Role of prey availability in microhabitat preferences of juvenile coral trout (Plectropomus: Serranidae)

Availability of specific microhabitat exerts a strong influence on recruitment and abundance of coral reef fishes, but the ecological basis for microhabitat selection is not always clear. This study used a combination of field-based sampling and aquarium-based experiments to test microhabitat preferences of juvenile coral trout (mostly, Plectropomus maculatus), and assess whether microhabitat selection is related to prey access. In the field, coral trout use live Acropora corals situated over sand 3 times more than any other microhabitat, even through these specific microhabitats accounted for only 12.8% of habitat area. Field-based surveys revealed that live coral habitats support higher densities of potential prey species (71.73 individuals per m2 ± 8.4 SE for fish; 423.36 individuals per m2 ± 91.8 SE for crustacean) compared to dead corals (21.92 individuals per m2 ± 3.9 SE for fish; 146.67 individuals per m2 ± 38.1 SE for crustacean). Furthermore, structural microhabitats on sand have higher densities of prey (57.61 individuals per m2 ± 9.6 SE for fish; 539.04 individuals per m2 ± 79.0 SE for crustacean) compared to comparable microhabitats on consolidated carbonate substrata (36.05 individuals per m2 ± 6.7 SE for fish; 129.36 individuals per m2 ± 15.9 SE for crustacean). In the absence of prey, juvenile coral trout did not distinguish between live versus dead corals (37.18% ± 8.2 SE and 35.48% ± 6.1 SE), but both of these microhabitats were preferred over rubble (16.21% ± 3.5 SE), macroalgae (11.09% ± 6.1 SE) and sand (0%). In tank-based studies of prey use, juvenile coral trout consumed prey fishes that associate with non-coral habitats (e.g., Eviota zebrina; 33.28% ± 3.4 SE) and mid water species (e.g., Aioliops tetrophthalmus; 47.97% ± 2.8 SE), but did not consume those fishes with an obligate association with live corals (4.7% ± 1.9 SE; 6.03% ± 2.2 SE; 7.9% ± 2.8 SE). Our results suggest that studies of microhabitat preferences should consider both the structure and location of specific microhabitats. It is presumed that structural microhabitats are essential for evading predators, while occupation of live corals positioned over sandy substrata maximizes accessibility to a diverse array of potential prey fishes and crustaceans.

► Cryptic prey fishes strongly associate with live or dead coral.
► Oppositely, cryptic crustaceans associate with solid or loose substrata.
► Live and dead coral both are preferred shelter of juvenile coral trout.
► Strong preferences of juvenile coral trout for prey fishes may be related to prey swimming ability.