Fish and coral communities shape elasmobranch reef use in southern Mozambique

Few studies have explored whether a reef's bioecological structure affects the presence of elasmobranchs. To examine if the structure of a reef's fish and coral community influences the likelihood of observing certain elasmobranch species, we deployed a remote underwater video station (RUVS) on four reefs in southern Mozambique. A single RUVS was deployed monthly on each reef for 12 months, resulting in 48 deployments and 140 h of video recordings. Images were extracted from the video recordings to estimate the relative abundance of teleost fish and following each camera deployment a 30 m² belt transect was completed to measure the percentage cover of corals. Coral and fish abundances were then separated into common functional metrics describing each community. NMDS and PERMANOVA were used to estimate if the calculated metrics and observations of elasmobranchs by RUVS varied between the four reefs. Metrics were then analysed for their influence on the composition of each reef's elasmobranch community within the NMDS ordination space. The relative abundance of coral species was primarily found to be linked with the depth of the reef surveyed. Relative abundances of coral measured on the shallow reef site were distinct from the other examined reefs in ordination space, with less coral cover and a lower overall abundance of teleost and elasmobranch fish. The richness and abundance of teleost fish species, particularly piscivorous fish, was highest on the northern reef where the elasmobranch community was dominated by several species of reef shark. The southern reef also had a distinct richness and abundance of teleost fish species, with a heightened abundance of herbivorous and cleaner fish, and the observed elasmobranch community was mostly comprised of Mobula rays and guitarfish. Our findings suggest that fish and coral communities can significantly differ between reefs with similar abiotic conditions in a relatively small region, and that this can lead to spatially heterogenous patterns of reef use by elasmobranchs. This may suggest that including the protection of reefs with different biological characteristics within local conservation strategies may promote rare and vulnerable regional elasmobranch species ranging from stingrays, guitarfishes, reef sharks, and pelagic rays.