Predation as a driver of gastropod distribution in north-eastern New Zealand kelp forests

Abstract

Gastropods play an important ecological role in kelp forests; however, this role is dependent on where exactly in such communities these animals are located. We assessed the spatial and temporal patterns in the utilisation of available reef and macroalgal substrates by three gastropods in a north-eastern New Zealand kelp (Ecklonia radiata (C. Agardh) J. Agardh, 1848) forest, focusing on predation as a factor influencing these patterns. Although kelp provided a large habitable surface area for gastropods, much of this area was under-utilised. During the day, gastropods on E. radiata were largely confined to the primary laminae. At night, gastropods on the reef migrated into the algal canopy where they occupied regions of the kelp that were not occupied during the day. Over a 36-day period, 93% of the gastropods tethered to the reef were consumed by predators, whereas none tethered in the algal canopy was consumed. We consider that night-time vertical migration and dispersion through the algal canopy may be primarily a response to predation by diurnally feeding fish and nocturnal benthic predators such as lobsters. Our research highlights the importance of considering diel changes in epifaunal distribution and abundance when assessing their ecological role.