Depth patterns in microhabitat versatility and selectivity in coral reef damselfishes

Increasing disturbances on coral reefs threaten fish species with close microhabitat associations in shallow waters, but deep reefs may provide refuge habitats. Assessing this potential requires a comprehensive understanding of how versatility in microhabitat use, preference, and selectivity interact with changes in habitat composition along depth gradients. We examined six damselfish species categorized by versatility of shallow-water microhabitat association ('complex-coral-specialists', 'coral-associates', and 'generalists'), along a depth gradient from 10 to 30 m in Kimbe Bay, Papua New Guinea, and tested four important hypotheses. (1) We examined associations with hard-coral and complex-coral microhabitats. Hard-coral association declined with depth more among generalists than coral-associates but complex-coral microhabitat association declined for all species except one complex-coral-specialist. (2) We studied whether microhabitat selectivity declines with depth. Unexpectedly, selectivity increased with depth among both generalist and specialist species. (3) Within species, we tested for positive relationships between fish abundance and preferred microhabitat availability at each depth. However, relationships were stochastic across depths for all but one complex-coral-specialist. (4) Finally, we tested for positive relationships between the number of microhabitats selected by a species and the species' abundance at each depth, finding that species' abundances were not consistently related to microhabitat versatility. Our results suggest that several species currently utilize deep coral microhabitats (30 m), including specialists that strongly associate with vulnerable coral habitats in shallow water. Considerable microhabitat plasticity occurred along the gradient, even amidst stable preferences, and versatile species were not habitat limited, though restricted versatility may limit refuge potential for some species