Abrolhos Bank Research Articles

Sailing into the past: Nautical charts reveal changes over 160 years in the largest reef complex in the South Atlantic Ocean

Coral reefs are in global decline due to unprecedented anthropogenic threats that have escalated and accumulated over decades to centuries. In order to assess the magnitude and drivers of changes on reefs, it is necessary to reconstruct the history of changes of these ecosystems over this longer time scale. We compiled and assessed historical records of naturalists that visited Abrolhos reefs over the last 202 years, and compared a 160-year-old nautical chart with modern charts to quantify losses in the spatial extent of coastal reefs in the Abrolhos Bank, Brazil. We found a 28% loss in the overall spatial extent of inshore reefs, with some areas experiencing declines up to 49% over the past 160 years. Such reefs with more dramatic changes (Guaratibas reefs) are the closest to the coast (∼7 km), where local impacts such as the past extraction of coral for lime since the 19th century, as well as increased coastal sedimentation and siltation due to deforestation are concentrated and that, combined, may have caused the observed decline. Collectively, this set of historical information captures coral reef changes over time, and helps update conservation and restoration goals for the Abrolhos reefs seascape.

Mid- to Late Holocene sealevel changes at Abrolhos Archipelago and Bank, southwestern Atlantic, Brazil

This study presents spatiotemporal paleo-sea-level reconstructions from Abrolhos archipelago and Abrolhos Bank, and fill in a coastline gap of 500 km where no precise paleo-sea level reconstruction exists. The reconstructions are based on sedimentary, biological and geomorphological evidences. The data indicates sea-levels up to 2.9 m higher than the current one between the Mid- to Late Holocene, in agreement with the empirical sea-level envelope and with predictions of geophysical sea-level models for the Brazilian coast. The data suggests that there was little, if any, hydroisostatic compensation across 55 km of the continental shelf in the study area, between the archipelago and the mainland coast, given that similar elevations of the post-glacial sea-level maximum exist in both places.

Habitat-specific fish fauna responses to different management regimes in the largest coral reef complex in the South Atlantic

While marine protected areas (MPAs) are increasing worldwide, it is still needed to assess the effectiveness of those already consolidated. Methods and ecological assessments to understanding integrated and habitat-specific management regimes are still scarce and insufficient for policy implications and biodiversity conservation. Through Baited Remote Underwater Video (BRUV), we used fish assemblages as proxy of ecological and managerial status in two reef habitat types along three protection levels at Abrolhos Bank - the largest and most biodiverse coral reef complex of the South Atlantic. We found completely distinct responses in the fish fauna between the top (shallow) and bottom (deep) habitats of the unique “chapeirões” pinnacle reef formations. In the most protected zone (no-take), higher richness and abundance of commercial fish and more diverse trophic structure was observed. Particularly, large (sharks and groupers) and small carnivores (snappers) were more abundant and distributed more homogeneously over both reef habitats in the strictly enforced no-take zone. Abundance of these top-predators decreased from the low enforcement no-take zone to the multiple use area, where they were often absent while their typical preys (primary and secondary consumers) were thriving, notably in the top habitats. These outcomes highlight the importance to focus investigations not selectively on a single habitat type or depth zone in order to properly assess MPA effectiveness. Consequently, the monitoring and protection of fish species supported by marine spatial planning may benefit from an improved understanding of ecological functioning provided by MPA performance.

The Fundão dam failure: Iron ore tailing impact on marine benthic macrofauna

The Fundão dam failure, the worst environmental disaster in Brazilian history, launched 50 million m3 of iron ore tailings mud through the Doce River, reaching the Atlantic Ocean. Generally, mine tailings increase the sediment inflow, leading to mud burial of epibenthic macrofauna, and the raise of metal(oid)s concentration causing macrofauna long-term changes. After almost four years, tailings mud was still spreading on the Doce River Shelf, while impacts on marine macrofauna were still unknown. Herein, the IMS index (a tracer of Fundão dam tailings mud), sediment variables, organic pollutants, and metal(oid)s were integrated to uncover the drives of macrofauna structure from Costas da Algas to Abrolhos bank MPAs. Tailings mud was present only in Doce River Mouth and Degredo, organic pollutants and metal(oid)s above safety levels were concentrated in those same areas. Tailings mud (IMS index) drastically reduced species richness and diversity, favoring the abundance of opportunistic species. Mud, IMS index and Al, Ba, and V, metal(oid)s linked to dam failure, structured macrofauna composition in this impacted area, dominated by resistant groups as Nuculidae, Spionidae, and Magelonidae. Conversely, an opposite pattern was found for further and deeper sites with high CaCO3 content and total nitrogen that also showed large grain size, in areas known to harbour biogenic structures, sustaining a macrofauna composition distinct from the impacted areas, dominated by Syllidae and Crassatellidae, sensitives to impacts. Macrofauna composition was most structured by sediment variables, followed by the intersection between metal(oid)s-IMS and Mud, both gradients acting almost entirely on a broad spatial scale. Benthic macrofauna at the Doce River Shelf is still impacted by Fundão dam tailings mud, even after almost four years of the disaster, and may continue to, since the influx of tailings does not stop, and sediment resuspension is a recurrent source for those impacts.

Benthic Cyanobacterial Diversity and Antagonistic Interactions in Abrolhos Bank: Allelopathy, Susceptibility to Herbivory, and Toxicity

Benthic cyanobacterial mats (BCMs) are conspicuous components of coral reef communities, where they play key ecological roles as primary producers among others. BCMs often bloom and might outcompete neighboring benthic organisms, including reef-building corals. We investigated the cyanobacterial species composition of three BCMs morphotypes from the marginal reef complex of Abrolhos Bank (Southeastern Brazil). Also, we assessed their allelopathic effects on coral zooxanthellae, their susceptibility to herbivory by fish, and their toxicity to brine shrimp nauplii. Morphology and 16S rDNA sequencing unveiled the cyanobacteria Moorena bouillonii, Okeania erythroflocculosa, Adonisia turfae, Leptolyngbya sp., and Halomicronema sp. as components of BCMs from Abrolhos. BCMs cell-free filtrates and extracts exerted an allelopathic effect by reducing the growth of the ex hospite Symbiodinium sp. in culture. BCMs-only treatments remained untouched in field susceptibility assays in contrast to macroalgae only and mixed BCMs-macroalgae treatments that had the macroalgae fully removed by reef fish. Crude aqueous extracts from BCMs were toxic to brine shrimps in acute assays. Besides unveiling the diversity of BCMs consortia in Abrolhos, our results cast some light on their allelopathy, antiherbivory, and toxicity properties. These antagonistic interactions might promote adverse cascading effects during benthic cyanobacteria blooms and in gradual shifts to BCMs-dominated states.

Habitat use plasticity by the dog snapper (Lutjanus jocu) across the Abrolhos Bank shelf, eastern Brazil, inferred from otolith chemistry

Many reef fishes move between different coastal systems throughout their ontogeny, but these movements are complex and often not understood. In this study, we examined how the dog snapper (Lutjanus jocu) uses marine and estuarine habitats across the Abrolhos Bank shelf (eastern Brazil) through the analysis of elemental signatures in otoliths. Specimens were sampled in an estuary and adjacent marine region. Ba/Ca, Sr/Ca, Mg/Ca and Mn/Ca were measured by LA-ICPMS along the otolith growth axis to cover the entire lifetime of the individual. Change-point analysis, principal component analysis and BRT modeling were used for the objective identification of habitat-use patterns of the species. Otolith Ba/Ca ratios performed better than other elements for tracking L. jocu movements between estuarine and marine habitats, which may result from small variations in salinity and high turbidity levels, as these characteristics are typical of the Abrolhos Bank. Two contrasting habitat-use patterns were identified for L. jocu: i) marine residents (56% of sampled fish) - fish that remain in marine systems throughout their lifetime; and ii) marine migrants (37%) - juveniles inhabit estuaries and move to marine systems with age. These categories were successfully re-classified, which suggests that they are coherent and reliable. Following recent findings of flexible habitat-use patterns in many other fish species, L. jocu habitat requirements also appear to be quite malleable. As the dog snapper has been facing commercial overexploitation in the region, this plasticity in habitat use should be considered in future fisheries management.

Using Nd[sbnd]Sr isotopes in suspended sediments in the Abrolhos coral-reef (SW Atlantic, Brazil) to assess potential contamination from the 2015 Fundão dam collapse

The Abrolhos bank is home of the richest coral reef system of the Southwestern Atlantic, where endemic coral species are found. It has been reported that Abrolhos' corals are under intense stress due to increasing of Marine Heat Waves during the last decades. Additionally, anthropic interventions along the adjacent coastal regions are a factor of concern since they contribute to the increase in the sediment load and to organic debris input in the reef domain. In November 2015, the collapse of the Fundão mining tailings dam resulted in the release of approximately 50 million m3 of iron oxide and quartz-rich slurry into the Doce River. Aiming at using a fingerprint of the tailings and to assess the presence of traces of the Fundão dam material from this event on the Abrolhos bank, this work presents new 87Sr/86Sr and 143Nd/144Nd isotope ratios of marine suspended sediment samples collected between 2016 and 2020 from a network of sediment traps throughout the reef and complementary suspended material at sea. In parallel, we monitored meteo-oceanographic parameters and modeled surface marine currents as an attempt to identify the sediment transport between the Doce River mouth and Abrolhos bank. The r isotopes were used as provenance proxies based on the fact that minerals and rocks tend to have specific isotopic signatures reflecting their own geological derivation. In this context, the isotopic ratios of various potential regional sources for the sedimentation in Abrolhos bank were evaluated. Our monitoring and isotopic measurements indicate that Doce River signatures are detected at Abrolhos bank, following the seasonal Doce River discharge at sea. Isotopic signature of Doce River at Abrolhos bank was also observed during the austral winter (July–August) when cold fronts migrate at the Brazilian coast with higher frequency and energy.

Breviolum and Cladocopium Are Dominant Among Symbiodiniaceae of the Coral Holobiont Madracis decactis.

The scleractinian reef building coral Madracis decactis is a cosmopolitan species. Understanding host-symbiont associations is critical for assessing coral's habitat requirements and its response to environmental changes. In this study, we performed a fine grained phylogenetic analyses of Symbiodiniaceae associated with Madracis in two locations in the Southwest Atlantic Ocean (Abrolhos Bank and St. Peter and St. Paul Archipelago). Previous studies have argued that Madracis is a specialist coral, with colonies harboring a single symbiont from the genus Breviolum (formerly clade B). However, these previous studies have not precisely addressed if Madracis is colonized by several types of Symbiodiniaceae simultaneously or whether this coral is a specialist. The hypothesis that Madracis is a generalist coral host was evaluated in the present study. A total of 1.9 million reads of ITS2 nuclear ribosomal DNA were obtained by Illumina MiSeq sequencing. While Symbiodiniaceae ITS2 sequences between two sampling depths were almost entirely (62%) from the genus Breviolum (formerly clade B), shallow (10-15m) populations in Abrolhos had a greater diversity of ITS2 sequences in comparison to deeper (25-35m) populations of St. Peter and St. Paul Archipelago. Cladocopium (formerly clade C) and Symbiodinium (formerly clade A) were also found in Abrolhos. A single Madracis colony can host different symbiont types with > 30 Symbiodiniaceae ITS2-type profiles. Abrolhos corals presented a higher photosynthetic potential as a possible result of co-occurrence of multiple Symbiodiniaceae in a single coral colony. Multiple genera/clades of Symbiodiniaceae possibly confer coral hosts with broader environmental tolerance and ability to occupy diverse or changing habitats.

Metals and organic matter baselines in sediments in a cross-shelf gradient at Abrolhos Bank, SW Atlantic

The present study performed geochemical fractioning of major and minor elements in a cross-shelf gradient of the Abrolhos Bank, where the largest and most diverse coral reefs in the South Atlantic are concentrated. The fractioning was performed using sequential extractions to determine the degree of availability and toxicity of the elements. The mobility pattern of the elements investigated were in the following order: Ca > Mn > Pb > Cr > Zn > Fe > V > Cu > Ba>Al > Ni > Ti. For elements, such as (Ti, Ni, Al, Ba, Cu, V, Fe, Zn, Cr, Pb), the highest concentrations were in the residual phase at some sampling sites. As established by Environment Canada (Threshold Effect Level - TEL and Probable Effect Level - PEL), Ba, Cr, and Ni produced values higher than the limits, associated with higher concentrations of other elements. In addition, significant proportions of these elements were found in mobile phases in the same sites. Thus, more rigorous measures are critical to avoid alarming levels of chronic environmental pollution inside and outside protected areas of the region. To enhance the sustainability of the region, more effective enforcement is crucial to prevent anthropic contamination that may threaten its biodiversity. The results provide the baseline for future studies regarding the potential impacts of the breach of the tailings dam in the region of Mariana, Minas Gerais.

Coastal trapped waves propagation along the Southwestern Atlantic Continental Shelf

This study investigates the propagation of coastal trapped waves (CTWs) along the Brazilian continental shelf between 34°S and 11°S using in situ data combined with the outputs from a high-resolution ocean simulation with HYCOM. The CTWs generation area covers a wide region ranging from the Patagonian shelf to the southern Brazilian shelf. The spectral analysis of coastal sea level series between 54°S and 10.5°S shows three bands of high energy associated with periods from 5 to 12 days, 15–22 days, and 25–40 days. The energy of the CTWs decreases along their propagation for all frequency bands, showing a drastic reduction north of 22°S, due to abrupt variations in the width and depth of the continental shelf between Tubarão Bight and Abrolhos Bank. Their phase speed propagation varies along the coast, being faster (>25 m/s) in the southernmost region (between 42°S and 41°S), reaching ~11 m/s north of 41°S, and reducing to ~3 m/s further north (equatorward of 24°S). The free Continental Shelf Wave theory supports the notion that the intense deceleration north of 24°S can be explained by the narrowing of the continental shelf. The stratification parameter indicates that the Brazilian continental shelf has a barotropic response to wind-generated disturbances.

Coral distribution and bleaching vulnerability areas in Southwestern Atlantic under ocean warming

Global climate change is a major threat to reefs by increasing the frequency and severity of coral bleaching events over time, reducing coral cover and diversity. Ocean warming may cause shifts in coral communities by increasing temperatures above coral’s upper thermal limits in tropical regions, and by making extratropical regions (marginal reefs) more suitable and potential refugia. We used Bayesian models to project coral occurrence, cover and bleaching probabilities in Southwestern Atlantic and predicted how these probabilities will change under a high-emission scenario (RCP8.5). By overlapping these projections, we categorized areas that combine high probabilities of coral occurrence, cover and bleaching as vulnerability-hotspots. Current coral occurrence and cover probabilities were higher in the tropics (1°S–20°S) but both will decrease and shift to new suitable extratropical reefs (20°S–27°S; tropicalization) with ocean warming. Over 90% of the area present low and mild vulnerability, while the vulnerability-hotspots represent ~ 3% under current and future scenarios, but include the most biodiverse reef complex in South Atlantic (13°S–18°S; Abrolhos Bank). As bleaching probabilities increase with warming, the least vulnerable areas that could act as potential refugia are predicted to reduce by 50%. Predicting potential refugia and highly vulnerable areas can inform conservation actions to face climate change.

The first biological survey of the Royal Charlotte Bank (SW Atlantic) reveals a large and diverse ecosystem complex

The Southwestern Atlantic harbors unique reef environments with high proportions of endemic species. The most prominent reefs are located in the Abrolhos Bank, a 46,000 km2 extension of the South American continental shelf. However, just 100 km north of Abrolhos is the Royal Charlotte Bank (RCB), an area still poorly investigated. From a biological perspective, the only scientific information available is the historical record of lobster fisheries in the region. Hence, we performed an expedition to investigate what macrohabitats are found in the RCB and perform a preliminary biodiversity assessment. A dropcam was deployed in 67 sites and recorded images of macrohabitats and associated biodiversity. Four different macrohabitats were detected: rhodolith beds, macroalgal forests associated with rhodolith beds, calcareous sand deposits and coral reefs. The former two were the most frequent, and both rhodolith and macroalgae densities were higher on the outer shelf. A total of 83 species of fish, invertebrates and algae were identified, which comprises a comparatively high diversity for visual reef biodiversity assessments in the Southwestern Atlantic. Our findings show that the RCB is a large and diverse ecosystem complex mostly composed of rhodoliths, and also that it may be already undergoing anthropogenic impacts associated with climate change and fisheries. Therefore, further investigations are necessary to understand the extent of biodiversity and its main threats and evaluate the possible need of conservation and management measures.

Genome sequence of Vibrio fluvialis 362.3 isolated from coral Mussismilia braziliensis reveals genes related to marine environment adaptation.

Vibrio fluvialis is a halophilic bacterium frequently found in estuarine and coastal watersenvironments. The strain 362.3 was isolated from Mussismilia braziliensis coral of Abrolhos Bank. In this study, to gain insights into the marine adaptation in V. fluvialis, we sequenced the genome of 362.3 strain, which comprised 4,607,294bp with a G + C content of 50.2%. In silico analysis showed that V. fluvialis 362.2 encodes genes related to chitin catabolic pathway, iron metabolism, osmotic stress and membrane transport.

Different responses of massive and branching corals to a major heatwave at the largest and richest reef complex in South Atlantic

In 2019, a major coral bleaching event affected reefs worldwide, including marginal reefs within the Abrolhos Bank (16°40′–19°40′S, 39°10′–37°20′W), the largest and richest coral reefs in the South Atlantic. Between March and May 2019, this area was affected by the strongest heatwave since 1985. The health trajectories of the branching hydrocoral Millepora alcicornis and the endemic reef-building coral Mussismilia braziliensis were recorded during this thermal stress event. The degree heating week value reached its historical maximum (DHW 19.65), causing bleaching in 100% of Millepora alcicornis and 80% of Mussismilia braziliensis colonies. Bleached Millepora alcicornis were rapidly covered by cyanobacteria, followed by algal turfs and calcareous algae, leading to 90% mortality. Conversely, 90% of Mussismilia braziliensis colonies recovered to a healthy state after bleaching. The high post-bleaching recovery capacity and resistance to mortality of this massive reef-building coral suggests these marginal reefs can be resilient to thermal stress events, despite losing structural complexity due to high mortality of branching and less abundant hydrocorals.

Spatial and temporal patterns of spawning aggregations of fish from the Epinephelidae and Lutjanidae families: An analysis by the local ecological knowledge of fishermen in the Tropical Southwestern Atlantic

Local knowledge is a fundamental source of information for starting spawning aggregation studies in areas where this phenomenon is still unknown or little studied. Among the species that present this reproductive strategy, groupers and snapper represent two of the most relevant components of artisanal and commercial capture worldwide and are highly susceptible to overfishing. We conducted interview-based surveys to examine if local ecological knowledge can determine potential areas of spawning aggregations in southeast Brazil. Fifty-one local fishermen targeting groupers and snappers were asked about spawning aggregation areas and seasonality using charts and geographic information system (GIS) analysis. Information was obtained for 31 potential spawning aggregation sites, where black grouper (Mycteroperca bonaci) represented the most important resource for the fishermen interviewed, followed by yellowtail snapper (Ocyurus chrysurus). In addition, red grouper (Epinephelus morio), mutton snapper (Lutjanus analis) and dog snapper (Lutjanus jocu) were also mentioned as important resources that have spawning in aggregation as a reproductive strategy. The main possible spawning aggregation areas indicated occur within the Abrolhos Bank, the largest and richest reef complex in the South Atlantic. The lack of published records of spawning aggregations in Brazil, hinders the suitable implementation of measures that can protect this phenomenon and consequently the perpetuation of these and potentially other species. Therefore, additional studies and particularly in situ validation, are needed to determine the occurrence and status of the aforementioned aggregations.

Environmental conflicts and management of marine resources in the Cassurubá Complex, Bahia, Brazil

The Cassurubá Complex, located in the Abrolhos Bank, has the highest concentration of marine biodiversity in Brazil. This region also concentrates on many uses of natural resources, such as shipping of eucalyptus, tourism, and artisanal fishing. In this scenario of diverse territorial configurations, this study seeks to analyze the environmental conflicts that influence the territoriality of artisanal fishermen in the Cassurubá Complex. Based on participant observation (2017–2020), semi-structured interviews (2019), participatory mapping (2019), and focus groups (2019) were developed with 37 artisanal fishermen. The main conflicts highlighted were those between types of fishing equipment (trawling and gillnets, lobster nets and longline) and between the local population and development projects, including conflicts with the pulp sector and the disruption caused by the collapse of the Fundão dam. These conflicts were systematized and analyzed based on category, actors, scope, and arenas of dispute. The loss of fishing territory was noted in the interviews and the main form of resistance on the part of the local population in the face of disputes over resource use and complaints of environmental degradation happens through social movements. Finally, it is necessary that the analysis of environmental conflicts be taken into account when making decisions on local spatial planning.

Caecidae (Gastropoda: Truncatelloidea) Associated with Unconsolidated Carbonate Substrates of the Abrolhos Coral Bank (Bahia State, Brazil)

In this study, we present mollusks of the family Caecidae Gray, 1850 collected between 2007 and 2008 from unconsolidated carbonate substrates of the Abrolhos coral bank during the PROABROLHOS Project (Productivity, Sustainability and Use of the Abrolhos Bank Ecosystem). A total of 649 individuals belonging to two genera and six species were collected from nine stations at depths of 15.6 to 22 m in the dry and rainy seasons. The most abundant species were Caecum brasilicum de Folin, 1874 and Caecum floridanum Stimpson, 1851. Caecum circumvolutum de Folin, 1867, Caecum metamorphosicum Lima, Santos & Absalao, 2013, Meioceras cubitatum de Folin, 1868 and Meioceras nitidum (Stimpson 1851) altogether comprised approximately 6.5% of the total number of individuals collected. Among the 14 species previously recorded for the Abrolhos coral reef area, Caecum metamorphosicum is for the first time registered in the area in this study. This calls attention that, overall, there is a need for more researches focused on the carbonate substrate in coral areas, especially on micro specimens.

Martin Vaz island geochronology: Constraint on the Trindade Mantle Plume track from the youngest and easternmost volcanic episodes

The oceanic basins are dotted by seamounts, guyots and islands formed by the mantle plumes and oceanic lithosphere interaction. These plumes are responsible for several intraplate volcanisms such as the Emperor-Hawaii Chain in the Pacific Ocean with a remarkable bend at ca. 47 Ma. Comparatively, the Vitória-Trindade Ridge (VTR) in the South Atlantic Ocean was also generated by a mantle plume and in response to the lithosphere interaction and tectonic settings it shows three remarkable bends through time. One occurred after 85 Ma associated with the Trindade plume tail movement under the Archean São Francisco Craton, and another one ca. 52 Ma after the formation of the Abrolhos Bank in the Brazilian platform (Mohriak, 1989; Thompson et al., 1998) when the Trindade Plume encountered a thinner lithosphere in the Brazilian coast and formed a chain of seamounts and islands of W-E direction. The last bend marked in the Trindade plume trajectory is ca. 20°00′lat, around Davis Bank, marking a Miocene (21.07 Ma - 40Ar/39Ar whole-rock method) subtle clockwise rotation in the South American Plate. The easternmost part of this ridge is composed of Trindade-Martin Vaz Archipelago subject of this study. Located ca. 1200 km away from the Brazilian coastline at the Vitória (ES) parallel, its geology is an important preserved record of an alkaline Pliocene-Pleistocene volcanism, the youngest one recorded in the Brazilian territory. Martin Vaz and the nearby islets are located on the easternmost part of the VTR. Its geological features include phono-tephritic to tephri-phonolitic domes; nosean-phonolitic dykes and sub-horizontal layers formed by pyroclastic rocks and subordinate lava flows (melanephelinites) of Volcanian-style magmatism (mostly). 40Ar/39Ar ages yielded values ranging from 336 to 721 ka representing a young and short period of intraplate magmatic activity in the South American Plate offshore. These new ages associated with compiled radioisotopic ages from onshore and offshore volcanic rocks represent a strong decreasing age correlation related to Trindade Mantle Plume. Moreover, Trindade-Martin Vaz Archipelago is a contemporaneous product of a terminal plume expression in the offshore portion of a long-lived track (ca. 90 Ma) with a slow shear velocity (VS) placing its origin at the Upper Mantle suggesting a shallow mantle plume rising from the asthenosphere.

Shelled-Molluscs Fauna at Abrolhos Bank (Brazil): Assessment of Both Total Species Richness and the Completed Distribution of Species Frequencies by Numerical Extrapolation of a Partial Survey

Numerous anthropogenic threats to the exceptionally rich coral-reef ecosystem at Abrolhos Bank (Brazil) arguably require implementing drastic conservation policy and meanwhile, urge for the prior detailed assessment of species richness and the species distribution across the Bank. Due to their unavoidable incompleteness, the already implemented “Rapid Assessment Surveys” at Abrolhos Bank deserve being completed, at least numerically, by implementing an appropriate extrapolation procedure, to avoid serious bias precisely due to ignoring both the number and the frequency distribution of those species still remaining undetected after Rapid Assessment Surveys. Complying with this concern, I report on the results of a numerical extrapolation of a previously achieved partial survey of the soft-bottom shelled-mollusc fauna at Abrolhos Bank. This numerical extrapolation provides least-biased estimates regarding not only the number of species which have remained unrecorded but, moreover, additional information on the respective frequencies of these still unrecorded species. As a result, the extrapolated total species richness at Abrolhos Bank reaches at least 435 shelled-molluscs species (instead of only 293 species actually recorded by the Rapid Assessment Survey), out of which 30 species (instead of 19) are expected to be Brazilian endemics. Accordingly, the soft-bottom shelled-mollusc fauna – an admittedly fairly reliable indicator for the whole marine biodiversity – definitely demonstrate the major biological interest of the whole reef ecosystem at Abrolhos Bank and the imperative necessity of implementing truly efficient conservation programs of this ecosystem.

Use of recurrence plots for identification and extraction of patterns in humpback whale song recordings

ABSTRACT Humpback whale song is comprised of well-structured distinct levels of organisation: combinations of sounds, repetition of combinations, and a sequence of repetitions, which have no clear silent intervals. This continuous sound output can be hard to delimit, rather, it could be interpreted as a long series of states of a system. Recurrence plots are graphical representations of such series of states and have been used to describe animal behaviour previously. Here, we aim to apply this tool to visualise and recognise structures traditionally used in inferences about behaviour (songs and themes) in the series of units manually extracted from recordings of humpback whales. Data from the Abrolhos bank, Brazil were subjected to these analyses. Our analytical tool has proven efficient in identifying themes and songs from continuous recordings avoiding some of the human perception bias and caveats. Furthermore, our song extraction is robust to errors coming from both manual and automated transcriptions, constructing a level of description largely independent of the first stage of analysis.