Invertebrate biodiversity associated with algal turfs on a coral-dominated reef

Abstract

This study is the first to quantify the diversity and composition of the mobile invertebrate fauna associated with algal turfs on a coral reef, and was conducted at Sodwana Bay, South Africa. Invertebrates were extracted from five 25 × 25-cm quadrats taken from algal turf biotopes at each of six depth zones, ranging from the upper intertidal to a depth of 22 m. A total of 2,316 invertebrates, representing 314 species, were recorded from these samples. Arthropoda were the most diverse group, with 119 species recorded, followed by the Annelida with 82 species and Mollusca with 81. Species composition differed dramatically with depth and indeed 67 % of species were exclusive to just one depth zone. Invertebrate biodiversity increased with depth (r 2 = 0.358), with intertidal and surf-zone samples notably less diverse than those from deeper reefs. This occurred despite algal biomass and species richness being considerably greater at shallower stations. In spite of the high faunal diversity reported here, the fauna of these algal turfs remains under-sampled, both because this study did not examine all taxa present and because insufficient samples were taken for species accumulation curves to asymptote. This study supports the contention that smaller invertebrates inhabiting specialised reef habitats represent the bulk of total biodiversity present in coral reef habitats. These components of biodiversity, however, still remain largely undocumented globally.