Date Published: June 8, 2018
Publisher: Public Library of Science
Author(s): Anaide W. Aued, Franz Smith, Juan P. Quimbayo, Davi V. Cândido, Guilherme O. Longo, Carlos E. L. Ferreira, Jon D. Witman, Sergio R. Floeter, Bárbara Segal, Heather M. Patterson.
As marine ecosystems are influenced by global and regional processes, standardized information on community structure has become crucial for assessing broad-scale responses to natural and anthropogenic disturbances. Extensive biogeographic provinces, such as the Brazilian Province in the southwest Atlantic, present numerous theoretical and methodological challenges for understanding community patterns on a macroecological scale. In particular, the Brazilian Province is composed of a complex system of heterogeneous reefs and a few offshore islands, with contrasting histories and geophysical-chemical environments. Despite the large extent of the Brazilian Province (almost 8,000 kilometers), most studies of shallow benthic communities are qualitative surveys and/or have been geographically restricted. We quantified community structure of shallow reef habitats from 0° to 27°S latitude using a standard photographic quadrat technique. Percent cover data indicated that benthic communities of Brazilian reefs were dominated by algal turfs and frondose macroalgae, with low percent cover of reef-building corals. Community composition differed significantly among localities, mostly because of their macroalgal abundance, despite reef type or geographic region, with no evident latitudinal pattern. Benthic diversity was lower in the tropics, contrary to the general latitudinal diversity gradient pattern. Richness peaked at mid-latitudes, between 20°S to 23°S, where it was ~3.5-fold higher than localities with the lowest richness. This study provides the first large-scale description of benthic communities along the southwestern Atlantic, providing a baseline for macroecological comparisons and evaluation of future impacts. Moreover, the new understanding of richness distribution along Brazilian reefs will contribute to conservation planning efforts, such as management strategies and the spatial prioritization for the creation of new marine protected areas.
Understanding how marine biodiversity varies on local and regional scales serves as the foundation for studies in ecology, biogeography, and conservation [1–2]. One of the most pervasive large-scale patterns of biodiversity is the latitudinal diversity gradient, in which the highest richness commonly occurs towards the equator and declines towards higher latitudes [3–7], a pattern that has been described for many groups of organisms in terrestrial and marine environments [4,7]. Despite the existence of a relatively consistent pattern across different groups, the latitudinal diversity gradient is somewhat variable among taxa and regions [2, 6]. For example, marine diversity patterns of fish and invertebrates in the Atlantic differ between eastern and western shelves  and between northern and southern hemisphere [9–10]. Despite these examples, we still lack a comprehensive and quantitative description of large-scale patterns of benthic communities in the Atlantic.
Our results provide the first broad-scale baseline of abundance and diversity patterns for shallow water benthic communities along the Brazilian coastline and oceanic islands. Reefs of the Brazilian Province have low reef-building coral cover and are dominated by algal turfs and macroalgae, even at biogenic reef systems, and among coastal and oceanic reef localities. High algae cover has been observed on reefs elsewhere, but not to the same extent as documented here for the Brazilian Province. For instance, macroalgae cover on Caribbean reefs is ~23.6%  and 1% of the reefs in the Indo-Pacific show macroalgae cover higher than 50% . Turf algae were the most abundant benthic group on Curaçao reefs (percent cover ranging from 20.3–41%; ), in the Mediterranean (percent cover ranging from 50–70%; ), South Australia (percent cover of 39%; ), and at the remote reefs of the Line Islands (36% cover; ), but none of these studies recorded such a high cover of algal turfs as noted here.