Title: EVALUATING POTENTIAL MECHANISMS UNDERLYING TROPHIC ASSEMBLAGE SHIFTS IN REEF FISHES FROM SHALLOW TO MESOPHOTIC DEPTHS IN HAWAII

Abstract: Herbivorous reef fishes are considered integral components of healthy coral reef ecosystems, yet initial studies of mesophotic coral reefs (>30m) indicate vast reductions in herbivorous reef fish communities compared to their shallow congeners despite observations of high algal abundance at mesophotic depths. Preliminary hypotheses regarding the reduction in herbivorous fishes with depth propose that 1) decreased light levels may reduce habitat quality, 2) reductions in water temperature inhibits fishes' digestion of algal tissues, and 3) algal abundances are reduced or chemically defended on deep reefs. We conducted surveys along stratified depth gradients in West Hawaii to assess variability in reef fish trophic assemblages, temperature, and habitat metrics with depth. We then conducted choice experiments to determine the palatability of common algal species in mesophotic depths. Our findings support previous studies of reduced herbivorous reef fish abundances with depth, yet the absence of herbivores at depth does not appear to be associated with variations in temperature, habitat complexity or turf algal cover. Instead, herbivore reductions were positively associated with reductions in coral cover and negatively associated with increasing macroalgal cover with depth. Algal choice experiments revealed that deep algal species are edible and quickly consumed by shallow herbivorous fishes. These findings suggest changes in herbivore populations with depth are more complex than habitat quality, temperature, or food availability previously hypothesized.

Authors: Kane CN, Tissot BN

Presentation: Oral

Session: 29

Date: 06/21/16

Time: 15:00

Location: 308 A/B

Back