Secondary engineering of rhodolith beds by the sand tilefish Malacanthus plumieri generates distinctive habitats for benthic macroinvertebrates and fish

Abstract

Whilst the importance of foundation species for biodiversity conservation has been largelyacknowledged (e.g., coral and bivalve reefs, seagrass, kelp and rhodolith beds), the role oftheir associated species as secondary habitat engineers has just begun to be appreciated.Here, we evaluated whether secondary engineering of rhodolith beds by the sand tilefishMalacanthus plumieri influences the composition and β-diversity of benthic macroinvertebratesand reef fish assemblages. Our findings indicate that, by selecting, relocating, andrearranging rhodoliths into mounds, M. plumieri creates a distinctive habitat for macroinvertebratesand fishes. M. plumieri mounds increase fish abundance by 57% in rhodolithbeds, with an 82% species turnover rate between mounds and non-mounded areas. In contrast,the macroinvertebrates in M. plumieri mounds are largely a subset of the species fromnon-mounded areas, with an 86% species nestedness rate. Despite decreasing the abundanceof macroinvertebrates in the mounds by half, M. plumieri increases the heterogeneityand structural complexity of rhodolith beds, affecting the composition of associated fishassemblage at a larger spatial scale. Our results suggest that, by increasing the structuralcomplexity of rhodolith beds and shaping their associated biodiversity, the abundance ofM. plumieri mounds could be a useful proxy to define priority areas for conservation acrossthe South Atlantic rhodolith beds, especially in the light of ongoing impacts related to offshoreoil exploitation, overfishing and carbonate mining.