SHORT-TERM DYNAMICS OF A SEAWEED EPIFAUNAL ASSEMBLAGE

This paper examines short-term stability and movement patterns of the mobile epifaunal assemblage inhabiting a dense subtidal bed of the fuc alean seaweed Carpophyllum plumosum var. capillifolium (A. Richard) Li ndauer, in northeastern New Zealand. Four-hourly sampling of plants ar ound the clock during all four lunar phases revealed no clear patterns in the abundance of total animals or of most individual taxa. The onl y exceptions were cumaceans, mysids and eusirid amphipods, which were more abundant on (or near) the plants at night. Recolonization experim ents revealed a night-time turnover of 35-42% of total epifaunal indiv iduals on plants within clumps (i.e. plants in physical contact with o ther plants). Turnover rates were much lower on clumped plants during the day (8-22%), and on plants isolated in small coralline turf patche s during day and night (4-12%). For the major epifaunal groups, night- time turnover on clumped plants was highest for amphipods (55-69% of i ndividuals), followed by isopods (17-60%), and gastropods (11-16%). To gether, these results indicate that epifaunal movement was mainly by c rawling from plant to plant, rather than by swimming at night as a com ponent of the demersal zooplankton. This contrasts with the findings o f some previous studies, where epifauna recolonized isolated plants at higher rates than clumped plants, apparently because isolated plants acted as a sink for epifauna resettling from the water column at dawn. It is suggested that the density of plants within macrophyte beds det ermines the extent to which epifauna disperse by crawling versus swimm ing in the water column. (C) 1998 Elsevier Science B.V.