MEPS 541:65-73 (2015)  -  DOI: https://doi.org/10.3354/meps11569

ABSTRACT: Rhodoliths are free-living calcareous nodules composed of non-geniculate coralline Rhodophyta algae. One potential rhodolith bioturbator is the sand tilefish Malacanthus plumieri, which builds mounds with these nodules over sand bottoms. Here, we tested (1) whether mounds act as a different habitat within a rhodolith bed, supporting specific associated assemblages, and (2) the potential role of M. plumieri as a bioturbation agent on rhodolith beds. We used multiple techniques (benthic and fish assemblage assessments, and videos with marked rhodoliths to assess fish behavior) to compare fish-built mounds with non-mounded control areas. M. plumieri was not observed removing rhodoliths from mounds; however, it spent 15% of its time rearranging mounds or adding new rhodoliths to the mound. A higher fish richness was recorded on mounds (mean = 9.4 ± SE 1.7) compared with the non-mounded control areas (5.5 ± SE 2.7) (t = -2.2; p < 0.05). The benthic assemblages also differed between the mounds and the control areas (PERMANOVA, Pseudo-F = 11.8 and p < 0.01). The categories that contributed most to dissimilarity between mounds and non-mounded control areas (SIMPER) were crustose coralline algae free of epiphytes and sand (15.5%), Dictyota jamaicensis (9.8%), Dictyota pulchella (9.4%), sand (9.3%) and Dictyopteris justii (8.2%). Because of their contribution to seascape heterogeneity, we suggest that the presence of M. plumieri mounds is an important variable in predicting diversity in rhodolith beds.

KEY WORDS: Rhodophyta · Dispersion · Benthic assemblages · Reef fish assemblages · Oceanic island · Seascape · Rhodolith · Ecological engineers