Prey of Deep-water Hydra in Lake Superior

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Specimens of Hydra attached to a soft-substrate bottom were collected from a manned submersible at a 275-m-deep station near the Keweenaw Peninsula in Lake Superior. Near-bottom zoo-plankton were collected to assess Hydra feeding preference. We identified and counted the zooplankton samples, and identified the zooplankton prey found in the Hydra. Of 86 Hydra, 21 contained remains of 23 prey of 4 zooplankton taxa. Compared with expected numbers based on the proportions of the net samples, these Hydra appeared to be feeding selectively, with a preference for larger zooplankton. The large calanoid copepod Limnocalanus macrurus was particularly selected. A very provisional estimate of the rate of Hydra predation on the bottom of Lake Superior is one prey per 4 days. The relatively constant environmental conditions, lack of commensals and predators, and the zooplankton food source suggest that the bottom of Lake Superior is a stable habitat for Hydra. © 1995, International Association for Great Lakes Research. All rights reserved.

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Journal of Great Lakes Research