Predation on Encapsulated Larvae by Adults: Effects of Introduced Species on the Gastropod llyanassa obsolete

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Abstract
The abundant and ubiquitous marine snail I. obsoleta is not a major food item of any predator. Several species prey heavily upon its egg capsules, which spend 1 or more weeks attached to solid objects in the intertidal zone. Predation losses in caging experiments conducted in Barnstable Harbor, Massachusetts (USA) averaged 52%, but in 1 case exceeded 85% in 10 days. Predation on encapsulated larvae of this population equals or exceeds that on planktonic stages. Much of this mortality was associated with introduced species. Predation rates (egg capsules individual-1 2 day-1) measured in the laboratory were: native hermit crabs Pagurus longicarpus, 141; introduced green crabs Carcinus maenas, 330 and introduced periwinkles Littorina littorea, 11. L. littorea was the most abundant egg consumer in the mid-intertidal zone where most egg capsules were laid. Capsules detached by the predators released larvae as did whole capsules defecated by L. littorea. Two native predators on mollusks, moonsnails (Polinices duplicatus) and juvenile horseshoe crabs (Limulus polyphemus), did not eat egg capsules.