Heteroantagonism observed in mixed algal cultures.

Abstract

RUSSELL1 has referred to the curious lack of interest shown by marine ecologists in species competition, especially in view of the suitability of existing cultural techniques for investigating this problem. Certainly much more experimental work using mixed cultures has been carried out by examining competition in planktonic algae2,7 than in benthic algae8. This is perhaps surprising in view of the wealth of information, particularly that derived from studies on the algal colonisation of cleared or new substrata, which suggests that competition factors also play active roles in benthic community structuring and may even, as deduced by Den Hartog9, influence zonation. Particularly interesting in this respect are the growing number of reports10–14 that polyphenols (‘tannins’) are actively liberated from the surfaces of brown algae, and that these compounds possess both antibacterial and antialgal properties15–20. Indeed, the fucosan-vesicles or physodes commonly found in brown algal cells have been attributed the function of polyphenol storage21–23. Although the antifouling properties of these secretions have been recognised7,16,17,19,20, very little is known of their ecological influence beyond the surface of the host. Here I report on some observations of mixed cultures of the brown crustose alga Ralfsia spongiocarpa Batt. and the two crustose red algea Porphyrodiscus simulans Batt. and Rhodophysema elegans (Crouan frat. ex J. Ag.) Dixon.