The influence of giant kelp Macrocystis pyrifera on the growth of subantarctic marine bacteria

Abstract

The short-term effects of giant kelp Macrocystis pyrifera C.A. Agardh on the growth of subantarctic bacterial microflora were followed under various seasonal conditions in coastal seawater of the Kerguelen Archipelago. Artificial degradation experiments were carried out in 3-m3 tanks (daily sampling allowed a regular survey of bacterial changes in the supplemented seawater). The results clearly revealed a significant response of the subantarctic bacterial community to macrophyte addition. Bacteria grew rapidly on freshly harvested or stranded kelp. Doubling time had a mean value of 40 h for total bacteria and 8 h for heterotrophic bacteria. Bacterial growth peaked within the first 3-5 days but declined thereafter. Both total and heterotrophic bacterial increases were higher in stranded or detritic kelp experiments than in freshly harvested kelp experiments. The amphipod Parathemisto gaudichaudii Guerin was used to assess the stimulating effect of macrofaunal breakdown on the bacterial decomposition of the kelp. © 1991.