Uncharted coral reefs from the Inhambane Province, Mozambique

Abstract

Mozambique has the third-largest coastline in the western Indian Ocean with a large and diverse reef area. Those reefs provide food and income for a large proportion of coastal communities but remain scarcely studied. As a baseline assessment, we sampled four uncharted shallow reefs (Baixo Africa, Baixo Zambia, Pomene and Baixo Silvia) within a 56 km stretch line from 5 to 32 meters deep. The fish abundance and assemblage composition were assessed by underwater visual census (25x2m, n = 112). The benthic community was characterized by digital images (0.5x0.5m, n = 164) and the invertebrate megafauna by direct counting (25x2m, n = 52). A total of 209 reef fish species was observed, with similar mean richness (22.4 ± 7.2 species.100 m−2) at all reefs. Invertivorous (n = 79) and planktivorous fish species (n = 36) represented 55% of species total. Trophic composition was similar among sites and with large contribution of planktivores. The presence of large shoals (>100 ind.100 m−2, e.g., surgeonfish, fusiliers, snappers) and large-bodied fishes (>90 cm) (e.g., groupers) was a clear indication of local productivity and health conditions of reefs. Seventy-nine taxa were observed on the benthic cover with the largest richness found at Baixo Silvia (28.5 ± 7.4, species.100m −2, mean ± SD). Turf algae dominated the benthos (31.5% ± 16.4) at all sampled reefs. Coral cover was variable between sites (9.3 – 25.8%), dominated by branching and plate corals, and <1% of colonies showed signs of diseases/bleaching. The baseline assessment indicated large biomass of fishes and negligible evidence of large impacts on coral formations which indicated a good conservation status of those areas. Based on these findings, a marine protected area is proposed for establishment in collaboration with environmental authorities and the local community.