Silver (Ag) is widely released into aquatic environments through industrial and municipal discharges, with concentrations often reaching toxic levels for aquatic organisms. Its further extensive use in antimicrobials, especially during the COVID-19 pandemic, has increased environmental inputs. As Ag+ is the most toxic form of Ag, understanding its ecological risks remains critical for environmental regulation and ecosystem protection. Thus, we investigated multigenerational and transgenerational toxicity of Ag+ as AgNO3 on the ecologically important species midge Chironomus riparius using two complementary long-term life-cycle experiments. Experiment 1 simulated exposures with pulsed high environmentally relevant concentrations and recovery phases (nominal 3 µg/L), while Experiment 2 assessed continuous low environmentally relevant concentrations (nominal 0.01, 0.1, 1 and 3 µg/L) across four exposed generations of C. riparius followed by three recovery generations. Endpoints included survival, development, reproduction, growth as well as the population growth rate (PGR). Continuous Ag+ exposure produced cumulative increases in mortality and declines in emergence, reduced fertility and eggs per rope, delayed development (especially in females), and progressive reductions in PGR. Notably, adverse effects emerged or intensified over generations and were detectable at very low concentrations: some reproductive and survival endpoints showed significant impairment at the European Union’s environmental quality standard (EU-EQS) level (0.01 µg/L) by the fourth generation, while transgenerational effects persisted at ≥0.1 µg/L. Partial recovery occurred after removal of contamination at the lowest concentrations but not after higher exposures. The present study not only indicates that chronic, low-level Ag+ contamination can produce persistent, population-level adverse impacts on C. riparius, but also underscores the necessity for long-term ecological assessments to establish more protective standards and maintain ecosystem stability.

The energetic link in the benthic community is based on physiological characteristics of the low food absorption efficiency of sea urchins. Low food absorption efficiency of sea urchins is correlated with the activity of digestive enzymes and the duration of food in their gut. Thus, the digestive enzymes activities (pepsin and amylase enzyme activities) and gut emptying are important indicators in assessing nutrient digestion and absorption in sea urchins. In the present study, the relationship between these indicators and molecules related to digestive physiology were quantified in sea urchins. We found (1) an inter-regulatory relationship existed between Transient receptor potential cation channel, subfamily A, member 1 (TRPA1), and serotonin (5-hydroxytryptamine; 5-HT) in the gut of Strongylocentrotus intermedius; (2) digestive enzyme activities were negatively correlated with the TRPA1 and concentration of 5-HT in the gut of S. intermedius; (3) gut emptying rate was positively correlated with TRPA1 and concentration of 5-HT in the gut of S. intermedius. The present study revealed that the digestion and absorption of food are correlated with the TRPA1 and 5-HT in the gut of S. intermedius, which provides valuable information about the digestive physiology of sea urchins. This novel finding is relevant to understanding the low food digestibility of sea urchins. It also provides valuable information to the digestive physiology of sea urchins, which are key to maintaining the stability of food webs in the marine ecosystem.

底播增殖是一种提高中间球海胆(Strongylocentrotus intermedius)产量的有效方法.底播增殖受到多种内在和外在因素的影响,其中温度发挥着十分重要的作用,因此确定中间球海胆适宜增殖温度范围至关重要.本实验将大(23.29±0.27)mm、小(18.78±0.19)mm两种规格的中间球海胆放置在3个温度环境下(10℃、15℃、20℃)养殖6周,观察并测定其生存、生长和行为.实验结果表明,3个温度条件均不会造成海胆死亡.20℃组的两种规格海胆摄食量显著高于15℃和10℃组(P＜0.01).10℃、15℃组小规格海胆的觅食时间显著大于20℃组(P＜0.01),觅食距离显著小于20℃组(P＜0.05).在趋光实验中,20℃组小规格海胆的运动时间显著大于15℃组(P＜0.01);运动路程显著小于15℃、10℃组(P＜0.05).在避光实验中,两规格海胆20℃组的运动时间均显著大于15℃、10℃组(P＜0.05),运动路程均显著小于15℃、10℃组(P＜0.01);15℃、10℃组两种规格海胆口器咬合频率显著大于20℃组(P＜0.01).15℃、10℃组两种规格海胆的壳径、壳高、体重、性腺重、肠重、口器长、口器重、壳重、壳压力均大于20℃组;15℃、10℃组两种规格海胆的口器长/壳径、壳高/壳径均大于20℃组.综上所述,在10℃和15℃的水温下,中间球海胆均表现出显著更好的行为和生长,10～15℃是中间球海胆幼胆底播增殖的适宜增殖温度范围,在该环境下放流中间球海胆幼胆预期能够提升底播增殖生产效率.

Poor growth and disease transmission of small sea urchins Strongylocentrotus intermedius in summer greatly hamper the production efficiency of the longline culture. Reducing the adverse effects of high stocking density while maintaining high biomass is essential to address these problems. Here, we conducted a laboratory experiment to simulate the multi-layer culture for sea urchins at ambient high temperatures (from 22.2 to 24.5 °C) in summer for ~ 7 weeks. Survival, body size, lantern growth, gut weight, food consumption, Aristotle's lantern reflex, 5-hydroxytryptamine concentration, pepsin activity and gut morphology were subsequently evaluated. The present study found that multi-layer culture led to significantly larger body size than those without multi-layer culture (the control group). This was probably because of the greater feeding capacity (indicated by lantern growth and Aristotle's lantern reflex) and food digestion (indicated by morphology and pepsin activity of gut) in the multi-layer cultured sea urchins. These results indicate that multi-layer is an effective approach to improving the growth efficiency of sea urchins at high temperatures. We assessed whether eliminating interaction further improve these commercially important traits of sea urchins in multi-layer culture. This study found that eliminating interactions displayed greater body size and Aristotle's lantern reflex than those not separated in the multi-layer culture. This approach also significantly reduced the morbidity compared with the control group. These novel findings indicate that eliminating interactions in multi-layer culture greatly contributes to the growth and disease prevention of sea urchins at high temperatures. The present study establishes a new technique for the longline culture of sea urchins in summer and provides valuable information into the longline culture management of other commercially important species (e.g. scallops, abalones and oysters).

The appropriate light spectrum for reseeding small sea urchins is crucial for stock enhancement. Here, we investigated righting, foraging behavior and growth of small sea urchins Strongylocentrotus intermedius exposed to five light spectra (blue light: 440–490 nm, green light: 510–550 nm, red light: 630–670 nm, yellow light: 570–600 nm and white light) for 60 days. In the present study, S. intermedius exposed to red light had a smaller test diameter than those exposed to other light spectra (P < 0.05). No significant difference of daily weight gain was found among light spectra groups (P > 0.05). Consistently, the lantern length and weight of S. intermedius under red light were smallest among five light spectra. These results indicate that red light significantly inhibits the growth of S. intermedius. The successful foraging proportion showed no significant difference among the five light spectra (P > 0.05). Righting response time and foraging time, however, were significantly higher in S. intermedius under blue light than those exposed to other light spectra (both P < 0.01). This highlights the importance and necessity of kelp beds and shelters at the reseeding site to avoid the long-term effects of blue light on foraging and righting behaviors.

Interaction among sea urchins remains largely uninvestigated, although the aggregation of sea urchins is common. In the present study, 1, 15 and 30 sea urchins Strongylocentrotus intermedius (11.06 ± 0.99 mm in test diameter) were placed in a 1 m 2 circular tank, respectively. Movement behaviors were recorded for 12 min to investigate potential interactions among sea urchins. After the 12-min control period, we added food cues into the tank and recorded the changes in sea urchins’ behaviors. For the first time, we here quantified the interactions among sea urchins in laboratory and found that the interactions varied with food cues and with different densities. The sea urchins dispersed in random directions after being released. There was no significant difference in the movement speed and the displacement of sea urchins among the three density groups (1, 15 and 30 ind/m 2 ). The interaction occurred when sea urchins randomly contacted with the conspecifics and slowed down the movement speed. The speed of sea urchins after physical contacts decreased by an average of 40% in the density of 15 ind/m 2 and 17% in the density of 30 ind/m 2 . This interaction resulted in significantly higher randomness in the movement direction and lower movement linearity in 15 and 30 ind/m 2 than in 1 ind/m 2 . After the introduction of food cues, the movement speed, displacement and dispersal distance of sea urchin groups decreased significantly in all the three densities. The dispersal distance and expansion speed of sea urchins were significantly lower in 30 ind/m 2 than those in 15 ind/m 2 . The present study indicates that the interaction among sea urchins limits the movement of individual sea urchin and provides valuable information into how large groups of sea urchins are stable in places where food is plentiful.

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.

The detection of light intensity and subsequent phototaxis are essential for the fitness of sea urchins in intertidal and shallow subtidal waters, where light intensity varies in accordance with the depth and other hydrographic conditions. The molecular basis of photoresponse, however, remains largely unknown. We compared the expression of SiOpsin4, SiPax6, and SiOpsin5 among tube feet, coelomocytes, gonads, and gut of the sea urchin Strongylocentrotus intermedius. All three genes showed the significantly highest expression in tube feet. To test whether r-opsin genes (for example, Opsin4) and Pax6 in tube feet, rather than chaopsin genes (for example, Opsin5), are involved in the molecular responses to light intensity, we investigated the expression of Opsin4, Pax6, and Opsin5 among four light intensities. Both Opsin4 and Pax6 expressions were significantly higher in the sea urchins at 1,500 lx than at 100, 300, and 700 lx, indicating a co-upregulation of Opsin4 and Pax6 expressions in sea urchins exposed to the high light intensity (for example, 1,500 lx). However, there was no significant difference of SiOpsin5 expression among the four light intensity groups. Consistent with our hypothesis, there was no significant difference in either Opsin4 or Pax6 expression between the two light intensity environments (low light intensity environment: 50-100 lx; high light intensity environment: 330-1400 lx). This indicates that positive phototaxis and negative phototaxis probably regulate the expression of Opsin4 and Pax6 to a similar level when sea urchins are exposed to the high and low light intensities, respectively. The present study provides new insights into the molecular basis of light intensity detection and subsequent phototaxis of eyeless species.

Ocean warming increasingly endangers the fitness of marine invertebrates. Transgenerational effects (TE) potentially mitigate the impacts of environmental stress on the embryos of marine invertebrates. The molecular mechanisms, however, remain largely unknown. Using high-throughput RNA sequencing technology, we investigated the gene expression patterns of embryos (the gastrula stage) of the sea urchin Strongylocentrotus intermedius at different developmental temperatures, whose parents were exposed to long-term (15 months) elevated temperature (A) or not (B). The temperatures at which adults were held for ~4 weeks prior to the start of the experiment (21 °C for A and 18 °C for B) were also used for the development of offspring (high: 21 °C and ambient (laboratory): 18 °C) resulting in four experimental groups (HA and HB at 21 °C, and LA and LB at 18 °C). The embryos were sampled ~24 h after fertilization. All samples were in the gastrula stage. Twelve mRNA libraries (groups HA, HB, LA, LB, 3 replicates for each group) were established for the following sequencing. Embryos whose parents were exposed to elevated temperatures or not showed 1891 significantly different DEGs (differentially expressed genes) at the ambient developmental temperature (LB vs LA, LB as control) and 2203 significantly different DEGs at the high developmental temperature (HB vs HA, HB as control), respectively. This result indicates complex molecular mechanisms of transgenerational effects of ocean warming, in which a large number of genes are involved. With the TE, we found 904 shared DEGs in both LB vs LA (LB as control) and HB vs HA (HB as control) changed in the same direction of expression (i.e., up- or down-regulated), indicating that parental exposed temperatures affect the expression of these genes in the same manner regardless of the development temperature. With developmental exposure, we found 198 shared DEGs in both HB vs LB (HB as control) and HA vs LA (HA as control) changed in the same direction of expression. Of the 198 DEGs, more genes were up-regulated at high developmental temperature. Interestingly, embryos whose parents were exposed to high temperature showed fewer differently expressed DEGs between high and low developmental temperatures than the individuals whose parents were exposed to ambient temperature. The results indicate that gene expressions are probably depressed by the transgenerational effect of ocean warming. The roles of hsp70 and hnf6 in thermal acclimation are highlighted for future studies. The present study provides new insights into the molecular mechanisms of the transgenerational and developmental effects of ocean warming on the embryos of sea urchins.

Light is an important environmental factor for the fitness of small sea urchins. It is thus important to reveal the appropriate light environments for their stock enhancement. However, the effects of light spectra on fitness related behaviors of sea urchins remain mostly unknown. To reveal appropriate light spectra for stock enhancement of the sea urchin Strongylocentrotus intermedius, we investigated the effects of light spectra on the foraging behavior, phototaxis, Aristotle's lantern reflex of S. intermedius (test diameter: 10.35 +/- 0.05 mm). There were five light spectra, including red (630-670 nm), yellow (570-600 nm), green (510-550 nm), blue (440-490 nm) and white light (a mix of blue-based and a little red). We found that successful foraging proportion under blue light (65 %) was obviously higher than those under other light spectra, although no significant difference was detected (P > 0.05). The foraging time of S. intermedius was significantly higher under red light than under blue (P < 0.05) and white light (P < 0.01). Light spectra did not significantly affect the movement distance of S. intermedius (P> 0.05). Light spectra showed no significant effect on phototaxis of S. intermedius (P > 0.05). This indicates that the effect of light spectra on the foraging behavior is not due to phototaxis and movement distance in S. intermedius. Further, Aristotle's lantern reflex of S. intermedius under white light was significantly higher than that under red light (P < 0.01). In summary, S. intermedius showed significantly better foraging and feeding ability, when they were exposed to blue and white light. Since most of the spectrum is short-wavelength light (blue light) in the water below 10 m, we suggest that small S. intermedius are appropriate to be reseeded into clear water areas with the depths more than 10 m.

Mass mortality of the long line culture of the sea urchin Strongylocentrotus intermedius in summer, which is greatly associated with their disease, energy storage and resistant abilities, is the most serious problem for the development of the aquaculture. Here, a feeding experiment was conducted for similar to 9 weeks to investigate the survival, growth and gonadal development of small S. intermedius (similar to 3 cm) fed either brown algae Sargassum horneri or Saccharina japonica. Subsequently, we assessed their resistant abilities via observing the behaviors of righting, tube feet extension and Aristotle's lantern reflex at both moderately elevated and acutely changed water temperatures. Sea urchins fed S. horneri showed significantly fewer diseased individuals and slower gonadal development than those fed S. japonica. Consistently, significantly greater Aristotle's lantern reflex occurred in sea urchins fed S. horneri at moderately elevated temperatures. These findings suggest that S. horneri has direct application potential as food for the long line culture of S. intermedius in summer because of the advantage in health, energy storage (avoid the energy loss caused by gonadal development at small body sizes) and resistance abilities. In comparison, sea urchins fed S. japonica outperformed those fed S. horneri for all experimental behaviors under the acutely changed water temperatures. These findings clearly suggest that S. intermedius fed S. japonica is more suitable for the areas with cold water mass in summer, because it can effectively avoid or reduce the negative impacts of acute changes of water temperature on sea urchins. The present study provides valuable information into the management of the long line culture of S. intermedius in summer.

Probiotic is well known because of its health benefit on the host, including improve growth, treat disease, and enhance immunity. Currently, probiotic has been widely used in aquaculture. However, there is little information about the effect of probiotic on turbot. Therefore, an effort was made to explore the effect of a multi-strain probiotic on growth performance, non-specific immune response, and intestinal health of juvenile turbot, Scophthalmus maximus L. One hundred eighty juvenile turbot (20.04 ± 0.23 g) were randomly divided into three groups (T0, T1, T2), and fed diet were formulated to contain 0%, 1%, and 5% multi-strain probiotic, respectively. Sixty days after the feeding experiment, the growth performance, body composition, enzyme activities, and intestinal microorganism of turbot were analyzed. T2 and T1 showed better growth performance and significant higher (P < 0.05) enzyme activities than T0 (except lysozyme). Moreover, the IV (intestinal villus), IW (intestinal wall), and GC (goblet cell) were well modulated in probiotic treatments. Furthermore, Lactobacillus was found colonized in the intestine of the group fed with 5% multi-strain probiotic. These results suggested adding dietary multi-strain probiotic could positively affect for turbot aquaculture.

Thermal perception is crucial for the fitness of marine invertebrates in intertidal and shallow waters. TRPA1 is a non-selective cation channel that belongs to the TRP family with pivotal roles in initiating signal transduction of thermal perception. We investigated expression patterns of SiTRPA1 in different tissues (tube feet, coelomocytes, gonads and gut) of the sea urchin Strongylocentrotus intermedius. SiTRPA1 expression patterns under acute and long-term temperature stimuli were investigated in tube feet of sea urchins. In the present study, the highest expression of SiTRPA1 was detected in tube feet of S. intermedius. The SiTRPA1 expression level in tube feet were significantly 235.7-fold, 450.0-fold and 3299.7-fold higher than those in the coelomocytes, gonads and gut (df = 3, F = 47.382, P < 0.001). Expression levels of SiTRPA1 in the other tissues (coelomocytes, gonads and gut) were not significantly different (df = 3, F = 47.382, P = 0.972). There was no significant difference of SiTRPA1 expression among all groups in the acute temperature increase experiment (df = 4, F = 0.25, P = 0.902). In the acute temperature decrease experiment, the expression of SiTRPA1 showed no significant difference among all groups (df = 4, F = 1.802, P = 0.205). With long-term exposure (6 weeks) to different temperatures, SiTRPA1 expression in the low temperature group (10 degrees C) was significantly higher than those in the high temperature (20 degrees C) and the control groups (15 degrees C) (df = 2, F = 9.57, P = 0.014). There was no significant difference of SiTRPA1 expression between the high temperature (20 degrees C) and the control temperature (15 degrees C) groups (df = 2, F = 9.57, P = 0.808). These results indicate that SiTRPA1 expression significantly responds to long-term low temperature but not to acute temperature decrease. The present study provides new insights on the distribution and temporal expression of TRPA1 in marine invertebrates after acute and long-term temperature stimuli.

Small sea urchins Strongylocentrotus intermedius (1-2 cm of test diameter) are exposed to different environments of light intensities after being reseeded to the sea bottom. With little information available about the behavioral responses of S. intermedius to different light intensities in the environment, we carried out an investigation on how S. intermedius is affected by three light intensity environments in terms of phototaxis, foraging and righting behaviors. They were no light (zero lx), low light intensity (24-209 lx) and high light intensity (252-2,280 lx). Light intensity had obvious different effects on phototaxis. In low light intensity, sea urchins moved more and spent significantly more time at the higher intensity (69-209 lx) (P = 0.046). S. intermedius in high light intensity, in contrast, spent significantly more time at lower intensity (252-690 lx) (P = 0.005). Unexpectedly, no significant difference of movement (average velocity and total distance covered) was found among the three light intensities (P > 0.05). Foraging behavior of S. intermedius was significantly different among the light intensities. In the no light environment, only three of ten S. intermedius found food within 7 min. In low light intensity, nine of 10 sea urchins showed successful foraging behavior to the food placed at 209 lx, which was significantly higher than the ratio of the number (two of 10) when food was placed at 24 lx (P = 0.005). In the high light intensity, in contrast, significantly less sea urchins (three of 10) found food placed at the higher light intensity (2,280 lx) compared with the lower light intensity (252 lx) (10/10, P = 0.003). Furthermore, S. intermedius showed significantly longer righting response time in the high light intensity compared with both no light (P = 0.001) and low light intensity (P = 0.031). No significant difference was found in righting behavior between no light and low light intensity (P = 0.892). The present study indicates that light intensity significantly affects phototaxis, foraging and righting behaviors of S. intermedius and that ~200 lx might be the appropriate light intensity for reseeding small S. intermedius.

Transgenerational effects are important for phenotypic plasticity and adaptation of marine invertebrates in the changing ocean. Ultraviolet-B (UV-B) radiation is an increasing threat to marine invertebrates. For the first time, we reported positive and negative transgenerational effects of UV-B radiation on egg size, fertilization, hatchability and larval size of a marine invertebrate. Strongylocentrotus intermedius exposed to UV-B radiation showed positive transgenerational effects and adaptation on egg size, hatching rate and post-oral arm length of larvae. Negative transgenerational effects were found in body length, stomach length and stomach width of larvae whose parents were exposed to UV-B radiation. Sires probably play important roles in transgenerational effects of UV-B. The present study provides valuable information into transgenerational effects of UV-B radiation on fitness related traits of sea urchins (at least Strongylocentrotus intermedius ).

Stock enhancement as an effective method of increasing production of Mesocentrotus nudes has prompted increasing interest in both China and Japan. Ifs essential to reveal the optimal temperature range for stock enhancement of M. nudes. In order to achieve this aim, we carried out a simulated laboratory experiment including three levels of water temperatures (10 degrees C, 15 degrees C and 20 degrees C) to investigate effects of different temperatures on the survival, food consumption, growth and behaviors of small, medium and large size M. nudes for similar to 50 days. According to our investigation, all the three size M. nudes exposed to 15 degrees C showed significantly better growth, faster righting speed among the three temperature levels. All the three size M. nudes exposed to 20 degrees C showed faster righting speed, better growth and longer movement distance than those exposed to 10 degrees C. We suggest aquafarmers to release M. nudes onto the sea floor when the natural water temperature reaches 15-20 degrees C for stock enhancement, which is more benefit for their survival, behavior and growth than the range of 10-15 degrees C.

Ozone depletion induced by anthropogenic gases has been increasing the transmission of solar ultraviolet-B radiation (UV-B, 280–315 nm) through the atmosphere, which may impact the fitness of marine invertebrates in intertidal and shallow waters. To our knowledge, however, the responses of fitness related behaviors to UV-B radiation at different intensities have been rarely studied in marine invertebrates. For the first time, the present study investigated the effects of exposure of one hour to UV-B radiation at different intensities on foraging behavior, Aristotle’s lantern reflex and righting behavior of the sea urchin Strongylocentrotus intermedius. Exposure of one hour to UV-B radiation at 10 μW/cm2 significantly reduced foraging behavior. An intensity dependent effect of exposure to UV-B radiation was found in the duration of the Aristotle’s lantern reflex. Exposure to UV-B radiation at 20 μW/cm2 for one hour significantly reduced the duration of the Aristotle’s lantern reflex, but 10 μW/cm2 did not. There was no significant difference of righting response time among sea urchins exposed to 0, 10 and 20 μW/cm2 for one hour. To test potential carryover effects, the behavioral traits were re-measured three days later. We found significant carryover effects of UV-B radiation on foraging time and righting response time, but not on the duration of the Aristotle’s lantern reflex. The present study indicates that a brief exposure of one hour to UV-B radiation can significantly affect the duration of Aristotle’s lantern reflex, righting response time and foraging behavior of a sea urchin, although the immediate impacts and carryover effects were highly trait dependent. This study provides new information into the behavioral responses of marine invertebrates to exposure to UV-B radiation. Future studies should be carried out to investigate long-term carryover effects of UV-B radiation on behavioral and physiological fitness related traits.

Triplicate groups of sea cucumbers (4.83 ± 0.15 g) were exposed to one of the four nominal concentrations of dietary mercury [0 (control), 67.6, 338, and 676 mg/kg dry weight, and actually total mercury were 17.55, 87.00, 275.50, 468.50 mg/kg, respectively; Table 3] for 21 days. Mercury accumulation in the intestine showed the greatest mercury burden (77.96 ± 1.20 mg Hg/kg tissue wet weight basis). However, survival rate (SR) was not affected. Body weight gain after the 676 mg Hg/kg treatment was significantly lower than the control group. The feed conversion rate of the 676 mg Hg/kg treatment group was significantly higher than the control group. Additionally, the superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) of sea cucumbers decreased as the mercury dose increased. SOD, T-AOC and alkaline phosphatase of the 676 mg Hg/kg treatment group were significantly lower than the control group. However, there were no significant differences between the four groups in acid phosphatase and catalase (CAT) activity.

Although the potential link exists between behavioral responses to UV-B radiation and the maximization of fitness, molecular mechanisms of these UV-B induced behaviors remain poorly understood. For the first time, we investigated the transcriptomes of covered (CB), sheltered (SB) and non-protected (NA) sea urchins Strongylocentrotus intermedius exposed to UV-B radiation. A total of 330 differentially expressed genes were revealed by transcriptome comparisons. By comparing with the group NA, we found 79 up-regulated and 118 down-regulated genes in SB group, as well as 26 up-regulated and 67 down-regulated genes in group CB. There were 34 up-regulated genes and 52 down-regulated genes in group SB, compared with group CB. These differentially expressed genes failed to enrich either Gene Ontology (GO) or Kyoto Encyclopedia of Genes and Genomes (KEGG), only except an enrichment in KEGG. We highlighted TRPA1 and Opsin as key neurobiological genes involved in the molecular mechanisms of covering and sheltering behaviors of sea urchins exposed to UV-B radiation. What's more, other identified genes provide valuable resources for future investigations on the molecular basis of covering and sheltering behaviors of sea urchins.

Transgenerational effects, which involve both selection and plasticity, are important for the evolutionary adaptation of echinoderms in the changing ocean. Here, we investigated the effects of breeding design and water temperature for offspring on fertilization, hatchability, larval survival, size, abnormality and metamorphosis of the sea urchin Strongylocentrotus intermedius, whose dams and sires were exposed to long-term (~15 months) elevated temperature (~3°C above ambient) or ambient temperature. There was no transgenerational effect on fertilization and metamorphosis of S. intermedius, while negative transgenerational effects were found in hatchability and most traits of larval size. Dam and sire effects were highly trait and developmental stage dependent. Interestingly, we found S. intermedius probably cannot achieve transgenerational acclimation to long-term elevated temperature for survival provided their offspring were exposed to an elevated temperature. The present study enriches our understanding of transgenerational effects of ocean warming on sea urchins.