Conservation status of the southernmost reef of the Amazon Reef System: the Parcel de Manuel Luís

The Parcel de Manuel Luís (PML) is located at the southern end of the Amazon Reef System, which comprises the northernmost reef formations of the Brazilian biogeographical province. Its unique position and singular seascape make the PML an important stepping-stone for marine organisms between the Brazilian and Caribbean provinces. Yet, due to its distance from the shore, high tidal amplitude, and strong currents associated with a series of pinnacles exposed during low spring tides, the PML is one of the least studied reefs in the Western South Atlantic. Here, we integrated sessile benthic community data, fish assemblage surveys, and remote filming of fish interactions to establish the most complete community assessment of the PML reefs to date. In our surveys, we documented 78 sessile benthic taxa, with a taxonomic dominance of macroalgae (54 taxa), including two new occurrences of sponges for the North Brazilian Shelf, as well as four endemic species, such as the fire coral Millepora laboreli . The fish assemblage comprised 59 reef fish species, with biomass dominated mainly by large carnivorous species (e.g., groupers and snappers). Intra- and interspecific interactions were dominated by herbivorous fishes, particularly underpinned by grazing behavior and chasing by territorial species. The considerably high biomass and large-bodied species found in our surveys is rarely seen elsewhere in the Western South Atlantic, suggesting a low level of fishing compared to most other places, and only a few changes were observed in the fish assemblages since the first assessment made in 1998. We also highlight the usefulness of an integrated approach for continued assessment of Western South Atlantic reefs, particularly given emerging threats from mining and oil exploration, and the heavy traffic of commercial vessels in the region. Our findings support the PML as an area of critical conservation interest for reef systems, emphasizing the need for continued enforcement of this marine protected area and its integration in long-term plans of offshore oil and gas development projects.