ENDOPHYTIC ALGAE OF CHONDRUS-CRISPUS (RHODOPHYTA) .4. EFFECTS ON THE HOST FOLLOWING INFECTIONS BY ACROCHAETE-OPERCULATA AND A-HETEROCLADA (CHLOROPHYTA)

The rhodophycean seaweed Chondrus crispus was infected under laboratory conditions by the green algal endophytes Acrochaete operculata and A. heteroclada. Such infections resulted in detrimental effects on host performance, including slower growth and carrageenan yields. Regeneration capacity of the host was diminished, with the extent determined by the density of the infection. Infections also caused softening of host tissue in both laboratory-infected arid wild fronds; in the former the degree of softness was directly related to density of infections. Infected C. crispus was preferred over non-infected material when offered to Idotea baltica and Gammarus oceanicus, and the consumption of infected fronds was similar to that of the highly palatable chlorophyte Ulva sp. In general, infection by A. heteroclada affected the 2 life-history generations of the host similarly, whereas A. operculata affected mainly sporophytic fronds. This study shows that A. operculata and A. heteroclada are pathogens of C. crispus, and that their effects on the host, either as primary cause of dysfunctions or as agents facilitating secondary infections by other pathogens, can have major effects on both natural and cultivated populations.