Herbivorous fish assemblages and herbivory pressure on Laamu Atoll, Republic of Maldives

While herbivory is recognized as a fundamental process structuring coral re ef communities, herbivore assemblages and processes are poorly described fo r reefs in the Indian Ocean region. We quantified herbivorous fish assembla ge structure (abundance and diversity) in Laamu Atoll, Republic of Maldives , in four reef habitat types: faro reef flats, faro reef slopes, inner and outer atoll reef slopes (20 sites in total). Herbivorous fish assemblages, representing a total of 30 species, grouped strongly by habitat type, with the highest absolute abundance observed on faro reef flats and lowest abund ance on inside atoll rim reef slopes. Removal of Thalassia seagrass blades by ambient herbivore assemblages was used in a bioassay to assess relative herbivory pressure among four habitat types (eight sites). Also, at one sit e a choice herbivory assay was performed to assess herbivore preference amo ng four benthic plants across three depth zones. Relative herbivory, as ind icated by Thalassia assays, was highest on inside atoll rim reef slopes and lowest on outside atoll rim reef slopes. Thalassia consumption did not cor respond to overall herbivorous fish abundance, but corresponded more closel y with parrotfish abundance. In the choice assays, herbivores showed strong preferences among plant types and consumption of most plant types was high er at mid-depth than in the shallow reef flat or deep reef knoll zones.