Recolonization of intertidal macroalgae in relation to gap size and molluscan herbivory on a rocky shore on the east coast of southern Africa

Abstract

The low intertidal on rocky shores in the Transkei region is characterized by extensive turfs of coralline algae, punctuated by small gaps maintained by patellid limpets. Recolonization of macroalgae in experimentally cleared gaps of different sizes was monitored. All quadrats were rapidly recolonized by a green/brown algal component, consisting of Ralfsia spp., Ulva spp., Enteromorpha spp. and Iyengaria sp. Although this component remained dominant there was some growth of coralline algae (Arthrocardia spp. and Jania spp.). Rate of recolonization was directly related to gap size, with the smallest gaps remaining relatively free of algae, and the largest showing greatest recovery after 12 mo. Even after 24 mo, however, the total algal cover was only 10-50% of that in undisturbed control quadrats. Grazer density (Patella longicosta, P. oculus, Oxystele tabularis) was highest in small gaps and there was a direct relationship between the number of grazers and the ratio of bare rock to algae. -from Author