The Abrolhos Seascape, despite being home to the highest known marine biodiversity in the Southern Atlantic Ocean (Dutra et al. 2011b; Freitas et al. 2011), has important knowledge gaps that hinder the effective conservation and sustainable use of its biodiversity. Mapping key habitats and ecosystems is of great importance to advance in the planning of MPAs (Cogan et al. 2009). The updated map of the Abrolhos habitats obtained from the compilation and analysis of various sources of information brings a synthesis of the current knowledge about the seascape bottom (Fig. 2). In this new effort, we expanded the habitat map to important areas, such as the Royal Charlotte Bank, and the Vitoria-Trindade Seamount Chain, adding to previous efforts focused on specific habitats or in the Abrolhos Bank only (Prates 2003; Moura et al. 2013).
Detailed mapping efforts of habitats, such as mesophotic and deep reefs, can add important information about the biodiversity distribution in the Abrolhos Seascape. Recognizing that there are still large information gaps on mesophotic, slope and deep habitats and ecosystems, we make available the database obtained here for future reanalysis and improvements.
The analysis of habitat representativeness in the current network of MPAs of the study area (Fig. 3; Table SI1) indicates that although some habitats, such as shallow reefs, mangroves, estuaries, and deep ocean habitats, are relatively well represented within the present MPA network, other habitats, such as rhodolith beds, mesophotic reefs, shelf slopes and sinkholes (buracas), have very low or no representativeness. These ecosystems are unique and ecologically linked and have key roles for biodiversity conservation and fisheries sustainability in the region (Olavo et al. 2011; Simon et al. 2016, 2022; Lesser et al. 2018). The sinkholes (buracas) – depressions in the shelf formed by geophysical and biological processes - are unique structures recently described in Abrolhos (Bastos et al. 2013, 2016). These productive habitats have high concentrations of fish, lobsters, and other marine fauna (Cavalcanti et al. 2013), plausibly deserving protection.
Shallow reefs and surrounding algae bottoms are important nursery sites for key and threatened species (Eggertsen et al. 2017; Roos et al. 2020) and harbors the highest biological importance in the present study (Fig. 6). Mesophotic and shallow water coral reefs are linked physically and biologically, being important refuges for shallow coral reef taxa such as coral and sponges. Also, these areas are considered as a source of larvae that could contribute to the resiliency of shallow water reefs (Lesser et al. 2018).
The rhodolith beds also have an important role as reef fish habitats, including those endemic to Brazil (Moura et al. 2021), and work as a migration matrix linking shallow coastal reefs and mesophotic ones (Santos et al. 2023). The shelf-edge reefs are also very important for maintaining reef fish diversity, life cycles, and are essential for supporting multi-species fisheries (Olavo et al. 2011). Data available about fish reproductive aggregations corroborates with the importance of rhodolith beds, shelf breaks, and mesophotic reefs as of extreme importance for reef fish species conservation in the Abrolhos Seascape (Freitas et al. 2011; Bezerra et al. 2021).
The offshore banks and seamounts of the Vitória-Trindade chain, are also key for biodiversity conservation in the region (Pinheiro et al. 2015; Meirelles et al. 2015; Guabiroba et al. 2022). They work as stepping stones for reef fishes between mainland and the oceanic islands of Trindade and Martim Vaz, thus shaping their patterns of speciation (Pinheiro et al. 2017).
The maps of biological richness (Fig. 4) and richness of threatened species (Fig. 5) highlight the importance of shallow and mesophotic reefs, as well as the rhodolith beds for concentrating biodiversity. However, it is worth noting that the method of analysis of these maps disregards the higher relative importance of species with restricted distribution, such as species that occur exclusively in the Vitória-Trindade Seamount Chain. This relative importance is weighted in the final map of this study, which was generated by using the method of weighted endemism for all species (Fig. 6).
Our map of Priority Areas for Biodiversity Conservation in the Abrolhos Seascape (Fig. 6) shows that the areas of highest biological importance (Class 4) are concentrated in the shallowest parts of the continental shelf and in the seamounts of the Vitória-Trindade Chain. These areas have relatively high representation in the current network of coastal MPAs in the Abrolhos Bank, including shallow reefs, mangroves, and estuaries, but remain virtually unprotected in the Royal Charlotte Bank and the Vitória-Trindade Chain (Fig. 7).
The important biodiversity of the Abrolhos Bank shallow reefs is known for decades (Leão 1982, 1999; Leão et al. 2003; Dutra et al. 2006) and has driven the creation of the Abrolhos National Park in the 80’s (Mazzillo 2005). Apart of being poorly investigated compared to the Abrolhos Bank reefs, recent inventories confirm the ecological importance of both, the Royal Charlotte Bank (Negrão et al. 2021) and the Vitória-Trindade Chain (Pereira-Filho et al. 2012; Pinheiro et al. 2015; Meirelles et al. 2015; Guabiroba et al. 2022), strengthening the importance of protecting these areas. The Class 1 areas have the second highest protected percentage, which is due to the presence of the mosaic of protected areas of Trindade, Martin Vaz and Columbia seamount, which comprises mainly deep oceanic habitats. These are also the least known areas of the seascape. It is notorious that the areas of Classes 2 and 3 are mostly unrepresented in the current MPA network (Fig. 7) and concentrate species that occur in mesophotic reefs, rhodolith beds, buracas and shelf slopes, not coincidentally also among the least protected (Fig. 3).
The present work paves the pathway for the refinement of the biodiversity conservation component of the Priority Areas and Actions for Biodiversity Conservation, Sustainable Use and Benefit Sharing of Brazilian Biodiversity (MMA 2018). For example, in the Biological Importance map of this National effort, there is no differentiation in importance between mesophotic reefs and rhodolith beds, which is due to the broader (national) scale of this effort. It is important to note that in the final map of the National Priority Areas effort, the areas of the Abrolhos Region and the Vitória-Trindade Chain analyzed in the present work were considered of "Extremely High Biological Importance". Thus, the classes 2, 3 and 4 of biological importance represented here (Fig. 6), are equivalent to a subdivision of the “Extremely High Biological Importance” class of the national effort and should not be viewed as downgraded in importance.
By comparing results from this study with data about the main human uses in the region (Marchioro et al. 2005; Teixeira et al. 2018), there are clear overlaps between priority areas and potentially degrading human activities. The first clear overlay is with fisheries, which are concentrated in the shelf, including reef and sediment domain habitats (Teixeira et al. 2018). Part of the fisheries communities have organized and requested the creation of sustainable use MPAs such as Extractive Reserves for improving the sustainable management of their fishing areas (Moura et al. 2009; Dutra et al. 2012b), but most fishermen operate in open access areas. A well designed MPA network has the potential to improve fisheries (Green et al. 2014), but previous processes for expanding MPAs in the region have faced conflicts with this sector (Teixeira et al. 2018). Improvements on the design of the MPA network in Abrolhos to protect biodiversity, fisheries and other compatible uses are needed, as well as a broader understanding about the potential benefits of the network to local communities.
Previous efforts for the spatial compilation of biodiversity and geological data had important roles in avoiding the uncontrolled expansion of economic activities in the region, such as oil and gas exploitation and shrimp farming (Dutra et al. 2012b; Marchioro et al. 2005). The expansion of these activities was avoided, creating favorable conditions for the sustainable development in the region, favoring activities such as fisheries and tourism that have better conditions to be compatible with biodiversity conservation (Dutra et al. 2012a). The present work represents an updated and comprehensive contribution for the biodiversity conservation of the Abrolhos Seascape. Both the analysis of the representativeness of the habitats and the species analyzed show that there are important gaps in the current MPA network in the region. As next steps, we recommend comparing this effort with information from the different current uses in the region, providing analysis of costs and opportunities, for advancing in a systematic conservation planning process.
This effort and similar approaches can qualify the decision-making processes, sharing updated information in the adequate scale for advancing on marine conservation and planning, and be used as a baseline information for the ecosystem-based Marine Spatial Planning effort Brazil will be implementing in the following years.