Sea Urchin Strongylocentrotus Intermedius Research Articles

Effect of Phlorethol from the Brown Alga Costaria costata (Turn.) Saund. (Order Laminariales) on Gametes and Embryogenesis of the Sea Urchin Strongylocentrotus intermedius (A. Agassiz, 1864)

The effect of a fraction of phlorethol (CcPh), one of the polyphenolic compounds isolated from the brown alga Costaria costata (Turn.) Saund (Laminariales), on gametes and embryogenesis of the sea urchin Strongylocentrotus intermedius (A. Agassiz, 1864) was studied. Using a model of developing sea urchin embryos, it was shown that phlorethol at concentrations ≤700 µg/mL did not exert cytotoxic effect on early developmental stages (from zygote to 16-celled stage blastomere). The embryotoxic effect of phlorethol, causing death of 50% of embryos, was expressed in a concentration (I) range of 50 I ≤ 100 µg/mL only after 24 h of incubation, in the blastula stage. When exposed to concentrations of ≥100 µg/mL, embryos that survived to the blastula stage did not develop further and died after 36 h of incubation. Under the effect of phlorethol, the fertilizing capacity of sea urchin spermatozoa and oocytes reduced. The concentration of phlorethol inhibiting fertilization by 50% (IC50) when acting on sperm was 1.28±0.38 µg/mL and when acting on oocytes was 3.83±0.82 µg/mL. Thus, phlorethol reduces the fertilizing capacity of sea urchin gametes at concentrations much lower than embryotoxic concentrations and can potentially find practical application as part of new contraceptive drugs for mammals and humans.

Multi-omics analysis of sea urchin (Strongylocentrotus intermedius) adaptation to salt stress reveals epigenetic regulatory mechanisms

Increased precipitation and surface runoff due to global warming has reduced surface seawater and nearshore water salinity, affecting marine organism survival. Nevertheless, the epigenetic mechanisms underlying the adaptation of sea urchins (Strongylocentrotus intermedius) to low-salinity stress remains unknown. This study utilized response surface methodology to formulate growth models for S. intermedius at different salinity levels and shell diameters. Whole genome bisulphite sequencing, RNA-sequencing, and metabolome analysis were performed on low-salinity stressed sea urchins, and a total of 3006 differential methylated regions, 945 differential methylated genes, 886 differentially expressed genes, and 271 differential metabolites were identified. Multi-omics analysis revealed significant alterations in the gene expression and DNA methylation of key genes (e.g., SPHK2, Arpc1a, and SLC23A1) in S. intermedius under low-salinity stress conditions. These changes subsequently influenced the metabolism of substances, including sphingosine-1-phosphate, ethanolamine phosphate, vitamin C, taurine, and choline. These alterations impacted functions related to immunity, osmoregulation, and energy metabolism in the organism. This study was to comprehensively elucidate the epigenetic mechanisms of S. intermedius under low-salinity stress from the perspective of DNA-RNA-metabolites, providing new insights into salinity adaptation of marine invertebrates.

Feeding Behavior, Gut Microbiota, and Transcriptome Analysis Reveal Individual Growth Differences in the Sea Urchin Strongylocentrotus intermedius.

Growth differentiation among farmed sea urchins (Strongylocentrotus intermedius) poses a significant challenge to aquaculture, with there being a limited understanding of the underlying molecular mechanisms. In this study, sea urchins with varying growth rates, reared under identical conditions, were analyzed for feeding behavior, gut microbiota, and transcriptomes. Large-sized sea urchins demonstrated significantly higher feeding ability and longer duration than smaller ones. The dominant phyla across all size groups were Campylobacterota, Proteobacteria, and Firmicutes, with Campylobacterota showing the highest abundance in small-sized sea urchins (82.6%). However, the families Lachnospiraceae and Pseudomonadaceae were significantly less prevalent in small-sized sea urchins. Transcriptome analysis identified 214, 544, and 732 differentially expressed genes (DEGs) in the large vs. medium, large vs. small, and medium vs. small comparisons, respectively. Gene Ontology and KEGG pathway analyses associated DEGs with key processes such as steroid biosynthesis, protein processing within the endoplasmic reticulum, and nucleotide sugar metabolism. Variations in phagosomes and signaling pathways indicated that size differences are linked to disparities in energy expenditure and stress responses. These findings provide a foundation for future investigations into the regulatory mechanisms underlying growth differences in S. intermedius and provide clues for the screening of molecular markers useful to improve sea urchin production.

Molecular cloning and functional study of a Rel homologous gene in sea urchin Strongylocentrotus intermedius

NF-κB (Nuclear factor-kappa B) family proteins are versatile transcription factors that play crucial regulatory roles in cell development, growth, apoptosis, inflammation, and immune response. However, there is limited research on the function of these key genes in echinoderms. In this study, an NF-κB family gene (SiRel) was identified in sea urchin Strongylocentrotus intermedius. The gene has an open reading frame length of 1809 bp and encodes for 602 amino acids. Domain prediction results revealed that the N-terminal of SiRel protein encodes a conserved Rel homology domain (RHD), including the RHD-DNA binding domain and the RHD-dimerization domain. Multiple sequence comparison results showed that the protein sequences of these two domains were conserved. Phylogenetic analysis indicated that SiRel clustered with Strongylocentrotus purpuratus p65 protein and Rel protein of other echinoderms. Results from quantitative real-time PCR demonstrated detectable SiRel mRNA expression in all tested sea urchin tissues, with the highest expression level found in the gills. And SiRel mRNA expression levels were significantly induced after LPS (Lipopolysaccharide) and poly(I:C) (Polyinosinic:polycytidylic acid) stimulation. In addition, SiRel protein expression can be found in cytoplasm and nucleus of HEK293T cells. Co-immunoprecipitation results showed that SiRel could interact with sea urchin IκB (Inhibitor of NF-κB) protein. Western blotting and dual-luciferase reporter gene assay results indicated that overexpression of SiRel in HEK293T cells could impact the phosphorylation levels of JNK (c-Jun N-terminal kinase) and Erk1/2 (Extracellular signal-regulated kinases1/2) and activate interleukin-6 (IL-6), activating protein 1 (AP-1), interferon (IFN)α/β/γ, and signal transducer and activator of transcription 3 (STAT3) reporter genes in HEK293T cells. In conclusion, this study reveals that SiRel plays an important role in the innate immune response of sea urchins and enriches our understanding of comparative immunology theory.

Heterosis of the interspecific sea urchin hybrids between Strongylocentrotus intermedius and Heliocidaris crassispina

In order to study the heterosis of the interspecific hybrids between sea urchin Strongylocentrotus intermedius and Heliocidaris crassispina, comparative culturing experiments were conducted on individuals of the same age from four groups: S. intermedius (SI), H. crassispina (HC), S. intermedius ♀ × H. crassispina ♂ (SH), and H. crassispina ♀ × S. intermedius ♂ (HS). Growth rate at different stages of development, gonadal production and quality, high-temperature tolerance, and resistance to black-mouth disease were compared among these four species. The results were as follows: in the juvenile sea urchin stage, SH sea urchins exhibited 79.11% and 55.28% body weight heterosis at 16 and 20 °C, respectively, with particularly high single-parent heterosis observed at 16 °C compared to the male parent HC (247.79%). In the young sea urchin stage, SH sea urchins displayed mid-parent heterosis in body weight at all temperatures except 28 °C, reaching a maximum of 94.62% at 12 °C. HS Sea urchins showed mid-parent heterosis only at 12, 24, and 28 °C, with the highest observed at 28 °C (36.51%). The body weight specific growth rate of SH sea urchins was significantly higher than those of the other three species (P < 0.05), and they achieved the largest body weight (48.43 g) by the end of the experiment. The gonad wet weight of SH sea urchins was significantly higher than those of the other three species (P < 0.05). While there was no difference in gonad index between SH and SI sea urchins, it was significantly higher than those of HC and HS sea urchins. In terms of high-temperature tolerance, the upper thermal tolerances (UTT) of HC and HS sea urchins were significantly higher than those of SI and SH sea urchins (P < 0.05). Regarding resistance to black-mouth disease, there was no statistically significant difference in survival rates between SH sea urchins and SI sea urchins after infection with Vibrio echinoideorum at a concentration of 1 cfu/mL. However, the survival rate of HS sea urchins was significantly higher than that of SI. The study demonstrated that the SH hybrid sea urchins exhibit notable advantages in growth and gonad yield compared to its parental species, suggesting its potential as a valuable candidate for the cultivation of new sea urchin varieties in aquaculture. These findings hold significant promise for enhancing the efficiency and sustainability of sea urchin farming practices.

HIF-1α interacting with miR-2013-3p regulates pathogen-induced energy production changes via targeting glutamate dehydrogenase in the sea urchin Strongylocentrotus intermedius

ABSTRACT To investigate the functions of hypoxia inducible factor-1α (HIF-1α) homologs, we cloned and characterized the full-length cDNA of a novel HIF-1α homolog (SinHIF-1α) from the sea urchin Strongylocentrotus intermedius. We then explored the functions of SinHIF-1α and its regulatory factor (miR-2013-3p) in the pathogen-induced metabolic response of S. intermedius. The results showed the following: 1) The full-length cDNA of SinHIF-1α was 4265 bp, with a high level of sequence conservation across the phylum Echinodermata. 2) MiR-2013-3p could bind to the 3’-UTR of SinHIF-1α and negatively regulate the expression of SinHIF-1α in S. intermedius. 3) Both SinHIF-1α silencing and miR-2013-3p overexpression suppressed the relative content of adenosine triphosphate (ATP) in coelomocytes as well as the relative expression (mRNA and protein) and total enzyme activity of glutamate dehydrogenase (GDH) in S. intermedius. 4) The miR-2013-3p/SinHIF-1α axis may regulate ATP production at 6–24 h and 48–72 h post-pathogen infection through accompanied by alterations in the relative expression and enzyme activity of GDH in S. intermedius. In summary, all observations from this study indicated that the pathogen utilizes the miR-2013-3p/SinHIF-1α axis to reduce ATP production and thereby attenuate the antimicrobial capability of the host via targeting GDH.

Establishment of Parentage Identification Method for Sea Urchin Strongylocentrotus intermedius Based on SSR-seq Technology.

To establish a parentage identification method for Strongylocentrotus intermedius, 15 microsatellite loci and simple sequence repeat sequencing (SSR-seq) technology were used to perform SSR sequencing and typing of the validation population with known pedigree information and the simulation population. Cervus v3.0 was used for gene frequency statistics, simulated analysis, and parentage identification analysis. The results showed that, in validation population, using 15 microsatellite loci, the highest success rate of parent pairs identification was 86%, the highest success rate of female parent identification was 93%, and the highest success rate of male parent identification was 90%. The simulated population was analyzed using 12-15 loci, and the identification rate was up to 90%. In cases where accurate parentage was not achieved, individuals could exhibit genetic similarities with 1-3 male or female parents. Individuals identified as lacking a genetic relationship can be selected as parents to prevent inbreeding. This study shows that parent pairs or single parents of most offspring can be identified successfully using these 15 selected loci. The results lay a foundation for the establishment of a parentage identification method for S. intermedius.

Interactive effects of chronic ocean acidification and warming on the growth, survival, and physiological responses of adults of the temperate sea urchin Strongylocentrotusintermedius

To investigate the interactive effects of chronic ocean acidification and warming (OAW) on the growth, survival, and physiological responses of sea urchins, adults of the temperate sea urchin Strongylocentrotus intermedius were incubated separately/jointly in acidic (ΔpHNBS = −0.5 units) and thermal (ΔT = +3.0 °C) seawater for 120 days under lab-controlled conditions based on the projected ocean pH and temperature for 2100 put forward by the Intergovernmental Panel on Climate Change (IPCC). Survival rate (SR), average food consumption rate (FCR), gut index (GuI), specific growth rate (SGR), digestive capability, energy production, and antioxidant capability were subsequently determined. The results showed that 1) the SR, FCR, GuI and SGR decreased sharply under OAW conditions. Significant interactive effects of OAW on SR and SGR were observed at 120 days post-incubation (dpi), and on FCR this occurred at 90 dpi. 2) OAW altered the activities of both digestive and antioxidant enzymes. There were significant interaction effects of OAW on the activities of amylase, trehalase, and superoxide dismutase. 3) The relative gene expression levels and activities of key enzymes involved in glycometabolism pathways (i.e., glycolysis and the tricarboxylic acid cycle) were significantly affected by OAW, resulting in an alteration of the total ATP content in the sea urchins. Interaction effects of OAW were observed in both relative gene expression and the activity of enzymes involved in glycolysis (hexokinase), the transformation of glycolysis end-products (lactate dehydrogenase), the tricarboxylic acid cycle (citrate synthetase), and ATP production (Na+/K+-ATPase). The data from this study will enrich our knowledge concerning the combined effects of global climate change on the survival, growth, and physiological responses of echinoderms.

TMT-based proteomics analysis of sea urchin (Strongylocentrotus intermedius) under high temperature stress

In the context of global warming and continuous high temperatures in the northern part of China in summer, the mortality rate of Strongylocentrotus intermedius through the summer reaches 70–80 %. The protein regulatory mechanism of S. intermedius in response to high temperature stress is still unclear. In order to investigate the protein expression of S. intermedius under high temperature stress, the study was conducted with the high-temperature resistant strain of S. intermedius and the control group of S. intermedius. Tandem Mass Tag (TMT) tagging technique was applied to resolve the protein expression profile of S. intermedius in response to high temperature stress. The results showed that, compared to 15 °C，136 DEPs were screened in high-temperature resistant strain groups of S. intermedius under high temperature stress and 87 DEPs were screened in the control group of S. intermedius. There were 33 common differential proteins in the two groups, such as APOLP, HSP 70, CDC37 and CALM. Further Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analyses revealed that the up-regulated proteins CALM and HSP70 are significantly enriched in the “Phosphatidylinositol signaling system” and “Protein processing in endoplasmic reticulum” in heat-tolerant S. intermedius strains under high temperature stress. The control group of S. intermedius DEPs were significantly enriched in protein processing in the endoplasmic reticulum. These results provide a theoretical basis for the molecular mechanism of sea urchin heat tolerance and fundamental data for sea urchin selection and breeding for high temperature tolerance.

An Investigation on the Effects of Dietary Vitamin E on Juvenile Sea Urchin (Strongylocentrotus intermedius): Growth, Intestinal Microbiota, Immune Response, and Related Gene Expression.

A 90 d feeding experiment was conducted to investigate the effects of vitamin E (VE) on growth, intestinal microbiota, immune response, and related gene expression of juvenile sea urchin (Strongylocentrotus intermedius). Six dry feeds were made to contain graded levels of VE (78, 105, 152, 235, 302, and 390 mg/kg); these were named E78, E105, E152, E235, E302, and E390, respectively. Dry feed E50 and fresh kelp (HD) were used as the control diets. There were six replicates of cages in each dietary group, and each cage held 20 sea urchins with an initial body weight of approximately 1.50 g. Results exhibited that weight gain rate and gonadosomatic index (GSI) of the sea urchins were not significantly affected by dietary VE ranging from 78 to 390 mg/kg. Sea urchins in the dry feed groups showed poorer growth performance, but significantly higher GSI than those in the fresh kelp groups. The pepsin and lipase activities were not significantly promoted by low or moderate VE, but were inhibited by a high level of VE (302-390 mg/kg), while amylase and cellulase activities were significantly increased by low or moderate VE, with the highest values observed in the E105 and E235 groups, respectively. VE addition at a low dosage (105-152 mg/kg) showed inhibitory effects on immune and antioxidant enzyme activities and expression of inflammation-related genes, but showed no beneficial effects at moderate or high dosage (235-390 mg/kg), while a moderate or relatively higher level of VE (235-302 mg/kg) significantly increased the expression of several immune-related genes. The relative abundance of Proteobacteria, Actinobacteria, Ruegeria, and Maliponia in the intestine of the sea urchins increased with the increase in VE in the dry feeds. On the contrary, the relative abundance of the Firmicutes, Bacteroidetes, Escherichia-Shigella, Bacteroides, and Clostridium sensu stricto 1 gradually decreased as VE content increased. These results indicated that a moderate level of VE (172.5-262.4) can achieve ideal digestive enzyme activities and growth performance, but a relatively higher level of VE (235-302 mg/kg) was beneficial for maintaining the immune and antioxidant capacity of juvenile S. intermedius by regulating the expression of inflammation- and immune-related genes and abundance of some bacteria to a healthy state.

Effects of Supplementary Kelp Feeding on the Growth, Gonad Yield, and Nutritional and Organoleptic Quality of Subadult Sea Urchin (Strongylocentrotus intermedius) with Soya Lecithin Intake History.

A 23-week feeding experiment was conducted to investigate the effects of supplementary kelp feeding on the growth, gonad development, and nutritional and sensory properties of sea urchin (Strongylocentrotus intermedius) with soya lecithin (SL) intake history. The feeding experiment was divided into experimental phase I and phase II. During phase I, 48 subadult sea urchins (initial weight: 6.28 ± 0.07 g) were fed one of the feeds with different levels of SL (0%, 1.6%, 3.2%) or kelp (Saccharina japonica) for 12 weeks. Then, all sea urchins were fed kelp for the next 11 weeks during the phase II. Each diet was randomly allocated to six cages of sea urchins. The results of phase I showed that weight gain rate (WGR), gonadosomatic index (GSI), gonad sensory properties (color and texture), and essential amino acid (EAA) contents were not significantly affected by SL level in the feed groups. High level (3.2%) of SL suppressed gonad development of S. intermedius with retarded gametogenesis in the 3.2% SL group (stage Ⅱ) compared to those fed 0% and 1.6% SL groups (stage Ⅲ). Sea urchins fed dry feeds exhibited significantly lower WGR and values of color (redness and yellowness) and texture (hardness and gumminess) but higher contents of EAA in the gonads than those fed kelp. The n-3/n-6 polyunsaturated fatty acid (PUFA) and eicosapentaenoic acid (EPA) of gonads in the groups fed with dry feeds showed no significant differences, but were significantly lower than that of kelp group. At the end of phase II, the gonad yellowness and EPA content of gonads in all dry feed groups were significantly increased by supplementary kelp feeding, with a higher increase observed in S. intermedius with SL intake history, while arachidonic acid (ARA) content was significantly improved by supplementary kelp feeding in S. intermedius with SL intake history. Gonad texture was improved to some extent by supplementary kelp feeding. These results indicated that S. intermedius fed dry feeds showed significantly higher GSI and EAA but poorer organoleptic quality and lower n-3/n-6 PUFA and EPA than those fed kelp. Kelp supplementary feeding improved the fatty acid value and organoleptic quality of gonads, especially for the sea urchins with SL intake history.

Chitinolytic and Fungicidal Potential of the Marine Bacterial Strains Habituating Pacific Ocean Regions.

Screening for chitinolytic activity in the bacterial strains from different Pacific Ocean regions revealed that the highly active representatives belong to the genera Microbulbifer, Vibrio, Aquimarina, and Pseudoalteromonas. The widely distributed chitinolytic species was Microbulbifer isolated from the sea urchin Strongylocentrotus intermedius. Among seventeen isolates with confirmed chitinolytic activity, only the type strain P. flavipulchra KMM 3630T and the strains of putatively new species Pseudoalteromonas sp. B530 and Vibrio sp. Sgm 5, isolated from sea water (Vietnam mollusc farm) and the sea urchin S. intermedius (Peter the Great Gulf, the Sea of Japan), significantly suppressed the hyphal growth of Aspergillus niger that is perspective for the biocontrol agents' development. The results on chitinolytic activities and whole-genome sequencing of the strains under study, including agarolytic type strain Z. galactanivorans DjiT, found the new functionally active chitinase structures and biotechnological potential.

Integrated microRNA-mRNA analysis provides new insights into gonad coloration in the sea urchin Strongylocentrotus intermedius

Comparative microRNA (miRNA) and mRNA transcriptome analyses were performed on Strongylocentrotus intermedius of the same sex with significant gonadal color differences. The results indicated that 1) the color of female gonads was generally superior to that of males. 2) Comparative and integrated miRNA and mRNA transcriptome analyses identified differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs) in female and male individuals with significant gonadal color differences. Common and sex-specific DEGs and “DEM-DEG” pairs involved in carotenoid absorption, accumulation, and transformation were identified as candidates correlated with gonad coloration in S. intermedius. Collectively, the results from this study have enriched our knowledge of the process of sea urchin gonad coloration and should provide additional clues for increasing the gonad quality of commercial sea urchins from molecular and metabolic aspects.

Molecular mechanisms that regulate the heat stress response in sea urchins (Strongylocentrotus intermedius) by comparative heat tolerance performance and whole-transcriptome RNA sequencing

In the context of climate change and extreme high temperature, the commercially important sea urchin Strongylocentrotus intermedius suffers high mortality during summer in Northern China. How sea urchins respond to high temperatures is of great concern to academia and industry. How to understand the heat tolerance of sea urchin from the whole transcriptome level. In this study, the heat-resistant S. intermedius bred by our team and its control group were used as the research objects, then we applied whole-transcriptome RNA sequencing to detect differentially expressed mRNAs, microRNAs, long noncoding RNAs that respond to heat stress in the heat-resistant and control S. intermedius. A competitive endogenous RNA (ceRNA) regulatory network was constructed with predicted pairs of differentially expressed mRNAs and noncoding RNAs and revealed the molecular regulatory mechanisms in S. intermedius responding to heat stress. A functional analysis suggested that the ceRNAs were involved in basal metabolism, calcium ion transport, endoplasmic reticulum stress, and apoptosis. This is the whole-transcriptomic analysis of S. intermedius under heat stress to propose ceRNA networks that will provide a basis for studying the potential functions of long noncoding RNAs and miRNAs in the heat stress response in S. intermedius and provide a theoretical basis for the study of the molecular mechanism of sea urchins in response to environmental changes.

Effects of soya lecithin on the growth, gonad development, transcription of genes related with fatty acid synthesis and inflammation between sexes of sea urchin Strongylocentrotus intermedius (A. Agassiz, 1864)

A 28-day feeding experiment was performed to investigate the effects of soya lecithin (SL) addition on the growth, gonad development, fatty acid composition, transcription of genes related with fatty acid synthesis and inflammation between sexes of sea urchin Strongylocentrotus intermedius (A. Agassiz, 1864). Three experimental diets were prepared with increasing levels of SL (0%, 1.6%, and 4%). Each diet was randomly assigned to eight male and eight female sea urchins individually cultured in floating cages. The results showed that SL addition significantly decreased the weight gain rate of male sea urchins but had no significant effects on that of female individuals. The gametogenesis of male S. intermedius was markedly accelerated by SL addition at a moderate level (1.6%), reflected by more spermatozoa and fewer nutritive phagocytes in the testis. By comparison, the gametogenesis of female individuals was only slightly promoted by 1.6% and 4% SL addition, with no oocytes observed in the ovary. The contents of arachidonic acid (ARA) in the digestive tract and gonads, and eicosapentaenoic acid (EPA) in the gonads of male and female S. intermedius were increased by SL addition at a moderate level, although their contents were still lower than the initial values. Similarly, the transcription of most fatty acid synthesis-related genes was significantly increased by 1.6% SL addition in both sexes of S. intermedius. The transcription of almost all inflammation-related genes increased with the increase of SL addition in both male and female S. intermedius. Notably, male S. intermedius showed higher ARA contents and transcription of most fatty acid synthesis and inflammation related genes than their female counterparts, especially in the SL1.6 and/or SL4 groups. In summary, SL addition showed no beneficial or negative effects on growth performance but markedly promoted gonad development and ARA and EPA accumulation in S. intermedius, especially at a moderate level (1.6%). Males showed faster gametogenesis than females possibly due to relatively higher ARA synthesis and cyclooxygenase-2 mediated eicosanoid production. The retarded growth and gametogenesis of male S. intermedius fed diets with the addition of 4% SL could be due to excessive inflammation. These results could be helpful for understanding the dosage-dependent and sex-related physiological effects of SL on growth and gonad development of S. intermedius.

Dietary protein requirement for somatic growth and gonad production in the sea urchin Strongylocentrotus intermedius at different life stages

The rise in the demand for sea urchin aquaculture requires the optimization of dietary protein levels to maximize somatic growth and gonad production throughout the aquaculture process. This study aimed to investigate the dietary protein requirement for somatic growth and gonad production of the sea urchin Strongylocentrotus intermedius at different life stages considering protein leaching from diets during seawater immersion. Feeding trials were performed on three sizes of S. intermedius: S, small urchins prior to gonad differentiation; M, medium urchins following gonad differentiation; and L, large urchins close to the biological minimum size. Two feeding trials using diets with different gluten (protein source) levels (experiment I; 5, 10, 15, 20, 30, and 40%: experiment II; 0, 2, 4, 7, and 10%) were conducted for each size group. The diet ingredients were selected to minimize protein leaching, and the protein content of each diet was determined from the average content after immersion in seawater for 24 and 72 h. No significant differences were observed in the specific growth rate (SGR) of body weight in experiment I in all size groups. The SGRs of the body weight of urchins fed 4 and 7% gluten diets were significantly higher than those fed diets containing 0% gluten in experiments SII and MII, and a similar tendency was observed for SGRs for the body weight and test diameter of large urchins. Gonad indices of sea urchins increased with an increase in dietary protein content in experiments MII and LII, and the gonad indices of urchins fed 15 and 20% gluten diets were significantly higher than those fed 5% gluten diet in experiments MI and LI. Broken-line regression analyses on urchins in experiment II estimated the protein requirement for somatic growth to be 2% regardless of the urchin size, which is well below the range of feed protein contents (9–50%) used in previous studies. The analyses on urchins in experiment I estimated the protein requirement for gonad production of medium and large urchins to be 13% and 15%, respectively, which was lower than that previously reported (>20%). These results indicate that previous studies overestimated the protein requirement owing to protein leaching during the immersion of feed in seawater. Our findings indicate that protein content in sea urchin feed diets can be considerably reduced irrespective of their cultivation stage from seed to market size.

Pathogenicity and immune response of the sea urchin Mesocentrotus nudus to Vibrio coralliilyticus infection

Bacterial infectious diseases, as one of the serious threats to sea urchins, have brought great economic losses to the farming industry in East Asia. In the present work, we isolated a pathogen named Vibrio coralliilyticus G2–37 from the sea urchin Strongylocentrotus intermedius with overt disease symptoms. Here, we first confirmed this bacterium as a potential pathogen of the sea urchin Mesocentrotus nudus and then assessed its impacts on the survival, histology, and immune responses of M. nudus. The median lethal dose (LD50) for G2–37 on M. nudus was determined to be 4.486 × 105 CFU/mL by a bacterial challenge experiment. Histopathological examination showed that V. coralliilyticus caused severe damage to the intestine, gonad, and perioral membrane of M. nudus in the late stage of infection. Flow cytometry demonstrated that V. coralliilyticus could significantly induce the apoptosis of M. nudus coelomocytes. Moreover, we found that M. nudus presented complex tissue-specificity and time-dependent immune responses after V. coralliilyticus infection. Principal Component Analysis (PCA) revealed that the physiological states of the intestine, coelomocyte lysate supernatant (CLS), and cell-free coelomic fluid (CCF) from M. nudus were strongly affected with increasing duration of infection. Integrated biomarker response (IBR) analysis proved that V. coralliilyticus infection could decrease the immune capacity and increase the oxidative damage of M. nudus, leading to potential consequences for sea urchin health. M. nudus might exist for a certain steady period at 60 h after pathogen infection, but they still face a survival crisis under the long-term challenge of the pathogen.

How ocean warming and acidification affect the life cycle of six worldwide commercialised sea urchin species: A review

AbstractOngoing global changes are expected to affect the worldwide production of many fisheries and aquaculture systems. Because invertebrates represent a relevant industry, it is crucial to anticipate challenges that are resulting from the current environmental alterations. In this review, we rely on the estimated physiological limits of six commercialised species of sea urchins (Loxechinus albus, Mesocentrotus franciscanus, Paracentrotus lividus, Strongylocentrotus droebachiensis, Strongylocentrotus intermedius and Strongylocentrotus purpuratus) to define the vulnerability (or resilience) of their populations facing ocean warming and acidification (OW&amp;A). Considering that coastal systems do not change uniformly and that the populations’ response to stressors varies depending on their origin, we investigate the effects of OW&amp;A by including studies that estimate future environmental mutations within their distribution areas. Cross‐referencing 79 studies, we find that several sea urchin populations are potentially vulnerable to the predicted OW&amp;A as environmental conditions in certain regions are expected to shift beyond their estimated physiological limit of tolerance. Specifically, while upper thermal thresholds seem to be respected for L. albus along the SW American coast, M. franciscanus and S. purpuratus southern populations appear to be vulnerable in NW America. Moreover, as a result of the strong warming expected in the Arctic and sub‐Arctic regions, the local productivity of S. droebachiensis is also potentially largely affected. Finally, populations of S. intermedius and P. lividus found in northern Japan and eastern Mediterranean respectively, are supposed to decline due to large environmental changes brought about by OW&amp;A. This review highlights the status and the potential of local adaptation of a number of sea urchin populations in response to changing environmental conditions, revealing possible future challenges for various local fishing industries.

Nanoplastics affect the growth of sea urchins (Strongylocentrotus intermedius) and damage gut health

Nanoplastics (NPs) are abundant and widespread throughout the ocean, not only causing severe environmental pollution, but also worsening the aquatic organisms. To elucidate the mechanism of biological toxic effects underlying the responses of marine invertebrates to NPs, Strongylocentrotus intermedius was stressed with three different NPs concentrations (0 particles/L, 102 particles/L and 104 particles/L). Specific growth rates, enzyme activity, gut tissue section observation and structural characteristics of the gut bacterial community were analyzed. After 28 days of exposure, the specific growth rate of S. intermedius decreased significantly with NPs groups. Further, both lysozyme, pepsin, lipase and amylase activities decreased, while the superoxide dismutase activity increased, indicating that NPs negatively affected digestive enzyme and immune enzyme activity. The analysis of gut tissue sections revealed that NPs caused atrophy and cytoplasmic reduction in the epithelial cells of the S. intermedius intestine. Moreover, the structural characterization of the gut bacterial community indicated significant changes in the abundances of members from Campylobacterota, Chlamydiae, and Firmicutes. Members from Arcobacteraceae, Christensenellaceae and Clostridia were endemic to the NPs treatment. The KEGG database analysis demonstrated that the metabolic pathways specific to the NPs treatment group were significantly associated with growth, energy metabolism, and immunity. In summary, NPs have negatively affected on physiological response and altered gut microecological environment.

Characterization of a novel glutamate dehydrogenase gene and its response to heat stress in the sea urchin Strongylocentrotus intermedius

Glutamate dehydrogenase (GDH), a key metabolic enzyme that is ubiquitous across almost all living species, is essential for cell survival. To elucidate the characteristics and functions of the GDH gene in the sea urchin, we cloned and characterized the full-length cDNA of a novel GDH homolog from Strongylocentrotus intermedius, herein designated SiGDH. The full-length SiGDH gene was 2499 bp, with an open reading frame (ORF) of 1635 bp, encoding 544 amino acids. Bioinformatic analyses revealed that the predicted SiGDH protein contained the conserved ELFV_dehydrog_N and ELFV_dehydrog domains and that this protein had the highest sequence identity with the GDH protein from Strongylocentrotus purpuratus. Tissue-specific differences in SiGDH relative expression patterns and enzyme activity levels were observed, and the highest relative expression and total enzyme activity of SiGDH were determined to be in the gonad. Changes in SiGDH relative expression and enzyme activity in the gonad were observed after both gradual and acute heat stress. Together, our observations help to clarify the characteristics of this GDH homolog, as well as its associations with heat resistance in echinoderms.