Molluscan Larvae Research Articles

Studies on changes in blood glucose in Prometon (weedicide) induced fresh water fish, Mystus bleekeri (day)

Zooplankton, the microscopic and free-swimming animal component of an aquatic ecosystem plays an important role on its energy flow process. From the fishery point of view, zooplankton forms the vital links in the pelagic food chain. Many micro zooplanktons also constitute the major food items of the larvae of crustaceans, molluscs and fishes. Thus, abundance of zooplankton practically acts as an ideal index to assess the fertility of given water mass. The present study deals with the quantitative and quantitative diversity of zooplankton in Chilika lagoon. Four zooplankton group viz.,Copepoda, Protozoa, Cladocera and Rotifera were recorded. Theabundance of zooplankton during the sampling period varied between 1775-4840 u/l. Pre-monsoon registered highest abundance (4675-4217 u/l) with average value (2223 u/l) followed by post-monsoon (u/l) with average value 2047 u/l and monsoon (1775-3522nos/m-3) with an average value 1324nos m-3. Copepods had emerged as the most dominant group (57%) throughout the study period. The shared group followed by protozoa (19%), cladocera (14%) and rotifera (10%).. KEYWORDS :Chilika, Zooplankton, Diversity, Abundance.

Diversity and abundance of zooplankton in chilika lagoon, Odisha

Zooplankton, the microscopic and free-swimming animal component of an aquatic ecosystem plays an important role on its energy flow process. From the fishery point of view, zooplankton forms the vital links in the pelagic food chain. Many micro zooplanktons also constitute the major food items of the larvae of crustaceans, molluscs and fishes. Thus, abundance of zooplankton practically acts as an ideal index to assess the fertility of given water mass. The present study deals with the quantitative and quantitative diversity of zooplankton in Chilika lagoon. Four zooplankton group viz.,Copepoda, Protozoa, Cladocera and Rotifera were recorded. Theabundance of zooplankton during the sampling period varied between 1775-4840 u/l. Pre-monsoon registered highest abundance (4675-4217 u/l) with average value (2223 u/l) followed by post-monsoon (u/l) with average value 2047 u/l and monsoon (1775-3522nos/m-3) with an average value 1324nos m-3. Copepods had emerged as the most dominant group (57%) throughout the study period. The shared group followed by protozoa (19%), cladocera (14%) and rotifera (10%).. KEYWORDS :Chilika, Zooplankton, Diversity, Abundance.

High‐volume plankton tow net sampling improves eDNA detection of invasive zebra mussels (Dreissena polymorpha) in recently infested lakes

AbstractAquatic invasive species are a serious and growing threat to biodiversity. Zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) are freshwater invaders causing substantial ecological and economic damage across Europe and North America. Early detection of invasive mussels and other non‐indigenous species is increasingly needed to prevent their establishment and spread. Environmental DNA (eDNA) techniques potentially offer higher sensitivity monitoring tools to complement more conventional methods for surveying adult and juvenile mussels and veliger larvae. eDNA assays are typically performed on small‐volume (0.5–5 L) water samples that are concentrated by filtration prior to extraction and downstream processing. Sampling using a towed plankton net of a larger (64 μm) pore size can process orders of magnitude larger water volumes with the potential for increasing eDNA detection sensitivity. We compared the sensitivities of high‐volume plankton tow net water sampling to filter sampling in three recently infested lakes in Canada and Minnesota, USA. Paired filtration and tow net samples were analyzed for Dreissena DNA using an established quantitative polymerase chain reaction assay for the genus. Higher yields of Dreissena eDNA (more DNA copies) were recovered from plankton tow than from filtered samples in all 33 paired comparisons. In some cases, plankton tow samples were positive for Dreissena eDNA while lower‐volume filtering produced a false negative detection. Our results demonstrate the effectiveness of plankton tow net sampling for eDNA early detection of invasive mussels, a method that can be used exclusively or as a supplement to filter sampling. Our results further suggest that eDNA testing could be incorporated into monitoring programs that routinely use plankton tows for visual detection of invasive mollusk larvae, as well as other aquatic invasive and non‐invasive species ranging from plankton to metazoans, including many fish.

Sustainable oyster shell incorporated artificial reef concrete for living shorelines

An innovative pervious concrete containing recycled oyster shells for artificial reef structures has been developed. The new artificial reef concrete incorporating oyster shells contained higher amounts of supplementary cementitious material and sea sand instead of river sand. Investigations on homogeneity, strength characteristics, pH levels and mussel larvae (Mytilus galloprovincialis) settlement were performed to verify the effectiveness of different constituents. The proposed concrete mixes have the potential for use in artificial reef construction representing improved characteristics with regards to weight, cost, environmental sustainability, carbon footprint and attachment of shellfish larvae to the reef, enabling nature-based coastal protection solutions, or ‘living shorelines.

2022 ЖЫЛҒЫ КІШІ АРАЛ ТЕҢІЗІ ЗООПЛАНКТОНЫНЫҢ ТҮРЛІК ҚҰРАМЫ ЖӘНЕ САНДЫҚ СИПАТТАМАСЫ

Abstract. This article presents data on the state of zooplankton of the Small Aral Sea in May-June-September in 2022. During the periods of research, 32 taxa of true plankters were identified in the zooplankton of the Small Aral Sea: rotifers – 19, cladoceras– 7 and copepods – 6 species. Temporary plankters – larvae of bivalve mollusks, ostracoda, hadistediversicolorand chironomids were also noted. Zooplankton was created to varying degrees by four groups of invertebrates, but in both periods of research, copepods were in the lead. This is closely related to the development of the acclimatizant – Calanipeda quaedulcis. The leadership of this group of copepods was maintained throughout the PR (fishing area) of the sea. In general, the average values of zooplankton biomass corresponded to a very low trophic level. This may be due to the timing of material collection, the depth of sampling and the lack of a significant level of development of the group of cladoceras.

Ecological benefits of artificial light at night (ALAN): Accelerating the development and metamorphosis of marine shellfish larvae

Urbanization has led to increasing use of artificial light at night (ALAN), which has rapidly become an important source of pollution in many cities. To identify the ALAN effects on the embryonic development of the Pacific abalone Haliotis discus hannai, we first exposed larvae to natural light with a light period of 12 L:12D (control, Group CTR). We then exposed larvae to three different light regimes. Larvae in Group NL were exposed to full spectrum artificial light from 18:00 to 00:00 to simulate the lighting condition at night, whereas Groups BL and YL were illuminated at the same time interval with 450 nm of short-wavelength blue light and 560 nm of long-wavelength orange light, respectively, to simulate billboard lighting at night. There were significantly higher hatching success and metamorphosis rates of larvae in Group BL than in Group YL or CTR (P < 0.05). The larvae in Group YL had the highest abnormality rate and took the longest time to complete metamorphosis. Transcriptomic studies revealed significantly higher expression levels of genes related to RNA transport, DNA replication, and protein processing in endoplasmic reticulum pathways in Group BL compared to the other groups. In the metabolomic analysis, we identified prostaglandin B1, tyramine, d-fructose 6-phosphate, L-adrenaline, leukotriene C4, and arachidonic acid as differential metabolic markers, as they play a vital part in helping larvae adapt to different ALAN conditions. Multi-omics correlation analysis of pairwise comparisons between all of the groups suggested that the biosynthesis of unsaturated fatty acids (FAs) and arachidonic acid metabolism pathways were significantly enriched (P < 0.05). Further quantitative analysis of the fatty acid (FA) contents revealed that 42 out of 50 FAs were down-regulated in Group BL and up-regulated in Group YL, which suggested that the synthesis, catabolism, and metabolism of FAs are crucial for the larval response to different spectral components of ALAN. For the first time, we report positive rather than negative effects of artificial blue light at night on the embryonic development of a benthic marine species. These results are significant for unbiased and full-scale assessment of the ecological effects of ALAN and for understanding the structural stability of the marine benthic community.

Metabolic Regulation of Copper Toxicity during Marine Mussel Embryogenesis.

The development of new tools for assessing the health of cultured shellfish larvae is crucial for aquaculture industries to develop and refine hatchery methodologies. We established a large-volume ecotoxicology/health stressor trial, exposing mussel (Perna canaliculus) embryos to copper in the presence of ethylenediaminetetraacetic acid (EDTA). GC/MS-based metabolomics was applied to identify potential biomarkers for monitoring embryonic/larval health and to characterise mechanisms of metal toxicity. Cellular viability, developmental abnormalities, larval behaviour, mortality, and a targeted analysis of proteins involved in the regulation of reactive oxygen species were simultaneously evaluated to provide a complementary framework for interpretative purposes and authenticate the metabolomics data. Trace metal analysis and speciation modelling verified EDTA as an effective copper chelator. Toxicity thresholds for P. canaliculus were low, with 10% developmental abnormalities in D-stage larvae being recorded upon exposure to 1.10 μg·L-1 bioavailable copper for 66 h. Sublethal levels of bioavailable copper (0.04 and 1.10 μg·L-1) caused coordinated fluctuations in metabolite profiles, which were dependent on development stage, treatment level, and exposure duration. Larvae appeared to successfully employ various mechanisms involving the biosynthesis of antioxidants and a restructuring of energy-related metabolism to alleviate the toxic effects of copper on cells and developing tissues. These results suggest that regulation of trace metal-induced toxicity is tightly linked with metabolism during the early ontogenic development of marine mussels. Lethal-level bioavailable copper (50.3 μg·L-1) caused severe metabolic dysregulation after 3 h of exposure, which worsened with time, substantially delayed embryonic development, induced critical oxidative damage, initiated the apoptotic pathway, and resulted in cell/organism death shortly after 18 h of exposure. Metabolite profiling is a useful approach to (1) assess the health status of marine invertebrate embryos and larvae, (2) detect early warning biomarkers for trace metal contamination, and (3) identify novel regulatory mechanisms of copper-induced toxicity.

Production and Growth Performance of Nannochloropsis oculata (Droop) Hibberd in the Helical Photobioreactor

Phytoplankton species preferred in marine fish farming are the primary food source in the larval and young stages of bivalve mollusks, along with some fish and shellfish larvae. For this reason, selecting the appropriate phytoplankton and production technique for feeding marine fish larvae is crucial. Nannochloripsis oculata microalgae species, widely used in rearing sea bream and sea bass larvae and feeding rotifers, has an essential place in our country. N. oculata microalgae species, which is used in rearing sea bream and sea bass larvae and feeding rotifers, was produced in a helical photobioreactor by applying a continuous production technique at 30 ‰ salinity, and its growth performance was aimed to be investigated. In the study, N. oculata was grown in a helical photobioreactor at 30‰ salinity by applying the continuous production technique for two weeks, and the daily cell number and specific growth rate were determined. The study was repeated three times. The supply of live feed for marine fish fry and hatcheries established for this purpose is one of the most critical problems. The latest technology in the production of microalgae, which is the primary link of the live feed chain in this sector, is continuous algae production in helical tubular reactors. The helical tubular reactor used in the study consists of a transparent hose system consisting of a completely tubular helical reactor designed for microalgae production. The helical tubular continuous production system offers more efficient and economically more convenient alternatives than existing production systems. One of the most essential advantages of this system is that the system can be designed without requiring significant capital. The continuous culture technique allows the application of long-term and safe algae cultures. With this system, besides providing continuity in production, the negativities in batch production can be eliminated with adequate light. Since the algae production with the continuous method in the spiral photobioreactor remains in the maximum growth phase for a longer time than the batch production, it is a system with high production efficiency and quality, and production capacity is guaranteed. In addition, the algae product harvesting in the continuous system ensures the daily harvesting of algae as much as half of the system volume. A helical reactor enables automation in algae production and high-quality production over long periods. In the study, the sowing density of N. oculata was determined as 1.068x106 ±0.006 cells/mL. Algin cell growth increased logarithmically during the first five days. From the 5th day to the 15th day, the increase in the number of cells was determined as 12.35x106±0.165 cells/mL at the highest and 8.76x106±0.709 cells/mL at the lowest. However, on the 13th day, it was determined that the increase in algin cells was 12.35x106±0.165 cells/mL, and the specific growth rate decreased by 0.189±0.016 divisions/day. As a result of the study, the number of cells of N. oculata algae 5-15 increased. It was determined that it increased 10 times between days. In this context, it was possible to harvest half of the reactor volume of algae daily at maximum cell density for long periods in the helical reactor

Sea bed disturbance increases flat oyster recruitment for low to moderate stock densities

Abstract It has long been suggested by commercial fishing interests that the sea bed benefits from being trawled or disturbed. Evidence to support increased benthic food web productivity in areas disturbed by trawling has suggested that this is the case, and that some mobile consumers can benefit from this increased productivity. The same hypothesis has been put forward for shellfish recruitment, that disturbance of the sea bed, e.g. ‘harrowing’, increases the exposure of suitable settlement substrates for shellfish larvae. This is an approach often taken in shellfish mariculture in private fisheries, and has led to calls for support of expanding such activities into publicly managed areas to promote shellfish recovery and restoration. Increased seabed disturbance, however, may not align with conservation policy or societal objectives for natural recovery of the seabed landscape. Furthermore, evidence for increased shellfish recruitment from seabed disturbance is mixed, and many attempts to elucidate whether relationships exist receive criticism for operating at small spatial and temporal scales. An analysis is presented from 3 years of data (2016–2018) from a stock survey of a private European flat oyster, Ostrea edulis, fishery operating in the Blackwater estuary, Essex, UK. Using data for adult and recruit oyster abundance and distribution in 2018, with ‘harrowing’ effort from 2016–2018, it is asked whether oyster recruitment was related to disturbance effort. It was found that oyster recruitment is positively related to increased seabed disturbance, but only up to intermediate adult oyster abundance equivalent to 60 oysters/100 m dredge, beyond which harrowing results in recruitment declines. This has implications for approaches to oyster fishery recovery, but also for restoration projects seeking evidence‐led guidance on which ways may be appropriate to kick‐start natural recovery in historical oyster areas that are habitat limited.

Expanded utilisation of microalgae in global aquafeeds

AbstractUtilising novel ingredients in aquafeeds is necessary for the continued expansion and intensification of aquaculture production. Microalgae are utilised widely in aquaculture for a variety of purposes; as live feed for fish and shellfish larvae and juveniles, for the production of algae‐based meals and oils to replace marine derived raw materials in aquafeeds, and for the production of astaxanthin, the carotenoid that gives salmon flesh its characteristic reddish colour. Notably, long‐chain polyunsaturated fatty acids, amino acids, proteins, fibres, antioxidant pigments, vitamins and minerals are among the compounds in microalgae with great biological value. A growing collection of experimental data has demonstrated that these substances are crucial for increasing larval survival and enhancing the growth and well‐being of fish and shellfish. In this review, the processing of microalgae utilised as aquafeed ingredient, the health promoting compounds in microalgae and their role in growth, immunity and disease resistance of fish and shellfish are described and discussed. Simultaneously, major hurdles in the commercial use of microalgae in aquafeed, and future research and development perspectives are all critically discussed.

A Rapid Assessment of Microalgal Concentration Using Turbidity Measurement for Shellfish Hatchery Seed Production

The goal of this study was to develop a rapid assessment of microalgal concentration using a turbidity meter to serve commercial shellfish hatcheries for feeding shellfish larvae and broodstock. We used four commonly used algal species, Tetraselmis suecica, Isochrysis galbana, Chaetoceros calcitrans, and Chaetoceros gracilis, generating serial dilutions of each and measuring cell concentrations and turbidity of each sample. We identified linear correlations between cell concentration and turbidity and established standard equations between cell concentration and turbidity for each species. We sampled and quantified algae from a shellfish hatchery using these equations and compared hemocytometer counts. No differences were found (P ≥ 0.174), indicating the accuracy of the equations. We expect that this method can provide a quick, accurate, easy method for shellfish hatcheries to quantify algal concentration and avoid either over- or underfeeding larvae and broodstock.

SPAWNING SEASON OF GREEN MUSSEL, PERNA VIRIDIS (LINN. 1758), FROM THE MOHESHKHALI CHANNEL, BAY OF BENGAL, BANGLADESH

Spawning periodicity of the green mussel, P. viridis (Linn. 1758), from the Moheshkhali channel of the Bay of Bengal, Bangldesh was determined by ‘larval abundance’ method for a period of one year from November 1990 and October 1991. Higher larval abundance of P. viridis was recorded during pre-monsoon (January to April) and post-monsoon (September to December) months. Two significant peaks in spawning were recorded- the major peak in September (post-monsoon period) and a minor peak in April (pre-monsoon season). The abundance of the green mussel larvae was found to be correlated with high abundance of other mollusc larvae. However, a water temperature, salinity and the abundance of zooplankton showed negative correlation with the abundance of P. viridis larvae.

Evidence of potential synergy between aquaculture and offshore renewable energy

Worldwide increased demand for offshore renewable energy (ORE) industries and aquaculture requires developing efficient tools to optimize the use of the offshore space, reducing anthropic pressure. The synergetic development of marine renewable energy infrastructure with mariculture has been hypothesized as a way to reduce costs through shared infrastructure. In the Irish Sea, blue mussels (Mytilus edulis L.) represent 40 - 50 % of the total gross turnover of Welsh shellfish industries and the industry has been operating sustainably for over 50 years in North Wales. However, the region is also attractive for tidal energy projects, with strong tidal currents (&gt; 2m/s) occurring, and offshore wind farms, with shallow waters (approx. 50 m) and consistent winds. In this context, it is of scientific and economic interest to study the potential impact of ORE on shellfish larvae recruitment. A numerical approach has been developed using an Eulerian hydrodynamic model coupled with a Lagrangian particle tracking model, which allowed the simulation of tidal currents, wind-driven currents and larval dispersal. Results show: 1) interannual variability of density distribution of larvae; and 2) strong connectivity between commercial shellfish beds and ORE sites. This study shows the importance of ORE site selection in order to: 1) reduce biofouling on ORE infrastructures and 2) develop multi-use platforms at sea to combine needs for ORE and for mariculture.

Prokaryotic and Eukaryotic Microbial Community in Kumamoto Oyster (Crassostrea sikamea) Larvae: Response to Antibiotics in Trace Concentration

Antibiotic treatment is regarded as an emergency measure to avoid disease occurrence of aquatic animals during metamorphosis in an aquaculture system, which is very common in hatcheries of bivalve mollusc larvae. However, it is still unclear how and to what extent the antibiotic addition affects the prokaryotic and eukaryotic microbial communities of marine bivalve larvae. We profiled the community compositions and dominant taxonomies of prokaryotic and eukaryotic microbiota of Kumamoto oyster (Crassostrea sikamea) larvae exposed to seawater with antibiotics in trace concentration. A total of 500,664 16S rRNA and 501,933 18S rRNA gene fragments were selected for classification, resulting in 714 prokaryotic Operational Taxonomic Units (OTUs) and 47 eukaryotic OTUs. Antibiotic exposure altered the structure of larval microbiome and increased the prokaryotic but decreased the eukaryotic microbial diversity. Larval microbiota was sensitive to antibiotics, as evidenced by alternation of the dominant bacterial phyla Proteobacteria, Bacteroidetes, Firmicutes, Chlamydiae, and Actinobacteria, and eukaryotic phyla Streptophyta, Cercozoa, Chlorophyta and Haptophyta. Similarly, a significant effect was observed at the family and genus level, especially the increased bacterial Devosiaceae, Microbacteriaceae, Halieaceae, Vibrionaceae families, and Devosia, Stappia and Vibrio genera, and eukaryotic Isochrysidaceae and TAGIRI1-linage family and Tisochrysis genus. These results indicate that antibiotic treatment may induce a shift in the larval microbiome, which may cause an unstable community structure and in turn affect the oyster health.

RNA-seq transcriptome analysis and identification of the theromacin antimicrobial peptide of the copepod Apocyclops royi

Copepods, including Apocyclops royi, are small aquatic crustaceans and one of the important foods for fish and shellfish larvae. However, studies of the host-pathogen interactions and understanding of infectious disease in copepods are still very limited, yet they are likely to be a significant factor in the sustainable development of copepod aquaculture. In the present study, we performed de novo RNA sequence analysis of A. royi-TH (a Thai isolate of A. royi), which yielded 4.80 Gb bases of clean data and a total of 29,786 unigenes. Annotation was then performed by comparison against seven functional databases, yielding 17,617 (NR: 59.15%), 2,969 (NT: 9.97%), 15,023 (SwissProt: 50.44%), 14,543 (KOG: 48.82%), 15,077 (KEGG: 50.62%), 6,763(GO: 22.71%), and 15,841 (InterPro: 53.18%) unigenes. In comparison to the components of the shrimp Toll pathway, LGBP, Spätzle, Toll receptors, MyD88, Pelle, TRAF6, Dorsal, and Cactus homologs were successfully identified in A. royi-TH. Additionally, a novel antimicrobial peptide (Theromacin-like) was characterized in A. royi (ArTM-like). The ArTM-like ORF was 279 bp and predicted to encode for 92 amino acid residues, with a mature peptide of 75 amino acids and a molecular mass of 8.56 kDa. The genomic organization of the ArTM-like gene consisted of three exons and two introns. Expression analysis indicated that ArTM-like mRNA was abundantly expressed in copepodid and adult stages as an immune responsive gene after infection with the pathogenic Vibrio parahaemolyticus-(AHPND)-causing strain. Altogether, the knowledge obtained in this study will provide a basis for future functional studies of the molecular mechanisms in copepod immunity that may eventually be applied for disease prevention in copepod aquaculture.

Comparison of Vibrio coralliilyticus virulence in Pacific oyster larvae and corals.

The bacterium Vibrio coralliilyticus has been implicated in mass mortalities of corals and shellfish larvae. However, using corals for manipulative infection experiments can be logistically difficult compared to other model organisms, so we aimed to establish oyster larvae infections as a proxy model. Therefore, this study assessed the virulence of six wild-type V. coralliilyticus strains, and mutants of one strain with deletions of known virulence factors, between Pacific oyster larvae (Crassostrea gigas) and Hawaiian rice coral (Montipora capitata) infection systems. The wild-type strains tested displayed variable virulence in each system, but virulence levels between hosts were not necessarily comparable. Strains RE98 and OCN008 maintained a medium to high level of virulence across hosts and appeared to be more generalist pathogens. Strain H1, in contrast, was avirulent towards coral but displayed a medium level of virulence towards oyster larvae. Interestingly, the BAA-450 type strain had a medium level of virulence towards coral and was the least virulent to oyster larvae. A comparison of known virulence factors determined that the flagellum, motility or chemotaxis, all of which play a significant role in coral infections, were not crucial for oyster infections with strain OCN008. A genomic comparison of the newly sequenced strain H1 with the other strains tested identified 16 genes potentially specific to coral pathogens that were absent in H1. This is both the first comparison of various V. coralliilyticus strains across infection systems and the first investigation of a strain that is non-virulent to coral. Our results indicate that the virulence of V. coralliilyticus strains in coral is not necessarily indicative of virulence in oyster larvae, and that the set of genes tested are not required for virulence in both model systems. This study increases our understanding of the virulence between V. coralliilyticus strains and helps assess their potential threat to marine environments and shellfish industries.

Determinants of food selection by bivalve larvae

Selection of food particles for consumption by larvae impacts nutritional gain needed for growth, development, and metamorphosis. Past work has suggested that molluscan larvae are capable of collecting food within a narrow size range. Recent studies have found evidence of size-independent food selection in molluscan larvae, but relatively little is known about the characteristics of particles that larvae preferentially capture. Therefore, we conducted experiments with the larvae of two mussels, Mytilus trossulus and Mytilus edulis, to determine whether they are selective feeders, and if so, whether we could determine the characteristics of particles selected as food. We fed larvae microalgae and polystyrene microspheres of different sizes, nutritional content, surface charge, and hydrophobicity. We found that for both species, there was no effect of size on particle selection for particles 2–8 μm, but, surprisingly, these two congeners preferentially captured particles with different characteristics. Larvae of M. trossulus preferentially captured particles that were more hydrophilic and had a more negative surface charge, but there was no effect of nutritional content. The larvae of M. edulis showed a different pattern; they preferentially captured particles with low surface charge and greater food value, but hydrophobicity did not affect selection. Larvae of these two congeners are indeed selective in which particles they collect but appear to be using different rules for selection. More work is needed to determine whether there are any general patterns that govern particle selection for larvae and mechanisms that could produce the observed patterns. Such work is needed to help us to determine whether individual species use different rules or whether there are general patterns in the types of particles larvae select.

Holoplanktonic and Meroplanktonic Larvae in the Surface Waters of the Onnuri Vent Field in the Central Indian Ridge

The dispersal of organisms in an isolated environment of a hydrothermal vent remains unclear. Here, we provide direct evidence that meroplanktonic larvae may migrate thousands of meters above the ocean floor. The morphological quantitative measurements of mesozooplankton were conducted in the Onnuri Vent Field (OVF), the Solitaire Fields (SF), and the reference site (ref-site). Only one species of bivalve larva that appeared at the OVF and the ref-site (0–200 m) was similar to Bathymodiolus spp. Sixteen species of gastropod larvae were distinguished, among which, species 1–4, 6, and 13 had holoplanktonic features (Atlanta, Oxygrus, and Limacina), whereas species 5, 7–12, and 14–16 had meroplanktonic features. Species 5, 11, and 12 appeared only at the OVF, 9 and 10 appeared only in the SF, 14–16 appeared only at the ref-site, and species 7 and 8 appeared in all surveyed stations. The species 5, 8, 12, 14, and 15 have morphological features similar to Vetulonia spp., and species 7 was similar to Lepetodrilidae; species 9–11 and 16 were similar to Phymorphynchus protoconchs. The morphologically distinguished mollusk larvae in the upper layers of the water column (0–200 m) indicate that larvae associated with deep-sea hydrothermal vents may disperse approximately 2000 m above the vents.

Mesozooplankton distribution in relation to the salinity gradient in a tropical hypersaline lake

Fluctuations in salinity are known to influence coastal marine communities. In this study, we present the effect of salinity on the distribution characteristics of mesozooplankton in Pulicat lake, the second largest lagoon situated along the south east coast of India. During different seasons of the study period, salinity varied from hyposaline (12.57) to hypersaline (139.74) in the lake. Salinity values were moderate in southern (33.75 ± 0.7) and northern inlets (29.38 ± 4.33), which were connected with the sea; while in the central region of the lake salinity was observed to be higher (52.32 ± 4.57). Mesozooplankton biovolume and abundance were high in the southern and northern inlets whereas a severe reduction in diversity and abundance was observed in the central region of the lake manifesting that increase in salinity is negatively impacting the mesozooplankton distribution. Copepod (Acartia tonsa, Acrocalanus gibber, Paracalanus parvus, Oithona brevicornis and Oithona similis), crustacean and molluscan larvae dominated the mesozooplankton abundance. A. tonsa predominance (79%) over the lake and across different seasons indicates its tolerance to a wide range of salinity fluctuations i.e., brackish to hypersaline environment of the Pulicat. The distribution of euryhaline species A. tonsa in all the sampling locations throughout the study period indicated their prevalence in the lake. Multilinear analysis between biotic and abiotic components through redundancy analysis (RDA) also suggested that salinity is the major constraint factor for the distribution of mesozooplankton. In conclusion, this study showed that the increased salinity levels have profound effects on mesozooplankton community and distribution.

Transcriptome Profiling Based on Different Time Points After Hatching Provides a Core Set of Gene Resource for Understanding Larval Immune Response Mechanisms Against Vibrio anguillarum Infection in Amphioctopus fangsiao

Immune defense systems are indispensable for living organisms. Within an immune network, problems with any given link can impact the normal life activities of an organism.Amphioctopus fangsiaois a cephalopod that exists widely throughout the world’s oceans. Because of its nervous system and locomotive organs, it has become increasingly studied in recent years.Vibrio anguillarumis one of the most common pathogenic bacteria in aquaculture organisms. It is highly infectious and can infect almost all aquaculture organisms.V. anguillaruminfection can cause many adverse biological phenomena, including tissue bleeding. Study the immune response afterV. anguillaruminfection would help us to understand the molecular mechanisms of immune response in aquaculture organisms. In this research, we infected the primary incubationA. fangsiaowithV. anguillarumfor 24 h. We analyzed gene expression inA. fangsiaolarvae via transcriptome profiles at 0, 4, 12, and 24 h after hatching, and 1,385, 734, and 6,109 differentially expressed genes (DEGs) were identified at these three time points. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to identify immune-related DEGs. Protein–protein interaction networks were constructed to examine interactions between immune-related genes. Twenty hub genes involved in multiple KEGG signaling pathways or with multiple protein–protein interaction relationships were identified, and their differential expression verified by quantitative RT-PCR. We first studiedV. anguillaruminfection ofA. fangsiaolarvae by means of protein–protein interaction networks. The results provide valuable genetic resources for understanding immunity in molluscan larvae. These data serve as a theoretical basis for the artificial breeding ofA. fangsiao.