Rhodolith Beds Along the Southwest Atlantic Ocean: From Shallow to Mesophotic Habitats. Review of a Singular Ecosystem

Rhodolith beds are one of the major marine coastal ecosystems. Knowing the spatial distribution, environmental characteristics and composition is not only scientifically pertinent but also crucial to allow comparisons in case of changes due to local and global anthropogenic pressures. With slow algal growth rates, high associated diversity and potential importance as nursery grounds, rhodolith beds are present along the Brazilian coast of the Southwest Atlantic Ocean. This study provides an updated map of shallow and mesophotic rhodolith distribution after a systematic literature review. The prevailing oceanographic conditions along most parts of the Brazilian coast render the environment suitable for the developing rhodolith beds (a total of 68 taxa in this review), with 63 taxa along the East Brazilian Shelf, seven taxa for the North Brazilian Shelf and 10 taxa in the South Brazilian Shelf. According to composition, shallow and mesophotic communities were more similar in each large marine ecosystem than among them. In addition to gaps in terms of distribution, there are uncertainties about the taxonomic composition of the rhodoliths, associated fauna and flora and oceanographic and geological characteristics of the bottoms, which call attention to the importance of further studies, mainly in the mesophotic. This review provides a more precise distribution of these habitats along the Brazilian coast of the Southwest Atlantic Ocean. It contributes to a more detailed taxonomic composition of calcareous algae in an extremely relevant marine ecosystem, which is crucial for many species, including the endemic kelp, Laminaria abyssalis.