In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers
In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers
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密西西比河和俄亥俄河双壳类软体动物（Dreissena polymorpha）捕食性调节的原位实验
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发表时间：
1998
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影响因子：
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通讯作者：
A. Casper
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作者：
J. Thorp;Michael D. Delong;A. Casper
1.在密西西比河和俄亥俄河进行的现场围隔实验确定了鱼类捕食在调节斑马贻贝(Dreissena Polypha)方面的重要性，斑马贻贝是这两条河底栖无脊椎动物群落中日益重要的组成部分。
2.研究了捕食性鱼类对密西西比河上游滩涂河段和俄亥俄河自然限制河段斑马贻贝的密度、生物量和大小分布的影响。部署了50个六面的捕食者排斥网箱和50个部分网箱(仅在上游端有网眼)，一半的网箱装有柳条和一半的粘土瓷砖，悬挂在底部以上12-16厘米。从1994年7月至10月，大约每月每隔一个月，从每个笼子上取下一个钉子或瓷砖样品。通过在两条河流的网箱附近进行电捕，评估了软体动物鱼类的类型和相对丰度。使用两条河流的底栖生物样本测量了幼年斑马贻贝在底质上的实际和潜在的招募数量，并根据浮游绒毛虫的数量估计了(仅限俄亥俄河)。
3.密西西比河上游至少有3种鱼类(主要是鲤鱼、鲤鱼和红马鱼，Moxostoma sp.)食用斑马贻贝。和俄亥俄河的5个物种(主要是小口水牛、Ictiobus bubalus和斑点叉尾鲨)，但潜在的补充似乎足以取代被吃掉的贻贝，至少在俄亥俄河是这样。在开始繁殖后不久，底栖贻贝幼体的数量与绒毛密度没有明显的联系。笼子类型不影响幼虫在障碍物和瓷砖上的招募(因此消除了潜在的混杂的“笼子效应”)。
4.鱼类对贻贝种群有显著影响，但对密西西比河上游低密度种群的影响往往最大。两条河流的密度和生物量在网箱类型(网箱内较高)、底物(在瓷砖上较大)和日期(随时间增加)方面有所不同。推定的体型选择性捕食在密西西比河中存在(较大体型的类群更大)，但在俄亥俄州并不明显。我们假设，密西西比河的鱼可以更容易地从低密度种群中选择更大的猎物；而在俄亥俄州，对紧密聚集的斑马贻贝进行大小选择性捕食将是困难的。
5.虽然鱼类可以减少两条河流中的多态德氏杆菌的数量，但由于斑马贻贝的繁殖力很大，目前的捕食水平似乎不足以调节斑马贻贝的密度。然而，最近斑马贻贝的入侵可能会导致更多的鱼类种群，同时促进更大的碳保持和整个生态系统的次生生产。
1.In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers.
2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six-sided, predator-exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers.
3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’).
4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size-selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size-selective predation on tightly packed zebra mussels in the Ohio would be difficult.
5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.