个体规格对毛蚶C、N、P营养要素收支的影响OA

This study investigated how differences in individual size affect respiratory metabolism and the carbon(C),nitrogen(N),and phosphorus(P)budgets of Scapharca subcrenata.Three size classes were selected based on shell length:small(29.43±0.88 mm),medium(36.42±0.43 mm),and large(42.53±0.59 mm),and subjected to static-water experimental conditions.For each size group,feeding,fecal production,oxygen consumption,ammonia excretion,and phosphorus excretion rates were measured.Based on these parameters,comprehensive C,N,and P budget equations were constructed to quantify nutrient absorption,utilization,and loss,thereby providing an integrated assessment of how size variation influences the energy balance and nutrient utilization efficiency of this species. The results revealed that all measured metabolic indices decreased significantly with increasing body size(P＜0.05).Specifically,small individuals exhibited notably higher feeding,oxygen consumption,and excretion rates than medium and large individuals.This indicates that small S.subcrenata are characterized by more active physiological metabolism and greater nutrient turnover,reflecting their higher energy demand during rapid tissue growth and organ differentiation.In contrast,larger individuals displayed lower metabolic activity,consistent with a physiological shift toward metabolic maintenance and homeostasis at later developmental stages.These results agree with the general pattern observed in bivalves,in which metabolic intensity tends to decrease with increasing body size. Significant differences were observed among the size groups in nutrient allocation.The small-sized group allocated the highest proportions of assimilated C,N,and P to growth,accounting for 38.0％,42.2％,and 37.0％of their respective budgets.These proportions were significantly higher than those of the medium-and large-sized groups(P＜0.05),indicating that small individuals invested more assimilated energy and nutrients in biomass accumulation and structural growth.Conversely,large individuals showed markedly higher proportions of assimilated carbon consumed through respiration(58.6％)and of N(59.5％)and P(23.7％)lost through excretion(P＜0.05). This allocation pattern suggests that large individuals invest more resources in sustaining basic metabolic functions than in synthesizing new tissue.The calculated growth scopes for C,N,and P declined markedly with increasing body size.The growth scope of small individuals was approximately 50％greater than that of large individuals,highlighting their superior nutrient conversion efficiency and growth potential.As body size increased,the growth scope decreased significantly,implying that physiological energy allocation gradually shifted from biosynthetic activity to metabolic maintenance.This change is consistent with ontogenetic metabolic scaling,whereby the metabolic rate per unit body mass decreases as organisms grow because the proportion of metabolically active tissue declines. These findings reveal distinct size-dependent strategies of energy and nutrient allocation in S.subcrenata.Small individuals exhibit a growth-oriented strategy characterized by high assimilation efficiency,elevated metabolic rates,and active anabolism,which support rapid somatic growth.In contrast,larger individuals demonstrate a maintenance-oriented strategy in which energy and nutrient resources are directed primarily toward respiration and excretion to sustain physiological equilibrium.This ontogenetic transition from growth-dominated to maintenance-dominated metabolism demonstrates the adaptive physiological plasticity of this species and may influence its ecological functions across life stages. From an ecological perspective,these results provide new insights into how population size structure regulates elemental cycling in coastal bivalves.Differences in C,N,and P utilization among size classes suggest that populations dominated by small individuals may contribute more effectively to carbon fixation and biomass accumulation,whereas populations dominated by large individuals may play a greater role in nutrient regeneration through excretion.Consequently,variation in population size structure may directly influence the carbon sequestration potential and nutrient-cycling efficiency of bivalve communities in aquaculture environments. Moreover,the detailed C,N,and P budget equations established in this study provide a quantitative framework for evaluating elemental metabolism in S.subcrenata.These data provide important references for assessing the species' role in benthic biogeochemical cycles and predicting how environmental factors and aquaculture practices may alter its ecological functions.The findings have broader implications for optimizing shellfish aquaculture systems,particularly for developing low-impact,carbon-neutral mariculture models that integrate ecological efficiency with sustainable production. In summary,individual body size significantly affects respiratory metabolism and nutrient budgets in S.subcrenata,resulting in distinct metabolic strategies among size groups.Small individuals exhibit higher nutrient utilization efficiency and greater growth potential,whereas large individuals shift toward metabolic maintenance and lower energy turnover.These findings improve our understanding of size-dependent metabolic regulation in bivalves and emphasize the importance of population size structure in determining ecological roles in C,N,and P cycling.They also provide a theoretical basis for evaluating the carbon storage potential of bivalve populations and developing future strategies for nutrient management and sustainable mariculture.