Biondi, Marcus T. & Erik V. Thuesen. The Evergreen State College. Olympia, WA 98505
Megalopae and juveniles of the crab Cancer gracilis and amphipods, Hyperia medusarum, were found in large numbers riding the scyphomedusa Phacellophora camtschatica during the spring and summer of 1994 in Puget Sound. Crab densities ranged from 0 to 225 C. gracilis per host medusa (n = 10), and as many as 447 amphipods were found on one host. Megalopae congregate on the exumbrella of P. camtschatica but will hide within the oral arms if the medusa is disturbed. As larvae progress from megalopae to juveniles, they migrate towards the subumbrella near the tentacles. Amphipods are exclusively subumbrellar, and concentrate on the oral arms. They are rarely found in gonadal tissue or gastric pouch. P. camtschatica likely provides refuge and a possible food source. Medusae may also serve as a form of energy-saving vertical transportation that increases retention and survival of C. gracilis larvae within the estuary.
Photograph of Phacellophora camtschatica by Steve
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