AbstractMetamorphosis appears to be a particularly sensitive stage in marine invertebrate development, with potential carryover effects of larval experience on the postlarval stage. We investigated the impact of salinity exposure history (22‰-34‰) for 2-4 days on the ability of competent crown-of-thorns sea star ( sp.; CoTS) brachiolaria larvae to form a normal five-armed juvenile. The decreased salinity levels used were commensurate with levels that these larvae may encounter in their habitat on the Great Barrier Reef (25‰-34‰), and the extreme low level (22‰) was used to assess salinity tolerance. At metamorphosis, low-salinity stress (<34‰) for a few days prior to settlement-as may be experienced by larvae during a runoff pulse-resulted in negative carryover effects, even when the larvae were placed in control salinity during settlement assays. A larval experience of ≤30‰ resulted in smaller juveniles. The low-salinity treatment (22‰) resulted in a large proportion of juveniles deviating from the normal five-armed profile of newly metamorphosed CoTS. Juvenile mortality was high if they were generated from larvae exposed to 22‰ and 25‰ salinity levels. Our findings highlight the importance of ecological developmental biology in understanding potential carryover effects beyond metamorphosis. These insights could help link the exposure of CoTS larvae to terrestrial runoff conditions with juvenile performance and the postmetamorphic processes that influence recruitment into the adult population.

AbstractPycnogonids (sea spiders) are benthic invertebrates exhibiting unique reproductive strategies including paternal brood care by the male in many species. To date, the mating systems of brooding Antarctic sea spiders have yet to be investigated molecular methods, despite their dominance and importance in the Southern Ocean. To better understand how sea spiders reproduce and maintain their natural populations in this region, we employed 3RAD-derived single nucleotide polymorphisms to investigate genetic mating systems of the abundant, and putatively circumpolar, Antarctic sea spider . By analyzing single nucleotide polymorphisms in genomes of individual larvae taken from offspring-carrying males, we inferred paternal full- and half-sibships and parentage for specimens of collected from the eastern Antarctic continental shelf. Notably, exhibits a polygynandrous mating system where both males and females engage in multiple mating events. Male brood partitioning on their ovigerous legs varied, with some males partitioning offspring into clutches by female genotypes and others carrying progeny from multiple female genotypes in a single clutch. However, we found no evidence of cuckoldry, where males inadvertently raise offspring sired by other males, indicating that this species has a high assurance of paternity for the progeny carried by each individual male. These findings provide foundational insights into the genetic mating system of Antarctic sea spiders and contrast with the cuckoldry frequently observed in other male brood care systems. This contrast highlights some of the evolutionary pressures acting on reproductive strategies in polar environments.

AbstractMany organisms may rely on microbes that seed the host body and are typically maintained as a consortial symbiosis. Marine invertebrates have highly diverse microbiomes and offer many different life history traits across which to explore the members and functions of these symbionts but are largely absent from the holobiont and microbiome literature compared to humans and vertebrates. We tracked the microbiome of larvae and examined the role of vertical transmission gametes and the role of horizontal transmission diet and seawater for seeding the developing larvae with microbes potentially critical to holobiont health and fitness. We used short-read sequencing to track the composition and relative abundances of bacteria associated with diet (microalgae) and with habitat (filtered seawater), as well as with gametes and larvae under standard lab rearing conditions. The larval microbiome differed across developmental stages and between filtered seawater and algae, and specific bacterial taxa were associated with those differences. In this experiment, developing larvae selected and maintained a unique microbiome compared to their diet and habitat. Eggs were a potentially significant source of vertical transmission during embryonic development (genus ), while horizontal transmission filtered seawater was the main contributor to larval feeding stages, suggesting that filtered seawater is likely the most important source of potential symbionts. Gaining new insights into how marine invertebrate larval microbiomes are seeded and with what taxa is important for endangered-species aquaculture and for ecosystem restoration and management to protect inoculation sources for early-life stage organisms.

AbstractHorseshoe crabs (, , , and ) are experiencing population decline. A systematic review of 326 papers was conducted to assess the state of conservation of these species and provide recommendations for horseshoe crab conservation in Long Island Sound, USA. Major present-day threats to horseshoe crabs include overharvest and bycatch, habitat loss and degradation, climate change, and insufficient management. The declining populations of horseshoe crabs impact shorebirds and marine organisms, contributing to the threats facing endangered species. Protecting and restoring spawning areas and juvenile habitat, adopting alternative sources for use in the fishing and the biomedical industry, exploring captive breeding and head-starting programs, and public education present promising conservation strategies. Urgent action will be necessary to conserve horseshoe crabs and their vital ecological role in Long Island Sound.

AbstractFecundity and egg size vary among females, depending on environmental conditions experienced by mothers, known as maternal effects. Temperature, salinity, food availability, competition, and predation can influence maternal allocation. We evaluated temporal changes in the reproductive biology of the pea crab in the context of local spatial competition with the yellow clam mediated by the ghost shrimp . We assessed physical environmental variables and compared size-dependent reproductive parameters-fecundity and egg volume-between two contrasting periods at Monte Hermoso Beach (38°59' S, 61°19' W): clam-period, characterized by the dominance of in the macrobenthic community, and crab-period, marked by the dominance of . Additionally, we calculated reproductive output for crab-period and examined the relationship between brood and female size. Fecundity did not differ between periods, whereas egg volume was greater during clam-period across all female sizes. Since no differences were found in physical environmental variables, larger egg volume was interpreted as increased allocation per offspring, suggesting adaptive allocation to counteract the negative effects of density-dependent exclusion of pea crabs, leading to offspring with greater dispersal potential and/or better ability to survive and perform under adverse conditions. Larger eggs without fecundity cost indicate greater reproductive allocation during clam-period, possibly reducing investment in other life history traits. While no correlation was found between brood and female weight, an isometric relationship was observed between brood weight and female size. Future studies should focus on how maternal effects influence the population dynamics of the species.

AbstractThe chiton is a common species in the intertidal shores of the southwestern Atlantic Ocean. This study investigates the age, individual growth, and mortality of on an intertidal boulder shore in San Antonio Bay (40°45' S, 064°56' W), Patagonia, Argentina. Growth rings on the valves were validated as annual, forming during the warm season, a pattern unusual among chitons. The age structure showed a stable population, with most individuals between 2 and 7 years and a maximum observed longevity of 11 years. The growth pattern, analyzed through both polynomial models and the von Bertalanffy growth model, indicated rapid growth during early years, followed by slower growth in later stages. Mortality was best described by the Siler mortality model, indicating variable mortality rates across the lifespan, with higher risks during early and late life stages. These findings provide insights into the life history of , emphasizing the influence of environmental factors on growth and mortality in this species.

AbstractIn ponds of the northeastern United States, benthic macroinvertebrates can dominate the local biomass. Isopods, predatory leeches, and fingernail clams can attain dense populations and suffer heavy predation pressure by fish. We predicted that pond benthic macroinvertebrates would recognize the proximity of predatory fish and avoid or vacate that area as an inducible behavioral defense. We deployed cages with and without predatory fish (sunfish and golden shiners) in a naturally fishless pond in October and November of 2020 and 2021. After at least 2 days, we collected leaf packs from directly under the cages and compared the number of invertebrates residing within. Surprisingly, the population densities of the dominant taxa (isopods, leeches, and clams) suggested that they did not avoid fish. Leeches and isopods may even reside in higher numbers near live sunfish, perhaps because feces from the fish augment the locally available food and nutrient levels. Our present field results support earlier laboratory findings: benthic macroinvertebrates in ponds may not respond to fish cues. Bottom-up control may dominate in ponds, providing important implications for conservation of these threatened ecosystems.

AbstractDecapod crustaceans with wide distributions have shown different patterns of population structure in certain species, which clarified processes related to population dynamics and intraspecific variation. The aim of the current study is to assess phylogeographic patterns of the intertidal crab H. Milne Edwards, 1837, as well as its wide distribution in the western Atlantic Ocean, from the US to Brazil. We hypothesize that the genetic structure of is influenced by the interaction of different geographic barriers. We analyzed partial sequences of the mitochondrial gene cytochrome oxidase subunit I deriving from specimens collected along the western Atlantic distribution of . The phylogenetic reconstruction, haplotype networks, demographic history, divergence time, and discrete phylogeography of do not confirm our hypothesis. The wide distribution can be explained by the potential of larvae to disperse through northern Brazilian and Brazilian currents, which helps maintain gene flow across natural barriers. In addition, population size has increased in the Atlantic Ocean over the past 0.01-0.10 million years, with emphasis on two large separate groups and on the north-to-south spatiotemporal diffusion of its populations. While there is some evidence of genetic differentiation between the tropical northwestern Atlantic and the tropical/warm-temperate southwestern Atlantic regions, the overall genetic structure is low. The Amazon-Orinoco Plume appears to have limited influence as a barrier, further emphasizing the species' capacity for larval dispersal and genetic homogenization across its range. These findings highlight the importance of oceanographic features in shaping genetic patterns of widely distributed marine organisms and underscore the value of C. integer as a model for studying genetic connectivity in marine ecosystems.

AbstractThe Atlantic white shrimp, , is a commercially important species that is abundant along the United States' east coast and Gulf of Mexico. Like other similar organisms, this species is vulnerable to black gill disease, where gills become heavily melanized as part of an immune response associated with gill irritants or parasitic infection. The melanization blackens the gills, making the disease obvious. Black gill is thought to be stimulated by high temperature, high salinity, and low oxygen. In this study, we investigated whether the presence of black gill influences the ability of shrimp to take up oxygen across the gills. Shrimp were made to exercise on an underwater treadmill while measurements of oxygen uptake were made. Measurements were made in well-oxygenated water (100% air saturation) and moderate (50% air saturation) and severe (30% air saturation) hypoxia. In quiescent animals, there was no difference in oxygen uptake between control shrimp with no black gill and those with obvious black gill infections. Oxygen uptake increased by as much as twofold when shrimp were active on the treadmill. In both control and black gill groups, oxygen uptake declined in hypoxia, but the decline was greater in black gill shrimp, suggesting an impairment to taking up oxygen. Thus, black gill significantly impairs the ability of shrimp to take up oxygen under hypoxic conditions when shrimp are active. These results provide a mechanistic basis for potential negative impacts of shrimp populations suffering with outbreaks of black gill.

AbstractMany marine invertebrates possess biphasic life histories, during which larvae develop in the plankton and adults inhabit the benthos. The transition between phases entails the settlement of larvae onto substrata, completion of metamorphosis, and survival as vulnerable early juveniles. The perimetamorphic period, encompassing settlement and the interval immediately following settlement, is a key determinant of adult abundance and distribution. However, because settling larvae and early juveniles are difficult to observe in the field, the ecology of this period remains poorly understood. We performed experiments to elucidate the settlement preferences of and , keystone predators on the east coast of North America, on substrata common to their intertidal habitats. Larval exhibit clear selectivity in settlement, with shells of the blue mussel, , most preferred. The algae and crustose coralline algae also induced high rates of settlement, while little settlement was observed on rocks with biofilm and no settlement occurred in controls. When inductive cues were subsequently added to controls, high frequencies of settlement occurred immediately, confirming the competency of larvae to settle and their ability to delay metamorphosis in the absence of appropriate cues. Our results demonstrate that larvae have specific settlement preferences and that settlement can be postponed in this species if no suitable substrate is available.

AbstractRibbed mussels are typically found in salt marshes and can form dense aggregations along low marsh shorelines and tidal creeks. The presence of ribbed mussels within marshes is well documented, and many studies have examined their importance in these ecosystems. However, it is not known whether mussels settle preferentially in habitat and what factors influence observed aggregations of mussels. Knowing this is important for current efforts in salt marsh restoration. Therefore, we conducted experiments with competent larvae to test whether chemical or physical cues of or adult conspecifics stimulate settlement and metamorphosis. More larvae settled and metamorphosed in the presence of a leaf, although not on the leaf, and in water conditioned with than in seawater controls. The presence of chemical or physical cues from conspecifics had no effect on settlement and metamorphosis relative to controls. Larvae settle and metamorphose in response to chemical cues from , resulting in ribbed mussels being found predominantly in habitat. However, because there was no response to conspecifics, other factors are likely responsible for their aggregated distribution. Further work is required to determine the factors resulting in mussel aggregation, including movement of juvenile mussels and environmental filtering.

AbstractHatschek published the first comprehensive description of amphioxus development in the late nineteenth century. For him, a key event in early embryology was the evagination of the anterior end of the pharynx to form a right diverticulum and a left diverticulum-precursors, respectively, of the rostral coelom and preoral organ. Here we reexamine Hatschek's proposed diverticula with serial block-face scanning electron microscopy, a technique for generating fine-structural models of tissues in three dimensions. We find that no such diverticula ever form in the embryo. Instead, the anterior tip of the gut transforms into a mass of irregularly organized cells, the source of the peritoneal lining of the rostral coelom. Moreover, a cluster of cells associated with the first left segment is the likely source of the preoral organ. The discussion considers how the absence of Hatschek's gut diverticula impacts previously suggested homologies relating deuterostome head cavities.

AbstractCold acclimation is a biological process that allows animals to survive at low temperatures. The freshwater invertebrate is subject to broad changes in environmental temperature and does not have the required motility in order to move to warmer environments during the winter. For this reason, had to develop robust mechanisms to achieve cold acclimation at the onset of winter. How detects the onset of winter and activates its acclimation mechanism is unknown. Here, we used thermocyclers to induce cold acclimation in and study its properties. We found that cultured at room temperature does not survive an abrupt transition from 22 to 4 °C. However, it can be treated to become cold acclimated and survive at 4 °C by exposure to intermediate temperatures such as 12 °C if the treatment duration exceeds more than a week. Once cold acclimated, is considerably more robust to thermal changes. It survives repeated abrupt transitions from 4 to 22 °C and from 22 to 4 °C. However, acclimation is reversible, and if a cold-acclimated stays at room temperature for more than a week, it will gradually lose its cold acclimation. We developed a mathematical model representing the dynamics of this process and used it to predict survival according to temperature data recorded in one of their natural habitats. The results of these simulations provide an explanation for how survives winter under natural conditions. Accordingly, daily fluctuations are too short to cause injury, and seasonal fluctuations, which are long enough to be lethal, allow acclimation to incrementally build up and protect the animal. Cold acclimation in is therefore an example of a strategy that has adapted during evolution to match the animal's needs for survival.

AbstractBleeding of horseshoe crabs () for the biomedical industry can have both sublethal and lethal impacts. Bleeding induces a significant drop in the concentration of hemolymph hemocyanin, as well as decreased levels of activity. Furthermore, horseshoe crabs with low hemocyanin prior to being bled have been found to be more likely to die after the procedure. The goal of this project was to determine whether feeding horseshoe crabs after bleeding them could enhance the recovery of their hemocyanin levels and, in doing so, improve their physiological status. The feeds tested in separate experiments included (1) natural forage items, blue mussels () or softshell clams (); (2) a formulated diet containing green crabs () and hemolymph; and (3) a modified commercially available shrimp () broodstock aquafeed. Horseshoe crabs ( = 63) were bled and then either fed or not fed, and their hemolymph hemocyanin concentrations were measured before they were bled and for the following 6-14 days. An additional 25 horseshoe crabs were treated in the same manner but not bled. In three experiments, horseshoe crabs that were fed consistently showed significantly higher hemolymph hemocyanin concentrations compared to those that were not fed. These data suggest that relatively simple modifications of the industrial bleeding procedure, such as feeding horseshoe crabs after bleeding them, may improve their physiological status prior to release.

AbstractIndividuals with similar biological requirements frequently compete for resources. Males and females have evolved different reproductive strategies in which females invest more in fecundity and males in intrasexual competition for mates. Although less common than within-sex competition, intersexual contests may occur to obtain resources. Interindividual differences in fighting ability bias the benefits and costs between opponents, and those differences are expected to be greater in intersexual contests. We compared the chela size, muscular strength, metabolic rate, and relative boldness of males and females of Bouvier, 1898. We further investigated how these traits influence intra- and intersexual contests for shells, with both sexes assuming roles as attackers and defenders. Males and females do not differ in chela size, muscular strength, or boldness. While males exhibited higher metabolic rates, this did not explain contest initiation or outcomes. Surprisingly, females initiated fewer contests against males than against females, and those that did often lost. However, this outcome was not attributed to sexually dimorphic traits. Instead, fighting success correlated with individual boldness and rapping frequency. Interestingly, rapping performance did not correlate with boldness, metabolic rate, or muscular strength, contrary to expectations. Our result reaffirms the common disadvantage of females as attackers in intersexual contests. However, they proved adept at defending their shells in both intra- and intersexual scenarios. This result, in addition to their typically efficient exploratory ability, raises questions about resource acquisition and distribution pathways in each sex.

AbstractThe distance that offspring disperse from their parents affects how a species responds to habitat disturbance, climate change, and interspecific interactions. For many benthic species, this dispersal is planktonic larvae, but the distance these larvae disperse is difficult to observe directly. Dispersal distance has usually been estimated indirectly by combining an observed quantity (, the rate of spread of an invasive organism or genetic similarity between locations) with a model that links that quantity to the dispersal of larvae. The estimates of dispersal distance based on the speed of spread of invasive organisms have led many researchers to conclude that the larvae of most of these organisms disperse much less than would be expected if they were being passively transported by the expected ocean currents (Shanks ; Shanks). I argue that the discrepancy is instead caused by the choice of model linking dispersal distance to invasion speed. Their model neglected the impact of life history, population growth, and oceanographic parameters on invasion speed. When dispersal distance is estimated from a more complete model of invasion speed, it is found that larval dispersal distance is not much less than would be expected for larvae drifting in the observed ocean currents.

AbstractSexual dimorphism typically arises as a result of sexual selection or sex-specific natural selection. Species that exhibit cryptic coloration provide an excellent system for studying sex-specific selection for sexual dichromatism. In this study, we examined the sexually dichromatic use of chromatophores in the seawhip shrimp, (Borradaile, 1920), which commonly resides on colonies of (Lamarck, 1815), a gorgonian octocoral that occurs in multiple color morphs. We documented the frequency of cryptic coloration in and tested colony color preference in relation to their current color. In the field, individuals always matched the color of the colony they were found on or were largely translucent. However, when given a choice, individuals chose colonies at random, independent of color. Additionally, we quantified locations across the bodies of males and females that differ most in chromatophore usage and tested the ability of both sexes to change color over 7 days. Females housed with colonies that differed in color from their starting color changed their coloration over the 7 days to better match the colony, while males remained translucent regardless of the color of colony they were housed with. individuals differed most in their coloration in regions corresponding to the saddle region and areas of the abdomen, locations in which females carry their eggs during development. These findings provide insight into the ecological factors underlying sexual dichromatism and shed light on the potential sex-specific selective mechanisms responsible for sexually dimorphic traits.

AbstractThe order Fecampiida, a group of parasitic turbellarians, has been poorly studied in terms of its species diversity, morphology, and ecology. Fecampiida is positioned within the monophyletic clade Adiaphanida, along with Tricladida and Prolecithophora, but their phylogenetic relationships are not well understood. Although the nervous and muscular systems of only two species in Fecampiida have been studied, recent research inferred morphological similarities between Fecampiida and Prolecithophora. In this study, we collected fecampiid cocoons and juveniles at depths of 1861-4438 m in Japanese waters. We identified the species on the basis of swimming juvenile specimens and by using histological and molecular methods, while we also examined its musculature and nervous system. Our study revealed a more complex nervous system than previously reported, with dorsal, lateral, and ventral pairs of longitudinal nerve cords connected through an anterior neuropile and posterior transverse commissures. While the nervous and muscular morphology suggested similarities with Prolecithophora, our phylogenetic analysis did not support a close relationship between Fecampiida and Prolecithophora.

AbstractThe Pacific razor clam, (Sugpiaq: Cingtaataq, Dixon, 1789), is vital to commercial, recreational, and subsistence fisheries across the Pacific Northwest Coast of North America. Despite the species' status as one of the most popular shellfish species harvested in the Pacific Northwest, British Columbia, and Alaska, its larval development has never been fully characterized. Generating a developmental times series, and describing development fully, is crucial for guiding targeted management, developing a mariculture strategy for the species, and providing a more pointed avenue for studies examining the response of to ocean change. This study presents the first photographic documentation of larval development in , including the timing of key transitions during embryogenesis and early larval development. Scanning electron microscopy revealed that the larval shell forms a concretion, a process typically documented in early gastropod development. This novel characterization is pertinent, as it conveys the need for the inclusion of alternative bivalve development processes, such as a concretion, in bivalve research. This study also compared development in to a global assortment of bivalve species, including two other members of the Pharidae family, determining that the timing to D-veliger and trochophore stages was similar to the majority of bivalves surveyed. While bivalve response to climate change is a topic of great interest, not all species of concern have undergone comprehensive developmental assessments, a requisite benchmark for designing climate change studies that examine early life history sensitivity to such changes. This research supports the use of comprehensive developmental studies as prerequisites for designing climate change experimentation, establishes the necessity of high-magnification and high-resolution scanning electron microscopy within developmental assessments, and provides information about the development of a cornerstone bivalve species.

AbstractThe insulin-like androgenic gland hormone is a crucial sexual regulator that is involved in the masculine sexual differentiation of crustaceans. As an insulin-like peptide, the insulin-like androgenic gland hormone has been proposed to act through the insulin receptor-mediated pathway. The present study cloned and characterized two insulin receptors ( and ) from the swimming crab hallmarked with a conserved intracellular tyrosine kinase catalytic domain and several other typical insulin receptor domains in their deduced amino acid sequences. Both insulin receptors were predominately expressed in the testis and the insulin-like androgenic gland hormone-producing organ androgenic gland. Their testicular expression during the annual cycle suggested that they may play critical roles in spermatogenesis. By using the protein colocalization analysis in HEK293 cells, interactions of PtIAG with the two PtIRs were further confirmed. In addition, the insulin receptor antagonist was found to attenuate the stimulatory effects of androgenic gland homogenate on the phosphorylated MAPK levels in testis explants, suggesting that the insulin receptor-dependent MAPK pathway may be essential for insulin-like androgenic gland hormone functions.

AbstractGulf of Maine waters are warming rapidly, prompting a reevaluation of how commercially important marine species will respond. The goal of this study was to determine the respiratory, cardiac, and locomotory responses of American lobsters () to increasing water temperatures and to compare these to similar published studies. First, we measured the heart rate and ventilation rate of 10 lobsters that were confined in a temperature-controlled chamber while exposing them to gradually warming temperatures from 16 to 30 °C over 7 h. Both heart rate and ventilation rate increased along with the temperature up to a break point, with the mean heart rate peaking at 26.5 ± 1.6 °C, while the ventilation rate peaked at 27.4 ± 0.8 °C. In a subset of these trials ( = 5), oxygen consumption was also monitored and peaked at similar temperatures. In a second experiment, both the heart rate and activity of five lobsters were monitored with custom-built dataloggers while they moved freely in a large tank, while the temperature was increased from 18 to 29 °C over 24 h. The heart rate of these lobsters also increased with temperature, but their initial heart rates were lower than we recorded from confined lobsters. Finally, we confirmed that the low heart rates of the freely moving lobsters were due to the methods used by comparing heart rate data from eight lobsters collected using both methods with each individual animal. Thus, while our overall results are consistent with data from previous studies, they also show that the methods used in studies of physiological and behavioral responses to warming temperatures can impact the results obtained.