern oysters Crassostrea virginica settle near inlets in a lagoonal estuary: spatial and temporal distribution of recruitment in Mid-Atlantic Coastal Bays (Maryland, USA).

Declines of the Eastern oyster, Crassostrea virginica, and its numerous ecological benefits have spurred oyster restoration initiatives. Successful restoration of a self-sustaining oyster population requires evaluating the temporal and spatial patterns of recruitment (settlement and survival) of oyster larvae in the target waterbody. Restoration of the Eastern oyster population in the Maryland Coastal Bays (MCBs), USA, a shallow lagoonal estuary, is of interest to federal, state, and non-governmental, but the location and timing of natural recruitment is not known. We assessed the spatial and temporal variation in oyster larval recruitment throughout the MCBs using horizontal ceramic tiles and PVC plates. Newly settled oyster larvae (recruits) were monitored biweekly from June to September 2019 and 2020 at 12 sites in the MCBs and a comparison site in Wachapreague, Virginia. Water quality measurements collected included temperature, salinity, dissolved oxygen, pH, and turbidity. The objectives of this study were to determine (1) the most effective substrate and design for monitoring oyster recruitment, (2) the spatial and temporal distribution of oyster larval recruitment in the MCBs, and (3) patterns in oyster larval recruitment that would be applicable to other lagoonal estuaries. (1) Ceramic tiles were more effective than PVC plates for recruiting oyster larvae. (2) Peak settlement began during the period from late June through July, and oyster recruitment was greatest at sites closest to the Ocean City and Chincoteague inlets. (3) Areas near broodstock that have slow flushing rates to retain larvae may provide the best environments for recruitment of oysters to lagoonal estuaries. As the first study on oyster larval recruitment in the MCBs, our results provide insight into their spatial and temporal distribution, methods that can serve as a foundation for future recruitment studies in other lagoonal estuaries, and baseline data that can be used to inform stakeholders and evaluate the success of oyster restoration projects in MCBs.

A second unveiling: Haplotig masking of the eastern oyster genome improves population-level inference.

Genome assembly can be challenging for species that are characterized by high amounts of polymorphism, heterozygosity, and large effective population sizes. High levels of heterozygosity can result in genome mis-assemblies and a larger than expected genome size due to the haplotig versions of a single locus being assembled as separate loci. Here, we describe the first chromosome-level genome for the eastern oyster, Crassostrea virginica. Publicly released and annotated in 2017, the assembly has a scaffold N50 of 54 mb and is over 97.3% complete based on BUSCO analysis. The genome assembly for the eastern oyster is a critical resource for foundational research into molluscan adaptation to a changing environment and for selective breeding for the aquaculture industry. Subsequent resequencing data suggested the presence of haplotigs in the original assembly, and we developed a post hoc method to break up chimeric contigs and mask haplotigs in published heterozygous genomes and evaluated improvements to the accuracy of downstream analysis. Masking haplotigs had a large impact on SNP discovery and estimates of nucleotide diversity and had more subtle and nuanced effects on estimates of heterozygosity, population structure analysis, and outlier detection. We show that haplotig masking can be a powerful tool for improving genomic inference, and we present an open, reproducible resource for the masking of haplotigs in any published genome.

Production potential of seaweed and shellfish integrated aquaculture in Narragansett Bay (Rhode Island, U.S.) using an ecosystem model

Integrated aquaculture systems combining macroalgae with traditional fish and shellfish production represent an ecologically sound and economically attractive solution for farmers. To evaluate the potential of growing sugar kelp (Saccharina latissima) at existing oyster (Crassostrea virginica) farms in Narragansett Bay (NB; Rhode Island, U.S.), we developed an ecosystem model based on individual Dynamic Energy Budget models for kelp and oysters forced offline by a coupled 3D hydrodynamic-water quality model. Kelp growth during the cold winter months provides ecosystem services through the removal of nutrients in the bay as well as serving as an additional source of revenue for farmers. Locations with the most nutrient-rich waters at the northern end of the bay seem most suitable for kelp aquaculture, with oyster growth also reaching maxima at the same locations. Predictions of kelp biomass grown on lines ranged from 0.97 kgWW m–1 at the easternmost site at the Bay Entrance to 2.03 kgWW m–1 at the northernmost site in the Upper Bay, or 1.6 and 3.4 tons ha–1 on 6 m spaced line-farms, respectively. For denser production in 1.5 m spaced line-farms, estimates ranged between 6.5 and 13.5 tons ha–1. Depending on the different farm setups, we estimated the potential profits (based on delivered cost for consumer product) at $4,468 for a 6 m spaced line-farm of 1 ha and $17,872 for a 1.5 m spaced line-farm. The N and C fixation of kelp ranged depending on spacing of longlines and time of harvest but reached maximum values of 1117 and 6184 kg ha−1, respectively. These estimates offer valuable information that should help producers and managers in their decision to direct efforts and investments into this developing activity in the U.S.

Drone lidar-derived surface complexity metrics as indicators of intertidal oyster reef condition

Eastern oysters (Crassostrea virginica) generate structurally complex reef systems that offer diverse ecosystem services. However, there is limited understanding of how reef structure translates into reef condition. This knowledge gap might be better addressed if oyster reef structure could be more rapidly assessed. Conventional in situ monitoring techniques are often time-intensive, invasive, and do not provide spatially continuous information on the reef structure. Unoccupied Aircraft Systems (UAS), commonly referred to as drones, equipped with optical sensors can rapidly and non-invasively map intertidal oyster reef surfaces. We demonstrate how a digital surface model from UAS-based light detection and ranging (lidar) can enable very high-resolution characterization and monitoring of intertidal oyster reef surface morphology. Generalized linear models (GLMs) identified relationships between in situ live oyster counts and surface complexity metrics derived from digital surface models produced from lidar point clouds. Statistically significant relationships between surface complexity metrics (e.g., gray level co-occurrence features, volume to area ratio, skewness of elevation) and live oyster counts suggest that surface complexity provides useful proxies for reef condition. Advancing the application of remote sensing to intertidal oyster reefs can help identify reefs that are prone to degradation and inform conservation and restoration strategies.

Fitness of Wild and Selected Eastern Oyster (Crassostrea virginica) Larvae under Different Conditions

The eastern oyster, Crassostrea virginica, has been an important fishery species in the United States for hundreds of years. The emergence of population devastating diseases such as MSX and Dermo was met with the development of disease-resistant lines. Although selectively bred oysters have shown improved survival and growth under diseases in the field, it is unknown if long-term selection has altered larval fitness. In this study, the larval fitness of a selected line (DBX) was studied and compared with that of the Delaware Bay wild (Wild) population under hatchery and natural conditions with the latter using untreated seawater, 50% feeding, and declining salinity. No difference in growth was observed between DBX and Wild larvae under either condition, but DBX exhibited a higher survival under hatchery conditions (P = 0.090), whereas the Wild performed equally well under both conditions. Under natural conditions, the DBX larvae had higher survival during the first week when the salinity was high, but lower survival later under low salinity. The DBX larvae had a much higher setting success and a preference for oyster shells as substrate compared with the Wild larvae. Results of this study indicate that selective breeding has unintentionally altered larval fitness of DBX and led to adaptation to hatchery and high salinity conditions with greater setting success, and the Wild larvae have wider adaptability to different conditions. These findings suggest that careful evaluation is needed to fully assess the recruitment potential of selected stocks used in aquaculture and restoration.

Nonconsumptive Effects of Crustaceans and an Echinoderm on Spat of the Eastern Oyster Crassostrea virginica (Gmelin, 1791)

Predation by crustaceans and echinoderms is a significant driver of mortality for sessile invertebrates in near-shore marine ecosystems. As a response, shellfish growers use predator exclusion cages to grow their product. Oysters grown in these cages and clams in and under nets have been observed to exhibit thinner, brittle shells, which is not optimal for market, nor for those being grown for restoration purposes. Here, the nonconsumptive predator effects of several native and nonnative predators on shell morphology of Crassostrea virginica oyster spat. Juvenile (1–3 mm) seed oysters were exposed separately to chemical cues of five different predators and one nonpredator crab were investigated and compared with control (no exposure) spat. Significant effects of predator presence on the total wet weight (g) of the spat was demonstrated, with the highest increase for spat exposed to black-fingered mud crabs (Panopeus, 1.70 mg d–1) and the biggest decreases for spat exposed to the European green crabs (Carcinus maenas—1.34 mg d–1) and the sea stars (Asterias rubens—1.47 mg d–1). Changes to oyster length (mm) and shell density (crushing resistance) were not significant. Implications for aquaculturists and wild bivalve populations are that growth could be negatively affected by the lack of predators on these important organisms.

Consequences of Salinity Change, Salinity History, and Shell Morphology on Early Growth of Juvenile Oysters

Estuaries provide valuable habitat for the eastern oyster (Crassostrea virginica). Although salinity at a given location fluctuates regularly with tides, upbay and downbay salinity differences span a broad estuarine salinity gradient. Higher salinity habitats downbay support faster oyster growth, whereas lower salinities upbay act as a refuge from predation and disease but slows growth. Two experiments were performed to investigate the effect of salinity, postsettlement salinity changes, and shell morphology on juvenile oyster growth. One experiment used wild oyster spat collected from three distinct Delaware Bay salinity zones that were then transplanted into various salinity conditions in the laboratory, where growth was monitored. Transplanting into low salinity led to decreased growth compared with transplanting to higher salinity, and growth of oyster spat was overall highest for spat from the lowest salinity source. Growth did not differ among shell morphologies. A second experiment used hatchery reared larvae set in one of four different salinity conditions. Those spat were maintained in settlement salinities 22, 16, 10, and 6 for 2–3 wk postsettlement, then measured before fully factorial transfer into new salinity conditions with measurement 3 wk later. Lower final salinity treatments were associated with lower growth, lower initial salinity treatments were associated with faster final treatment growth, and final growth depended on the interaction between initial and final salinity. Therefore, in addition to the effects of acute salinity changes on growth, early postsettlement hyposalinity stress can generate compensatory juvenile oyster growth. As increased freshwater events due to climate change are expected in the Delaware Bay and regionally in the Northeast, these results indicate that nonlinear early life stress responses are important to quantify to better understand oyster stock resilience and plan management.

Hypoxia and Anoxia Tolerance in Diploid and Triploid Eastern Oysters at High Temperature

Increasing reliance on the use of triploid oysters to support aquaculture production relies on their generally superior growth rate and meat quality over that of diploid oysters. Reports of elevated triploid mortality have generated questions about potential trade-offs between growth and tolerance to environmental stressors. These questions are particularly relevant as climate change, coastal activities, and river management impact water salinity, temperature, nutrients, pH, and oxygen levels within key estuarine oyster growing areas. In particular, the co-occurrence of warm water temperatures and low dissolved oxygen concentration (DO) events are increasingly reported in estuaries, with potentially lethal impacts on sessile, oyster resources. To investigate potential differences in DO tolerance, diploid and triploid market-sized or seed oysters were exposed to continuous normoxia (DO > 5.0 mg L–1), hypoxia (DO < 2.0 mg L–1), and anoxia (DO < 0.5 mg L–1) at 28°C and their mortalities were monitored. The hemolymph of the market-sized oysters was collected to measure cellular and biochemical changes in response to hypoxia and anoxia, whereas their valve movements were also measured. In general, about half of market-sized oysters died within about 1 wk under anoxia (LT50: 5.7–8.9 days) and within about 2 wk under hypoxia (LT50: 11.9–19.4 days) with diploid oysters tending to die faster than triploid oysters. Seed oysters took longer to die than market-sized oysters under both anoxia (LT50: 9.5–12.1 days) and hypoxia (LT50: 21.8–25.0 days) with diploid oysters (LT50: 9.5–11.8 days) dying slightly faster than triploid oysters (LT50: 11.8–12.1 days) under anoxia. Hemolymph pH decreased and plasma calcium and glutathione concentrations increased with decreasing DO, with values under anoxia being different than those under normoxia. Hemocyte density was also lower under anoxia than under either normoxia or hypoxia. Overall, few differences in physiological responses to hypoxia and anoxia were found between diploid and triploid oysters suggesting that ploidy (2N versus 3N) had limited effect on the tolerance and response of eastern oysters to low DO.

Oyster aquaculture cages provide fish habitat similar to natural structure with minimal differences based on farm location

Oyster aquaculture gear may augment natural seafloor by providing structured habitat for economically important fish species. Underwater video census was used to assess fish abundance and community composition on eastern oyster (Crassostrea virginica) shelf and bag style aquaculture off-bottom cages and within natural rock reef habitat. During 2018, underwater cameras were mounted on four study cages at a dense shellfish farm of 40-100 commercial cages (dense cage farm), on four single cages interspersed on low relief seafloor (sparse cage farm), and amongst four boulders on a rock reef (rock reef), within an embayment off Milford, Connecticut, which is part of Long Island Sound, in the United States. In 2019, cameras were similarly deployed on two study cages per farm at each of three shellfish farms off Milford, Norwalk and Westport, CT. Video was recorded hourly in eight-minute segments from 7 am to 7 pm. Data loggers monitored seawater temperature, light intensity, and current speed. Fish abundance (MaxN) was calculated for all videos. We compared fish abundance and community composition between May and September, on cage and boulder habitat, on cages at dense and sparse farms and on cages across farm locations. In 2018, abundance of black sea bass (Centropristis striata), scup (Stenotomus chrysops) and tautog (Tautoga onitis) was significantly higher on cages than boulders, regardless of cage number. Cunner (Tautogolabrus adspersus) abundance was significantly higher on boulders than cages when cage sites were grouped. However pairwise comparisons indicated that cunner were significantly higher at the sparse cage farm versus the rock reef but cunner abundance on the dense cage farm and rock reef sites was not significantly different. Abundance of black sea bass, scup, tautog, and cunner were not significantly different across 2019 farm locations. Young-of-the-year fish occurred episodically at all sites during both years, with black sea bass and scup most abundant. Fish abundance corresponded to seasonal changes in seawater temperature and was highest at the warmest temperatures. Light intensity and current speed explained less variation in fish abundance relative to temperature, and relationships were inconsistent across habitats and farm locations Our results suggest that multi-tiered oyster aquaculture cages contribute structure to seafloor environments that provide habitat for temperate reef fish similar to natural rock reefs.

Of missions and marshes: Stable isotope analysis of Mission-Era Guale oyster harvesting on St. Catherines Island, Georgia

This article presents the results of oxygen stable isotope analysis on eastern oyster (Crassostrea virginica) samples (n = 25) from a Mission-Era (ca. AD 1565–1680) site, Pueblo Santa Catalina de Guale, on St. Catherines Island, GA. Stable isotope analysis was used to assess the seasonality of oyster harvesting on St. Catherines Island during the Mission Era to better understand how Spanish colonization and the Catholic mission system may have impacted Guale foodways. Five eastern oyster left valves were sampled from each known neighborhood of Pueblo Santa Catalina de Guale. Existing data regarding the seasonality of pre-colonial mollusk collection on St. Catherines Island and elsewhere in the coastal Southeast are discussed in conversation with the results of this analysis. This work indicates that Guale residents of St. Catherines Island during the Mission Era were harvesting oysters most intensely during cooler months. This pattern is consistent with estimates of pre-colonial shellfishing seasonality across the region and may even represent a modest increase in the seasonal constriction of shellfishing when compared to data from the preceding period. Salinity estimates based on the isotope data also suggest Guale people during the Mission Era were collecting from a comparatively narrower range of estuarine habitats. We argue that these subtle shifts are a consequence of the reorganization of Guale labor associated with missionization.

Changes in Larval Oyster Swimming Behavior with Salinity and Larval Age.

AbstractEastern oysters (Crassostrea virginica) are sessile, relying on a larval phase to disperse in estuaries. Oyster larval swimming behavior can alter dispersal trajectories and patterns of population connectivity. Experiments were conducted to test how both (1) acclimation time to new environmental conditions and (2) larval swimming behavior change with salinity and larval age. Acclimation time to changes in salinity was longest in lower salinity (6 ppt) and decreased with age. To test changes in behavior with salinity, larvae were placed into four salinities (6, 10, 16, and 22 ppt) where swimming was recorded. To test changes in behavior with age, larvae aged 6, 12, and 15 days were recorded. In both experiments, swimming paths were mapped in two dimensions, behavior of each path was categorized, and speed, direction, and acceleration were calculated. The frequency of upward, neutral, and downward swimming behaviors did not differ across salinity treatments but did vary with age, whereas the frequency of behavior types varied with both salinity and ontogeny. As an example, diving was observed more frequently in low salinity, and more downward helices were observed in moderate salinity, while younger larvae swam upward with more frequency than older larvae. Surprisingly, diving was observed in 10%-15% of all larvae across all ages. Given the consequence of larval behavior to marine invertebrate dispersal, changes in swimming over larval age and in response to environmental changes have important implications to marine population stability and structure.

Prevalence and Distribution of Microplastics in Oysters from the Mississippi Sound

AbstractOysters are a foundational part of their ecosystem and research has shown they are negatively impacted by exposure to microplastics (MPs). High MP levels have been documented in waters surrounding oyster reefs, and as filter feeders, oysters can ingest MPs along with their food. Here, we determined MPs (&gt;30 µm) in oysters (Crassostrea virginica) from ten sites across the Mississippi Gulf Coast. Further, a subset of these samples was dissected to quantify MPs within specific tissues. Average concentrations ranged from 30.7± 11.5 to 4.7 ± 0.25 putative MPs/g wet weight (ww) of whole tissue, with sites inside bays near population centers displaying higher levels of MPs than those exposed directly to the Gulf. Mantle, gill, and adductor muscle tissues had similar concentrations of putative MPs (15.9 ± 13.4, 11.5 ± 8.6 and 12.8 ± 6.7 MPs/g, respectively), whereas digestive system tissues had lower concentrations (6.8 ± 6.1 MPs/g of tissue). This suggests that most MPs in an oyster likely adhere to external tissues and are not actually ingested. Most of the MPs retained were in the smallest size fraction of 30‐90 µm (80%), followed by 125‐250 µm (9%), 90‐125 µm (8%), and &gt;250 µm (3%). Analysis of samples from Biloxi Bay by µ‐FTIR to assess MP composition shows that polyurethane, polyethylene, and polyamide are common, but additional analyses are needed to fully characterize the MP profile across sites. Overall, this work provides much‐needed empirical data on the abundances and sizes of MPs in oysters from the Mississippi Sound, as well as the tissues where they reside.

Induced defenses as a management tool: Shaping individuals to their environment

Many prey species can adjust morphology to reduce predation risk in response to predator cues. Enhancing prey defenses using predator cues may improve survival of cultivated species and enhance species restoration efforts, but assessment of such benefits at industrially relevant scales is needed. We examined how raising a model foundation species, oysters (Crassostrea virginica), under commercial hatchery conditions with cues from two common predator species can improve survival across a variety of predator regimes and environmental conditions. Oysters responded to predators by growing stronger shells than controls, but had subtle variations in shell characteristics depending on the predator species. Predator-induced changes significantly increased oyster survival up to 600% and survivorship was maximized when cue source was matched with local predator regime. Overall, our findings demonstrate the utility of using predator cues to enhance the survival of target species across landscapes and highlight the opportunity to employ nontoxic methods to control pest-based mortality.