Vegetative propagation of the red alga Rhodochorton purpureum by means of fragments that escape digestion by herbivores

Abstract

Intertidal populations of the filamentous red alga Rhodochorton purpureum (Lightf.) Rosenv. (Nemaliales, Acrochaetiaceae) in the Northern Netherlands grow as dense velvety turfs in the understory of large fucalean algae. The small and rather constant size of the turf (1 to 1.5 mm) and the high percentage of 'decapitated' filaments suggest that the turf is continually 'shorn' by herbivores. Two grazing invertebrates were found on the turf: the gastropod Lhtohna littorea (L.) and the amphipod Gammarus salinus Spooner Differences between the 2 grazers in the size of ingested R. purpureum fragments and in the proportion of ingested fragments with intact apices were attributed to differences in their feeding mechanisms. Both species egested live R. purpureum fragments in their faecal pellets. These fragments had the capacity to regenerate into new filaments when cultured in the laboratory. In the field small tufts of R. purpureum filaments were found on bare substratum, originating from fragments contained in sticky, detntus-rich envelopes, probably faecal pellets. Experiments in unialgal cultures showed that the regenerative capacity of fragments is very high, as it proceeds over a broad range of temperature and light conditions, even in total darkness. We conclude that the capacity of R. purpureum fragments to escape digestion by herbivores probably plays an important role in vegetative propagation of the species.