Area closures allow fish and shellfish populations and associated habitats to recover from the effects of fishing. Determining the appropriate duration of rotational management closures for the Atlantic sea scallop (Placopecten magellanicus) fishery requires information on both the recovery of scallop populations for subsequent harvest and the resiliency of marine benthic ecosystems for conservation objectives. Here, the effects of scallop fishing on the benthic communities of the northern edge of Georges Bank were examined with a control-impact environmental study comparing an area that had been closed to fishing for over 20 y to an area continually fished. Substrate composition, faunal density, and taxonomic richness data were collected using drop camera surveys. These areas have similar substrate composition, mostly cobble and gravel. Sediment in the control area shifted to larger particle sizes over time, whereas the sediment in the impact area remained the same, suggesting fishing activity prevented this shift in the impact area. Comparing survey stations of like substrate showed that as fishing effort subsided from 2015 to 2017, there was a marked recovery of taxonomic richness and abundance in the impact area. The impact and control areas shifted in a similar manner but varied in the intensity of the shift. This suggests the benthic communities in this area of Georges Bank were relatively resilient to the effects of fishing effort with mean densities of all categories recovering within 2 years.

Bay scallops (Argopecten irradians concentricus Say, 1822) exhibit a strong association with seagrass habitat from the time of larval settlement, but alternative habitats, such as macroalgae species, may also serve as important habitats for this species. The association of Florida bay scallops with the percent cover of observed seagrass, macroalgal species, and several substrate types (e.g., mud, shell, and rocks) was examined to determine whether a variety of seagrass and macroalgal species significantly influences the abundance of bay scallops in Florida. Sampling occurred at eight study sites along the Gulf coast of Florida, from Tampa Bay in the south to St. Andrew Bay in the north. SCUBA divers used a point-intercept approach along a transect to assess habitat type and percent cover, in addition to recording bay scallop abundance. Generalized additive models for location, scale, and shape were used to model bay scallop abundance as a function of habitat type. Across all sites, bay scallop abundance was positively correlated with percent cover of seagrass and negatively correlated with bare substrate, such as mud and sand. Five out of the 13 habitat types observed in association with bay scallops in this study were significant factors in models of bay scallop abundance including Acetabularia spp. (J.V. Lamouroux, 1812), Caulerpa spp. (J.V. Lamouroux, 1809), Gracilaria spp. (Greville, 1830), Syringodium filiforme (Kütz, 1860), and Thalassia testudinum (Koenig, 1805). The two most important habitat variables were T. testudinum and Gracilaria spp., and there was an observed threshold response of bay scallop abundance to these habitat variables at low to medium percent cover. This is the first study to identify the importance of both seagrass and several macroalgal species for Florida bay scallops and suggests that bay scallop restoration efforts may benefit from restoring seagrass and macroalgae.

The Atlantic surfclam (Spisula solidissima) is an important commercial fishery resource on the U.S. MidAtlantic continental shelf. Although the 2016 stock assessment found that surfclams are neither overfished nor is overfishing occurring, uncertainty in the scale of spawning stock biomass persists. As a consequence of this uncertainty, the MidAtlantic Fishery Management Council (MAFMC) lowered the acceptable biological catch in 2016. A simulation analysis was developed for Atlantic surfclam to estimate the overfishing risk associated with the catch recommendation and its adherence to the MAFMC risk policy. Operating models conditioned on the 2016 stock assessment model structure generated simulations of the surfclam population, with alternative models to represent uncertainty in steepness (h) of the stock-recruitment curve and natural mortality (M). Simulations were forecasted under a variety of management procedures and evaluated with estimation models that spanned uncertainty in h and M. Results showed that current management decisions are more conservative than the stated risk-tolerance policies, though overestimating steepness in assessment models could lead to the misrepresentation of an overfished stock as within management thresholds. Further analysis evaluated future economic viability of the fishery by estimating proportion of fishable clam patches given forecasted biomass and historical observations of clam density. The proportion of fishable patches able to support fishery economic sustainability was generally stable despite biological uncertainties, though declined with increasing fishing pressure. This work contributes to the efforts to evaluate environmentally and economically sustainable fishery management strategies.

The ocean quahog, Arctica islandica (Linnaeus 1767), is a commercially important species along the western Atlantic continental shelf. It is a long-lived species, frequently reaching ages over 200 y. Uniquely, it is one of the few bivalves to display sexual dimorphism, in that females grow to sizes larger than those of males. This phenomenon is believed to occur because males reach sexual maturity before females and, thus, have slower growth rates earlier. The growth rates of A. islandica from four sites across the Mid-Atlantic Bight, Georges Bank, Long Island (LI), and north and south of the Hudson Canyon, were measured to determine patterns in growth between males and females. Females begin to outgrow males between the ages of 5 and 15 y at sizes 50–55 mm, though this varies amongst the sites and between decades. Each of the sites is unique in some way, but three sex-dependent growth dynamics are observed. Most commonly, the two sexes diverge in size with females outpacing males in growth rates after the first 5–15 y of life. This outcome occurs at all sites and is generally the most common outcome across decades. In a few cases, female growth rates outpace the males very early in ontogeny. Such cases occur at two sites north of Hudson Canyon, both on the LI continental shelf. Most rarely, the two sexes maintain similar growth rates. This is observed for a few decades at the most southern site. In the population as a whole, these rare outcomes have limited influence on the population so that female-to-male ratio consistently increases with increasing size. This sexually dimorphic growth is not caused by protandry, nor is it compensation for a differential mortality rate between the sexes. Cases where males grow as fast as females may be just as easily indicative of a constraint on female growth as a facilitation on male growth. Egg sizes in A. islandica are larger than those of most other bivalves with planktotrophic larvae. Accordingly, another viable hypothesis is that differential growth is an adaptation to support the large egg sizes in females, where larger female size is essential to counterweigh the consequent reduced fecundity due to larger egg volume.

The influence of oxygen content in sea water and 14-days starvation on respiration rate (RR) of the bivalve species, blood clam Anadara kagoshimensis (Tokunaga, 1906) has been studied. Clams with shell height 25–30 mm were used for experiments. The RR varied over a wide range, from maximal value 89.9 mgO₂·l^–1 (at 100% saturation) to 5.0 µgO₂·h^–1·gww^–1 (at 76% saturation) at salinity 17–18 and temperature 18°C. The oxygen consumption of the blood clam was substantially lower compared to other benthic bivalves. Results suggest the ability of A. kagoshimensis to transition rapidly from aerobic to anaerobic metabolism under conditions that are not critical for them. Two-week starvation led to an increase in RRs of the blood clam A. kagoshimensis, which indicates an intensification of oxidative processes of organism by 35%–55%. Metabolic processes that require increased oxygen consumption are discussed.

The starvation tolerance of the moonsnail Laguncula pulchella was examined under nonfeeding conditions in the laboratory using individuals at the early stages of development, which comprised subadults (≤19 mm shell width) and newly hatched juveniles (≤1.7 mm). The newly hatched juveniles survived for ≤86 days at 20°C, ≤56 days at 25°C, and ≤22 days at 30°C, whereas subadults survived for ≤323 days at 20°C and ≤181 days at 30°C. These starvation tolerance ranges were relatively greater than those of other gastropods. There was a positive correlation between shell size and the duration of juvenile survival, indicating that the juveniles hatched at larger sizes have more energy stores. The high starvation tolerance of L. pulchella might be contributing to its invasion success in habitats with low prey availability.

The aim of this study was to create an economic decision-making tool to allow farmers and stakeholders to make informed decisions around costs, benefits, and risks involved in production of sandfish, Holothuria scabra, and Babylon snail, Babylonia areolata, in different coculture arrangements based on a sound economic framework. A small-scale (0.16 ha) farm operation in Vietnam was modelled using production data obtained in previous studies to represent the costs and returns of rearing sandfish in tank-based nursery systems and in pond-based coculture grow-out systems. Sandfish and Babylonia monoculture was compared with three coculture models where the two species were separated, and the amount of pond area allocated to each ranged from 25% to 75%. A fourth coculture model (Co-4; “comingled”) was assessed where the two species were not separated and shared 100% of the substrate. The sandfish monoculture system produced 487 kg of sandfish at an annual cost of USD 5,616, providing an annual return of USD –3,521. The largest annual cost associated with sandfish monoculture was labor (USD 8.04 per kg). Pond monoculture of Babylon snail returned USD 1,876 annually, with an annual production cost of USD 19,858. Feeding represented the largest production cost associated with Babylonia monoculture of USD 14,340 per annum, or USD 5.11 per kg. Sandfish monoculture and Babylonia monoculture returned benefit–cost ratios of 0.37 and 1.09, respectively. The coculture model with pond area divided 50:50 between sandfish and Babylonia during grow-out, produced 258 kg of sandfish and 2,584 kg of Babylonia over a 359-day production cycle. This equates to USD 1,108 and USD 20,001 annual production of sandfish and Babylonia, respectively. After production costs, this model provided a return of USD 2,309 annually at a benefit–cost ratio of 1.12. The comingled culture model, Co-4, provided the greatest annual return of USD 6,019 and a benefit–cost ratio of 1.24. Results of this study build on previous research into practical aspects of sandfish/Babylonia coculture and provide a more complete picture of the potential application of this research to improve livelihoods and income of small-scale farmers in Vietnam.

The spider-like strombid Lambis lambis is widely distributed in the Indo-Pacific region and possesses morphological diversity. In the present study, the complete mitochondrial genomes of two morphologically different specimens of L. lambis that were collected in Sanya (SY) and Zhaoshu (ZS) islands of the South China Sea (namely L. lambis-SY and L. lambis-ZS) were sequenced. They were also compared with that of L. lambis previously published and sampled from coastal waters of Quanfu (QF) Island of the South China Sea (namely L. lambis-QF). The newly sequenced mitochondrial genomes L. lambis-SY and L. lambis-ZS contained 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes, and several noncoding regions, indicating a similar pattern with respect to genome size, gene order, and nucleotide composition compared with that of L. lambis-QF. Although L. lambis-SY and L. lambis-ZS differed in shell morphology, the genetic distance between them was small. On the other hand, considerable genetic distance values were detected between L. lambis-QF and L. lambis-SY/L. lambis-ZS, suggesting that the former might be a possible cryptic species within L. lambis. The divergence of the cryptic lineage L. lambis-QF was dated to 4.6 Mya, falling in the lower Pliocene that corresponded to a paleoclimatic transition from cool to warm conditions. This study, therefore, suggests a correlation between paleoclimate change and speciation event.

There is considerable interest in developing hatchery techniques for the tropical spiny lobster, Panulirus ornatus. Although some progress has been made toward identifying effective foods and feeding protocols for this species, the density at which food is first provided to larvae varies greatly in practice. This study examined relationships between food density and the activities of major digestive enzymes in P. ornatus to evaluate larval feeding protocols from a nutrient utilization perspective. Specifically, activities of α-amylase, nonspecific esterase, and trypsin-like protease were quantified to determine the response of newly hatched larvae of P. ornatus to provision of Artemia nauplii at three different densities. Results showed that food density significantly (P < 0.01) influenced α-amylase and nonspecific esterase activities during the first 24 h of feeding, but had minimal effect (P ≥ 0.09) on trypsin-like protease activities. Based on enzyme activities, there is no advantage to increasing food densities above 2.5 Artemia mL^–1, but when food density decreased to 0.5 Artemia mL^–1, the availability of dietary nutrients became limiting. An optimal density at which to provide Artemia nauplii to newly hatched larvae of P. ornatus is likely between 0.5 and 2.5 Artemia mL^–1. The comparative analyses of enzyme activities presented in this study represents an innovative approach to identify potentially excessive or insufficient food densities quickly (within 24 h) for larval crustaceans.

Crustacean female sex hormone (CFSH) plays a pivotal role in developing adult-specific female characteristics, specifically the mating and parental care system of the female blue crab, Callinectes sapidus, manifested after the puberty-terminal molt. Therefore, this study aimed to determine if there is a relationship between CFSH and the development of phenotypes specific to the female C. sapidus during its life cycle and if the continued presence of CFSH is required for developing adult-specific features during the prepuberty molt cycle. First, CasCFSH transcripts in females steadily increase, starting from crab stages 3-4 to prepuberty, except for a decrease at crab stages 15-16. The prepuberty females have the highest CasCFSH transcripts, with ∼5.6-fold higher than adults. CFSH protein levels at prepuberty are the highest but similar to adults. The first and visible secondary female characteristics include a pair of gonopores or a triangular abdomen and four pairs of pleopods seen as early as crab stages at ∼3 (carapace width, CW, 5-7 mm) - 5 (CW 8-10 mm), respectively. The adult-specific female morphological features that are developed gradually throughout the prepuberty molt cycle are manifested only after the puberty-terminal molt. A CasCFSH knockdown study by injecting CasCFSH-dsRNA into prepuberty females at specific molt stages provides further evidence: the continued presence of CasCFSH is required for gradually developing adult-specific morphological features during the prepuberty molt cycle. Overall, the abdomen size is first determined at the intermolt stage. Then, the abdominal shape, gonopores, sternal tubercles, spermathecae, and ovigerous setae and hairs are formed at the intermolt and early premolt stages. Finally, the plumose hairs are developed during intermolt, early, and late premolt stages.

This study evaluated the effects of different sources of dietary carbohydrates on the growth, antioxidant capacity, and digestive enzyme activity, and carbohydrate metabolic enzyme activity of Litopenaeus vannamei were evaluated. The experimental diets, including glucose, sucrose, potato starch, corn starch, and wheat starch, were fed to L. vannamei for 35 days. We found that shrimp fed on corn starch and wheat starch grew better, whereas shrimp fed on wheat starch showed the highest digestive enzyme activity. In addition, the starch group showed higher total superoxide dismutase (T-SOD) activity and lower malondialdehyde (MDA) content. The glucose, sucrose, starch, and corn starch fed shrimp showed significantly higher levels of hepatopancreatic hexokinase (HK), whereas those fed on glucose and potato starch also showed significantly higher levels of hepatopancreatic phosphofructokinase (PFK) activity. The activities of phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase) were higher in shrimp fed on glucose, whereas higher fructose 1,6-bisphosphatase (FBPase) activity was observed in shrimp fed on wheat starch, glucose, and sucrose. The insulin content of shrimp in the glucose group and potato starch group was higher, whereas that of the glucose group was higher than that of the potato starch group. In brief, the addition of wheat starch to the diet plays a positive role in the growth, glycolysis, gluconeogenesis, and antioxidant activity of shrimp, and is a promising choice for juvenile shrimp culture.