Data from: How are coastal benthos fed?

Water movement can influence the distribution of benthic suspension feeders, in part, by increasing food delivery; however, the impact of advective transport and turbulent diffusion on organic matter flux to nearshore benthic communities is not well quantified, and sediment trap-derived estimates of food delivery in these systems are often lower than what is required to support observed benthic respiration. In this study we used two naturally occurring daughter/parent radionuclide pairs (234Th/238U and 90Y/90Sr) to measure particulate organic carbon (POC) and particulate phosphorus flux from the water column to the nearshore bottom of Lake Michigan, where quagga mussel tissue biomass on rock surfaces was assessed at 117 ± 39 g DW m-2. Estimates of carbon respiration and total phosphorus excretion by mussels were derived from coincident benthic chamber measurements of O2 consumption and total dissolved phosphorus excretion. Although mussel carbon respiration and phosphorus excretion fluxes were concordant with water column nutrient fluxes, estimates of POC flux to the lakebed and mussel carbon respiration were up to six times higher than published estimates of local primary production. We found that advective onshore transport and vertical convective mixing increased POC flux to the nearshore benthos by a factor of ~15 over offshore trap-derived estimates of POC flux. From these results, we hypothesize that high benthos population densities are related to an edge effect created when the dominant mechanism of particle delivery transitions from gravitational settling to convection.水流运动可通过提升食物供给量，在一定程度上影响底栖悬浮食性生物（benthic suspension feeders）的分布；然而，平流输运（advective transport）与湍流扩散（turbulent diffusion）对输入近岸底栖群落（benthic communities）的有机质通量的影响尚未得到充分量化，且利用沉积物捕集器（sediment trap）估算的此类系统中的食物供给量，往往低于维持观测到的底栖呼吸作用所需的水平。本研究采用两种天然存在的子体-母体放射性核素对（²³⁴Th/²³⁸U与⁹⁰Y/⁹⁰Sr），测量了密歇根湖（Lake Michigan）近岸底床的水柱颗粒有机碳（particulate organic carbon, POC）与颗粒磷（particulate phosphorus）通量；该区域岩石表面的斑驴贻贝（quagga mussel）组织生物量经评估为117±39 克干重·米⁻²。贻贝的碳呼吸速率与总磷排泄量的估算值，来自同步开展的底栖箱（benthic chamber）耗氧与总溶解磷（total dissolved phosphorus）排泄测量结果。尽管贻贝的碳呼吸与磷排泄通量与水柱营养盐通量相符，但估算得到的湖床POC通量与贻贝碳呼吸速率，较已发表的本地初级生产力（primary production）估算值最高高出6倍。我们发现，与离岸沉积物捕集器得到的POC通量估算值相比，近岸平流输运与垂直对流混合（vertical convective mixing）使抵达底栖生物的POC通量提升了约15倍。基于上述结果，我们提出假说：当颗粒物输运的主导机制从重力沉降（gravitational settling）转变为对流作用时，会产生一种边缘效应（edge effect），而高底栖生物种群密度与该边缘效应存在关联。