RUI: Dissolution Mortality of Juvenile Bivalves in Coastal Marine Deposits.

尽管在了解控制无脊椎动物向底栖生物群落补充的因素方面取得了重大进展，但关于双壳类动物幼虫后幼鱼死亡率极高的原因仍然存在许多问题。现在人们普遍认识到，碳酸盐欠饱和是温带、沿海、富含有机物的表层沉积物的共同特征，这些沉积物以沉积物为食的底栖生物为主，其中许多生物具有碳酸钙外壳。这种不饱和可能使最近定居的双壳类幼体难以形成外壳，因此外壳溶解可能是双壳类幼体死亡的重要原因。如果这是真的，这将对底栖生物群落的招募、生存以及早期成岩过程与底栖生物群落形式和功能之间的耦合产生重要影响。在这项研究中，圣约瑟夫学院的PI将进行多方面的研究，将：(1)确定沉积物-水界面碳酸盐饱和状态对潮间带泥中双壳类幼体从幼体过渡到新幼体后的补充和生存的影响；(2)评估控制这些泥中饱和状态的化学（反应）和生物（运输）过程；(3)在碳酸盐循环变化的饱和“情景”下，建立基于阶段/成岩的双壳类幼体溶蚀死亡耦合模型。将对具有商业价值的物种沙螺和沙螺进行研究。实地工作将在缅因湾卡斯科湾的两个地点进行，这两个地点的生物学和成岩特征不同，但都有大量的雇佣兵和米亚。野外研究将集中于Mya和雇佣军的队列监测以及碳酸盐矿物饱和状态对幼体丰度变化的影响。“沉积物缓冲”实验将用于辨别表层沉积物的CaCO3缓冲是否通过限制幼体的外壳溶解来防止欠饱和。地点比较将允许检查溶解死亡率作为生物和成岩环境的功能的重要性。在每个地点的低潮和潮间带中上高度取样，将检查溶解死亡率随潮汐暴露的变化情况。实验室实验将人为调节表层沉积物的饱和状态，从而调节双壳类幼鱼的栖息地，同时保持上覆水体的过饱和状态。溶解死亡率实验将确定“阈值”饱和状态，低于该阈值，外部外壳溶解死亡率会发生在雇佣兵和Mya （2.0 mm）的特定尺寸类别中。另外的实验室实验将利用直接观察和水槽实验相结合的方法，确定双壳类对不同饱和状态的沉积物表面的直接反应。来自野外和实验室的集体结果将用于模拟由于碳酸盐循环的人为和自然变化而导致的两种物种的溶解死亡率情景。这项研究的广泛影响包括极其强大的教育成分和重要的社会效益。缅因圣约瑟夫学院是一所本科院校，学生中约有70%是女性。学生对研究的投入将建立在PI先前的CAREER奖的基础上，并促进学生参加和/或在国家/国际会议上发表研究成果，作为手稿的共同作者。提高对双壳贝幼鱼死亡率的认识对沿海渔业管理具有重要影响。最后，这项研究将把沿海的幼年双壳类动物种群与具有碳酸盐壳的开放海洋浮游生物和珊瑚放在一起，这些浮游生物目前预计会遭受类似的壳形成和随后的死亡问题。

ABSTRACTProposal # OCE-0622999Despite major advances towards understanding the factors controlling invertebrate recruitment to benthic communities, many questions remain regarding causes of the extreme juvenile mortality of post-larval bivalves. It is now widely recognized that carbonate undersaturation is a common feature in temperate, coastal, organic-rich surface sediments that are dominated by deposit feeding benthos where many organisms have calcium carbonate shells. Such undersaturation may make it difficult for recently settled, juvenile bivalves to form their shell, and so shell dissolution could represent a significant source of mortality for juvenile bivalves. If true, there would be important implications for benthic community recruitment, survivorship, and the coupling between early diagenetic processes and benthic community form and function. In this research, a PI from St. Joseph's College will conduct a multi-faceted study that will: (1) determine the effect of carbonate saturation state at the sediment-water interface on recruitment and survivorship of juvenile bivalves following their transition from pediveligers to new juveniles in intertidal mud, (2) evaluate the chemical (reaction) and biotic (transport) processes that control saturation state in these same muds and, (3) develop coupled stage-based/diagenetic models of juvenile bivalve shell dissolution mortality under "scenarios" of carbonate saturation due to variability in the carbonate cycle. Studies will be conducted on the commercially valuable species Mya arenaria and Mercenaria mercenaria. Fieldwork will be conducted at two sites in Casco Bay, Gulf of Maine, that differ in their biological and diagenetic characteristics, yet both have substantial sets of Mercenaria and Mya. The field research will focus on cohort monitoring of Mya and Mercenaria and the effect of carbonate mineral saturation state on the variability in juvenile abundance. "Sediment buffering" experiments will be used to discern if CaCO3 buffering of surface sediments immediately following the set prevents undersaturation by limiting external shell dissolution of juveniles. The site comparisons will permit examination of the importance of dissolution mortality as a function of both the biotic and diagenetic setting. Sampling at low water and mid-upper intertidal heights within each site will examine variability in dissolution mortality as a function of tidal exposure. Laboratory experiments will artificially regulate surface sediment saturation state, and thus juvenile bivalve habitat, while maintaining supersaturated conditions in the overlying water. Dissolution mortality experiments will determine "threshold" saturation states below which external shell dissolution mortality occurs for specific size classes of Mercenaria and Mya (2.0 mm). Additional laboratory experiments will determine the immediate response of bivalves to sediment surfaces of different saturation states using a combination of direct observations and flume experiments. The collective results from the field and laboratory will be used to model scenarios of dissolution mortality in both species due to anthropogenic and natural changes in carbonate cycling.Broader impacts of this study include both an extremely strong educational component and important societal benefits. Saint Joseph's College of Maine is an undergraduate institution with about 70% of women in the student body. The immersion of students into research will build on the PI's prior CAREER award and promote students attending and/or presenting research results at national/international conferences contributing as coauthors on manuscripts. Improved understanding of juvenile bivalve mortality could have important impact on management of coastal fisheries. Finally, this research would place coastal populations of juvenile bivalves into context with open ocean plankton with carbonate shells and corals that are currently expected to suffer from similar problems with shell formation and subsequent mortality.