Size-selective predation on the sea urchin Echinometra sp. A by Japanese spiny lobster Panulirus japonicus

Abstract

Size-selective predation by Japanese spiny lobster Panulirus japonicus on the sea urchin Echinometra sp. A was examined in outdoor tanks with a roof using 20 lobsters (carapace length, CL: 59-93 mm) and four size classes (10-19, 20-29, 30-39 and 40-49 mm in test diameter, TD) of sea urchins. High levels of predation were found to occur in the period, at least until 5 days before and again from 3 days after molting. The maximum TD of eaten sea urchins increased with CL. The success rate of predation (ratio of the number of prey eaten to the number of predation attacks) was high (~75%) for the smallest size class of urchins but low (<11%) for the largest class over the experimental range of CL, and the success rate increased with CL for the intermediate classes, suggesting that large (>40 mm) sea urchins may be less vulnerable to predation even by large (>90 mm) lobsters. Prey remains after lobster predation showed that the tests of large (mostly >30-40 mm TD) sea urchins tended to remain largely intact with an enlarged peristomial opening while entire tests were eaten for smaller urchins.