Purcell J E, Cresswell F P, Cargo D G, Kennedy V S
Biol Bull. 1991 Feb;180(1):103-111. doi: 10.2307/1542433.
We investigated predation on bivalve veligers by the scyphozoan Chrysaora quinquecirrha and the ctenophore Mnemiopsis leidyi. We found that the medusa stage of C. quinquecirrha captures, but does not digest, veliger larvae: 99% of oyster veligers (Crassostrea virginica) caught by medusae were egested alive within 7 h of capture, and 98% survived for 24 h after egestion; 98% of oyster, mussel (Mytilus edulis), and clam (Mulinia lateralis) veligers placed on the oral arms of medusae were rejected; all bivalve veligers in field-collected medusae were closed and full of tissue. Our laboratory evidence suggests that the shell of larval bivalves probably offers protection from medusae: 23% of dead, open veligers were ingested by medusae compared with 0.7% of live, closed veligers; open veligers were retained longer than closed veligers; and tissue excised from recently settled oyster larvae was ingested and digested. Freeswimming C. quinquecirrha ephyrae ingested but did not digest veligers. By contrast, the benthic scyphistoma stage ingested 69% of veligers that contacted their tentacles and digested 48% of those ingested. Each scyphistoma consumed an average of 1 veliger/day at densities of 0.3 veligers ml-1. However, larval settlement was not reduced on oyster shells bearing scyphistomae. By contrast to the results on C. quinquecirrha, ctenophores egested only 4% of veligers alive, and 25% of the veligers in their gut contents were digested. Predation on veligers by ctenophores was estimated to be 0.2 to 1.7%/day in Chesapeake Bay. We conclude that C. quinquecirrha medusae are not important predators of bivalve veligers, but rather may reduce their mortality by consuming ctenophores, which do eat veligers.
我们研究了钵水母纲的金色海蜇（Chrysaora quinquecirrha）和栉水母纲的侧腕水母（Mnemiopsis leidyi）对双壳类面盘幼虫的捕食情况。我们发现，金色海蜇的水母体阶段会捕获但不消化面盘幼虫：被水母体捕获的牡蛎面盘幼虫（弗吉尼亚牡蛎，Crassostrea virginica）中有99%在捕获后7小时内被活着排出，排出后98%能存活24小时；放置在水母体口腕上的牡蛎、贻贝（紫贻贝，Mytilus edulis）和蛤（侧褶泥蛤，Mulinia lateralis）面盘幼虫中有98%被排出；野外采集的水母体中的所有双壳类面盘幼虫都紧闭着且充满组织。我们的实验室证据表明，双壳类幼虫的壳可能为其提供了免受水母体捕食的保护：死去的、张开的面盘幼虫中有23%被水母体摄取，而活着的、紧闭的面盘幼虫中这一比例为0.7%；张开的面盘幼虫比紧闭的面盘幼虫在水母体中留存的时间更长；从刚附着的牡蛎幼虫上切下的组织会被摄取并消化。自由游动的金色海蜇碟状体摄取但不消化面盘幼虫。相比之下，底栖的螅状体阶段摄取了69%接触到其触手的面盘幼虫，并消化了其中48%。在面盘幼虫密度为0.3个/毫升时，每个螅状体平均每天消耗1个面盘幼虫。然而，在带有螅状体的牡蛎壳上，幼虫的附着并没有减少。与金色海蜇的结果相反，栉水母排出的活的面盘幼虫仅占4%，其肠道内容物中的面盘幼虫有25%被消化。在切萨皮克湾，栉水母对面盘幼虫的捕食率估计为每天0.2%至1.7%。我们得出结论，金色海蜇水母体不是双壳类面盘幼虫的重要捕食者，相反，它可能通过捕食确实会吃面盘幼虫的栉水母来降低面盘幼虫的死亡率。
