Oysters have throughout history been one of the most important marine invertebrate animals used, whether as human food or as a cultural base. Today, they represent one of the most exploited natural resources, are produced by aquaculture activities, and are one of the most studied groups of shellfish. This is most evident in temperate zones, whereas studies in tropical zones have been comparatively scarce and somewhat disorganized. The present review organizes the studies of a dozen species that are grouped as oysters of the tropical and subtropical American Pacific, considering their taxonomy and identification, as well as their distribution, and establishing an identification key using the characteristics of the shell. Aspects of their biology are described, referring to general anatomy with a type species, the Cortez oyster Crassostrea corteziensis, as well as the life cycle, taking as reference the recent studies carried out on the rock oyster Striostrea prismatica. In the same way, a description of their populations and ecological interactions is provided, emphasizing the reproduction of the different species and ordering the description of the main stages in the gametogenic development of the populations in a latitudinal form. The main diseases and some uses of oysters as bioaccumulating organisms are also described, as well as phylogenetic and population genetic studies. Finally, possible future actions are discussed to provide a more comprehensive knowledge of oysters from the tropics and subtropics of the American Pacific based on the conservation and use of the resources.

Oyster reefs (OR) once dominated coastal estuaries but are now one of the most severely impacted marine habitats on Earth. There is little information available regarding the status of natural OR in China. This study examined the seasonal and temporal changes in the Kumamoto oyster Crassostrea sikamea population and associated benthic macrofaunal communities at the largest intertidal OR (Liyashan) of the China Sea in four field surveys (spring and fall in 2013 and 2018). The oyster densities exhibited no evident seasonal variations in either 2013 or 2018 but showed significant temporal changes and declined by 89.66% in spring and 96.27% in fall between 2013 and 2018. The total densities of benthic macrofaunal communities at the reef area of the OR were significantly higher than those at the degraded oyster habitat (DOH) and dramatically decreased by 80.73% in spring and 64.87% in fall between 2013 and 2018. Nonmetric multidimensional scaling ordination indicated the benthic macrofaunal communities differed significantly between the OR and DOH or among the four sampling periods. Analysis of similarity indicated that the benthic communities at the OR had greater seasonal and temporal changes than did those at the DOH, and that temporal changes in benthic communities were greater than seasonal changes at each habitat. The study concluded that the OR had decreased habitat values as the oyster populations and the benthic macrofaunal communities dramatically declined from 2013 to 2018.

As efforts for restoring Olympia oyster Ostrea lurida populations have expanded, there is an increased need to understand local factors that could influence the long-term success of these projects. To address concerns over potential limitations to recruitment at a restoration site in northern Puget Sound, WA, a study was developed to characterize physical processes governing larval transport in conjunction with larval abundance and environmental factors. Larval presence was not associated with tide cycle, season, or a combination of tide cycle and season. In terms of location, larvae were more likely to be present at offshore and intertidal sites versus the estuarine lagoon, where the adult population resides. Larval density was higher during late summer ebbs versus early summer floods. Across sampling dates and locations, larval sizes ranged from 184 to 263 µm, indicating that larvae were released into the water column throughout the reproductive season and retained in the embayment for at least ∼16 days. Throughout different tidal cycles in Skagit Bay, acoustic Doppler current profilers were used to measure current direction and velocities, concurrent with plankton sampling. Surface currents in the study area alternated between a clockwise and a counterclockwise gyre during initial ebb and flood tides, respectively. Larvae exported from the source population during initial to midebbs are swept into a northward gyre and potentially retained at intertidal sites alongshore. These results will provide resource managers attempting to restore native bivalves with the ability to expand populations by identifying optimal areas for habitat enhancement through natural recruitment.

Globally, precipitation is expected to increase along with the rise of temperatures due to climate change, increasing the likelihood of freshwater intrusion into coastal ecosystems. In the spring and summer of 2019, heavy rainfall and snowmelt in the midwestern United States caused historic flooding of the Mississippi River, warranting two openings of the Bonnet Carré Spillway (BCS) to reduce pressure on levees in New Orleans, LA. These openings released an unprecedented volume of freshwater into Lake Pontchartrain and subsequently into the Mississippi Sound. This study investigated the impacts of these freshwater releases on populations of the eastern oyster Crassostrea virginica and water quality in the western Mississippi Sound and the Bay of St. Louis. Platforms housing oysters and water quality sensors that measured dissolved oxygen, salinity, and temperature were deployed at oyster reef sites. At each reef, native oyster populations were assessed via dredge sampling to determine oyster survival. After 13 days, deployed oysters suffered 100% mortality at all sites except the Henderson Point Reef and Kittiwake Reef, the sites farthest east of the BCS. On September 27, 2019, 62 days following the BCS closing, dredge sampling revealed no live native adult oysters or spat, even at sites where living oysters were collected earlier in the summer. If BCS openings increase in frequency or duration because of elevated precipitation, oyster populations in Mississippi could remain unsustainable for harvesting unless future freshwater intrusions are incorporated into management planning.

A mass mortality event that occurred in the Mississippi Sound in September 2016 provided an opportunity for the first natural field study of the rate of taphonomic loss of oyster shell. At the Pass Christian Reef, limited recruitment in the years following the mortality event resulted in little shell addition over a 2.67-y period, thereby permitting a direct comparison between shell present as living oysters in August 2016 and dead shell collected in April/May 2019. By April 2019, most oyster shell valves were riddled with holes, some of which perforated the valves. Deterioration of the shell surface was ubiquitous, and edge erosion was commonplace. Left valves were preferentially preserved: the left valves comprised 67% of the intact valves and 85% of the minor fragments after 2.67 y. Thus, at the time of collection, minimally 50% of the right valves originally present on the reef had disappeared. The increased differential between left and right valves of the minor fragments suggests a continuing differential in preservation, leading to cultch being overwhelmingly represented by left valves. Based on estimates derived from changes in shell weight at length and estimates of right-valve loss, by April 2019, between 30% and 51% of the carbonate originally added to the reef in 2016 was lost, yielding an estimated oyster shell half-life of between 2.6 and 5.1 y in the Mississippi Sound. The half-lives estimated from this first infield experiment fall precisely within the range of previous less direct estimates from laboratory experiments or survey time series. Oyster shell degrades rapidly: case histories now include a wide latitudinal range and a wide temperature range, which suggests that these rapid shell degradation rates are the norm over most of the range of the eastern oyster. Understanding the impermanence of oyster shell is crucial to the sustainable management of oyster reefs, as the addition of shell to the reef framework must balance rapid shell degradation rates to prevent stock collapse and ultimately the loss of reef structure.

Reefs formed by the eastern oyster Crassostrea virginica are ecologically and economically important in the estuaries along the east and gulf coasts of the United States. Reefs of C. virginica play a vital role in improving water quality in estuaries via filtration and by providing refugia for mobile benthic organisms that use the interstitial spaces of reefs for refuge, feeding, and reproductive activities. Consequentially, these organisms are essential as a food source for higher trophic-level organisms such as recreationally and commercially important fish that use oyster reefs as feeding stations. This project investigated the link between oyster reef communities and the trophic transfer of biomass to tertiary-level predator fish in Estero Bay, FL. Fish were captured in proximity to isolated reef structures and gut contents analyzed. Sampling of fish was carried out around oyster reefs using an entanglement net (also referred to as a gill net). Fish were sampled for analysis of stomach contents using importance index analysis. Prey items were identified and compared, with organisms classified as oyster-reef indicator species. A total of 294 fish belonging to seven species were sampled during spring and summer months. The results demonstrate that 53% of the total importance index were several key prey items identified as oyster-reef indicator species. These species contribute to oyster reef biomass transfer to higher trophic-level organisms, indicating the critical nature of oyster reefs.

The United States has a $16 billion seafood deficit that the U.S. Department of Commerce and states are attempting to close by legislative policies, encouraging expansion of aquaculture in the United States. One of these policies, the 2011 National Shellfish Initiative, recognizes the benefits to water quality of cultivation of bivalve shellfish aquaculture in addition to the provision of seafood product. More recently, research addressing these policies has resulted in approval of the use of harvested oysters as a nutrient best management practice in the Chesapeake Bay region. Also discussed, but not yet fully implemented, is the inclusion of oyster growers in nutrient credit trading programs where economic compensation is provided to oyster growers for the nutrient removal ecosystem service that their oysters provide. This study used field sampling and a local-scale oyster production model to compare water quality, oyster production, and oyster associated nitrogen removal at two bottom and four water-column Maryland Chesapeake Bay oyster farms. Objectives were to highlight differences in water quality (i.e., oyster food), resultant differences in oyster production, and differences in estimated oyster-associated nutrient removal among farms. An avoided, or replacement, cost economic valuation analysis was performed to also compare the potential payment to the oyster growers for the nutrient removal service if they were included in a fully developed nutrient credit trading program. Production at the six sites varied from 1.78 to 25 metric tons of harvestable oysters acre^–1 y^–1. Oyster filtration–related N removal was estimated to be at a range of 28–457 kg N acre^–1 y^–1. The potential economic value of the total N removed by a farm was estimated to be at a range of $0.56 × 10³–$12,446 × 10³ y^–1 among farm sites, depending on the alternative management measure used to assign the value.

The spatial relationship between adult eastern oyster Crassostrea virginica populations and recruitment to the benthos of their offspring is not well understood. It is well established that larvae can be widely dispersed, but the relationship between dispersal potential and actual recruitment patterns across the full range of spatial scales involved remains unknown. To explore this relationship, spat collectors were deployed on and near (up to 1 km distance) three natural oyster reefs in New Hampshire in 2014 and 2015. Spat densities on the reefs and within 400 m of the reefs were nearly 10-fold higher than densities more distant. These data do not negate the potential importance of widespread dispersal and recruitment, but they do indicate a surprising level of recruitment very near their likely source. Additional research is needed in other areas to test the generality of the findings and to assess potential causal factors for the observed patterns. The overall implication for choosing sites for oyster reef restoration projects, particularly in recruitment-limited areas, is that they may need to be located much closer to spawning adults than previously thought to maximize the likelihood of adequate natural recruitment and reef development.

The possibility that the economics of the oyster fishery impose a self-limitation on overharvesting has been proffered on occasion. The inefficiency of harvesting by the fishery has been evaluated and estimates of the exploitation rate permissible under conditions of maximum sustainable yield have been obtained in previous studies. The question becomes to what extent does the inefficiency of harvest interact with the economics of the fishery to compromise ready detection of overfishing? This study explores the possibility that the constraint of economics on the fishery occurs at oyster exploitation rates that are higher than maximum sustainable yield, leading ineluctably to overfishing if unconstrained and to the appearance of unduly limited fishing if properly constrained. A model is developed that simulates oyster harvesting by dredging. This model tracks vessel behavior and fishery performance in economic terms (CPUE) under varying stock densities and dredge efficiencies. Simulation results show that stock density and on-deck culling speed have the strongest effect on time required, profitability, and effectiveness of harvest, whereas dredge efficiency has a lesser influence. Evaluation of simulations shows that overfishing occurs at a stock density that provides near-optimal economic returns. The oyster fishery does not perceive a decline in the stock under sustainable conditions, as the on-deck processing capacity enables the catch rate to remain relatively stable until the stock declines well below sustainable levels. The consequence of setting fishing regulations such that a decline in catch is perceived is to assure routine and substantive overfishing, thereby creating a potential conflict between apparent and real sustainability. This conflict may explain the inability of state regulatory authorities to impose limitations consistent with long-term resource stability. The perception that a decline in the rate of catch should be observed under standard effort-based regulatory controls is a principal challenge that must be overcome if sustainability is to become normative in the U.S. oyster fishery.

Histological, histochemical, and biochemical changes were assessed in the Cortez geoduck Panopea globosa, during larval development to identify the main energy storage sites and biochemical patterns. Histological sections were stained with polychromic dye, whereas histochemical sections were stained for triglycerides and phospholipids (Sudan black) and for carbohydrates (Alcian blue). Spectrophotometric quantitation of proteins, lipids, and carbohydrates was carried out in 5–35 mg dry weight (DW) samples. Larvae of Panopea globosa showed the typical linear shell growth rate (21 µm d^–1) and allometric, power-type relationships between shell length and DW (exponent b = 2.73) or ash-free DW (b = 2.78). Early straight-hinged larvae exhibited a rudimentary digestive system. The crystalline style, intestine, and digestive gland were conspicuous when larvae reached the early umbonate stage, whereas the gills, foot, byssal gland, and adductor muscles were first observed in late umboned larvae. Triglycerides and carbohydrates were mainly stored as droplets in the digestive gland, and their size increased with increasing larval age. Acid mucopolysaccharides were also secreted by the byssal gland. Carbohydrate content was substantially higher than triglycerides in pediveliger larvae. These finding suggests that P. globosa larvae mainly rely on a carbohydrate-based metabolism, both as a biochemical component of the larval–postlarval byssus and as an endogenous energy source during metamorphosis.

The age and growth of horse clams Tresus keenae from Seto Inland Sea (SIS) and Ise Bay, western Japan, were investigated using a water-based marking pen on the edge of sectioned shells, after which unstained translucent zones at the chondrophore could be clearly observed. The translucent zone was formed once per year during autumn. The ages of all the samples were determined. The most frequent shell length (SL) in SIS and Ise Bay populations were 100–120 mm and 120–140 mm, respectively and mainly consisted of 3-y-old and 4-y-old clams, respectively. Clams in the SIS were found to be younger by about 1 y and 20 mm smaller on average than the Ise Bay population. The age–SL relationships of clams from each area were analyzed, using the original von Bertalanffy growth function (VBGF), a VBGF with a biological intercept, and the Gompertz growth function. The original VBGF showed the best fit with the SIS dataset, whereas the Gompertz growth model showed the best fit with Ise Bay clams. The parameters for each growth model were significantly different between SIS and Ise Bay, which may be due to clams younger than 2 y and smaller than 80 mm SL that were present only in the samples from SIS. Faster growth rate of the VBGF in Ise Bay than that in SIS would be affected by higher water temperature during the season of rapid growth.

The catch efficiency of a hydraulic dredge was tested on a population of the northern quahog Mercenaria mercenaria in Narragansett Bay, RI, to understand gear limitations and correct relative abundance time series data. In 2017 and 2018, 45 hydraulic dredge tows were conducted following a long-standing fisheries-independent survey protocol, with the dredge transects inspected on SCUBA to assess dredge catch efficiency. Bull raking and quadrat samples taken on SCUBA were also conducted alongside the transects to compare sampling methods. The average dredge catch efficiency across samples was 0.64 (±0.29 SD). Bottom type was the most significant determinant of dredge catch efficiency, with higher catch efficiency on hard bottom (0.73 efficiency) than on soft bottom (0.48 efficiency). The quadrat and bull rake samples reflected higher catch rates than the dredge, but relationships between relative abundance estimates from the alternate methods and the dredge were either weak or insignificant. Bottom type, sediment classification, depth, and observed abundance were used to model dredge catch efficiencies and predict fisheries-independent abundance indices to more accurate estimates. Applying corrections using a generalized linear model scaled abundances through time, with trends generally the same between time series both with and without the corrections applied. This work provides an example of addressing gear efficiency concerns through diverse collaborations and improving the science and management for a commercially and recreationally significant marine resource.

Hydraulic dredges used for bivalve harvest are known to create immediate biological and physical changes to the substrate, but the rate of recovery is often site specific and habitat specific. Hydraulic dredging for the Atlantic surfclam Spisula solidissima (Dillwyn, 1817) occurred off Provincetown, MA, from November 2014 through April 2015. Acoustic surveys following the dredge activity were conducted in 2015 (June–August) with a phase-measuring sidescan sonar, yielding colocated sidescan backscatter and swath bathymetry. Dredge tracks were documented in 7.9% (402,309 m²) of the 5.1 km² surveyed. The survey area was divided into 10 × 10 m grid cells, and track density was calculated within each grid by the aggregated count of dredge tracks within each grid cell. The resulting track densities ranged between 0% and 53%. On October 23, 2017, 875 days after the 2015 hydraulic clamming season, a subset (1.05 km² ∼20%) of the same area was acoustically surveyed. The 2017 survey (1.05 km²) revealed that dredge tracks covered a total area of 9,784 m² at a density of 0%–24%. Initial areas (2015) with dredge track density greater than 10% had not fully recovered in 2017, and the rate of dredge tracks remaining was proportional to disturbance (linear regression; r² = 0.95; F = 110.6; df = 1,7; P < 0.001; SE = 0.206). The adjacent dynamic shoreline and the persistence of dredge tracks reinforce the idea that nearshore energy regimes should not be assumed based solely on more visible shoreline processes.

Sex, maturity, and the incidence of males in a population of hermaphroditic Corbicula fluminea Müller from Shirakawa River, Kyoto, Japan, are reported. Two shell color types (yellow and green) of this species are recognized. High frequencies of females (63.3% yellow and 58.5% green) are represented among individuals in this population. Histological examination of gonads and measurements of shell length suggest this species first matures as a female before commencing spermatogenesis (i.e., it is a protogynous simultaneous hermaphrodite). Low frequencies of males (mostly less than 5%), the testes of which are filled with spermatozoa, are reported; no histological evidence for any change from males to hermaphrodites, or hermaphrodites to males, is found. Requirements for maintaining males, and for their successful reproduction in self-compatible hermaphrodite populations, are proposed as follows: (1) the protogynous nature of the hermaphrodite, (2) low self-fertilization rates of hermaphrodites, (3) more spermatozoa and greater survival of males than hermaphrodites, and (4) high population densities, ensuring males and hermaphrodites are in close proximity.

The aim of this study was to determine the effect of additional nucleus insertion and its corresponding position on the shell growth of Pteria penguin as well as the thickness of the resulting mabé pearls. The treatment applied was the insertions of nucleus: A (one into the left shell), B (two into the left shell), and C (one into each sides of the shell). After 4 mo of culture, the growth and structure of the layers in the pearl were observed. The development of pearl layers was observed using scanning electron microscope. Results show that the number of nuclei implanted in the shell has no significant impact on shell growth or thickness as well as the number of aragonite layers of mabé pearls. Growth data show changes in oyster shell height, length, and thickness of 11.55–14.78, 18.48–22.05, and 2.59–6.14 mm, respectively, for all treatments. The average thickness of nacre was 0.29–0.33 and 0.19–0.22 µm for the base and top of resulting mabé pearls, respectively. In general, the addition of two nuclei in a single pearl oyster can be used to increase mabé pearl production in the coastal areas of Palabusa Bay, Southeast Sulawesi, Indonesia, which is suitable for the growth of pearl oysters.

The lion-paw scallop Nodipecten subnodosus is a commercially important Pectinidae species. Basic research is being carried for its genetic improvement and breeding. In this study, trochophore larvae of N. subnodosus scallop were used to obtain metaphase spreads and to describe the karyotype. The diploid chromosome number (2n) of this species is 38, as the only other species of the same genus Nodipecten nodosus, and in almost all the species studied so far in the Pectinidae group. The relative length of the largest chromosome is 6.92 and for the smallest is 4.22. Based on the constructed karyo-ideogram, three distinctive chromosomes with the longest size (1–3) are in the area of submetacentric (sm) and subtelocentric (st) chromosomes, whereas the others in the karyo-ideogram are difficult to be distinguished between metacentric (m), submetacentric (sm), or m-sm. Additional estimates of the centromeric index values indicated that the karyotype consists of 3 m, 8 m-sm, 6 sm, 1 sm-st, and 1 st chromosome pairs. The number of arms is 38. There are polymorphisms in the presence/absence of secondary constrictions. In one karyotype, the constrictions were in the two homologous chromosomes of one pair, whereas in other karyotypes, there were pairs with only one chromosome bearing the constriction, and other karyotypes had none. The chromosome morphology described here for the species N. subnodosus can serve as a basis for comparisons between scallops of the Nodipecten genus, which is composed of eight species.

Understanding spatial and temporal patterns in the recruitment of marine invertebrates with complex life histories remains a critical knowledge gap in marine ecology and fisheries. As marine invertebrates are facing multiple stressors from overfishing and climatic stress, it is important to evaluate the conditions that facilitate recruitment in low-density populations. The red abalone Haliotis rufescens historically supported an economically important fishery in California, but the fishery was sequentially closed as stocks declined, and the last fished area was closed in 2018 following the collapse of the kelp forests in Northern California. Here, red abalone recruitment was evaluated annually from 2012 to 2016 and monthly from 2016 to 2017 in Central California where red abalone naturally occur in highly aggregated but low-density populations because of sea otter predation. Trends in wind-driven upwelling, temperature, wave forces, and food resources (kelp) were evaluated over the same time period as factors that could affect recruitment patterns. Recruitment was annually consistent except in 2015, when recruitment declined by 76%, likely because of reproductive failure during the second year of the North Pacific marine heat wave. The monthly recruitment assessment was the first field assessment of red abalone recruitment over a full year, and it showed that red abalone can recruit year-round. There were no clear recruitment patterns associated with seasonal wind-driven upwelling or relaxation patterns, and kelp density was constant over the study period; however, conditions at the study sites included three key features that may provide optimal conditions for consistent recruitment: (1) spatial abalone aggregation, (2) a sheltered embayment that may retain larvae, and (3) persistent algal food resources. These results can inform statewide and global abalone recovery and management programs.

This study is the first attempt to assess parasitic infestations in grow-out cage culture and land-based grow-out tanks of the donkey's ear abalone Haliotis asinina in the Philippines. This histopathological study of the parasites was conducted from 2010 to 2013. Using 30 samples of abalones collected monthly from two sites, samples were measured and fixed in 10% formaldehyde in seawater, and routine histological techniques were used to identify the parasites. Water temperatures of the grow-out floating sea cages and the abalone hatchery facilities whose abalones were collected measured 27.5°C–32.5°C and 26°C–29°C, respectively; salinity in the area of the sea cages was 32–34 ppt, whereas salinity of the abalone hatchery was 32–35 ppt. Examination of the shell from cage-cultured abalones revealed the presence of burrowing polychaetes belonging to the families Serpulidae (prevalence, 32.5%) and Dorvilleidae (prevalence, 30%); on the other hand, only Dorvilleidae (prevalence of 28.5%) was detected in abalones from the hatchery. Histological examination revealed the presence of unknown ciliates (prevalence, 37.5%), Nematopsis sp. (prevalence, 17%), and metacestode Tylocephalum sp. (prevalence, 8.5%) from the grow-out cage-cultured abalones, whereas unidentified ciliates (prevalence, 32.5%) and Nematopsis sp. (prevalence, 10.5%) were detected from hatchery stock. The data collected showed that there was low-intensity infection and prevalence of parasites in abalones from grow-out cages and hatchery. These records of parasites constitute baseline information for future research work on abalones.

Pinto abalone populations in Washington state have declined precipitously in the last few decades, despite closure of the fishery. Local restoration efforts have focused on outplanting juvenile abalone, which is costly because of the husbandry required to raise abalone to outplanting size. This study tested if hatchery-produced larval pinto abalone could be successfully outplanted and if postoutplant growth of larval abalone differed from hatchery-raised animals. Wild broodstock were spawned, and some larvae remained at the hatchery for rearing, whereas most were transported to the Shannon Point Marine Center (SPMC) for outplanting. At two sites in the Salish Sea, larvae were outplanted at a density of 13,000 larvae m^–2 into two types of larval abalone modules (LAM): tented LAM (125 µm Nitex tenting) and open LAM (no tenting). There were also control LAM with no tenting and no abalone. Larvae were also seeded in LAM in aquaria at SPMC to compare field and aquaria survival and to estimate emigration. Shell lengths of field, laboratory, and hatchery-reared abalone were measured to better understand if hatchery life compromises early growth. Four months after outplanting, abundance of settled abalone was significantly greater in tented LAM than open and control LAM. Control LAM contained no abalone, suggesting reproduction by wild abalone did not occur at the field sites. Open LAM had a mean outplant success of 0.1% (0–12 settled abalone) and tented LAM a mean success of 0.4% (16–35 settled abalone). Outplant success was higher in SPMC aquaria. Open and tented LAM had 1.5% and 3.0% success, respectively. Abalone found on aquaria walls outside the LAM accounted for 0.2% of the seeded abalone for both open and tented LAM. Four months after outplanting, shell lengths of field abalone were not significantly different from lengths of hatchery-reared abalone, suggesting hatchery conditions did not compromise growth rates of newly settled abalone. These findings suggest that releasing larval pinto abalone into tented field modules has potential to supplement wild stocks in the Salish Sea as a lower cost alternative to outplanting juveniles.

Despite the commercial and cultural values of conch (family: Strombidae), there is a paucity of biological and ecological information to assist with the management of many conch fisheries. The common spider conch Lambis lambis, harvested throughout the Indo-Pacific for its meat and shell, is an example of such a data-deficient conch species. This study used passive acoustic tracking to estimate the spatial requirement and broad movement patterns of L. lambis over a 13-mo period in an extremely shallow (depth < 2 m) lagoonal environment of the Cocos (Keeling) Islands (CKI). The mean kernel utilization density home range for L. lambis during the study period was estimated at 18,059 ± 3,298 m² (n = 14). The mean home range was also estimated monthly and was found to be significantly larger in January (austral summer) than in the preceding October and November, likely a function of the reproductive cycle of L. lambis at CKI. Estimated home range size and animal size were not found to be correlated, and there were no observed differences between the sexes. The results show that, in an environment of preferable habitat with adequate resources, L. lambis have a home range that is relatively small when compared with studies of the Caribbean queen conch Lobatus gigas. The information on the spatial requirement and movement ecology for L. lambis at CKI from this study will assist with informing management techniques, not only for this fishery but also for other small conch fisheries worldwide.

Marine gastropods in Florida are harvested by the marine-life trade, tourists (for shells), and traditional commercial fisheries, but stocks are not formally assessed for most species. The main goal of this project was to estimate biological variables that may be used to evaluate the Species of Greatest Conservation Need status of the banded tulip Cinctura lilium and six other large marine gastropod species that are commonly encountered in the targeted habitats. The principal target, C. lilium, was listed in the 2012 State Wildlife Action Plan. The densities and size structures of C. lilium and six co-occurring species of large marine gastropods in Tampa Bay were examined to evaluate population dynamics, seasonal variation, and habitat preferences of these species. Long-term trends in the densities of large, predatory marine gastropods in 10 regions from 2009 to 2017 were included. In Tampa Bay, strong habitat preferences were observed for all species studied: C. lilium and Melongena corona were most likely to be observed on oyster reefs, and Fasciolaria tulipa was found only in seagrass, whereas Strombus alatus, Triplofusus gigantea, Sinistrofulgur sinistrum, and Fulguropsis spirata were more common on soft sediments. Seasonal variations in densities were weak; seasonal differences in size structure were more pronounced. The smallest individuals of C. lilium appeared in spring and summer; F. spirata, S. alatus, and S. sinistrum reached a detectable size in fall. The smallest detectable M. corona appeared in winter. Regionally, there were more gastropods in southwestern bay grass beds (Tampa Bay, Sarasota Bay, and Pine Island Sound) than in coastal seagrass beds (Big Bend, Citrus, Hernando, Pasco, and coastal Pinellas) or northern bays (St. Joseph Bay and St. Andrew Bay), and each region had characteristic species. As a group, tulip snails exhibited modest local declines in densities at two sites, whereas the whelks and T. gigantea varied annually but did not exhibit consistent trends during 2009 to 2017. The present study establishes a baseline of abundance for seven species of common marine gastropods and recommends expanded monitoring in multiple habitats to improve future analyses of abundance trends.

Revealing cryptic biodiversity and understanding their evolutionary histories is important to predict how climate change promoted diversification. The marine gastropod Reticunassa festiva is a common species distributed along the coast of China Seas and possesses cryptic diversity. In the present study, the phylogeographic pattern of R. festiva is investigated to test the potential mechanism that drove its diversification in China coastal regions using the mitochondrial cytochrome oxidase subunit I (COI) and nuclear 28S rDNA sequences. Three highly divergent COI clades (Clades A, B, and C) with considerable differences in genetic distances, haplotype diversity, and nucleotide diversity among each other were identified. The estimated divergence time between the two dominant clades (Clades A and B) was 2.0711 Ma, corresponding to the third major cool period in the Pleistocene. The sea surface temperature fluctuation in the subtropical ancient East China Sea could be the major drivers for the diversification of the two R. festiva clades. It is also suggested that the distribution pattern of Clades A and B is shaped by two major ocean currents. This study provides evidence for the correlation between species diversification and climate change in the NW Pacific during the Pleistocene.

Basic information on shell dimensions, calcimass and periostracum mass, biomass, and the relation between the condition and reproduction of Mytilopsis leucophaeata was analyzed for a population in the North Sea Canal, the Netherlands. The mean dry flesh weight of individuals with a mean shell length of 12.5 mm showed a peak at the end of June. The mussel reached the highest mean dry flesh weight in the month before the spatfall started. The gonad index (GI) was high in June, followed by a period of decrease until September and a period of increase until November. The condition index (CI) peaked in June and decreased during the remainder part of the year. The range of CI was highest in May when the gonadal development progressed and was smallest in June when the gonadal development was complete. The CI decreased during the rest of the year. Quantile regressions showed a highly significant relation between CI and shell length. Based on the regression coefficients, the CI was maximal at a shell length of 11.4 mm and minimal at 12.5 mm. Condition index variation was highest within a shell length range of 10–15 mm.

Reproductive aspects of the golden clam Megapitaria aurantiaca in Puerto Libertad, Sonora, Mexico, were analyzed from March 2015 to March 2016. Through histological analysis, five phases of gonadal development were defined (cytolytic, preactive, active, emission, and postactive), the sexual portion was obtained, the relationship between environmental variables (temperature and chlorophyll a) and reproduction was determined through the gonadal index, and the diameter of the oocytes was measured. A seasonal reproductive cycle was exhibited by M. aurantiaca with a spawning phase from April to October which coincided with an increase in the temperature. Spawning clams were observed at a shell length of 69 mm. A sex ratio of 1:1 was recorded. Finally, for the first time, the presence of hermaphroditic organisms was reported for this species.

Physiological and environmental conditions affect carbohydrate, specifically glucose levels in the crustacean hemolymph. Trehalose, naturally occurring nonreducing disaccharide (a1–1a of two glucose), shows a protective role in the organisms experiencing stressful conditions such as cold, salinity, and anhydrobiosis. As the predominant sugar in the blue crab hemolymph Callinectes sapidus, the trehalose synthesis gene (trehalose-6-phosphate synthase, TPS) is expressed in most internal tissues, including the hepatopancreas. The present study shows the function of TPS in carbohydrate metabolism in decapod crustaceans. The blue crabs show ontogeny variations in carbohydrate metabolism, especially hemolymph glucose and trehalose. Trehalose increases with the animals becoming large, whereas glucose is higher in adult animals than juveniles. Food intake elevates glucose and trehalose both in the hemolymph and hepatopancreas. The significance of hepatopancreas TPS is defined using a double-strand RNA of TPS injection study of the animals after feeding and emersion. The dsRNA-TPS injection results in 60%–70% of reduced TPS transcripts and its enzyme activity in the hepatopancreas. In the animals that received dsRNA-TPS, feeding has significantly reduced levels of changes in glucose and trehalose in the hemolymph and hepatopancreas, compared with the control animals (saline and double-stranded green fluorescent protein injection groups). In response to emersion, the animals injected with dsRNA-TPS show the glucose increases in the hemolymph the same as in controls but with trehalose and lactate significantly lower than the controls. The hepatopancreas of dsRNA-TPS–injected animals contains significantly reduced trehalose and glycogen, compared with control animals. Carbohydrate metabolism in crustaceans appears to be rather complicated with trehalose and glycogen; both can serve the glucose source for hyperglycemia and need further investigations.

Long Island Sound (LIS) is near the northern limit for the range of year-round populations of the blue crab Callinectes sapidus (Rathbun, 1896). This study sampled blue crabs for 7 y with a trawl in LIS and with traps in the estuarine portion of three rivers in eastern Connecticut. Year-to-year abundance of blue crabs was highly variable. A strong correlation was found between the abundance in the summer and the water temperatures in the prior winter, suggesting that these large interannual fluctuations are caused by varying overwinter survival rates. Winter mortality due to low water temperatures may be the controlling factor in determining the northern range limit for resident populations of blue crabs and for their abundance in northern waters, such as LIS. Long-term trawl surveys in LIS show a shift in abundance from cold-temperate to warm-temperate species, which correlates with rising water temperatures. Longer term studies are required to determine whether the blue crab population in LIS is increasing as a result of global warming. Previous studies have not investigated the blue crab life cycle north of New Jersey, including LIS. This study found that all stages of their life cycle occur in LIS. Male and immature female blue crabs were found primarily in the upper, less saline sections of LIS subestuaries. Mature and egg-bearing females occurred primarily in the deeper, higher salinity waters of LIS. These results are consistent with the blue crab life cycle as described in locations south of LIS, such as Chesapeake Bay.

Of the total economic impact generated by the marine recreational fishing industry in the United States, the state with the largest contribution is Florida. Bait purchases can be a large portion of marine recreational angler expenditures. Despite this well-established industry, development of marine bait shrimp aquaculture to supply this significant market has been slow. Descriptive market information necessary to shape production and marketing strategies is lacking. The objectives of this project were to evaluate and describe the market for live marine bait shrimp in Florida and to assess the potential market for cultured bait shrimp. A survey instrument was designed and distributed to 224 bait shrimp retailers in 35 coastal counties of Florida. Surveys were developed to be concise and succinct, while still soliciting salient information vital to market evaluation. Bait shrimp retailer survey questions focused on business location, shortcomings of wild shrimp, preferred bait shrimp characteristics, quantities of bait shrimp sold, bait shrimp wholesale purchase prices, purchasing patterns as related to season and size, perceived bait shrimp market demand by region, perception of aquaculture, and interest in purchasing aquaculture-produced bait shrimp. A total of 98 surveys representing 31 counties were returned for a 43.8% response rate. Almost all respondents (95.9%) marketed live marine bait shrimp. The overall perception of aquaculture as a means to produce bait shrimp was 24.7% positive, 19.4% somewhat positive, 40.8% unknown, 9.7% somewhat negative, and 5.7% negative. Analysis of demand data by season for live marine bait shrimp suggests seasonal shortages exist for various size classes, with 50.6% of respondents saying they could sell more if supplied. These supply shortages could provide market share to aquaculture producers to supply retailers and possibly develop favorable pricing strategies during shortages. Compared with previous surveys conducted in Florida, the wholesale market price of live bait shrimp about tripled from 1997 to 2014. These survey results provide critical information to potential shrimp aquaculture producers seeking to enter the live marine bait shrimp market in Florida.

Emerging sea cucumber (Cucumaria frondosa) fisheries have recently developed off the coast of Atlantic Canada. The reproductive cycle, developmental stages, and feeding biology of this species have been described, but fishery-related metrics remain largely unknown. Measuring lengths and weights of individuals in fished populations is fundamental for stock assessment and management. These measurements are used to identify trends in individual size related to fishing pressure on the population over time. Length and weight measurements are recorded for commercially caught C. frondosa, but plasticity of their body makes precise measures difficult, resulting in varying techniques that lack consistency. Several methods of measuring and estimating size and weight of C. frondosa were tested for accuracy in a laboratory setting. Indices that accounted for the size of individuals on multiple planes proved more useful for estimating wet weight than length or width alone. Accurate wet weight estimates were possible from drop-camera images taken of individuals in situ using size indices that combined length and width, as well as area covered. Timing of measurements was a key variable. The time out of water significantly changed the wet weight measurements, with an average weight change of 31.93% (SD ± 14.92) over a 1-h period, but after the first 10 min, measures were consistent, suggesting animals expelled most of their fluid shortly after removal from the water. Although there are many sources of potential error when measuring C. frondosa, consistent timing and size metrics that incorporate overall size, as opposed to a single dimension, show promise for evaluating changes in individual size over time. Standardized methods will enable the collection of data that can be used in stock assessment to determine reference points and vital statistics for this developing fishery.

Neurotoxic shellfish poisoning caused by the ingestion of shellfish contaminated with brevetoxins threatens human health and economies reliant on the Gulf of Mexico. In the United States, the only federally approved method to test shellfish for brevetoxins is a mouse bioassay. Although effective in protecting public health, this assay has considerable shortcomings, including low throughput, lack of sensitivity and specificity, and reliance on live animal testing. Here, a commercially available enzyme-linked immunosorbent assay (ELISA) (MARBIONC) was validated, and results of field samples tested using ELISA and the mouse bioassay were compared. In this validation of the ELISA method for eastern oysters Crassostrea virginica and clams (Mercenaria spp. and sunray venus Macrocallista nimbosa), ELISA demonstrated strong recoveries, specificity, and ruggedness. Quantitative results were obtained for more than 90% of the 526 field samples tested by ELISA compared with only 26% of the samples tested by mouse bioassay. When quantitative data were available for both assays, significant correlations across methods were found. Based on this work, in 2017, the Interstate Shellfish Sanitation Conference approved the limited use of the MARBIONC ELISA in neurotoxic shellfish poisoning management.