Southwestern Atlantic Research Articles

Acoustic richness and composition changes of humpback whale (Megaptera novaeangliae) songs on breeding grounds off the coast of Ecuador

AbstractSong evolution and revolution events recorded through time are typical cultural features for humpback whale (Megaptera novaeangliae) populations worldwide. However, it is unknown if song dynamics are equivalent among subpopulations or breeding stocks of the South Pacific Ocean. To contribute to the understanding of the temporal song dynamics of humpback whale song off the coast of Ecuador, we analyzed acoustic richness and repertoire composition based on unit, phrase, and song composition over consecutive breeding seasons from 2012 to 2019. We observed incomplete song revolutions (all themes were replaced except one) and a nonsignificant variation in the acoustic richness during the study period. Our results show that over the years, humpback whale singers incorporate acoustic material from different subpopulations such as Central South Pacific (French Polynesia) and western South Atlantic (Brazil) into their song repertoire. The temporal acoustic contact of different subpopulations migrating through the eastern South Pacific may be reflected in their particular acoustic richness and temporal evolution. Off the coast of Ecuador, humpback whale song patterns point towards an alternative scenario of song evolution, indicating how cultural transmission among subpopulations can alter the song patterns in specific breeding grounds due lack of geographical barriers surrounding the southeastern Pacific region.

Evaluation of traditional and bootstrapped methods for assessing data-poor fisheries: a case study on tropical seabob shrimp (Xiphopenaeus kroyeri) with an improved length-based mortality estimation method.

Unrealistic model assumptions or improper quantitative methods reduce the reliability of data-limited fisheries assessments. Here, we evaluate how traditional length-based methods perform in estimating growth and mortality parameters in comparison with unconstrained bootstrapped methods, based on a virtual population and a case study of seabob shrimp (Xiphopenaeus kroyeri, Heller, 1862). Size data were obtained for 5,725 seabob shrimp caught in four distinct fishing grounds in the Southwestern Atlantic. Also, a synthetic population with known parameter values was simulated. These datasets were analyzed using different length-based methods: the traditional Powell-Wetheral plot method and novel bootstrapped methods. Analysis with bootstrapped ELEFAN (fishboot package) resulted in considerably lower estimates for asymptotic size (L ∞), instantaneous growth rate (K), total mortalities (Z) and Z/K values compared to traditional methods. These parameters were highly influenced by L ∞ estimates, which exhibited median values far below maximum lengths for all samples. Contrastingly, traditional methods (PW method and L max approach) resulted in much larger L ∞ estimates, with average bias >70%. This caused multiplicative errors when estimating both Z and Z/K, with an astonishing average bias of roughly 200%, with deleterious consequences for stock assessment and management. We also present an improved version of the length-converted catch-curve method (the iLCCC) that allows for populations with L ∞ > L max and propagates the uncertainty in growth parameters into mortality estimates. Our results highlight the importance of unbiased growth estimates to robustly evaluate mortality rates, with significant implications for length-based assessments of data-poor stocks. Thus, we underscore the call for standardized, unconstrained use of fishboot routines.

Population genetic structure of the bottlenose dolphin in the Turkish waters based on mtDNA sequences with implications for the Black Sea subspecies Tursiops truncatus ponticus

The bottlenose dolphin is a widely distributed species found in temperate waters, including the Mediterranean and Black Seas. The Black Sea population is recognized as a distinct subspecies, Tursiops truncatus ponticus, due to genetic and morphological differences. This study analyzed mitochondrial DNA (mtDNA) sequences of 73 bottlenose dolphin samples collected between 1999 and 2016 along the Turkish Black Sea coast, Turkish Straits System (TSS), Aegean, and Mediterranean Seas revealing 14 haplotypes, eight of which are reported here for the first time. The haplotype network shows two main nodes with star-like sub-networks, but no apparent geographic pattern. The lack of geographical groupings of haplotypes indicates the high mobility of the species within the sampled area. The northern Black Sea bottlenose dolphins (NBS) appear to be genetically differentiated from those in the southwestern Black Sea (SBS), Mediterranean, and Atlantic Ocean, but not from the TSS and Aegean Sea populations. Besides, SBS bottlenose dolphins were differentiated only from those in the western Mediterranean (WM) and the Atlantic. Therefore, NBS and SBS bottlenose dolphins should at least be categorized as different populations. However, contrary to some previous studies there was no evidence supporting the classification of Black Sea bottlenose dolphins as a separate subspecies. The TSS differs only from the Atlantic and the Aegean, and functions like a migratory ‘melting pot’ for surrounding populations. Despite the largest sample size, NBS bottlenose dolphins exhibited the lowest haplotype and nucleotide diversity. This low genetic diversity and potential isolation from adjacent populations highlight the need for prioritizing the conservation of NBS bottlenose dolphins.

The microbiome of the main deep-water scleractinian reef-framework engineers from the Southwestern Atlantic

Deep waters (>150 m) shelter half of the extant diversity of scleractinian corals, including framework reef-forming species. However, to date, the relationship between microorganisms and corals has focused mainly on their zooxanthellate shallow-water counterparts. Here, using 16S rRNA gene amplicon sequencing, we explore the microbiome of all major Atlantic deep-water scleractinian reef framework engineers (Desmophyllum pertusum, Solenosmilia variabilis, Madrepora oculata, and Enallopsammia rostrata), and correlated them with environmental characteristics. Colony fragments of each coral species used in the present study were sampled from three sedimentary basins off the Southeastern coast of Brazil, including two water masses (Antarctic Intermediate Water and South Atlantic Coastal Water). Although representing distant scleractinian evolutionarily lineages, some evolving apart for more than 300Ma, our results suggest a taxonomic homogeneity in their microbial profile. The species-specific microbial core, as well as the core common to all examined species, were identified. Such cores are composed of bacterial genera that have already been observed in other coral species, including those from zooxanthellate species. Such a pattern suggests an active selection of the microbial community by their hosts, a phenomenon that seems to be fundamental for holobiont fitness, especially in long-lived species, such as corals. Besides the microbial core, for all examined species, part of the determined microbiome was flexible and responded to environmental drivers. This flexibility is most probably related to the host's ability to adapt in ecological time scales. Taken together, these holobiont abilities may be crucial to its success in both ecological and geological timescales.

Chafing behaviour of great barracudas on sea turtles triggers escape response of external parasites

If chafing behaviours on the bottom or rocks are common, interspecific events are rare and usually involve smaller ray-finned fishes rubbing on larger sharks or manta rays. Reports on interspecific chafing between fishes and reptiles are even less common, with just one report of great barracudas (Sphyraena barracuda) using swimming hawksbill (Eretmochelys imbricata) and green turtles (Chelonia mydas) as chafing surfaces in the Southwestern Atlantic. Here, we describe a chafing interaction between a great barracuda and a hawksbill turtle in the Red Sea. Our observation provides evidence that this interaction is probably not localised but may represent a more widespread behavioural pattern than previously thought. This chafing behaviour is suggested to remove external parasites, and our observation documents the behaviour of the scraper and the scraped animal, as well as the reaction of the parasites during the same event, clearly demonstrating that chafing behaviour aims at the removal of parasitic copepods (Caligidae). We also report the evasive behaviour of the copepods during the event, providing novel information on parasite removal in reef fishes.

Reef fish species discrimination through acoustics: sound characteristics of three Haemulon species (Perciformes: Haemulidae) in the Southwestern Atlantic

ABSTRACT Marine fishes use sound for critical functions, including foraging, competition, and reproductive activities. Despite the biological significance of these sounds, research on the applicability of sound profiles to discriminate between fish species is limited. This study aimed to characterise and differentiate the vocalisations of Haemulon aurolineatum, Haemulon parra, and Haemulon squamipinna off the northeastern Brazilian coast. Seventy-two individuals were recorded, with 140 vocalisations per species. The analyses revealed a grunt profile with significant variation in time parameters across all species, characterised by irregular pulses with variable frequencies (1.8 to 5.9 kHz) and a dominant frequency of approximately 0.75 kHz. Differences among species were observed, with H. aurolineatum showing the highest values in most parameters. Cross-validation tests indicated an overall rate of 69.5% of single sounds correctly assigned to species. Haemulon squamipinna was the most discernible species, while H. parra had the lowest prediction accuracy, showing intermediate sound parameter values. The analysis of pharyngeal jaws revealed minor differences in morphology and tooth distribution in H. parra, but these could not be linked to sound differentiation. Our results indicate that it is feasible to distinguish Haemulon species using the sound characteristics of their vocalisations, offering new insights into their sound communication.

Molecular phylogeny, including a new species of Anindobothrium (Cestoda, Rhinebothriidea) from the Southern eagle ray Myliobatis goodei, finally solves the taxonomic enigma of Phyllobothrium myliobatidis

During a parasitological survey of tapeworms from Myliobatis goodei Garman, 1885 (Myliobatiformes: Myliobatidae) in coastal waters off Argentina in the Southwestern Atlantic, a new rhinebothriidean cestode species, Anindobothrium danielaesp. nov., is described using morphological and molecular techniques. This species differs from its congeners by a particular combination of features, including the configuration of the bothridia, the number of marginal loculi, and the number and distribution of testes. Additionally, Anindobothrium myliobatidiscomb. nov. is proposed based on several morphological traits, including the presence of stalked bothridia with marginal loculi and an apical sucker, euapolytic strobila, and postvaginal testes. The diagnosis of the genus Anindobothrium Marques, Brooks & Lasso, 2001 is amended to include the features exhibited by these two species; two species subsets are suggested based on the configuration of the bothridia. The presence of A. danielaesp. nov. and A. myliobatidiscomb. nov. in the studied area not only increases the number of cestodes in M. goodei here from eight to ten but also represents the first report of a rhinebothriidean cestode parasitizing stingrays of the family Myliobatidae in the Southwestern Atlantic.

First records of Glyphus marsupialis Filhol, 1884 (Decapoda: Pasiphaeidae) in southwestern Atlantic deep waters and extensions of the known distribution of two Pasiphaea species

The Pasiphaeidae Dana, 1852 are a marine shrimp family occurring in both shallow and deeper waters, with its greatest diversity occurring in tropical and subtropical deep seas. This family includes seven genera and 104 species, and is globally distributed. Currently, the genus Pasiphaea Savigny, 1816 includes 73 species, seven of them recorded in the southwestern Atlantic. The genus Glyphus Filhol, 1884 is monotypic and is known from the Indo-Pacific region, the East Pacific Ocean and in the Eastern Atlantic. Herein, we report the first record of the genus in the southwestern Atlantic, completing a cosmopolitan distributional pattern. Further, two new records of Pasiphaea species are commented upon (P. major Hayashi, 2006; P. tarda Kroyer, 1845) along the Northern coastline of the Brazilian coast (Amapá state), also reporting a new host interaction between Thalassomyces sp. and P. major. This is the first record of this Ellobiopsidae genus in the South Atlantic Ocean. The material herein analyzed was sampled by the ReviZEE Program/North, in 1996/2001, during deep-water trawls in the Amazonian slope (Amapá state), at depths from 250 to 1100 m. All material is deposited in the Coleção Carcinológica do Laboratório de Crustáceos (Labcrus)/Universidade Federal Rural da Amazônia (UFRA). The global distribution of Glyphus is commonly observed in deep species and although it has been occasionally contested by the discovery of species complexes (using very detailed morphological and molecular data analyses) with the currently available information, the present material is clearly identifiable as G. marsupialis.

Characteristics and drivers of marine heatwaves in the western South Atlantic

Marine heatwaves are events of extreme warming in the ocean and have devastating consequences for marine life. Here we used a K-mean clustering analysis to detect different types of marine heatwaves along the South American coast from 10°S to 45°S and identify their remote drivers. In the central part of the domain, marine heatwaves are associated with atmospheric blocking caused by wave trains triggered by the Madden-Julian Oscillation. On the other hand, marine heatwaves occurring along the northern and southern coast of South America are associated with El Niño and La Niña events, respectively. The intensity and duration of these marine heatwaves are modulated by the development phase and intensity of the Niño and Niña events. By identifying the climatic modes of variability leading to each type of marine heatwaves, our study can help develop adaptation strategies, such as early warning systems, to prevent the devastating effects of marine heatwaves.

Connectivity and high genetic diversity in populations of the dog snapper Lutjanus jocu (Lutjanidae: Perciformes) from the South Western Atlantic, recovered with multilocus analysis

Connectivity and high genetic diversity in populations of the dog snapper Lutjanus jocu (Lutjanidae: Perciformes) from the South Western Atlantic, recovered with multilocus analysis

Inferring the origin of new D-loop haplotypes of loggerhead sea turtles (Testudinata: Cheloniidae) from the Southwest Atlantic lineage

The populations of the loggerhead turtles, Caretta caretta, present four main D-loop mitochondrial haplogroups that are distributed across the Indo-Pacific, Mediterranean, and Atlantic oceans. The Southwestern Atlantic (SWA) is one of the Regional Management Units (RMUs) of loggerheads, characterized by unique haplotypes, high nest density, and distinct life history traits. Detecting new D-loop haplogroups is important, particularly endemic ones, as they can enhance our understanding of their life history within the RMUs and contribute to the resolution of mixed stock analysis. In this study, we conducted a series of phylogenetic delimitation and network analyses to identify, validate, and infer the origin of four new D-loop haplotypes detected in the loggerhead populations from the SWA. Our findings demonstrate that these new D-loop haplotypes are valid and unique to the SWA lineage, potentially aiding in the delimitation of individuals’ origins and the inference of their lineage.

Evolutionary biogeography and diversification of Ampithoidae (Crustacea, Amphipoda) in the southwestern Atlantic

Evolutionary biogeography and diversification of Ampithoidae (Crustacea, Amphipoda) in the southwestern Atlantic

When the Light Goes Out: Distribution and Sleeping Habitat Use of Parrotfishes at Night

Understanding the diurnal and nocturnal activity of organisms is a key topic in behavioral ecology, with implications for population structure and management strategies. In reef systems, parrotfishes play crucial roles as nominal herbivores, but overfishing has led to population collapses with detrimental effects on reef functions. Parrotfish are good models to study diel rhythms, as they are often easily observed while sleeping at night. We assessed the distribution, sleeping substrate selectivity and sleeping areas of parrotfishes during the night in a subtropical rocky reef of the Southwestern Atlantic. We performed replicated visual censuses (50 × 2 m) at different depths to estimate parrotfish abundance, while quantifying the structural complexity of sleeping sites. Among the seven recorded parrotfish species, we focused on the four most abundant to determine their sleeping habitat selectivity. Active telemetry was used for the two most abundant species to define their sleeping site areas and sleeping hotspots. All four species exhibited a preference for sediment as a sleeping substrate, while avoiding zoanthids. Species distribution was influenced by depth, with Scarus zelindae predominantly sleeping in high-complexity substrate at intermediate depths and Sparisoma tuiupiranga sleeping in the rock–sand interface at deeper depths. Tagged Sparisoma axillare and Sparisoma frondosum exhibited similar sleeping areas in terms of size and geographical locations; showing high site fidelity, they returned to the same sleeping sites over consecutive nights. These results represent the first assessment of parrotfish distribution and habitat use at night in the Atlantic. This information is crucial for guiding management actions, particularly in the planning of no-take zones for fishing control and population recovery.

Two new species of Stylopoma (Bryozoa, Cheilostomatida) from the Southwestern Atlantic

Two new species of the cheilostomate bryozoan genus Stylopoma are described from Brazil—Stylopoma anacarolinae sp. nov. and Stylopoma priscilae sp. nov. Stylopoma anacarolinae sp. nov. exhibits zooids with single or paired small avicularia and an orifice with a U-shaped sinus, in contrast to the long avicularia and orifice with a teardrop-shaped sinus of Stylopoma priscilae sp. nov. In addition to taxonomic description, a revised comparative table of living species worldwide is provided.

Trophic relationships of 13 small to medium-sized elasmobranchs in Central Patagonia, Southwestern Atlantic

Trophic relationships of 13 small to medium-sized elasmobranchs in Central Patagonia, Southwestern Atlantic

Sedimentological and geochemical proxies reveal changes in the South Atlantic Convergence Zone in Southeast South America during the Late-Holocene

Today, the South Atlantic Convergence Zone (SACZ), a convective band that extends across central Brazil to the western South Atlantic Ocean, modulates Southern Hemisphere summer rainfall in Southeastern Brazil. During the Holocene, however, the role of the SACZ over the rainfall regime in this part of South America is still under debate. This study aims to provide new insights into the SACZ Late-Holocene variability through analysis of the geochemical (XRF-based bulk sediment Metal/Metal ratios) and sedimentological (grain size and end-member modeling) variations along four cores retrieved in a coastal area (24–49 m water depth) located in the core of modern SACZ. Our records show an increase in Ti/Ca ratios, suggesting increased rainfall and that the terrigenous input to the Brazilian southeastern inner shelf changed in the Late-Holocene (last 4200 years). These changes are also followed by a decrease in the K/Ti ratio, indicative of an increase in chemical weathering in the sediment source, and an increase in the Mn/Ti, suggesting an increase in oxidation. Additionally, decadal-scale variability with periodicities of 25 and 55 years obtained by a time-series (Redfit) analysis highlights a potential role of the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation, respectively, as drivers of the SACZ variability over the last 4200 years.

Feeding ecology of Atlantic bigeye Priacanthus arenatus (Perciformes: Priacanthidae) from an upwelling ecosystem in the southwestern Atlantic

Feeding ecology of Atlantic bigeye Priacanthus arenatus (Perciformes: Priacanthidae) from an upwelling ecosystem in the southwestern Atlantic

Use of traditional tools and micro-computed tomography for the taxonomy of carnivorous bivalves from the deep waters of Southwestern Atlantic

Abstract In this study, we conduct a morphological integrative analysis, using traditional techniques and micro-computed tomography imaging, on Septibranchia species. Specimens deposited in malacological collections and samples collected aboard the research vessels Puerto Deseado and Austral off Mar del Plata (~36°S), San Jorge Gulf (~46°), and Marine Protected Area Namuncurá/Burdwood Bank area (~54°S), at depths ranging from 200 to 3000 m, are the subjects of this study. Seven species were identified, including Cardiomya cleryana (d’Orbigny, 1846), Cardiomya knudseni (Allen & Morgan, 1981), Lyonsiella cf. fragilis Allen & Turner, 1974, and Cetoconcha spinulosa (Thiele, 1912), previously found in the study area. Cardiomya fragilissima (E. A. Smith, 1885), an Antarctic/sub-Antarctic species, extends its distribution up to 36°S. Two new species, Cetoconcha gigas sp. nov. and Lyonsiella tentaculata sp. nov., are described. A lectotype is designated for Pholadomya adelaidis Hedley, 1916 and a neotype for Sphenia cleryana d’Orbigny, 1846. A detailed description of the morphological characters of each species and genus, along with insights into their geographical and bathymetric distribution, are provided. The micro-computed tomography analysis of Cardiomya cleryana, Cardiomya fragilissima, and Cetoconcha spinulosa contributed to a detailed anatomical inspection and revealed the presence of muscle bundles associated with the anterior portion of the visceral mass in the scanned specimens.

First geological survey and characterisation of a giant depression in carbonate strata at the Rio Grande Rise (southwestern Atlantic)

Pockmarks are submarine depressions often considered the result of fluid (gas and oil) expulsion from the seafloor. Recent geophysical surveys at the Rio Grande Rise (RGR - SW Atlantic) revealed extensive presence of seafloor depressions, generically interpreted as pockmarks. To date, direct observations or sampling from these depressions are lacking. Moreover, hydrocarbons have never been detected at the site, questioning the possibility of pockmarks formation by fluid expulsion. Here we present the first visual inspection and rock characterisation of a giant circular depression located inside the RGR central graben. The depression was discovered during multibeam prospection and surveyed with a Remotely Operated Vehicle, with rock sampling along a vertical transect. The depression is conical (350 m wide and 80 m deep) with walls of stratified, sub-horizontal, white fossiliferous wackestone, with incipient gravitational collapse. Lithological, mineralogical, and geochemical characterisation of the wackestone rule out methane in the formation of the depression. Based on geochemical data and on the finding of anhydrite III (forming at 110–300 °C), we propose a novel perspective on the formation of this kind of depressions, invoking hypogenic karstification and collapse, due to hydrothermal fluids along deep faults. Our geochemical approach complements previous geophysical observations of circular depressions at the RGR and contribute to the general understanding of the formation mechanisms of these intriguing seafloor features.

How many species of the gastropod genus Leucosyrinx (Conoidea: Pseudomelatomidae) are truly living in Southwestern Atlantic deep-waters?

A revision of the species cited in the genus Leucosyrinx from Argentine waters is conducted. Leucosyrinx argentina sp. nov. is described after material collected off Argentina in: the Mar del Plata Submarine Canyon (528–2212 m depth), at 39°53.381′S, 55°52.197′W off Buenos Aires province (772 m depth), and in the Burdwood Bank (approximately 54°S in 187 and 642 m depth). Radulae, penis, operculum, ornamentation and ultrastructure of the shell are described. In addition, partial sequences of the mitochondrial cytochrome c oxidase subunit 1 gene (COI) are provided. After a review of the species previously described in the genus Leucosyrinx from Argentine waters, we concluded that L. argentina sp. nov. is the only living species truly recognized as belonging in this genus from the Southwestern Atlantic. This is the first study of the genus Leucosyrinx from this region that revises both morphological and molecular characters.