Predator-prey interactions in seagrass beds. I. The influence of macrofaunal abundance and size-structure on the diet and growth of the western rock lobster Panulirus cygnus George

Abstract

Juvenile western rock lobsters Panulirus cygnus George at two Western Australian sites, Seven Mile Beach and Cliff Head, showed a range of diets and feeding strategies. Rock lobsters at Seven Mile Beach, an area with comparatively few animal prey, ingested large quantities of epiphytic coralline algae. Rock lobsters at Cliff Head primarily consumed invertebrates, with less food being ingested overall than at Seven Mile Beach. The diets of rock lobsters also varied greatly between different seasons, and between rock lobsters feeding in different habitats at Seven Mile Beach. On all sampling occasions, the diet of P. cygnus reflected the abundance and size distribution of benthic macrofauna. Selection of foraging habitat was not, however, found to be related to food availability. Rock lobsters consumed slow-moving, benthic prey, particularly molluscs, within the size range 2–5.6-mm sieve size. When such prey were in low numbers, rock lobsters incorporated large quantities of plant material into their diet. The dietary differences between sites were largely attributable to the trochid mollusc Cantharidus lepidus locally settling in extremely high densities (> 10000· m −2) at Cliff Head in late summer. Rock lobsters at Cliff Head grew nearly twice as rapidly as rock lobsters at Seven Mile Beach. The dietary and prey density data support the hypothesis of Chittleborough (1976) that these differences in growth between sites are associated with diet. Chittleborough's hypothesis can, however, now be refined: the localized recruitment of C. lepidus is postulated to be the primary cause of the high rock lobster growth rates at Cliff Head.