The Ecology of Lough Ine XVI. Predation and Diurnal Migration in the Paracentrotus Community

Abstract

In various parts of Lough Ine the sea urchin Paracentrotus lividus Lamarck populates the shallow sublittoral from low water down to about 1 m below this level, and keeps the bottom clear of algae by its grazing (Kitching & Ebling 1961). The most extensive areas regularly occupied by Paracentrotus are along the north shore of the lough, on boulders and on solid rock, and in Curlew Bay, on shell gravel fringed at low water mark with rocks. The sea bed slopes gently at these localities, and predators are few. Of the larger crabs only Carcinus occurs commonly, and starfish normally remain in slightly deeper water. On the other hand, filter feeders are present in large numbersPomatoceros triqueter (L.) (Polychaeta), Anomia ephippium L. (Lamellibranchia) and (less abundantly) Chlamys varia (L.) (Lamellibranchia). There are also substantial numbers of the grazing gastropod Gibbula cineraria (L.). New patches, dominated by Paracentrotus and bare of algae, have recently developed in many parts of the lough, and especially in the South Basin. In these places the shore is steep and heaped with boulders. There are additional predators-the starfish Marthasterias glacialis (L.), Asterias rubens L. and Asterina gibbosa (Pennant) under the boulders, the crab Portunus puber (L.) as a nocturnal visitor, and occasionally also the edible crab, Cancer pagurus L. Grazing and filter-feeding molluscs are much less abundant. This paper is concerned with the ecological inter-relations of important members of the Paracentrotus community. We have attempted to formulate the system of food chains operating within the community, and to interpret diurnal migrations of some of its members in relation to predation.