Submerged reefs in the Abrolhos Shelf: morphology and habitat distribution

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Submerged reefs in the Abrolhos Shelf: morphology and habitat distribution Lucas C. Ferreira1, Alex C. Bastos1, Gilberto M. Amado Filho, In memorian2, Marcos Daniel A. Leite1, Geandre´ C. Boni1, Fernando C. Moraes2, Ne´lio Secchin3, Laura S. Vieira4, Ricardo Bahia2, Natacha Oliveira1, Vale´ria S. Quaresma1 and Rodrigo L. Moura5 1

Oceanography Department, Universidade Federal do Espı´rito Santo, Vito´ria, Brazil 2Rio de Janeiro Botanical Gardens Research Institute, Rio de Janeiro, Brazil 3Aratu Research and Equipments, Vito´ria, Brazil 4Ocean and Earth Dynamics Graduate Program, Geosciences Institute, Instituto de Geocieˆncias, Universidade Federal Fluminense, Avenida General Milton Tavares de Souza, Nitero´i, Brazil 5Institute of Biology and SAGE/COPPE, Universidade Federal do Rio de Janeiro, Ilha do Funda˜o, Rio de Janeiro, Brazil

Abstract Reef morphology varies across the depth gradient of tropical shelves and the controlling drivers operate at different geological timescales. For instance, while Holocene sea level rise drowned wide expanses of offshore reefs, modern disturbance (i.e., hurricanes/storm regime) shapes coral and coralline reef morphology. Here we report a regional scale acoustic mapping using a high-resolution sidescan sonar along the Abrolhos Shelf (South Atlantic, Eastern Brazil) mapping the spatial occurrence of submerged reefs, from 5 to 90 m deep. A database comprising photographs and video footage taken by divers, ROV, and drop cameras complemented the acoustic surveys with information on finer-scale reef morphology and benthic communities. Results showed that reef structures were classified as pinnacles, reef banks, and paleovalley edges. An extensive rhodolith bed was also mapped in the outer shelf. Pinnacles and reef banks could also be classified into low- and high-relief structures. Reef morphology follows a cross-shelf trend, with high-relief structures dominating the shallow waters (shallower than 20 m), while low-relief structures dominate the offshore area up to 40 m deep. The outer shelf is covered by rhodoliths up to the shelf break. The benthic community changes from shallow to deeper reefs. The most significant change is in coral species richness. The transition from a reef to a rhodolith habitat is still a matter of investigation in order to understand the ecological dynamics of this change. Still, rhodoliths are known as hot spots of biodiversity. This means that more than 70% of the Northern Abrolhos shelf encompasses highly complex and diverse habitats that support high biodiversity and provide important ecosystem services, but most of the information about the structure and the dynamics of biological assemblages is restricted to the small portion of emerging reefs.

Keywords: Abrolhos Shelf; Brazil; coral reefs; reef morphology; rhodolith beds; backscatter; mesophotic reefs Seafloor Geomorphology as Benthic Habitat. DOI: https://doi.org/10.1016/B978-0-12-814960-7.00030-0 © 2020 Elsevier Inc. All rights reserved.

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Introduction Tropical and subtropical reefs are rigid carbonate structures where the main framework builders are corals, often associated with crustose coralline algae (CCA). Filter feeding organisms that mineralize calcium carbonate, such as bryozoans, may also be major reef builders in a few tropical localities (Bastos et al., 2018). Living biogenic carbonate reefs occur in shallow tropical and subtropical regions, where they are built under variable rates over geological timescales (kyrs) (Kiessling, 2009). Modern reef structure and distribution vary as a function of regional geological, climatic, and biogeographic histories, coupled with oceanographic conditions. Benthic assemblages may vary sharply in small spatial scales of a few meters, and biodiversity patterns are also widely variable following latitudinal/ longitudinal gradients, within and between ocean basins (Riding, 2002; Montaggioni, 2005). In addition to the macro- and mesoscale morphological variation, reefs are often categorized as a function of depth. Depth is negatively associated with light penetration and also depends on turbidity. Turbulence, which conditions reef and coral morphologies and is a major disturbance source to biological assemblages (Bastos et al., 2018), is also negatively associated with depth. Reefs subjected to intermediate to low light levels (mesophotic), shallow and deep, are receiving increased attention due to their potential roles as refugia to climate anomalies and other anthropogenic stressors (Bongaerts et al., 2010). While “typical” reef assemblages occur down to 10 20 m depths and are dominated by light-harvesting organisms, those in mesophotic reefs are characterized by a broader coexistence of zooxanthellate and azooxanthellate corals, as well as by a dominance shift from autotrophic to heterotrophic organisms’ (Hinderstein et al., 2010). In oligotrophic settings, mesophotic reefs start occurring at 30 m depths, but such limits are highly variable due to light penetration (Locker et al., 2010). The Abrolhos shelf (46,000 km2) is an open-shelf carbonate platform (no-barrier reef), encompassing the largest and richest coral reefs and rhodolith beds in the South Atlantic (Fig. 30.1). Rhodolith beds and reef areas comprise 20,900 and 8800 km2, respectively (Moura et al., 2013). The shelf is 200 km wide, with a shelf break around 90 m deep. Emerging or quasiemerging (shallow water) reefs occur along a nearshore (B12 km offshore) and a mid-shelf arc (B60 km offshore) (Lea˜o and Ginsburg, 1997). Such unique mushroom-like pinnacles are locally known as “chapeiro˜es” (Hartt, 1870) and comprise columns that develop sideways at their tops, resembling giant mushrooms (Hartt, 1870; Lea˜o and Ginsburg, 1997; Bastos et al., 2018). These pinnacles, which can reach up to 25 m in height and 50 m in diameter (Hartt, 1870) may coalesce to form extensive shallow reef banks. The distribution of submerged reefs in the Abrolhos was described by (Moura et al., 2013) extending from the nearshore arc to .60 m depths, and their structures range from pinnacles and banks to paleovalleys and sinkholes. Submerged reefs have a wide range of morphologies, including terraces, barrier reefs, platforms and shoals, pinnacles,

Abrolhos Reef Morphology and Habitats 521

Figure 30.1 Study location showing the Arco Interno (nearshore reefs) and the Arco Externo (mid-shelf reefs), the Abrolhos National Marine Park area, and the sidescan survey lines. Datum is WGS 84 and isobaths are in meters.

and patch reefs (Lea˜o et al., 2003; Moura et al., 2013; Bastos et al., 2015). These differences may be related to paleo sea level variation, but also to the complex history of the reef formation and antecedent geology (D’Agostini et al., 2015). Brazilian shallow-water reefs bear low diversity coral assemblages (B20 spp.) with high endemism levels (B50%) (Laborel, 1969; Lea˜o et al., 2003). Living coral cover is variable along the Brazilian coast (Moura et al., 2016), but resembles “marginal” Indo-Pacific and Caribbean reefs, with corals covering ,25% of reefs’ surfaces (Francini-Filho et al., 2013). The Brazilian endemic hermatypic corals of genus Mussismilia, in association with other corals and coralline algae, were regarded as the major reef builders of Holocene reefs in Abrolhos (Lea˜o et al., 2003). However, Bastos et al. (2018) demonstrated that, rather than a typical coralgal reef, Abrolhos mid-shelf reefs have a complex framework building system dominated by bryozoans, accounting for up to 44% of the reef framework, while CCA and coral accounted for less than 28% and 23%, respectively. The Abrolhos reefs occur within 2 60 m water depths. The oceanographic setting is characterized by temperatures ranging from 21.7 C to 29.6 C (Ghisolfi et al., 2015).

522 Chapter 30 Nutrient concentration in coastal reefs are generally above commonly assumed eutrophication thresholds (Bruce et al., 2012). The nearshore arc is under higher turbidity, with increased values during wintertime intrusions of polar fronts that induce seabed resuspension (Segal et al., 2008). Turbidity decreases offshore and is less variable yearround near the offshore reef arc (Ribeiro et al., 2018). Phytoplankton productivity corresponds to a mesotrophic condition in the mid- and outer shelf dominated by rhodolith beds (Ghisolfi et al., 2015). Long-term data on the dynamics of the Abrolhos’ reef-associated biological assemblages as are still scarce and largely restricted to the emerging reefs (Francini-Filho et al., 2013), impeding a comprehensive evaluation of the region’s conservation status. The longest time series of coral cover data (Ribeiro et al., 2018) accounts for a significant decline of Mussismilia braziliensis in the nearshore and mid-shelf arcs between 2006 and 2016. The coral decline was associated with a steady increase in allelopatic filamentous cyanobacteria (Lyngbia spp.), which was more intense in the no-take reefs among the offshore arc. Ribeiro et al. (2018) indicates that turbid zone reefs of Abrolhos Bank present unique functional properties that challenge the current models explaining the global decline of coral reefs, which are largely based on DOC, disease, algae, and microorganisms. Turf algae cover has increased across the region (Francini-Filho et al., 2013), whereas one of the main endemic reef corals, M. braziliensis, a stress-tolerant Neogene relic, is predicted to be nearly extinguished in less than a century if the current rate of mortality due to diseases is not reversed (Bruce et al., 2012). The Abrolhos reefs are distributed along a cross-shelf gradient of terrigenous influence and fishing effort (Moura et al., 2013), providing a propitious context to study the relative effects of coastal influence and protection. So overall the reef habitat condition can be considered as poor to very poor (Ward, 2011), and this does not consider any bleaching effects from the strong El Nino event during 2015 and 2016. In this scenario, coastal reefs are probably in a declining trend while the mid-arc reefs and the mesophotic reefs are in declining to stable conditions (medium condition). Here we provide a synthesis about the spatial distribution of submerged reef structures and their associated benthic biological assemblages. The study is based on an extensive database accumulated over the past decade, with emphasis on the northern part of the Abrolhos Shelf. We also describe the morphology of submerged reefs, providing additional elements to understand the evolution of the Abrolhos shelf. A sidescan sonar (Edge Tech 4100) operating at 100/500 kHz and swath ranging from 100 to 200 m was used to map the seabed on a regional scale. Surveys have been conducted since 2008 and cover 1200 km2 (Fig. 30.1). SonarWiz software (Chesapeak Technology) was used for processing the primary GeoTIFF images (1.0 m/pixels resolution), which were further integrated and processed in a GIS environment. Sonograms were interpreted based on acoustic patterns that include reflection intensity, roughness, shape, height, and texture. Reef heights were

Abrolhos Reef Morphology and Habitats 523 estimated using the acoustic shadow and reefs were classified as low-relief (heights ,5 m) and high-relief ( . 5 m). The regional scale mapping was undertaken by collecting acoustic images along cross-shelf transects spaced 10 km apart. More detailed data were acquired around the Abrolhos National Marine Park, one in the Abrolhos Channel and the other in the mid-shelf reef arc. Benthic assemblages were described using an extensive image database comprising video and photographic records acquired using standard SCUBA, mixed-gas and closed circuit diving, as well as ROV, manned submersible, and drop camera operations (Rede Abrolhos; www.abrolhos.org). Benthic organisms were identified from images and a few voucher specimens and are presented at the lowest possible taxonomic level.

Geomorphic features and habitats Two main geomorphic features dominate the Abrolhos seascape: reefs and rhodolith beds. The acoustic response in reef dominated areas show a rough texture, high backscatter, and a typical acoustic shadow (Fig. 30.2A E). Rhodolith beds are acoustically characterized by a high backscatter signal, but with the acoustic mapping scale used in this study, no texture was clearly observed related to irregular “gravel beds” (Fig. 30.2F). Submerged reefs were further classified as (1) pinnacles; (2) reef banks; and (3) paleovalley edges, the former two classes encompassing low- to high-relief structures (Fig. 30.2A D; Table 30.1). Pinnacles are isolated low- to high-relief features with oval to slightly elongated tops with lengths ranging from 5 to 50 m. Conversely, reef banks are larger and irregularly edged features, generally presenting a low relief. The mushroom-like morphology of the pinnacles (“chapeiro˜es”) is not well evident from acoustic imaging. Paleovalley edges are characterized by bioconstructions along the edges of paleochannels (Fig. 30.2E). Table 30.1 describes each type of reef morphology pointing to their morphology, depth range, and percent coverage. Submerged reef type and rhodolith bed distribution is shown in Fig. 30.3. The map indicates that submerged reefs with tops at 5 60 m water depths are patchily distributed in the shelf (Fig. 30.3), but tend to be gradually less expressive offshore, where they become smaller (low relief) and more isolated. Rhodolith beds are the most spatially representative habitat on the Abrolhos Shelf, occurring over an area of 20,900 km2, dominating the mid outer shelf and shelf break, from 40 to 120 m water depth. The pinnacles and bank reefs are the dominant habitat in the Abrolhos inner shelf. Pinnacles are the most representative reef feature at Abrolhos Shelf comprising 54% of the submerged reef structures, while reef banks represent 42% and paleovalleys correspond to only 4%.

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Figure 30.2 Acoustic images of: (A) low-relief pinnacles; (B) high-relief pinnacles; (C) high-relief reef banks; (D) low-relief reef banks; (E) paleovalley edges; and (F) rhodolith beds.

In terms of reef type and cross-shelf or water depth gradient, Fig. 30.4C shows a general trend in reef and rhodolith bed distribution. In the nearshore reefs, with water depths shallower than 20 m, high-relief reefs/pinnacles are the dominant habitat. The Abrolhos Channel, a low-lying mesoscale feature between the two emerging reef arcs, deserves further clarification in terms of its evolution and ecological roles. This channel, which is largely outside the National Park perimeter, bears sparse patches of pinnacles and rhodolith beds among soft sediments, and may function as an important connectivity corridor between the nearshore and offshore arcs. East and southeastward to the offshore arc (National Marine Park) low-relief reefs become the dominant reef type between 20 and 45 m depths, and mark the transition to the mid-shelf. These low-relief banks are morphologically distinct from nearshore reefs, comprising elongated structures 25 30 m across their tops. These reefs rarely reach .5 m above the sediment-dominated seabed and their surfaces are not as flat as the emerging reef banks and pinnacles tops that are ubiquitous nearshore (Fig. 30.5). This depth range is identical to mesophotic reefs and

Abrolhos Reef Morphology and Habitats 525 Table 30.1: Geomorphic features with their morphological, depth range distribution, and percentage coverage characteristics. Reef habitats High-relief pinnacles Low-relief pinnacles High-relief banks Low-relief banks Paleovalley edges Rhodolith beds

Acoustic morphology

Distribution depth

Coverage (%)

5 25 m

25.2

20 35 m

28.5

10 20 m

15.4

30 60 m

26.7

40 50 m

4.2

.40 m

N

Isolated features with a circular or oval shape. High backscatter signal with strong roughness, and a typical large acoustic shadow (Fig. 30.2B). Isolated feature, usually very sparse distributed, circular or oval shape. Very small acoustic shadow (Fig. 30.2A). Reef bank with heights .5 m, large surface areas, and relatively flat tops. High backscatter signal with a rough texture and large acoustic shadow (Fig. 30.2C). Reef bank with heights ,5 m, large surface areas with flat tops. A faint backscatter signal with small acoustic shadow (Fig. 30.2D). Bioconstruction associated with the edges of paleovalleys. Strong backscatter signal along the channel edges (Fig. 30.2E). Very strong backscatter showing no major roughness or acoustic shadow. The bed roughness was not acoustically determined possibly due to the mapping scale and the sidescan swath (Fig. 30.2F).

Figure 30.3 Spatial distribution of reef types and rhodolith beds.

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Figure 30.4 Cross-shelf distribution of the reef types: (A) location of bathymetric profiles; (B) bathymetric profiles; and (C) plot of the percentage covered by each reef type within water depth ranges.

banks mapped in the Gulf of Carpentaria by Harris et al. (2008) and in the Great Barrier Reef (Harris et al., 2013). In addition to such unique morphology, these reefs bear inexpressive coral cover, indicating that they drowned during the last deglaciation. In the outer shelf, in water depths greater than 40 m, paleovalleys were mapped, but rhodolith beds are the main habitat. Another interesting habitat that occurs locally in the Abrolhos mid and outer shelf are the Buracas (sinkholes), described by Bastos et al. (2013). Although they cover small areas, such isolated features represent critical habitats for fisheries management, once they represent biomass hotspots (Cavalcanti et al., 2013) and comprise potential reef fish spawning aggregation sites (Moura et al., 2013).

Biological communities The biological assemblages associated with the two arcs of emerging reefs have been relatively well assessed from taxon-based targeted surveys (Simon et al., 2016), highresolution photoquadrats (Francini-Filho et al., 2013), ROV images (Moura et al., 2013), decadal time series of repeated measures from photoquadrats (Ribeiro et al., 2018), and

Figure 30.5 Aerial and underwater photos of typical shallow water and mesophotic reef formations from ˜es” pinnacle reefs emerging from 25 m deep; (B Abrolhos Bank, Brazil. (A) Aerial view of “chapeiro ˜o” reef under natural light at 10 and 2 m deep, respectively; (D) “chapeira ˜o” under and C) “chapeira strobe light at 10 m deep, showing hydrocorals (Millepora alcicornis), Palythoa caribaeorum, CCA, and tube sponge (Aplysina fistularis); (E) California Reef pinnacle wall at 32 m deep, showing the bryozoan Steginoporella magnilabris and the octocoral Muricea flamma (background); (F) submerged reef formation at 35 m deep; (G) rhodolith bed at 50 m deep; (H) rhodolith bed covered by macroalgae at 28 m deep, showing carbonate nodules agglutinated by the sponge Aplysina lacunosa. Source: ´ thila Bertoncini, Fernando Moraes, Lucas Ferreira, and Rodrigo Moura/ Rede Abrolhos. Photos by A

528 Chapter 30 scuba dive panoramic video footage. Although there is latitudinal and cross-shelf variation in the benthic assemblages associated with emerging reefs, the main coral, octocoral, and zoanthid species are similar in both arcs, with a few exceptions such as the endemic fire coral Millepora nitida, which is abundant nearshore and rare offshore (Teixeira et al., 2019). The dominances of macroalgae (inshore) and cyanobacteria (offshore) comprise another remarkable contrast in the benthic assemblages of both arcs with emerging reefs (Ribeiro et al., 2018), but a detailed and fully comparable description of mesophotic assemblages is still unavailable. However, from the extensive image database gathered by the Abrolhos’ long-term ecology research program (PELD/Rede Abrolhos, www.abrolhos. org), it is already clear that there is a sharp turnover in the assemblage structure as depth increases and reef morphology changes (Table 30.2). Coral richness decreases sharply in deeper reefs, with a remarkable absence of M. braziliensis, M. hartii, and branching Table 30.2: Comparison between shallow and deep reef benthic fauna. Shallow reefs Scleractinian corals

Hydrocorals Octocorals

Agaricia fragilis Agaricia humilis Favia gravida Favia leptophylla Madracis decactis Meandrina braziliensis Montastraea cavernosa Mussismilia braziliensis Mussismilia hartti Mussismilia hispida Porites astreoides Porites branneri Scolymia wellsi Siderastrea spp. Millepora nitida Millepora alcicornis Carijoa riisei Leptogorgia punicea Plexaurella regia Plexaurella grandiflora Muriceopsis sulphurea Phyllogorgia dilatata

Black coral Sponges, crinoids, bryozoans, ascidians Zoanthids

Present Palythoa caribaeorum Zoanthus spp.

Deep reefs (reef top $ 15 m deep) Siderastrea spp. Porites branneri Montastraea cavernosa Mussismilia hispida Scolymia wellsi Madracis decactis

Millepora alcicornis (on top) Carijoa riisei Muricea flamma Phyllogorgia dilatata Neospongodes atlantica

Cirripathes spp. Antipathes spp. Present

Source: Shallow reef data were modified from Francini-Filho, R.B., Coni, E.O., Meirelles, P.M., Amado-Filho, G.M., Thompson, F.L., Pereira-Filho, G.H., et al., 2013. Dynamics of coral reef benthic assemblages of the Abrolhos Bank, eastern Brazil: inferences on natural and anthropogenic drivers. PLoS One 8, e54260, Supplementary Material.

Abrolhos Reef Morphology and Habitats 529 milleporans (three species) bellow 20 m depths. These species, together with Siderastrea spp., Mussismilia hispida, Porites astreoides and Porites branneri, Meandrina braziliensis, Favia gravida, and Agaricia spp. (approximately three species), are the most abundant coral species on shallow pinnacles’ tops (chapeiro˜es) (Fig. 30.5A D). The chapeiro˜es’ walls, which are poorly lit due to the expanded tops, are dominated by the coral Montastraea cavernosa and, secondarily, by Madracis decactis and Agaricia spp. A few other species such as Stephanocoenia intersepta and solitary corals (genus Scolymia) are also typical of the pinnacles’ poorly lit walls, but they are never abundant. Despite being monopolized by M. cavernosa, coral cover in pinnacles’ walls is often more extensive than that recorded on their tops, especially in the nearshore arc (Francini-Filho et al., 2013). The few coral species that dominate pinnacles’ walls (M. cavernosa, M. decactis, and Agaricia spp.), together with Scolymia spp., are also wide depth-ranging, occurring below 90 m depths, and also comprise the most abundant corals in deeper reefs. Comparing Abrolhos shallow and deeper reefs in terms of coral coverage, it is clear that the dominant shallow coral reef species tend not to occur in the mesophotic zone. Besides M. cavernosa dominance, deep-reef assemblages comprise black corals (Cirrhipathes and Antipathes), large gorgonians (e.g., Muricea), CCA, bryozoans, and sponges (Fig. 30.5E and F). Detailed accounts of reef builders and reef building processes are provided by (Amado-Filho et al., 2018) and (Bastos et al., 2018). Although not commonly considered as a reef, rhodolith beds are as important as reefs in terms of calcium carbonate production (Amado-Filho et al., 2012). Studies have also pointed out that extensive rhodolith beds are hot spots of diversity, supporting not only a rich cryptic fauna but also creating a complex 3D structure, supporting higher population densities (Steller et al., 2003; Foster et al., 2013). In terms of rhodolith-forming CCA, the Brazilian shelf holds the highest species richness of any other region of the world (AmadoFilho et al., 2017). So far 33 rhodolith-forming CCA species have been described in Brazil. On the Abrolhos Shelf 16 rhodolith-forming CCA species have been recognized so far (Amado-Filho et al., 2017). Amado-Filho et al. (2012) pointed out that the mean relative cover of rhodoliths was 69.1% 6 1.7%, while the mean density was 211 6 20 nodules m22. Fig. 30.5G and H shows a panoramic view of a rhodolith bed at a depth of 52 m. It is also important to highlight that with sea level rise during the Holocene, a reduction in bed activity (storm influence) increased the substrate stability on the outer shelf. Decreasing rhodolith movement but continued rhodolith growth caused the merging of individual rhodoliths or even the incrustation of other organisms, consolidating a “rhodolith pavement” type of mesophotic reef (Fig. 30.5H). The transition from a reef to a rhodolith habitat is still a matter of investigation in order to understand the ecological dynamics of this change. Still, as rhodoliths are known as hot spots of biodiversity, this means that more than 70% of the Northern Abrolhos shelf

530 Chapter 30 encompasses highly complex and diverse habitats (reefs and rhodoliths) that support a rich biodiversity.

Surrogacy No statistical analysis has been carried out so far to relate the benthic community with the physical setting. However, observations suggest that water depth and distance to the coast are physical variables that relate to coral richness. A decrease in coral richness follows the water depth. Reefs with their tops at depths greater than 30 m had a very low coral species richness when compared to shallow or even 10 20 m deep reef tops. Also seabed habitat distribution in the Abrolhos is definitely depth-related. Two cross-shelf bathymetric profiles (Fig. 30.4B) summarize that rhodoliths dominate the mid- to outer shelf habitat. Further studies might find that, indirectly, reef morphology, mainly in terms of its relief, can be a potential surrogate for coral distribution.

Concluding remarks The Abrolhos Shelf presents very singular reef morphologies that strongly influence the distribution of habitats. From shallow patch reefs and gigantic mushroom-like pinnacles to offshore low-relief banks, paleovalley biogenic edges, and an extensive rhodolith bed, a cross-shelf or depth gradient change in habitat characterizes this unique carbonate platform that encompasses the largest and richest coral reef complex in the South Atlantic. The habitat mapping studies carried out so far in the Abrolhos Park suggest that a major change in reef benthic community (mainly coral species) occurs around 25 30 m deep. This is still speculative, but general observations are pointing towards this finding. Reef morphology, but mainly reef relief, also present a major change around 20 25 m deep. More detailed studies are needed to investigate if reef relief and depth can be surrogates for coral species richness.

Acknowledgments The authors are thankful for Research Grants and specific funds that have been supporting studies in the Abrolhos Shelf: CNPq (SISBIOTA and PELD programs), CAPES (CIMAR II, IODP program), FAPERJ, FAPES, and BRASOIL/ANP. In memorian of Prof. Gilberto Amado Filho who passed away during the final editing of this case study. Prof. Gilberto was a leader for us all, passionate about seabed mapping, reefs and rhodoliths.

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