This study systematically evaluated the sediment remediation and nutrient cycling functions of sea cucumber (Apostichopus japonicus) across three size classes (small: 52.1 ± 4.22 g; medium: 88.5 ± 13.61 g; large: 119.24 ± 7.38 g) in a novel oyster (Crassostrea gigas) -kelp (Saccharina japonica) -sea cucumber integrated multi-trophic aquaculture (IMTA) system. Integrated methodologies included stable isotope analysis (δ13C, δ15N), carbon and nitrogen budget determinations, and monitoring of nutrient fluxes across sediment-water interface. Results sea cucumbers preferentially consumed aquaculture-derived biodeposits, which constituted the major component of surface sediments and possessed high nutritional value (>60% dietary contribution), primarily including oyster feces and suspended particulate matter (SPM) from oyster and kelp monoculture areas. Carbon and nitrogen budgets revealed a distinct size-dependent "low assimilation-high egestion" metabolic strategy, with small individuals exhibiting highest mass-specific oxygen consumption (0.013 mg O2·g-1·h-1), peak ammonia excretion (0.725 μg NH4+-N·g-1·h-1), and superior net removal efficiencies for sedimentary organic carbon (53.1%) and nitrogen (34.6%). Bioturbation significantly enhanced nitrogen and phosphorus cycling, jointly modulated by body size and temperature: at temperatures <20.97 ± 0.38 °C, large individuals drove dissolved inorganic nitrogen (DIN) and PO43--P fluxes 1.9 and 1.3 times higher, respectively, than small counterparts. Sustained exposure above this thermal threshold suppressed behavioral and metabolic activity across all size classes, progressively eliminating DIN and PO43--P flux differentials between bioturbation treatments and controls. Thermal stress additionally altered benthic dissolved oxygen dynamics and nutrient speciation patterns. These findings will provide a theoretical basis for optimizing bioregulatory strategies in multi-trophic aquaculture systems.

Many marine invertebrate larvae are influenced by environmental factors during development, with diatom biofilms playing a crucial role in the settlement and metamorphosis of bivalve larvae. This study found that Navicula sp. biofilms alter the larval microenvironment by increasing dissolved oxygen levels through photosynthesis and decreasing nitrate, ammonium, and phosphate levels in the surrounding water. Exposure to Navicula sp. biofilms induced directional swimming in larvae and significantly shortened the time required for settlement and metamorphosis. Biofilms formed by Navicula sp. contained effective substances and key infochemicals that promoted the settlement and metamorphosis of Mizuhopecten yessoensis larvae. Soluble polysaccharides containing β-1,4-glycosidic bonds secreted by the biofilm were recognized by the larvae, triggering settlement and metamorphosis signaling. Untargeted and targeted metabolomic analyses revealed increased levels of cGMP (Cyclic guanosine monophosphate), and GMP (Guanosine monophosphate), suggesting that larval settlement and metamorphosis may be associated with cGMP regulation. Based on these results, cGMP was selected for subsequent functional analyses. Treatments with the NO donor SNAP, the cGMP analog 8-Br-cGMP, and the sGC activator BAY 41-2272 significantly promoted metamorphosis, whereas the sGC inhibitor ODQ suppressed metamorphosis in a dose-dependent manner. These findings demonstrate that the NO–sGC–cGMP pathway positively regulates the settlement and metamorphosis of M. yessoensis larvae, with cGMP serving as a key effector. This study provides new insights into the mechanisms underlying larval settlement and metamorphosis in bivalves.

China,a major global shellfish aquaculture country,had a national shellfish aquaculture output of 16,659,000 t in 2024,of which marine aquaculture accounted for 98.81％.As the main farmed species,oysters have an annual output of 6,671,200 t,accounting for 40.52％of the total production of marine shellfish farming.Due to the over-expansion of certain traditional aquaculture areas,the ecological carrying capacity has been exceeded and the phytoplankton biomass available for oyster feeding has been reduced,resulting in lower fattening,quality,and market price,and higher mortality rates;therefore,exploring new oyster fattening sites and methods has become integral in solving the current problems in the industry.To investigate the feasibility of Crassostrea gigas pond fattening,a self-developed culture device of oyster ponds was used to enhance the water exchange around C.gigas by using the flow generated by the natural wind disturbance on the surface of the pond to increase the bait delivery efficiency to provide sufficient bait for the C.gigas,and to try to fertilize the diploid C.gigas,which have poor fattening degree,cultured in the sea area in the shrimp and crab ponds.We fattened diploid C.gigas with poor fattening in marine culture in shrimp and crab culture ponds.From November 2023 to May 2024(the experiment was suspended during the winter freezing period),we visited the experimental ponds every 20 days to collect samples and used the WTW multi-parameter water quality analysis to measure the water temperature,salinity,pH,and dissolved oxygen.We used a water collector to collect 2 L of water samples from each of the five points at the four corners of the ponds(5-10 m from the shore)and the center of the ponds and then stored them in water sample bottles.Next,referring to the Code of Practice for Marine Surveys,the water samples were fixed with 5％formaldehyde solution on site and transported back to the laboratory to measure nutrient salt,chlorophyll a,and particulate organic matter(POM)contents.Three sizes(S,M,L)of C.gigas were set up to determine the growth and physiological indices,with average wet weights of(54.86±3.26)g,(83.81±3.94)g,and(127.46±8.64)g,respectively,and were cultured in three mixed groups in oyster pond culture devices.For the physiological indices,eight replicates and one control were established for each specification treatment group,and a flow-through device comprising a buffer box,flow-through tank,and rectangular plastic box was used for feeding physiology and respiratory metabolism measurements.During the experimental period,a grapple-type mud collector was used to collect pond sediment underneath and around the aquaculture devices at the aquaculture site,artificial feed,suspended particles,and feces of C.gigas,which were used to determine the sediment of aquaculture ponds.The pond sediment was collected in different months.No significant differences(P＞0.05)were noted in water temperature,salinity,pH,dissolved oxygen content,chlorophyll a,and POM content of the culture ponds in different months;however,there were significant differences(P＜0.05)in PO43--P,NO2--N,NO3--N,and NH4+-N in the culture ponds in different months.The differences in fecundity of the three oyster sizes in the same month were not significant(P＞0.05);however,the differences in the water filtration,droppings,oxygen consumption,and ammonia discharge rates were all significant(P＜0.05),whereas those in fecundity of the same sizes of oysters in different months were significant(P＜0.05).The energy balance equation showed that all three oyster sizes used the most energy for growth in May,with the highest percentage of 48.64％;after 6 months of cultivation,the fattening degree of oysters increased by 31.7％,and the fastest growth rate of large-size oysters was 55.1％.Comparing the same batch of oysters from ponds and the sea area in the same period of time showed that the survival and fattening degree of oysters from pond culture were higher than those of oyster cultivation in the sea area(P＜0.05).An analysis of organic matter sources in the pond sediments showed that the further away from the aquaculture unit,the higher the contribution of suspended particles,whereas the opposite was true for artificial feed and feces.This study showed that C.gigas are more effective for fattening in marine shrimp and crab ponds,and it is recommended to begin the pond fattening production in autumn from mid-September to mid-October,and in spring from mid-March to mid-May,and to select C.gigas with larger sizes,so that the desired degree of fattening can be reached after 1-2 months.

Shellfish and macroalgae are usually known as environmental remediation species in aquaculture systems. However, the environmental issues are frequently found in shellfish and macroalgae large scale monoculture areas. Although shellfish and macroalgae IMTA might mitigate adverse effects of monoculture, the relationships among cultured organisms, plankton and environmental factors are unclear. This study evaluated the ecological impacts of Crassostrea gigas and Gracilaria lemaneiformis monoculture versus integrated multi-trophic aquaculture (IMTA) systems in Sanggou Bay, China, through a 5-day in-situ enclosure experiment. We assessed the nutrient levels, inorganic carbon system, plankton abundance, and Chl-a concentration under different aquaculture modes. Results revealed that oyster monoculture increased PO43--P levels, DIN concentrations and elevated CO₂ levels, exacerbating acidification risks. In contrast, IMTA systems with oyster-to-macroalgae ratios of 1:1 and 4:2 reduced PO43--P levels by 75 %, optimized DIN removal, and mitigated CO₂ accumulation. Moreover, oyster monoculture promoted pico-phytoplankton dominance by suppressing competitors (micro-/nano-phytoplankton) and predators (zooplankton), a trend reversed in IMTA systems where macroalgae limited pico-phytoplankton proliferation. Besides, Chl-a declined across all treatments. The in-situ enclosure experiment provided realistic insights into species-environment interactions, overcoming laboratory limitations of oversimplified systems. These findings underscore that IMTA ratios of 1:1 and 4:2 enhance nutrient cycling, stabilize carbonate system, and reduce eutrophication risks. This study advances sustainable aquaculture practices by demonstrating how optimized species ratios balance productivity and environmental health, offering actionable strategies for coastal management to mitigate ecological degradation in semi-enclosed bays.

Nutrients play a crucial role in sustaining marine ecosystems and supporting mariculture, especially in seaweed aquaculture. Currently, seaweed farming, such as kelp cultivation, is entirely dependent on the natural supply of nutrients. Sanggou Bay in Shandong Peninsula, Yellow Sea, is renowned for its 60-year history of kelp cultivation; however, it is recently facing an increasing demand for nitrogen and phosphorus due to the expansion in aquaculture scale and production. There is no doubt that nutrient addition can enhance and sustain the production, but it is crucial to understand its effect on kelp growth under current nutrients condition and the potential ecological risks. Our in-field nutrient enrichment experiments show that nitrogen and phosphorus additions promoted the kelp biomass during the early growth stages, and have no adverse effects on phytoplankton or seawater nutrient levels throughout the experiment. From a long-term perspective, increasing nutrient supply appears to be an essential strategy for sustaining the aquaculture of kelp.

Most cultivated abalone have to experience long-distance transportation under the current dominant relay aquaculture model in China, which produces more than 220 thousand metric tons of abalone annually. However, biogenic acidification caused by high stocking density during transportation may impair abalone physiology, including respiration, flipping behavior, feeding, and calcification, but remains poorly understood. In this study, juvenile abalone (Haliotis discus hannai) were incubated in either ambient seawater (control group) or seawater with elevated total alkalinity (TA-elevated group). We assessed changes in seawater carbonate chemistry and evaluated the physiological impacts of biogenic acidification. Specifically, the control group exhibited a significant decrease in pH and an increase in pCO(2), whereas the TA-elevated group showed the opposite pattern. After 24 h of incubation, there were significant differences in the respiratory metabolism between individuals from the two groups (P < 0.05). The average oxygen consumption rate of abalone from the control group was significantly lower than that from the TA-elevated group, whereas CO2 emission rate was significantly higher (P < 0.05). Respiratory quotient (C: O) was higher in the control group, though the difference was not statistically significant. In terms of flipping behavior, individuals in the TA-elevated group exhibited significantly lower flipping durations compared to those in the control group (P < 0.05). The feed consumption of individuals in the TA-elevated group was significantly higher than those from the control group (P < 0.05). Moreover, calcification rates in the TA-elevated group were significantly higher than those in the control group during both the initial (0-6 h) and final (17-24 h) stages of the simulated transportation period (P < 0.05). Our results demonstrated that biogenic acidification occurs during transportation and negatively affects the physiology of juvenile abalone, while increasing the carbonate buffering capacity of seawater by raising TA is effective in mitigating these negative impacts.

To clarify interactions among bivalves, macroalgae, and water column in the bivalve-macroalgae polyculture system, in-situ mesocosm cultivation was conducted for 24 h in both summer and winter. These experiments assessed seasonal variations in CO2 and components of dissolved inorganic carbon (DIC), nitrogen (DIN), and phosphorus (DIP) under three modes: monoculture of three sizes of oysters (Crassostrea gigas) (OA group), monoculture of kelp (Saccharina latissima) (KA group), and polyculture of oysters and kelp (KO group) at fixed wet weight ratio of 800: 200 g. The results revealed the OA group functioned as a CO2 source in both summer and winter, with summer increase rates of DIC, DIN, and DIP by oysters much higher than in winter and decreasing with larger oyster size. Pearson correlation analysis indicated a negative correlation between soft tissue dry weight of oysters and concentrations of NO2--N and NH4+-N. While, the KA group functioned as a CO2 sink, with winter decrease rates of DIC, DIN, and DIP by kelp being 14.24, 3.16, and 5.54 times greater than in summer, respectively. In the KO groups, oyster size and seasonal factors significantly affected water parameters, including pH, dissolved oxygen (DO), pCO(2), and various DIC, DIN, and DIP components (P < 0.05) and the system released DIC, DIN, and DIP in summer while absorbing them in winter. Subtraction calculations indicated that the culturing water in KO groups absorbed CO2, DIC, DIN, and DIP during both seasons, suggesting a synergistic bioremediation effect between phytoplankton and macroalgae at an appropriate cultivation ratio.

Low-salinity conditions are generally used in land-based cultivation to promote the germination and growth of Zostera marina L. and to improve the restoration effect of seagrass beds. Different salinity conditions lead to morphological and physiological differences. To investigate the impacts of salinity and osmotic pressure on the germination and early development of Zostera marina seeds, this study utilized seawater with different salinity conditions and PEG-6000 solutions to simulate various non-ionic osmotic pressures and examine the germination, cotyledon growth, and leaf differentiation over 28 days, as well as determine the biochemical traits on days 1, 3, 5, and 7. The results show that the cumulative germination rate in LS-0 was 91.6%, but it was not significantly affected by the PEG solutions. The different salinities (5, 10, and 15) had no significant effect on the germination rate, which ranged from 76.4% to 78.8%: low salinity and low osmotic pressure stimulated the germination by accelerating the water uptake through increased osmotic pressure differences. The leaf differentiation was regulated by the osmotic pressure and salinity. In LS-10, the most used condition, the leaf differentiation rate was 35.2%, while PEG-10 displayed 6.4%. The total soluble sugar and soluble protein in the seeds decreased. Antioxidant enzyme activities were activated under low-salinity conditions, which supported germination within a tolerable oxidative stress range.

This study investigates the optimal integration of shellfish (Mytilus edulis) and algae (Gracilaria lemaneiformis) aquaculture in semi-enclosed bay of Sanggou Bay, China, to enhance bioremediation and water quality. An enclosure experiment spanning five days was carried out to assess the impact of six mussel-to-algae wet weight ratios (3:5, 3:10, 6:5, 6:10, 9:5, 9:10) on dissolved oxygen (DO), pH, nutrient levels, inorganic carbon dynamics, plankton abundance, and chlorophyll-a (Chl-a) concentration in the integrated multi-trophic aquaculture (IMTA) system. The in-situ enclosure experiment provided realistic insights into species-environment interactions, overcoming laboratory limitations of oversimplified systems. Results revealed diurnal DO and pH fluctuations driven by mussel respiration and algal photosynthesis. Higher G. lemaneiformis proportions (3:10) elevated DO and pH (>8.7), reduced dissolved inorganic carbon (DIC) and pCO₂, but induced phosphorus limitation (PO₄3--P < 0.2 μmol/L), triggering pico-phytoplankton proliferation. Conversely, higher mussel ratios (9:5) lowered pH (7.7) and increased DIC, risking acidification. The ratios of 3:5, 6:5, 6:10, and 9:10 balanced ecological impacts, maintaining pH 7.8-8.5 (China's seawater standards), reducing nutrients (PO₄3--P removal: 51.3-62.0 %), and suppressing phytoplankton miniaturization. These ratios optimized nutrient levels, minimized eutrophication risks, and stabilized carbonate system, demonstrating their efficacy in sustainable IMTA. These findings highlight the importance of balancing mussel and algae proportions in IMTA systems to achieve sustainable aquaculture practices with minimal environmental impact. Moreover, this study optimizes the ratio of M. edulis and G. lemaneiformis to balance the stability of aquaculture water environment parameters, offering actionable strategies for coastal management to mitigate ecological degradation in semi-enclosed bays.

Eelgrass(Zostera marina),a perennial marine seed plant of Magnoliaceae,is commonly found in offshore shallows and river inlets and lives in submerged water.Eelgrass has important ecological services,such as water purification,protection of biodiversity,dike protection,disaster mitigation,and carbon sequestration.In recent years,with the increasing intensity of marine development and utilization and the impact of global climate change,seagrass bed resources have shown signs of increasing decline.The degradation rate of,China's seagrass beds also accelerates annually.Thus,the protection and restoration of seagrass bed resources cannot be delayed.In addition to taking effective management measures,scientific restoration of seagrass beds through human intervention is another important approach to protect existing seagrass beds.Transplanting artificially cultivated seagrass seedlings for seagrass bed restoration is also a way to utilize the seeds efficiently,and the evaluation of seed vigor status is the key to determine the germination rate and seedling establishment rate.Seed vigor is an important index for screening high germination rate,high seedling emergence rate,and other high-quality varieties.It is also the main index reflecting the rapid and neat emergence of seeds and the normal growth of seedlings.At present,methods commonly used to test eelgrass seed vigor are low-temperature germination assay,conductivity assay,enzyme vigor assay,and 2,3,5-tripheyl tetrazolium chloride(TTC)staining assay.However,low-temperature germination test cannot reflect the real vigor level of seeds well,especially in eelgrass seeds,because the germination time needs more than 2 weeks.Seedling growth determination,germination rate determination,and other traditional methods for detecting seed vigor need to be verified by a large number of repetitive experiments,which require large amounts of manpower,material resources,and time,as well as a large amount of investment in the development and development of eelgrass seeds.Similarly,conductivity measurement,enzyme activity measurement,and seedling growth rate measurement need to be validated by a large number of repetitive tests,which require a large investment of labor,material,and time,and may also damage seed samples.With the rapid development of technology,various non-contact,non-destructive,rapid seed viability testing methods have emerged.These methods include non-invasive micro-measurement,near-infrared spectroscopy,hyperspectral imaging,electronic nose detection.Among them,non-invasive micro-measurement determines seed viability by means of the sample.It also determines seed vigor by measuring the ion or molecular flow rate of drops on the seed surface.Given its advantages of non-damage,multi-electrode,multi-angle,high sensitivity,and high resolution,this technique has been applied in different plant research fields,such as plant salt resistance,plant pathology,and plant heavy metal resistance.In this study,we determined the Ca2+flow rate and direction in eelgrass seeds with different activities obtained from drying treatment by a non-invasive microbolometer system to investigate the relationship between Ca2+flow rate and eelgrass seed vigor,and provide a new method for the rapid,non-invasive,and in vivo identification of eelgrass seed vigor.Prior knowledge of seed viability status is a crucial aspect of artificial seedling cultivation,including eelgrass.In this study,eelgrass seeds were subjected to different degrees of drought stress for their special recalcitrant properties,and the same batch of eelgrass seeds was artificially treated to create differences in vigor.While different indicators were used to describe the physiological state of the seeds after the drying treatment,non-invasive micrometry was used to determine the Ca2+flow rate of the seeds and investigate the relationship between eelgrass seed vigor and Ca2+flow rate.In this study,drying treatments were used to artificially create viability differences in eelgrass seeds from the same batch,totaling five drying times(0,1,2,4,and 8 h)and 20 groups of samples.Germination rate,relative conductivity,water content,catalase activity,and malondialdehyde content were determined.Non-invasive micro-measurement was applied to the detection research of eelgrass seed vigor.Its primary objectives were to verify the feasibility of seed vigor grading through preliminary experiments,formulate a demonstration scheme,and further lay a solid foundation for the subsequent establishment of a standardized system for eelgrass seed vigor grading.Results showed that the germination rate gradually decreased and the relative conductivity increased with treatment time,the germination rate of the seeds after 4 h of treatment was 12％lower than that of the untreated seeds,and the germination rate after 8 h of treatment significantly reduced and was 68.7％lower than that of the untreated seeds.Catalase activity also significantly changed with treatment time.The Ca2+was effluxed,and the efflux rate increased with treatment time.The germination rate and Ca2+efflux flow rate were significantly negatively correlated,and the fitted linear equation was y=-0.192 2x+94.09,with an R2 of 0.860 6.This study proved that the Ca2+flow rate could serve as an eelgrass seed vigor detection index,providing a basis for the rapid and non-destructive identification of eelgrass seed vigor.

Crassostrea gigas,also known as Pacific oysters,are economic shellfish with the widest range of cultivation,the highest yield in the world,and the most important type of mariculture shellfish in China.However,many C.gigas have died during summer in coastal areas worldwide in recent decades.In 2008,the mortality rate of C.gigas cultured in France reached 40%-100%.In 2009,the mortality rate of C.gigas in some area of Sanggou Bay reached 51%.In 2019,the mortality rate of the Rushan area reached 50%-90%,with the death peak occurring in middle and late August.There were many reasons for the large-scale death of C.gigas,such as temperature,dissolved oxygen,salinity,disease,food availability,and reproduction levels,among which high temperature was the most important abiotic stress factor.The high temperature in summer disturbed the enzyme metabolism of C.gigas,resulting in slow or impeded growth.Furthermore,the reproduction and spawning of C.gigas caused a large amount of protein consumption,and physical weakness combined with high-temperature stress induced many deaths.Therefore,considering the problems faced by C.gigas culture during high summer temperatures,the introduction of new varieties will increase the economic benefits to the industry. Due to its high sterility,triploid C.gigas has attributes such as a fast growth rate,resilience excellent economic characteristics,and high energy conversion efficiency.In recent years,a certain farmed scale has formed in China,especially in northern coastal areas.There have been many studies on the biological and physiological differences between triploid and diploid C.gigas worldwide,mainly focusing on the differences in growth characteristics,soft tissue components,gonadal development,disease resistance,and gill structure.However,comparisons between triploid and diploid C.gigas feeding,metabolic physiology,energy budget,and carbon budget have not been reported.Focusing on the specific period of high temperatures in summer,this study investigated the feeding and metabolic physiological characteristics of triploid and diploid C.gigas using the field flow method,and compared and analyzed their energy allocation strategies in response to a high-temperature environment.The study provide data support for revealing the physiological differences caused by the ploidy effect of C.gigas in order to assist with evaluating the culture capacity. Triploid and diploid C.gigas were selected as research objects in August 2022 to analyze the differences in feeding and metabolic physiology and energy/carbon allocation strategies during high temperatures in summer.Physiological parameters related to intake and metabolism,such as water filtration rate,absorption efficiency,oxygen consumption rate,and ammonia discharge rate,were determined based on the field flow method in Sanggou Bay,Rongcheng,Shandong Province,and energy allocation and carbon allocation were estimated based on the principle of the energy budget.The results revealed that the water filtration rate and assimilation efficiency of triploid C.gigas were higher than those of diploid C.gigas,but there were no significant differences(P＞0.05).There were significant differences in the oxygen consumption rate and ammonia discharge rate between triploid and diploid C.gigas(P＜0.05).The oxygen consumption rate of triploid C.gigas was significantly lower than that of diploid C.gigas(P＜0.05),but ammonia discharge rate was significantly higher than that of diploid C.gigas(P＜0.01).The results of the energy and carbon budget analyses showed that the feeding energy/carbon and assimilation energy/carbon values of triploid C.gigas were higher than those of diploid C.gigas,but there was no significant difference(P＞0.05).There were significant differences in respiratory energy/carbon,excretion energy/carbon,and growth power between triploid and diploid C.gigas(P＜0.05).Respiratory energy/carbon values of triploid C.gigas were significantly lower than those of diploid C.gigas(P＜0.05),but excretion energy/carbon and growth power values were significantly higher than those of diploid C.gigas(P＜0.05).The oxygen/nitrogen ratio of triploid and diploid C.gigas fluctuated in the range of 7.91-14.11 and 59.81-94.19,respectively.Moreover,the main energy supply substances of triploid C.gigas were proteins,while the main energy supply substances of diploid C.gigas were carbohydrates and fats.These results revealed the differences in energy allocation patterns associated with the ploidy effect of C.gigas during high temperatures in summer. From the perspective of individual physiology and ecology,this study found that,compared with diploid C.gigas,triploid C.gigas showed certain advantages in energy allocation strategies by adjusting feeding and metabolic physiological behaviors during the high-temperature summer.However,the internal molecular mechanism of response strategies adopted by triploid C.gigas to cope with an adverse environment is still unclear.Further interpretation at the molecular level needs to be combined with omics and other systems biology techniques.

Farmed aquaculture species play an important role in regulating nutrient cycles in farming systems. Compared with nitrogen and phosphorus, the role of farmed species in the silicon (Si) cycle remains poorly understood. To help reduce this uncertainty, we clarified the sources and sinks of silicate and quantified the Si pools in an aquaculture system in Sanggou Bay (SGB). The results showed that dissolved inorganic nutrient levels were significantly lower during the dry season than during the wet. Dissolved silicate (DSi) is a potential limiting factor for phytoplankton growth during spring, and phosphorus limitation occurs during summer. The budget results indicated that large amounts of nitrogen, phosphate (DIP), and DSi were buried in the sediment or transformed into other forms during both the wet and dry seasons. The nitrogen and DIP cycles were strongly influenced by bivalve excretion and farmed species harvesting; however, these processes had little impact on the Si cycle. Si availability depends on both external inputs and internal recycling. DSi was primarily supplied from the Yellow Sea, with a minor contribution from the river due to river discharge during spring. However, during summer, riverine inflow (accounting for 83% of the total influx) was the major DSi source followed by benthic flux (12%). Biogenic silica (BSi) burial efficiency in the sediment was estimated to be 78% during spring and 23% during summer. The BSi preservation efficiency in bivalves during spring was high (53%), leading to a higher Si retention than in river discharge. Bivalves biodeposition plays an important role in the Si burial process. We suggest that this high retention is essentially controlled by the biodeposition mechanism, which is directly controlled by the exotic suspension feeders. Bivalves have the potential to alter Si retention in the bay by producing large amounts of biodeposits and accelerating the silica cycle, which may lead to more carbon dioxide being absorbed by diatoms.

The Pacific abalone (Haliotis discus hannai) is naturally distributed in the Bohai Sea and Yellow Sea. In China, the Pacific abalone is an important living marine resource. Over the past 40 years, the abalone industry has gradually developed from wild harvesting to aquaculture. Currently, the main cultivation method is long-line culture, especially north-south relay aquaculture. The north-south relay involves transporting abalone cultivated in the East China Sea to the Yellow Sea and Bohai Sea over summer, to avoid extreme temperature stress. Due to the consistent favorable temperatures, this method achieves high survival with a shortened cultivation cycle. The rapid development of this efficient cultivation model has supported a substantial increase in domestic abalone production, exceeding 200 000 tons in 2020. However, the north-south relay aquaculture has several deficiencies, such as a large influx of abalone being supplied to the market over a very limited period with a homogenized flavor. This has led to a sharp decline in price. Abalone grow slowly in the bottom-sowing model in northern waters, however, the quality exceeds that of north-south relay cultured abalone. The optimum growing temperature of Pacific abalone is 10~22 ℃. Bottom-sowing cultivation in the northern waters has a lower seawater temperature, occasionally below 0 ℃. In addition, in long-term north-south relay cultivation, abalone are always in a suitable water temperature environment, reducing the low temperature tolerance of abalone. The increasing investment in recent years in marine ecological protection (such as marine pastures, habitat restoration and abalone habitat creation) and the technological breakthroughs in the cultivation of low-temperature resistant seedlings has enabled the optimization of bottom-sowing culture, reducing many issues, such as high mortality while overwintering, which has been partially solved. However, the impact of both cultivation methods on the nutrient contents and the physiological index of abalone is rarely reported. In this study, the north-south relay and the northern bottom-sowing abalone cultures were investigated. The total sugar, protein, total organic matter, and amino acid content characterized the nutritional value of individuals from both culture methods. The oxygen consumption rate and heart rate identified their low temperature tolerance. We explore the differences in body composition and physiological mechanisms in response to low temperature stress using specimens from both farming methods. The results showed that the total sugar content of the bottom-sowing culture individuals was (3.20±0.00)%, the total organic matter was (27.60±3.70)%, and the essential amino acid content was (4.19±0.09)%, which were significantly higher than those in the individuals from the north-south relay culture (P < 0.05). At 24 ℃, the oxygen consumption rates of the bottom-sown abalone and relay cultured individuals were (0.077±0.024) mg/(g·h) and (0.082±0.012) mg/(g·h), respectively. The oxygen consumption rates of abalone in low temperature stress did not vary significantly, with (0.018±0.009) mg/(g·h) (bottom-sown abalone) and (0.017±0.006) mg/(g·h) (relay cultured abalone) (P > 0.05). At 24 ℃, the heart rates of bottom-sown and relay-cultured abalone did not vary significantly, with (45.05±6.79) and (46.95±5.01) BPM, respectively (P > 0.05). In low temperature, the heart rate of the bottom-sown abalone was (12.82±1.72) BPM, and the heart rate of the relay-cultured abalone was (18.11±2.79) BPM, statistically differing significantly (P < 0.05). The results indicate variation in the abalone responses to external low temperature stress between individuals from the different farming models. The low heart rate level in low temperature conditions indicates a low metabolic level, which can reduce energy consumption, improving survival in the low temperature stress of a northern winter. Studies have revealed different farming models can significantly affect the nutritional value of abalone and the physiological responses to low temperature stress. Abalone cultured by bottom-sowing have higher nutritional value and a low temperature tolerance. In addition, abalone heart rate is a highly sensitive indicator for studying physiological responses to low temperature stress in abalone and other shellfish.

The Ria de Aveiro is an important coastal lagoon for wildlife in Portugal, where the production of bivalves reaches approximately 2700 tons annually. However, the illegal overfishing of bivalves is frequent in this lagoon, which causes critical changes in the ecosystem. In this study, using a developed food-web model (Ecopath model), the ecological carrying capacity (ECC) and maximum sustained yield (MSY) of the Manila clam, Ruditapes philippinarum were estimated, and the effects of further increases in clam biomass on other species were investigated. The results showed that 1) the current biomass and legal catch of R. philippinarum do not yet exceed the ECC (172.40 tons km-2) or the MSY (86.20 tons km-2 year-1) in Ria de Aveiro; 2) the harvested Manila clams of the MSY represent removing from the ecosystem ∼ 581 tons carbon (C) and ∼83 tons nitrogen (N) annually, with substantial ecological and economic implications; and 3) a further increase in the biomass levels of this species may cause the ecotrophic efficiency of other groups to become unrealistic, potentially leading to decreases in ecosystem transfer efficiency, biodiversity and health. The results here are expected to guide the sustainable development and management of bivalve aquaculture in Ria de Aveiro and the protection of the local environment.

Rapana venosa is primarily distributed in the Yellow Sea and Bohai Sea of China, Japan, Korea, and Russia. In the natural sea area, the adult R. Venosa mostly inhabits the sand-mud bottom or the rocky bottom of the low intertidal zone up to 20 meters deep, and the young R. Venosa mostly inhabits the rocks near the coastal line. Its habitats are generally occupied by many other bivalves, such as Crassostrea gigas, Mactra chinensis, and Ruditapes philippinarum. The R. venosa is a large carnivorous Mollusca that mainly feeds on bivalves and other animal carcasses. R. venosa is often classified as an enemy of bivalve farming, but they can also be used to control fouling organisms, and it has potential for application in aquaculture and ocean engineering.In recent years, there have been some reports on the feeding selectivity of R. venosa, the effects of feed, temperature, and individual specifications on feeding, the effects of feed types, specifications, feeding amount, and breeding density on the survival and growth, the feeding preferences to different bivalves and the feeding cycle before and after reproduction. These studies mainly explored the effects of temperature, density, feed types, and specifications on its growth and development. The main purpose of these studies was to select suitable feed types and specifications for the temporary culture and breeding of R. venosa, to improve its growth and development speed, and increase economic benefits under artificial breeding conditions. However, the feeding selection and behavior process of R. venosa under natural conditions are not clear, and the feeding selection of R. venosa to C. gigas, Mytilus edulis and other fouling organisms was not clear under the environmental conditions of multiple bait bivalve habitats. Therefore, in this study, four kinds of bivalves (fixed type, attached type and buried type) were used as bait bivalves to understand the feeding selection. C. gigas and M. edulis are common fouling organisms in the habitat of R. venosa, while M. veneriformis and R. philippinarum are widely distributed in the habitat of R. venosa. The study attempts to simulate the habitat of R. venosa and different types of bait bivalves in the natural environment, to study its preference for bait bivalves species and feeding specifications, to compare and analyze the differences in feeding rates of different specifications of R. venosa, and further study its feeding rhythm and feeding process and to provide data reference for the feasibility of using R. venosa to control C. gigas, M. edulis and other bivalves fouling organisms, and improve the feeding habits of R. venosa.To achieve these objectives, three specifications of M. veneriformis, R. philippinarum, C. gigas, and M. edulis live baits were placed in the aquarium by simulating the natural environment. The feeding number, feeding weight, feeding specifications, feeding time, and feeding behavior process of three specifications of R. venosa to different baits were recorded. The experimental results showed that R. venosa fed on all four bivalves. The number and weight of R. venosa that fed on M. veneriformis with different specifications were significantly higher than those that fed on other bivalves (P < 0.05), and the feeding index was more than 50%, indicating its appetite. R. venosa fed normally on C. gigas and R. philippinarum, and only a small population of R. venosa fed on M. edulis with large specifications. In terms of the selection of feeding specifications, three specifications of R. venosa preferred large M. veneriformis and small C. gigas (P < 0.05). The feeding rate of the large specification R. venosa was 7.15%, which was significantly lower than that of the other two specifications (small specification, 10.98%; medium specification, 9.64%). Under the experimental conditions, the feeding cycle of R. venosa was apparent, feeding activities were carried out every three days, and the feeding time was 20:00–24:00 at night. The feeding process can be divided into four stages: Unfed stage, search stage, feeding stage, and feeding end. During the feeding process, the R. venosa actively searched for bivalves, removed them from the sand and wrapped them with their proleg, secreted mucus, and smacked them from the shell gap. After sucking the mollusks decomposed by digestive juice, the R. venosa dived into the sand or attached to the aquarium wall. The results showed that under the experimental conditions, R. venosa had a feeding preference for the species and specifications of bait bivalves. R. venosa preferred to eat M. veneriformis and rarely consumed M. edulis. Moreover, its feeding behavior was nocturnal and exhibited periodicity, feeding activity happened every three days in the first half of the night.

为研究养殖皱纹盘鲍(Haliotisdiscus hannai Ino)外壳附着牡蛎的防除方法,对比了疣荔枝螺(Thais clavigera Kuster)、润泽角口螺(Ceratostoma rorifluum)和甲虫螺(Cantharus cecillei)对鲍外壳表面牡蛎的防除效果.以桑沟湾筏式养殖鲍为研究对象,自7月中旬开始,每隔15 d左右分别投放3种螺到鲍养殖笼中,共投放6次,以始终未投放螺的养殖笼为对照组.结果显示,实验结束时甲虫螺组中鲍壳上平均存活牡蛎数目为(0.04±0.04)个/只,疣荔枝螺组和润泽角口螺组疣荔枝螺组分别为(2.49±0.91)个/只和(2.21±1.05)个/只,对照组为(3.33±0.46)个/只.投放3种螺组中鲍壳上存活牡蛎数均显著显著低于对照组(P＜0.05),甲虫螺也显著低于其他2种螺(P＜0.05).投螺时间也会影响螺防除牡蛎污损的效果,投放时间过晚会导致螺捕食牡蛎后有明显的壳残留,牡蛎的壳高达到0.5 cm左右再投放螺即可保证防除效果.另外甲虫螺组鲍壳上死亡牡蛎残留壳长度为(0.73±0.27)cm,显著低于疣荔枝螺组[(0.88±0.28)cm]、润泽角口螺组[(0.93±0.28)cm]和对照组[(0.92±0.24)cm](P＜0.05),表明甲虫螺所摄食牡蛎的规格小于另外2种螺.研究表明,3种螺均有显著的防除作用,甲虫螺防控牡蛎附着的作用最强;投螺时间会影响3种螺的牡蛎防除效果,需要选择合适的投放时间进行投放;在牡蛎已经大量附着且成长到一定规格时可选择疣荔枝螺和润泽角口螺作为补充.

海草床是浅海典型的生态系统之一,其积聚和储存碳的能力备受关注.沉积有机碳是海草床碳汇的重要组成部分,而沉积有机碳的来源与海草的种类及其所处的生态场景密切相关.本研究聚焦我国北方规模化养殖海湾桑沟湾2处主要鳗草(Zostera marina)分布区,基于稳定碳氮同位素(δ13C和δ15N)技术研究了潮间带鳗草床表层沉积有机碳的来源及其碳储量.结果显示,2处草床沉积有机碳均主要来自浮游植物,约占34.0％～41.4％,鳗草自身贡献约占8.3％和17.1％,贝类生物沉积物的贡献约为23.9％～25.3％,大型藻类约贡献25.0％.在楮岛草床周围,鳗草输出碳对周围2 km内站位表层沉积有机碳的贡献约为5.2％～10.7％.碳储量估算结果显示,2处草床沉积物为0～30cm的有机碳储量为2.01 MgC/hm2和3.75MgC/hm2,平均为2.88 Mg C/hm2,来自生物沉积的有机碳储量约为0.71 Mg C/hm2.研究结果为深入解析桑沟湾鳗草床分布区沉积碳汇的来源及与规模化海水养殖活动的贡献提供了数据支撑.

Bioturbation of infauna plays an important role in the biogeochemical processing of sediments. Infaunal animals build burrows and enlarge the sediment-water interface by their activities and so bioturbation is closely related with burrow structure and animal behavior in the sediment. The purpose of this study is to explore the characteristics of Perinereis aibuhitensis burrow structures with the factors of months and animal sizes (0-1g, 1-2g, 2-3g, 3-4g, and >4g), which would also provide useful knowledge of infauna behavioral ecology. The dimension and complexity of the burrows of P. aibuhitensis were measured by dissecting sediments. The results showed that there were three burrow shapes of P. aibuhitensis, i.e., I, Y and U shapes. Overall, the order of abundance of each of the three burrow shapes were I > Y > U. Larger P. aibuhitensis are inclined to build Y- and U-shaped burrows in June and August. There were significant differences in the tunnel diameter, burrow depth and burrow length separately between different polychaete size classes (P< 0.001). In February and August, the burrow depths and burrow lengths of P. aibuhitensis individuals with body weights of 1-2 g and 2-3 g were significantly greater than in other months (P< 0.001). P. aibuhitensis individuals of 1-2 g and 3-4 g body weight had significantly more burrow openings and branches in August than in February (P< 0.001). Within the same month, the burrow HEindex increased with increasing polychaete size, and when the sizes were 1-2 g, 2-3 g and 3-4 g, the complexity in August was higher than that in other months. This study suggests that I-shaped burrow dominants the burrow architecture of P. aibuhitensis. The polychaete with large size has a higher HEindex (burrow complexity) indicating a strong bioturbation ability. Y-shaped burrows are more conducive to the survival of P. aibuhitensis in hot weather. In order to adapt to environmental stresses outside, P. aibuhitensis usually builds deeper burrows.

为了更加细致地甄别滤食性贝类的食物组成,于2019年8月,以北方规模化典型养殖海湾——桑沟湾养殖的长牡蛎(Crassostrea gigas)为研究对象,运用Illumina高通量测序技术对长牡蛎的胃含物及所处养殖水体中的真核生物进行分析研究.结果显示,扩增18S rDNA V4区平均得到111,359个有效序列短片段,在97％相似性水平上划分OTUs(operational taxonomic units),聚类后得到239个类别.其中,长牡蛎胃含物中的真核生物分属于34个门,绿藻门(Chlorophyta)、甲藻门(Pyrrophyta)、链形植物(Streptophyta)、硅藻门(Bacillariophyta)和原生动物(Protozoa)等为主要类群.所处养殖水体中的真核生物分属于37个门,绿藻门、脊索动物门(Chordata)、节肢动物门(Arthropoda)、甲藻门和硅藻门等为主要类群.结果表明,浮游植物是长牡蛎的主要食物来源,链型植物和原生动物也有一定的贡献,分别占总食物贡献量的10.43％和4.11％.研究结果为深入认识滤食性贝类的摄食生态学及其在养殖生态系统物质循环和能量流动中发挥的作用提供了数据支撑.

为了解北方典型养殖海湾——桑沟湾水域浮游植物群落结构的时空变化特征及其影响因素,于2017年4月(春季)、7月(夏季)、11月(秋季)和2018年1月(冬季)对桑沟湾水域21个站点进行4个航次的大面调查.结果显示,调查期间,该湾共采集到浮游植物31属51种,其中,硅藻(Diatom)24属43种,甲藻(Dinoflagellate)3属4种,绿藻(Chlorophyta)2属2种,金藻(Chrysophyta)2种,蓝藻(Cyanophyta)1种.按照季节划分,春季22种,夏季20种,秋季23种,冬季20种.优势度指数分析结果表明,硅藻是绝对优势种,其中,具槽帕拉藻(Paraliasulcate)为全年优势种,数量百分比在18.6％～84.9％之间.浮游植物细胞丰度在0.16×103～12.20×103个/L之间,表现为冬季＞春季＞秋季＞夏季.物种多样性指数(Shannon)范围为0.69～1.35,物种均匀度指数J(Pielou)范围为0.42～0.70.磷酸盐是桑沟湾浮游植物生长的主要限制营养盐.研究结果揭示了桑沟湾养殖水域浮游植物的时空变化特征,为深入认识养殖生态系统的结构和功能提供了基础数据.