Sea Urchin Mesocentrotus Nudus Research Articles

Nuclear receptor gene expression during early gametogenesis in sea urchin Mesocentrotus nudus gonads

Nuclear receptor gene expression during early gametogenesis in sea urchin Mesocentrotus nudus gonads

Potential of Sea Urchin Mesocentrotus nudus as a Target Catch Species in the Pacific Ocean off Eastern Hokkaido, Japan.

Scientific reports on the distribution of Mesocentrotus nudus in Hokkaido are limited from Cape Soya to Cape Erimo along the coast of the Sea of Japan; however, fishery statistics show that its distribution has extended to the Sea of Okhotsk and Pacific Ocean off Hokkaido. In 2021, large-scale harmful algal blooms (HABs) occurred in the Pacific Ocean off eastern Hokkaido, resulting in the massive die-off of marine organisms, including M. nudus. This study aimed to redefine the distribution of M. nudus in the Pacific Ocean off eastern Hokkaido after the HABs. Field surveys were conducted in July, August, and December 2023 in Akkeshi, the site farthest from Cape Soya among the areas where irregular catches of M. nudus have been recorded in eastern Hokkaido, and the distribution of this species was confirmed in August and December. All sea urchins collected were >6 years of age, indicating that they survived the HABs. High gonad indices and spermatozoa-filled gonads were observed in the sea urchins collected in December, suggesting that the reproductive cycle of M. nudus in Akkeshi may be close to that observed in specimens off Wakkanai, Cape Soya. Warming trends may cause population increases in the future.

Temperature-Dependent Food Consumption Rates of the Sea Urchin Mesocentrotus nudus and Top Shell Turbo sazae: Potential Impacts on Seaweed Beds.

In Korea, the expansion of barren ground and a shift in macrograzer habitats due to increasing water temperatures associated with climate change are becoming increasingly problematic. This study assessed the potential effects of the sea urchin Mesocentrotus nudus and top shell Turbo sazae on seaweed beds by examining changes in their food consumption rates in response to changes in temperature. The food consumption rates of kelp (Saccharina japonica) for both species were estimated at 5 °C, 10 °C, 15 °C, 20 °C, and 25 °C in laboratory experiments. The rate for M. nudus increased with increasing water temperature, with the highest rate of 0.001 g g-1 d-1 at 15 °C and 20 °C, and the lowest at 25 °C, which killed some individual sea urchins. The rate for T. sazae also increased with increasing water temperature, with the highest being 0.087 g g-1 d-1 at 25 °C and the lowest being at 5 °C. T. sazae had a higher food consumption rate than M. nudus at all temperatures; as water temperature increased, the difference between species increased, with the largest difference occurring at 25 °C. These findings indicate that as water temperature increases, T. sazae places greater feeding pressure on macroalgae than M. nudus.

Alterations in sea urchin (Mesocentrotus nudus) microbiota and their potential contributions to host according to barren severity

Sea urchins are biotic factors driving the decline of kelp forests in marine ecosystems. However, few studies have analyzed the microbiota of surviving sea urchins in barren regions with scarce diet resources. Here, we analyzed the microbiota in the pharynx and gut of the sea urchin Mesocentrotus nudus located along the coast of an expanding barren region in South Korea. The ecological adaptation of genera in sea urchins was predicted using the neutral assembly model. The pharynx and gut microbiota were different, and microbes in the surrounding habitats dispersed more to the pharynx than to the gut. The gut microbiota in sea urchins is altered by barren severity and plays different roles in host energy metabolism. These findings help to understand the microbiota in sea urchins according to urchin barren and its contribution to the survival of sea urchins in severe barren regions with limited macroalgae.

Global Analysis of 2-Hydroxy Fatty Acids by Gas Chromatography-Tandem Mass Spectrometry Reveals Species-Specific Enrichment in Echinoderms.

Abnormal levels of 2-hydroxy fatty acids (2-OH FAs) are characterized in multiple diseases, and their quantification in foodstuffs is critical to identify the sources of supplementation for potential treatment. However, due to the structural complexity and limited available standards, the comprehensive profiling of 2-OH FAs remains an ongoing challenge. Herein, an innovative approach based on gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed to determine the full profile of these FA metabolites. MS and MS/MS spectra of the trimethylsilyl (TMS) derivatives of 2-OH fatty acid methyl esters (FAMEs) were collected for peak annotation by their signature fragmentation patterns. The structures were further confirmed by validated structure-dependent retention time (RT) prediction models, taking advantage of the correlation between the RT, carbon chain length, and double bond number from commercial standards and pseudostandards identified in the whole-brain samples from mice. An in-house database containing 50 saturated and monounsaturated 2-OH FAs was established, which is expandible when additional molecular species with different chain lengths and backbone structures are identified in the future. A quantitation method was then developed by scheduled multiple reaction monitoring (MRM) and applied to investigate the profiling of 2-OH FAs in echinoderms. Our results revealed that the levels of total 2-OH FAs in sea cucumber Apostichopus japonicas (8.40 ± 0.28 mg/g dry weight) and starfish Asterias amurensis (7.51 ± 0.18 mg/g dry weight) are much higher than that in sea urchin Mesocentrotus nudus (531 ± 108 μg/g dry weight). Moreover, 2-OH C24:1 is the predominant molecular species accounting for 67.9% of the total 2-OH FA in sea cucumber, while 2-OH C16:0 is the major molecular species in starfish. In conclusion, the current innovative GC-MS approach has successfully characterized distinct molecular species of 2-OH FAs that are highly present in sea cucumbers and starfish. Thus, these findings suggest the possibility of developing future feeding strategies for preventing and treating diseases associated with 2-OH FA deficiency.

Grazing pressure of sea urchin Mesocentrotus nudus estimated from seawater temperature and wave height, and its effects on the early growth of annual kelp Saccharina japonica in northeastern Japan

Grazing by the sea urchin Mesocentrotus nudus plays a vital role in the development of marine forests of annual kelp, Saccharina japonica, along the Pacific coast of northeastern Japan. The grazing rate of sea urchins, which are rigorously temperature dependent, affects the chance of germination/survival of the kelp during winter/spring when seawater temperatures in this region are highly variable among years. It has previously been found that if the mean seawater temperature between February and March remained below 5.5 °C, kelp forests in this region would establish later in the year. However, the mechanism leading to this success or failure of kelp forests to develop has yet to be investigated in detail.Laboratory experiments confirmed that the grazing rate and movement of the sea urchin decreased as seawater temperature declined from 12 °C to 3 °C. Field observations, using interval cameras from autumn to spring, revealed that the density of sea urchins on artificial reefs decreased at lower seawater temperatures and/or higher significant wave heights (SWH). Using these relationships, the grazing pressure by sea urchins (= grazing rate × density) in the site was estimated based on seawater temperature and SWH. Comparing the grazing pressures among past years with different states of kelp forests, conditions needed to establish kelp forests were revealed. Extremely low grazing pressure (< 0.5 g m−2 day−1) lasted for a total of 31 days in 2015 when kelp grew densely, while this condition occurred on 11 and 14 days respectively in 2019 and 2022 when kelp was sparse. Kelp did not grow in 2016 when the grazing pressure continuously remained above 0.5 g m−2 day−1. At this study site, such combinations of seawater temperature and SWH as 4 °C and 1.0 m, 6 °C and 2.3 m, and 8 °C and 3.7 m would equate to a grazing pressure of 0.5 g m−2 day−1. To develop a dense kelp forest, grazing pressure was required to be lower than 0.5 g m−2 day−1 for about a month as in 2015. Though these figures should be adjusted, a model and scheme of this study will be applied to the other areas where kelp forest restoration/management plans are required.

The lysosome-phagosome pathway mediates immune regulatory mechanisms in Mesocentrotus nudus against Vibrio coralliilyticus infection.

Sea urchins are a popular model species for studying invertebrate diseases. The immune regulatory mechanisms of the sea urchin Mesocentrotus nudus during pathogenic infection are currently unknown. This study aimed to reveal the potential molecular mechanisms of M. nudus during resistance to Vibrio coralliilyticus infection by integrative transcriptomic and proteomic analyses. Here, we identified a total of 135,868 unigenes and 4,351 proteins in the four infection periods of 0h, 20h, 60h and 100h in M. nudus. In the I20, I60 and I100 infection comparison groups, 10,861, 15,201 and 8,809 differentially expressed genes (DEGs) and 2,188, 2,386 and 2,516 differentially expressed proteins (DEPs) were identified, respectively. We performed an integrated comparative analysis of the transcriptome and proteome throughout the infection phase and found very a low correlation between transcriptome and proteome changes. KEGG pathway analysis revealed that most upregulated DEGs and DEPs were involved in immune strategies. Notably, "lysosome" and "phagosome" activated throughout the infection process, could be considered the two most important enrichment pathways at the mRNA and protein levels. The significant increase in phagocytosis of infected M. nudus coelomocytes further demonstrated that the lysosome-phagosome pathway played an important immunological role in M. nudus resistance to pathogenic infection. Key gene expression profiles and protein‒protein interaction analysis revealed that cathepsin family and V-ATPase family genes might be key bridges in the lysosome-phagosome pathway. In addition, the expression patterns of key immune genes were verified using qRT‒PCR, and the different expression trends of candidate genes reflected, to some extent, the regulatory mechanism of immune homeostasis mediated by the lysosome-phagosome pathway in M. nudus against pathogenic infection. This work will provide new insights into the immune regulatory mechanisms of sea urchins under pathogenic stress and help identify key potential genes/proteins for sea urchin immune responses.

Synthetic Calcium Silicate Biocomposite Based on Sea Urchin Skeleton for 5-Fluorouracil Cancer Delivery.

Synthetic calcium silicates and phosphates are promising compounds for targeted drug delivery for the effective treatment of cancerous tumors, and for minimizing toxic effects on the patient's entire body. This work presents an original synthesis of a composite based on crystalline wollastonite CaSiO3 and combeite Na4Ca4(Si6O18), using a sea urchin Mesocentrotus nudus skeleton by microwave heating under hydrothermal conditions. The phase and elemental composition and structure of the obtained composite were studied by XRF, REM, BET, and EDS methods, depending on the microwave heating time of 30 or 60 min, respectively, and the influence of thermo-oxidative post-treatment of samples. The role of the sea urchin skeleton in the synthesis was shown. First, it provides a raw material base (source of Ca2+) for the formation of the calcium silicate composite. Second, it is a matrix for the formation of its porous inorganic framework. The sorption capacity of the composite, with respect to 5-fluorouracil, was estimated, the value of which was 12.3 mg/L. The resulting composite is a promising carrier for the targeted delivery of chemotherapeutic drugs. The mechanism of drug release from an inorganic natural matrix was also evaluated by fitting its release profile to various mathematical models.

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.

Deterioration of an annual kelp Saccharina japonica forest and its effects on dominant herbivores, sea urchin Mesocentrotus nudus and abalone Haliotis discus hannai, in northeast Japan

A marine forest of the annual kelp Saccharina japonica was monitored at three depth sites (6, 9 and 12 m) along a 200-meter-long transect in the Pacific coast of northeastern Japan from 2014 to 2021, during which the abundance of the kelp plummeted, and the forest shifted to a crustose coralline bed. Colder seawater temperature in the winter/spring (February and March), which is regulated by the extension of the cold Oyashio Current, plays an important role in establishing the kelp forest through reducing the grazing of herbivores during the critical period of kelp germination and early growth. The Oyashio Current reached the region in 2014 and 2015 but not from 2016 to 2021, making a fundamental change in the kelp forest. Macroalgal abundance was strikingly different between these two periods. Biomass of S. japonica reached up to 38.6–45.4 kg-ww m−2 in the first two years, whereas macroalgal biomass was less than 3.2 kg-ww m−2 in the latter 6 years except for in 2016 when the biomass reached 9.0 kg-ww m−2 at the 6 m site. Gonad and somatic growth of sea urchin Mesocentrotus nudus declined during the kelp deforestation, while the density of the sea urchin moderately increased in 2017. Similarly, the density of abalone Haliotis discus hannai plummeted by about 90% and the mean shell length decreased from 83 mm in 2014 to 31 mm in 2020. Under the ocean warming scheme, ecosystems depending on the primary production of S. japonica are expected to be altered in the future, and thus urging the need of environmental monitoring.

Correction to: Production of high quality gonads in the sea urchin Mesocentrotus nudus (A. Agassiz, 1864) from a barren by feeding on the kelp Saccharina japonica at the late sporophyte stage

Correction to: Production of high quality gonads in the sea urchin Mesocentrotus nudus (A. Agassiz, 1864) from a barren by feeding on the kelp Saccharina japonica at the late sporophyte stage

Contamination of sea urchin Mesocentrotus nudus by radiocesium released during the Fukushima Daiichi Nuclear Power Plant accident.

Countless marine organisms were polluted with radioactive materials that were dispersed when the Fukushima Daiichi Nuclear Power Plant (FDNPP) was damaged in 2011 by the Great East Japan Earthquake. The aim of this study was to determine the degree to which marine herbivorous sea urchins, Mesocentrotus nudus, were contaminated with radiocesium because of the accident. We collected samples of sea urchins from four locations in Fukushima prefecture (at the coast and offshore from the Yotsukura and Ena stations) and investigated how the 137Cs activity concentrations changed. The biological half-life (Tbio) of 137Cs in the individual sea urchins was between 121 and 157 days. The ecological half-life (Teco) of 137Cs was 181–423 days and was high in places close to the FDNPP. The Teco values in the sea urchins were longer than previously reported. The results infer that the food sources of the sea urchins around the Fukushima coast strongly influenced their uptake of 137Cs.

Transcriptomes reveal the involved genes in the sea urchin Mesocentrotusnudus exposed to high flow velocities

Despite the importance of flow velocity in marine ecosystems, molecular mechanisms of the water flow induced behavioral and growth changes remain largely unknown in sea urchins. The present study compared the gene expressions of the sea urchin Mesocentrotusnudus at high flow velocities (10 cm/s and 20 cm/s) and low flow velocity (2 cm/s) using transcriptomes. A total of 490 and 470 differentially expressed genes (DEGs) were discovered at 10 cm/s and 20 cm/s, respectively. There were 235 up-regulated and 255 down-regulated genes at 10 cm/s, 213 up-regulated and 257 down-regulated genes at 20 cm/s, compared with sea urchins at 2 cm/s. Further, there were 72 overlapped DEGs involved in regulation at both 10 cm/s and 20 cm/s. Gene Ontology (GO) functional annotation showed that DEGs were mainly enriched to cellular process, cell part, binding, and metabolism process. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis found that DEGs were enriched in three pathways related to amino acid metabolism and lipid metabolism. A number of genes related to growth and metabolism of sea urchins were mobilized in high flow velocity environment. We further highlighted a muscle-associated gene ankyrin-1, which is correlated with the movement of tube feet at different flow velocities. The present study provides valuable information on the molecular mechanisms of changed behaviors and growth when sea urchins are exposed to high flow velocity.

Gonad traits in the sea urchin Mesocentrotus nudus fed on the kelp Eisenia bicyclis: Gametogenesis promotion and lack of sea urchin-like taste

Perennial Eisenia bicyclis kelp beds are one of the main fishing grounds for the sea urchin Mesocentrotus nudus, whose gonad is highly valued. However, little is known about the gonad quality of sea urchins fed on this species of kelp. Feeding with two other kelp species, the biennial Saccharina japonica blade or sporophylls of the annual Undaria pinnatifida, is known to improve the gonad quality of M. nudus. The present study investigated the dietary effects of blades of E. bicyclis on gonad quality of M. nudus in comparison with feeding on S. japonica blade or U. pinnatifida sporophylls. The gonad index of urchins fed E. bicyclis (UEB) increased from 8.2 to 16.9, similar to those fed on S. japonica (USJ), which was significantly lower than those fed on sporophylls of U. pinnatifida (UUP). Of UEB, 69% had premature gonads, indicating that UEB gonads were significantly advanced to maturation compared with those of USJ or UUP, most of which were still in the growing stage. The uncoupling of gonad size and advance to maturation is not explained by the high protein content in E. byciclis, suggesting that unknown substances in E. bicyclis can promote gonad maturation. UEB gonads improved color, texture and contents of glutamic acid, alanine, and arginine similar to results obtained with USJ. However, the methionine and valine contents of UEB gonads were below the threshold of detection, explaining the lack of sea urchin-like taste of the gonads. Many unpleasant odors were detected from the gonads of UEB. In conclusion, gonad flavor of UEB is inferior compared with that of USJ or UUP. Further research is required to understand the details of gametogenesis under dietary supplementation with the species-specific compounds present in E. bicyclis.

Fitness costs of alarm cues in sea urchins: Fertilization, hatching, and larval size

Sea urchins sense alarm cues extracted from crushed conspecifics and perform anti-predation behaviors in exposure to alarm cues. This indicates of the fitness benefits of alarm cues in sea urchins. The present study investigated whether fitness costs of alarm cues exist in fertilization, hatchability, deformity, and larval size of the sea urchin Mesocentrotus nudus. In the present study, we found that fertilization and hatching rates were significantly lower in the group with alarm cues than those in the group without alarm cues, indicating that fitness costs of alarm cues exist in sea urchins. However, there was no significant difference in deformity rate, larval length, stomach length, and stomach width of M. nudus with and without alarm cues. The group with alarm cues showed significantly shorter larval width than the group without alarm cues. This indicates that smaller larvae of sea urchins more probably survive in the environment with alarm cues. The present study reveals that fitness costs of alarm cues exist in sea urchins and sheds light on the ecological roles of alarm cues in kelp bed ecosystems.

Modest Dietary Protein Requirement for Sea Urchin Gonad Production Demonstrated by Feeding Trials with Consideration of Protein Leaching

This study is aimed at revealing the dietary protein requirement for gonad production in the sea urchin Mesocentrotus nudus, with consideration of protein leaching from diets during seawater immersion. Feeding trials were performed on M. nudus using two diet types with low capacities for protein leaching: starch diets (STG) containing 0–40% gluten in 10%, 5%, and 4% increments (experiments 1–3) and alginate diets (ALG) containing 5–25% gluten in 5% increments (experiment 4). The protein content in the diets was determined after they were immersed in seawater for 24 h or 72 h. The gonad indices of urchins fed STG with 11.4–19.3% protein were significantly higher than those fed STG with 7.8% protein. The protein requirement was estimated to be 12% based on a broken-line regression analysis of urchins fed STG in experiments 1–3. In experiment 4, the gonads became larger as dietary protein content increased from 4.5% to 12.0%, and the sizes were similar to those of urchins fed ALG with 12.0–21.1% protein. The estimated value of 12% was much lower than that reported previously (&gt;20%), indicating that the protein requirement for sea urchin gonad production is modest when the protein-leaching problem is addressed.

Cloning of cDNA encoding a newly recognized apolipoprotein-like protein and its expression in the northern sea urchin Mesocentrotus nudus

Cloning of cDNA encoding a newly recognized apolipoprotein-like protein and its expression in the northern sea urchin Mesocentrotus nudus

High fitness areas drive the aggregation of the sea urchin Mesocentrotus nudus.

Sea urchin aggregation is a common phenomenon in coastlines. However, it remains controversial whether sea urchins form resource aggregations or behavioral aggregations in a non-spawning season. To clarify, we studied the aggregative responses to food and predators in the sea urchin Mesocentrotus nudus when high fitness areas (HFAs) were scarce versus sufficient. By taking the occupied area of each sea urchin (test diameter + spines = 4.5 cm) as a square (4.5 cm × 4.5 cm), we set scarce HFAs for the sea urchins in Experiment 1 (the squares of HFAs: the area occupied by experimental sea urchins = 1:1) and sufficient HFAs for the sea urchins in Experiment 2 (the squares of HFAs: the area occupied by experimental sea urchins = 2:1). If M. nudus form resource aggregations, they would aggregate passively under the scarce HFAs conditions, but not in the sufficient HFAs conditions. Conversely, if M. nudus form behavioral aggregation, aggregation would occur in both scarce and sufficient HFAs. The present results showed that in the scarce HFAs, M. nudus in the food and predator groups were significantly closer to the food and further from predators, and had significantly more aggregated numbers in HFAs than those in the control group. Sea urchins did not aggregate in response to food or predators under the sufficient HFAs, although significantly more sea urchins of the experimental group was found in HFAs than that of the control group. Sea urchins (at least M. nudus) form resource aggregations that are driven by the scarce HFAs. This provides valuable information into the mechanisms of the aggregation of sea urchins.

Effects of the swimming crab Charybdis japonica on sea urchin Mesocentrotus nudus grazing: cage experiments in barren ground and land-based tanks

Effects of the swimming crab Charybdis japonica on sea urchin Mesocentrotus nudus grazing: cage experiments in barren ground and land-based tanks

Conspecific alarm cues are a potential effective barrier to regulate foraging behavior of the sea urchin Mesocentrotus nudus

A cost-effective approach to controlling foraging and feeding behaviors of sea urchins is essential for the management of kelp beds. Laboratory experiments were designed to investigate whether alarm cues from crushed conspecific urchins can effectively prevent the foraging and feeding behaviors of the sea urchin Mesocentrotus nudus under the static seawater condition. The present study found that the number of M. nudus that foraged successfully was significantly lower when alarm cues were placed between the kelp and the sea urchins. This result indicates that alarm cues could play an important role in critical kelp-bed areas. It probably prevents sea urchins from foraging by acting as a barrier. Further, we found that alarm cues around the kelp significantly affected foraging behavior of M. nudus, indicating that the alarm cues around the kelp are a potential effective way to prevent sea urchins from foraging for the kelp. In addition, the number of sea urchins that stopped feeding was significantly higher in the group in the presence of alarm cues than that in the control group. This indicates that alarm cues may have an application in stopping sea urchins from feeding. However, there was no significant difference of Aristotle's lantern reflex between the groups with and without alarm cues. These results indicate that alarm cues greatly affect foraging behavior, but not Aristotle's lantern reflex of M. nudus. All together, the present study suggests that alarm cues have an application potential in the management of the kelp beds as green engineering. Future studies are essential to further investigate the chemical basis of the alarm cues of sea urchins for the application in large-scale.