In situ exudation of phlorotannins by the sublittoral kelp Ecklonia radiata

Exudation of phlorotannins (polyphenolics) was measured in situ from the sublittoral kelp Ecklonia radiata at two locations near Sydney, New South Wales, Australia during 1992–1993. Minimally disruptive techniques were used in which individual plants were enclosed within clear plastic bags in order to concentrate exudates. Rates of exudation from E. radiata were low relative to most previous studies, with a mean rate (averaged across four seasons and two sites) of 5.5 g g (dry wt)^-1 h^-1. Exudation was greatest in summer and least in winter at one site, but there were no seasonal differences at a second, more protected site. There was no measurable diurnal variation in exudation rates. Exudation after a period of heavy storms was not significantly different from exudation during calm weather, but severe physical damage to the kelp did increase exudation. Our results suggest that exudation of phlorotannins in temperate Australian waters may be less ecologically important than has been suggested for coastal systems in the Northern Hemisphere.