Benthic Faunal Ecology in the Algal Turf Zone of a Bornean Rocky Shore: the Influence of Habitat-Forming Species

Abstract

Brunei lies within the highly diverse Palawan-North Borneo ecoregion, but taxonomic and ecological assessments of the benthic marine fauna are distinctly lacking. Local intertidal ecosystems are dominated by sandy beaches, mudflats and mangroves, with sparsely distributed rocky shores. We studied the fauna and community ecology associated with the low-shore algal turf zone of the only remaining ‘undisturbed’ natural rocky shore of Brunei (the Empire). We assessed the macrobenthic invertebrate species and tested whether assemblage structure related to turf habitat complexity (16 samples; 20×20 cm). Comparisons were made between two categories of substratum, (1) finely branched and (2) broadly expanded substrata, determined by the predominance of differently structured coralline and green algae, and sessile animals (sponge and mussels). More than 1099 macrofaunal specimens were retrieved from the samples, comprising 30 families and 46 OTUs (Operational Taxonomic Unit), with the most abundant groups being amphipods (12 OTUs), ostracods (2), tanaidaceans (2), isopods (3), polychaetes (5) and gastropods (22). Multivariate analyses based on 25 common OTUs revealed significant dissimilarity in assemblages associated with the different substrate types. Indicator species analysis identified amphipods (abundant in coralline algae) and tanaidaceans (abundant on flat substrates) as contributing the most to this differentiation (28.63% for three species). The gastropod, Zafra cf. troglodytes (17.7%) and the ostracod cylindroleberid sp. (14.3%) contributed the most to assemblage similarity of the finely branched and expanded substrates, respectively. The drivers of habitat preference, and local spatial and temporal variation in assemblage structure are discussed. This work adds to our knowledge of local rocky shore benthic ecology but reveals a dire need for dedicated taxonomic work to resolve the species, crucial for appropriate environmental conservation and management.