Coralline turf-associated fauna are affected more by spatial variability than by host species identity

Abstract

We examined the effects of host species identity and spatial variability on animals inhabiting subtidal coralline algal turfs, by comparing the assemblages of small (1–8 mm) mobile invertebrates associated with five coralline turf species across a number of subtidal rocky reefs in northeastern New Zealand. Coralline turf fauna were abundant (average of 16,000 to 80,000 ind.m−2) and diverse (129 taxa in total), with assemblages dominated by arthropods, gastropods and polychaetes. Despite substantial differences in the morphologies of the coralline turf species, host identity had little effect on total abundance and richness of the fauna, and a moderate effect on taxonomic composition. Spatial variation at the scale of 102–103 m had a stronger influence than host identity on all three assemblage-level properties, with wave exposure and depth having the most explanatory power of the environmental factors measured. Host-specificity was low, probably due to the close taxonomic relatedness of the host algal species and their inedibility (with consequent lack of dietary specialisation by fauna). For our study system, the results justify the common practice of lumping coralline turf species in ecological studies with regard to the description of the total abundance and richness of the associated fauna, but not the taxonomic composition of the fauna.