MEPS 288:87-102 (2005)  -  doi:10.3354/meps288087

ABSTRACT: Stands of the southern bull kelp Durvillaea antarctica (Chamisso) Hariot provide considerable biomass and a major habitat in the lower intertidal zone of exposed shores on the austral land masses. Whiplash effects of adult fronds (up to 10 m long) can affect recruitment, growth and survival of understorey species and potentially large brown algal competitors, thereby affecting community development. In southern New Zealand, D. antarctica is one of several species of large brown algae inhabiting the low intertidal zone. Effects of its canopy and its associated understorey coralline algae on community development were tested at 2 sites (Moeraki and Kaikoura) at different times of year between February 1999 and October 2001. Removal of D. antarctica canopies had surprising results compared to most studies where canopies of large brown algae were removed. The greatest initial recruitment of bull kelp occurred beneath intact canopies, usually in areas where corallines were removed. Recruitment was highly variable through time, with peaks occurring in June and October (austral winter–spring), depending mostly on when canopies were removed. There was an order of magnitude difference in recruitment between sites. The cover of turfing coralline algae, however, increased in all canopy removal treatments. A major source of mortality of young recruits was grazing by the herbivorous fish Odax pullus. Its distinct grazing marks were seen on recruits, almost exclusively outside the canopy of bull kelp where 80% of recruits were grazed. We show that D. antarctica has the ability to recruit beneath adult canopies, but that survival and growth ultimately depend on the extent of canopies, underlaying benthic algae and escapes from grazing by herbivorous fish.

KEY WORDS: Durvillaea antarctica · Recruitment · Intertidal algae · Substratum · Canopy ·Fish grazing