Non-reef habitats in a tropical seascape affect density and biomass of fishes on coral reefs

Non-reef habitats such as mangroves, seagrass, and macroalgal beds are
important for foraging, spawning, and as nursery habitat for some coral
reef fishes. The spatial configuration of non-reef habitats adjacent to
coral reefs can therefore have a substantial influence on the distribution
and composition of reef fish. We investigate how different habitats in a
tropical seascape in the Philippines influence the presence, density, and
biomass of coral reef fishes to understand the relative importance of
different habitats across various spatial scales. A detailed seascape map
generated from satellite imagery was combined with field surveys of fish
and benthic habitat on coral reefs. We then compared the relative
importance of local reef (within coral reef) and adjacent habitat
(habitats in the surrounding seascape) variables for coral reef fishes.
Overall, adjacent habitat variables were as important as local reef
variables in explaining reef fish density and biomass, despite being fewer
in number in final models. For adult and juvenile wrasses (Labridae), and
juveniles of some parrotfish taxa (Chlorurus), adjacent habitat was more
important in explaining fish density and biomass. Notably, wrasses were
positively influenced by the amount of sand and macroalgae in the adjacent
seascape. Adjacent habitat metrics with the highest relative importance
were sand (positive), macroalgae (positive) and mangrove habitats
(negative), and fish responses to these metrics were consistent across
fish groups evaluated. The 500-m spatial scale was selected most often in
models for seascape variables. Local coral reef variables with the
greatest importance were percent cover of live coral (positive), sand
(negative), and macroalgae (mixed). Incorporating spatial metrics that
describe the surrounding seascape will capture more holistic patterns of
fish-habitat relationships on reefs. This is important in regions where
protection of reef fish habitat is an integral part of fisheries
management but where protection of non-reef habitats is often overlooked.