Southwestern Atlantic Research Articles

Limited human access is linked to higher effectiveness in a marine sanctuary

Marine Protected Areas (MPAs) are a widely used tool for coral reefs conservation, but massive tourism activities inside MPAs worldwide can challenge their effectiveness. This study investigated the role of different levels of protection strictness (no-entry, low and high tourism-allowed zones) set for a marine sanctuary in shaping benthic cover and reef fish community structure in the richest and largest coral reef system of the Southwestern Atlantic. Reef fish community structure and benthic cover differed between protection levels. No-entry zones showed significant higher coral coverage and biomass of piscivores and herbivores than tourism-allowed zones. Highest differences were found between no-entry and high tourism intensity zones. Despite the fact that protection from fishing by itself can ensure conservation benefits, we show here that the establishment of no-entry zones improve MPAs effectiveness.

The historical and contemporary knowledge on the elasmobranchs of Cananeia and adjacent waters, a coastal marine hotspot of southeastern Brazil

In this study we present data on the richness of sharks and rays from the southern coast of São Paulo, southeastern Brazil, in a coastal area considered as an essential habitat for many species of elasmobranchs. Based on information produced between the 1950s and 1970s, we constructed a historical timeline about the knowledge of sharks and rays as well an updated and annotated list of elasmobranchs for Cananeia and adjacent waters, comparing the local richness with data from other areas. A total of 62 species (36 sharks and 26 rays) were recorded, which represent 68.1% of the species previously known to occur along the entire State of São Paulo and about 33.3% of the total richness known for marine elasmobranchs in Brazil. Problems related to a low number of peer-reviewed publications and a low taxonomic resolution of records in official fisheries databases since the end of the 1970s reflected a historical problem related to fisheries management of elasmobranchs in Brazil. Thus, a long-term monitoring that refines the categories of elasmobranchs landed is suggested for the proper orderly management of the fishing activity in an area that represents a hotspot for this group in the subtropical Southwestern Atlantic.

Mantle plume and rift-related volcanism during the evolution of the Rio Grande Rise

The Rio Grande Rise in the western South Atlantic Ocean has been interpreted as either an oceanic plateau related to the Tristan-Gough mantle plume, or a fragment of detached continental crust. Here we present new major and trace element data for volcanic rocks from the western and eastern Rio Grande Rise and the adjacent Jean Charcot Seamount Chain. The eastern Rio Grande Rise and older parts of the western Rio Grande Rise are comprised of tholeiitic basalt with moderately enriched trace element compositions and likely formed above the Tristan-Gough mantle plume close to the southern Mid-Atlantic Ridge. Younger alkalic lavas from the western Rio Grande Rise and the Jean Charcot Seamount Chain were formed by lower degrees of melting beneath thicker lithosphere in an intraplate setting possibly during rifting of the plateau. There is no clear geochemical evidence that remnants of continental crust are present beneath the Rio Grande Rise.

Occurrence of polychlorinated biphenyls (PCBs) in the sea anemone Bunodosoma zamponii, sediments and seawater from the southwestern Atlantic.

Polychlorinated biphenyls (PCBs) are persistent and bioaccumulable organic compounds. The occurrence of PCBs was assessed in two populations of the intertidal sea anemone Bunodosoma zamponii living under different anthropogenic strains. One location was in vicinity to a wastewater plant (Las Delicias, LD), and the other was a preserved location chosen as a reference site (Punta Cantera, PC). Anemone populations were sampled 4 times (spring, summer, autumn and winter) throughout a year, in addition to seawater and sediment from those areas. PCB loadings ranged from 2.89 to 79.41 ng L-1 in seawatersamples and from 0.07 to 6.61 ng g-1 dry weight in sedimentsamples. Total PCB levels ranged from 0.22 to 14.94 and 2.79 to 24.69 ng g-1 wet weight in anemonesfrom PC and LD, respectively. PCBs concentrations in anemonesfrom LD were significantly greater than PC during spring, summer and winter. The congeners 18 and 44 prevailed in seawatersamples, 44 and 52 in sedimentand 18 and 132+153 in anemones. Redundancy analysis integrated PCB levels from all matrixes and bolstered contrast between sampling sites. Seasonality was also a relevant factor since during winter PCB loading was greater in sedimentand anemone samples, coincident with the rainiest season. Disparity between sites could be due to LD's proximity to the wastewater plant, effect of littoral drift direction and/or asymmetries in anemonesphysiological condition.

A tale that never loses in the telling: Considerations for the shifting ethnobaseline based on artisanal fisher records from the southwestern Atlantic

An ethnoichthyological survey was conducted with fishers from traditional communities distributed between the Região dos Lagos and the northern Fluminense region, in the state of Rio de Janeiro, Brazil. The study was developed based on semi-structured interviews, with fishers with at least 30 years of experience. Fishers were asked about changes noted for the biological communities with which they interact with, such as reports concerning abundance changes, the disappearance of certain species or the insertion of new ones, as well as weight and size changes. The reported ethno-names were confirmed at the specific level whenever possible through photographs and complementary descriptions. Eighty-five fishers aged between 39 to 83 years old were interviewed. Fishing activity times ranged from 30 to 68 years, averaging 40.6 years. Fishers reported differing estimates from what was expected according to the known length-weight relationship for the reported species. In general, length estimates were closer to the expected for medium-sized fish from 0.3 m to 1 m. Sixty-nine ethno-names and their variations were identified, associated with 58 fish categories. Of this total, denominations were associated to 47 local fauna species or genera, while one ethno-name was not linked to any taxonomic identification. This study is the result of research financed by the Brazilian Fund for Biodiversity and the Pescarte Environmental Education Project, a mitigation measure required by the Federal Environmental Licensing, conducted by IBAMA.

Assessing effectiveness and side effects of likely “seal safe” pinger sounds to ward off endangered franciscana dolphins (Pontoporia blainvillei)

AbstractThe franciscana (Pontoporia blainvillei) is the most endangered dolphin in the western South Atlantic Ocean due to bycatch. Our goal was to test the efficiency of a likely “seal safe” pinger (Banana Pinger, Fishtek Marine Ltd.) to ward off franciscanas, as well as investigating possible side effects of habituation and habitat exclusion. We deployed the pinger within a grid of click detectors (C‐POD, Chelonia Ltd.) in Babitonga Bay, southern Brazil, and the narrow band high frequency sonar click trains were used as a proxy for presence of the franciscanas and response to the pinger. The presence of franciscanas next to the pinger and at 100 m away decreased by 19.4% and 15.4%, respectively, when the pinger was switched on, indicating that the franciscanas avoided the area of the pinger. This avoidance response could not be seen at 400 m away. No habituation effect was noted at any distance. There was a slight gradual decrease in detections over the course of the study at all distances, which is probably related to seasonal variation in the population's habitat use, but this requires attention in future studies. The likely “seal safe” pinger sounds effectively warded off franciscanas and thus has the potential to reduce bycatch.

Temporal and spatial differences between predicted and measured organic carbon in South Atlantic sediments: Constraints to organic facies modelling

The evaluation of total organic carbon (TOC) content from wells is a routine practice for assessing source rock potential, and empirical relationships to estimate TOC content have been proposed and used in organic facies modelling. However, no critical evaluations address how well the available TOC-predictive equations estimate the TOC content in recent and past sediments of the South Atlantic. In order to investigate the performance of the available TOC-predictive equations in this study, we compiled a large South Atlantic dataset composed of new and published modern TOC, dry bulk density, and sedimentation rate with the associated satellite-derived net primary productivity. We repeat this exercise for another time interval using the same input parameters but estimating net primary productivity using transfer functions. Our results indicate that all equations overestimate the modern TOC distribution, mainly at the continental margins and at the edges of the subtropical gyre. However, we must point out that this is partly due to our primary productivity values used as inputs, which exhibit higher values than the ones used in the calibration datasets of the TOC-predictive equations. In addition, the equations perform better, in terms of correlation, in the eastern compared to the western South Atlantic. We observe that in the west, the equation of Müller and Suess (1979) exhibited the highest correlation between predicted and measured TOC values, while in the east, the “Definition” equation using the carbon flux equation of Antia et al. (2001) and the burial efficiency equation of Betts and Holland (1991) showed the best results. In addition, we indicate that lateral transport of organic carbon at the margins might be influencing the correlation negatively. Overestimations the TOC content were also apparent for the downcore data, although with reduced magnitude, and correlation between predicted and measured TOC values was lower compared to the modern dataset. This can be explained by more sparse data in the glacial dataset and a strong lateral transport during this interval of low sea level. The reasons behind the different performances of equations are explained by the way they incorporate the input parameters into their formulations, which is especially relevant for primary productivity, sedimentation rates, and the inclusion of processes such as the carbon flux. We highlight that carbon flux equations should also be used with caution in very shallow and high productive systems, since they can produce unrealistic results. Our compilation indicates that the use of a single equation is not adequate to resolve the broad spatial TOC distribution in marine environments and that organic facies modelling software should consider regional aspects in order to produce adequate quantitative estimations of TOC content. Additionally, we used our dataset to investigate the optimal environmental conditions linked to organic-rich sediments in the South Atlantic. Our results show that high productivity, shallow depths, and optimal sedimentation conditions are required for the occurrence of organic-rich sediments. This can be viewed as important factors preconditioning the formation of black shales in the South Atlantic. Nevertheless, we highlight that orbitally-driven changes in hydroclimate and its impact in weathering-derived nutrient input probably played a major role on boosting productivity and preservation of marine organic carbon during sedimentation of high-TOC black shales in the South Atlantic.

Are dolphins modulating whistles in interspecific group contexts?

ABSTRACT Cetaceans depend highly on acoustic signals, such as whistles, for social communication. Mixed-species associations (MSAs), temporary or long-term encounters between different species, may play an important role on the acoustic dynamics of the species involved. Because of whistles’ communication function, we used these sounds to investigate the acoustic relationships of Tursiops truncatus when involved in different group contexts: in MSAs with two other delphinid species and in single species group. Acoustic recordings of T. truncatus single species groups and in associations with Globicephala melas and Grampus griseus were collected in the Western South Atlantic Ocean through a towed array of hydrophones. A total of 1267 whistles were analysed and acoustical parameters were extracted. To verify the differences among whistles produced in such contexts a support vector machine and random forest analysis were implemented. Both analyses revealed a clear separation of whistles from the single species versus the MSA as well as between both MSAs. The results indicate that interspecific associations may influence the whistle structure and suggests that T. truncatus whistles can be modified during interspecific interactions. These findings are useful to elucidate the possible factors underlying behavioural plasticity and interspecific associations and to understand dolphins’ acoustic communication.

Plastic in the inferno: Microplastic contamination in deep-sea cephalopods (Vampyroteuthis infernalis and Abralia veranyi) from the southwestern Atlantic

Microplastics are a relevant environmental concern in marine ecosystems due to their ubiquity. However, knowledge on their dispersion patterns within the ocean basin and the interaction with biota are scarce and mostly limited to surface waters. This study investigated microplastic contamination in two species of deep-sea cephalopods from the southwestern Atlantic with different ecological behaviour: the vampire squid (Vampyroteuthis infernalis) and the midwater squid (Abralia veranyi). Microplastic contaminated most of the evaluated specimens. V. infernalis showed higher levels of contamination (9.58 ± 8.25 particles individual−1; p < 0.05) than A. veranyi (2.37 ± 2.13 part. ind.−1), likely due to the feeding strategy of V. infernalis as a faecal pellets feeder. The size of extracted microplastics was inversely proportional to the depth of foraging. The microplastics were highly heterogeneous in composition (shape, colour and polymer type). Our results provide information regarding microplastic interaction with deep-sea organisms and evidence of the biological influence in the microplastic sinking mechanism.

Deep-sea dragonfishes (Teleostei: Stomiiformes) collected from off northeastern Brazil, with a review of the species reported from the Brazilian Exclusive Economic Zone

Abstract The Stomiiformes includes about 455 species of mostly mesopelagic fishes in the families Diplophidae, Gonostomatidae, Phosichthyidae, Sternoptychidae, and Stomiidae. Here we report 55 species of the order collected during the ABRACOS (Acoustics along the BRAzilian COaSt) expeditions off northeastern Brazil, including islands and seamounts of Fernando de Noronha Ridge. Triplophos hemingi (Diplophidae), Pachystomias microdon and Melanostomias biseriatus (Stomiidae) are recorded for the first time in the western South Atlantic. Eustomias bibulbosus, Grammatostomias ovatus and Photonectes achirus (Stomiidae) are recorded for the first time in the South Atlantic. Eustomias minimus (Stomiidae), previously known from four poorly preserved specimens, is reported for the first time in the Atlantic. Occurrences of 18 species are confirmed or recorded for the first time in the Brazilian Exclusive Economic Zone: Triplophos hemingi (Diplophidae), Gonostoma denudatum (Gonostomatidae), Aristostomias grimaldii, Astronesthes gudrunae, Bathophilus nigerrimus, Borostomias elucens, Eustomias bibulbosus, E. braueri, E. minimus, E. schmidti, Grammatostomias ovatus, G. dentatus, Leptostomias gladiator, Melanostomias biseriatus, M. bartonbeani, Pachystomias microdon, Photonectes achirus, and Photostomias goodyeari (Stomiidae). Diagnostic and distributional data for all species recorded are provided, with new anatomical information presented for Melanostomias bartonbeani and Grammatostomias ovatus. A checklist of the 108 species of Stomiiformes confirmed in Brazilian waters is also presented.

Habitat of Argentine squid (Illex argentinus) paralarvae in the southwestern Atlantic

Illex argentinus is one of Argentina’s most important commercial species and sustains one of the most important cephalopod fisheries worldwide. Catches, and presumably population abundances, show strong interannual fluctuations, probably forced by processes which occur during the species’ early life history. However, knowledge of paralarvae ecology and the influence of the environment on larval survival are fragmentary and limited. In this work, we describe the habitat of I. argentinus paralarvae caught in 4 research cruises between 34° and 42°S, taking into account information on seasonal transport of paralarvae by currents, chlorophyll a concentrations, characteristics of water masses and water column structure. Argentine squid paralarvae habitat is environmentally complex. Paralarvae occur in the plankton when the biological production in the area is relatively low but offshore transport is at a minimum, thus decreasing the chances of the paralarvae being exported to places unsuitable for survival. We discuss how the synchronization of the squid reproductive cycle relates to these environmental events and may improve paralarvae survival and recruitment.

Sedimentation in the adjacencies of a southwestern Atlantic giant carbonate ridge

Although carbonate mounds have been investigated for 100 years, few studies focus on the giant variety. The Alpha Crucis Carbonate Ridge (ACCR), a ~17 x 12-km ring-shaped ridge formed by hundreds of mounded structures, located between the 300 and 800-m isobaths and reaching a maximum height of 340 meters above the adjacent seafloor, is the first giant carbonate mounded feature described for the SW Atlantic margin. This study provides the first multiproxy approach to investigate sediments covering the ACCR and its adjacencies. Most of the area is located under the Intermediate Western Boundary Current (IWBC) flow, which carries the nutrient-rich Antarctic Intermediate Water (AAIW). Radiocarbon aging shows pronounced differences for the shallow layers (MIS3 for the top of the mounds and late Holocene for the adjacencies). Grain size data indicate the prevalence of sandy fractions on top of the mounds and muddy sediments in the adjacent areas. Fe/Ca and Ti/Ca proxies allowed for identifying mainly biogenic sedimentation in the area. However, the input of allochthonous terrigenous sediment is necessary for mound buildup, and values of Fe and Ti collected on the top of the mounds are significant. End-Members distributions and metal concentrations also allowed for recognition of distinct sources of sediment. εNd and Ln(Fe/K) indicated two primary terrigenous sources, the Precambrian rocks of the Brazilian shield (Cabo Frio end-member) and the multiple lithologies drained by the Rio de la Plata basin. Redox condition proxies indicated that the area is submitted to oxic conditions, probably reflecting the action of the IWBC. This work provides the first insight into an integrated grain-size and geochemical characterization of the Alpha Crucis Carbonate Ridge (southwestern Atlantic margin).

Wave climate trends and breakpoints during the Atlantic Multidecadal Oscillation (AMO) in southern Brazil

Understanding how wave climate variability and its trends change over time are crucial analyses required to mitigate potential wave-induced impacts and adapt coastal areas to such effects. The long-term trends and breakpoints of the wave energy flux (WEF) and its relationship with teleconnection patterns in southern Brazil were studied using ERA-5 wave reanalysis with validation using a waverider. We determined that the interannual mean WEF (WEFm) and extreme WEF (WEF98) that reaches the southern Brazil have increased over the past four decades, with a increment of 0.063 and 0.17 kW/m/year, respectively 0.63 and 0.29% per year. By the Muggeo method we determined that subperiods with increasing WEFm trends are related to the SSE and SSW quadrants and that these are also the most energetic ones and with the highest annual increment rates of WEFm and WEF98. Our results also suggest that the positive trends observed in interannual WEF values are likely related to the long term transition of cold to warm Atlantic Multidecadal Oscillation (AMO) phase in the western South Atlantic Ocean. From a coastal risk perspective, it is important to understand the relationship between climatic indices and the wave climate to support long-term coastal management policies.

Hemiurid and lecithasterid digenean trematodes and camallanid and cucullanid nematodes parasitizing flounders collected off the coast of Rio de Janeiro State, Brazil.

A total of 132 flounder specimens (60 Paralichthys isosceles, 36 Paralichthys patagonicus and 36 Xystreurys rasile) were collected off the coast of the state of Rio de Janeiro, Brazil. The fish were measured, necropsied, and had their organs investigated for hemiurid and lecithasterid digenean trematodes and camallanid and cucullanid nematodes. Taxonomic identification of the parasites was based on morphological and morphometric characters and was conducted using bright-field and scanning electron microscopies. The trematodes Lecithochirium monticellii and Aponurus laguncula were found parasitizing P. isosceles, P. patagonicus and X. rasile while the nematodes Procamallanus (Spirocamallanus) halitrophus and Cucullanus bonaerensis were found parasitizing P. isosceles and X. rasile and P. isosceles, P. patagonicus and X. rasile, respectively. Parasite indices of prevalence, mean intensity, mean abundance, and range of infection, as well as infection site, were evaluated for each parasite species. This study allowed to evidence the first occurrence of P. patagonicus by L. monticellii; X. rasile by A. laguncula and P. (S.) halitrophus; and P. isosceles and P. patagonicus by C. bonaerensis in the Western South Atlantic Ocean.

A new species of the rare deep-sea genus Sciadonus Garman, 1899 (Teleostei, Bythitidae) from off Brazil, with a discussion of the evolution of troglomorphism and miniaturization in the aphyonid clade

A new species of the rare, deep-sea genus Sciadonus Garman, 1899 (Bythitidae) is described based on two specimens obtained by the Brazilian R/V Alpha Crucis on the continental slope off São Paulo State, Southeastern Brazil, western South Atlantic. It differs from its congeners by the combination of the following characters: body pale lacking dark pigmentation except for on female claspers; a pair of dermal tissue flaps anteriorly on lower jaw; pelvic-fin rays present; precaudal vertebrae 39 or 40 and total vertebrae 74 or 75. The key to the species of Sciadonus is updated. A discussion of the presence and differentiation between troglomorphic and miniature characteristics among the species in the aphyonid clade is provided and compared with other bythitids.

Intraseasonal variability of ocean surface wind waves in the western South Atlantic: the role of cyclones and the Pacific South American pattern

Abstract. Extratropical cyclones are known to generate extreme significant wave height (swh) values at the ocean surface in the western South Atlantic (wSA), which are highly influenced by intraseasonal scales. This work aims to investigate the importance of intraseasonal timescales (30–180 d) in the regional climatology of waves and its atmospheric forcing. The variability is explained by analyzing the storm track modulation due to westerly winds. These winds present timescales and spatial patterns compatible with the intraseasonal component of the Pacific South American (PSA) patterns. The analyses are made using ECMWF’s ERA5 from 1979 to 2019 and a database of extratropical cyclones based on the same reanalysis. Empirical orthogonal function (EOF) analyses of the 10 m zonal wind and swh are used to assess the regime of westerlies and waves in the wSA. The EOF1 of the 10 m zonal wind (u10) presented a core centered at 45∘ W and 40∘ S, while the EOF2 is represented by two cores organized into a seesaw pattern with a center between 30–40∘ S and another to the south of 40∘ S. Composites of cyclone genesis and track densities as well as swh fields were calculated based on the phases of both EOFs. In short, EOF phases presenting cores with a positive (negative) u10 anomaly provide a favorable (unfavorable) environment for cyclone genesis and track densities and, therefore, positive (negative) swh anomalies. The modulation of the cyclone tracks is significant for extreme values of the swh. The spatial patterns of the EOFs of u10 are physically and statistically consistent with 200 and 850 hPa geopotential height signals from the Pacific, indicating the importance of the remote influence of the PSA patterns over the wSA.

Coupled changes in western South Atlantic carbon sequestration and particle reactive element cycling during millennial-scale Holocene climate variability

AbstractContinental shelves have the potential to remove atmospheric carbon dioxide via the biological pump, burying it in seafloor sediments. The efficiency of marine carbon sequestration changes rapidly due to variations in biological productivity, organic carbon oxidation, and burial rate. Here we present a high temporal resolution record of marine carbon sequestration changes from a western South Atlantic shelf site sensitive to Brazil Current-driven upwelling. The comparison of biological records to rare earth element (REE) patterns from authigenic oxides shows a strong relationship between higher biological productivity and stronger particle reactive element cycling (i.e. REE cycling) during rapid climate change events. This is the first evidence that authigenic oxides archive past changes in upper ocean REE cycling by the exported organic carbon. In addition, our data suggest that Brazil Current-driven upwelling varies on millennial-scales and in time with continental precipitation anomalies as registered in Brazilian speleothems during the Holocene. This indicates an ocean–atmosphere control on the biological pump, most probably related to South American monsoon system variability.

Time-spatial boundaries of bioecozonations (planktonic foraminifera) in the latest Quaternary: a case study from the western South Atlantic

Planktonic foraminifera assemblages accurately record climate fluctuations that occurred during the Quaternary. These assemblage variations (frequently abundance changes) are widely used to establish bioecozones. Since climate variations are neither synchronous nor spatially homogenous, this paper assesses the application of the bioecozonations from the south Brazilian continental margin to its understudied southern extreme. To accomplish this purpose, census counts were made on core SAT-048A, retrieved from the continental slope of the southern extreme, and were compared to published records from the south Brazilian continental margin. According to the age model, the sediment core SAT-048A spans the last 42 kyr. The last reappearance of the Globorotalia menardii complex is dated for the first time in the Pelotas Basin at 8.5 ka, marking the biochronologic limit of bioecozones Y/Z. The last disappearance of Pulleniatina spp., marker of the sub-bioecozones Y2/Y1, is dated at 25.7 ka, showing an asynchronous characteristic already reported for the Caribbean and Equatorial Atlantic, meanwhile, its last reappearance, that marks the Y1B/Y1A limit, is dated at 15.5 ka, agreeing with previous studies. The Pleistocene/Holocene boundary can be recognized based on the Last Abundance Peak of the Globorotalia truncatulinoides dextral morphotype (GtdLAP), also recognized in other cores of the south Brazilian continental margin.ResuméLes assemblages de foraminifères planctoniques ont enregistré avec précision les fluctuations climatiques qui se sont produites au cours du Quaternaire. Ces variations d'assemblages (souvent des changements d'abondance) sont largement utilisées pour établir des bioécozones. Puisque les variations climatiques ne sont ni synchrones ni spatialement homogènes, cet article évalue l'application des bioécozonations sur la marge continentale sud du Brésil jusqu’à son extrême sud, sous-étudié. Pour atteindre cet objectif, des comptages ont été effectués sur le carotte SAT-048A, prélevée sur le talus continental de l'extrême sud, et ont été comparés aux enregistrements publiés de la marge continentale sud du Brésil. Selon le modèle d'âge, la carotte de sédiments SAT-048A a enregistré les 42 derniers kyr. La dernière réapparition du complexe Globorotalia menardii est datée pour la première fois dans le Bassin de Pelotas à 8,5 ka, marquant la limite biochronologique des bioécozones Y/Z. La dernière disparition de Pulleniatina spp., marqueur des sous-bioécozones Y2/Y1, est datée à 25,7 ka, montrant une caractéristique asynchrone déjà signalée pour les Caraïbes et l'Atlantique équatorial, en attendant, sa dernière réapparition, qui marque la limite Y1B/Y1A, est datée de 15,5 ka, en accord avec les études précédentes. La limite Pléistocène/Holocène peut être reconnue sur la base du dernier pic d'abondance du morphotype dextral Globorotalia truncatulinoides (GtdLAP), également reconnu dans d'autres carottes récupérées sur la marge continentale sud du Brésil.

Size-related, seasonal and interdecadal changes in the diet of the Patagonian longfin squid Doryteuthis gahi in the South-western Atlantic

AbstractThe Patagonian longfin squid Doryteuthis gahi has an annual life cycle with two seasonal cohorts (autumn and spring spawners). Earlier studies on the Patagonian shelf found a predominance of Euphausiacea in the D. gahi diet, but no studies to date have investigated differences between feeding spectra of the two cohorts or decadal diet shifts. The present study investigated differences in diet of D. gahi on the Patagonian shelf sampled two decades apart, and differences between seasonal cohorts. Classical stomach content analysis and generalized additive models were used to investigate and model the influence of mantle length, sampling period and spawning cohort on the diet. Results revealed an ontogenetic diet change from ~70% Frequency of Occurrence of Euphausiacea in small squid to more than 60% FO of fish and Cephalopoda at larger sizes. Cannibalism was also frequently observed. Euphausiacea were ingested more frequently and in higher amounts during the austral summer and therefore were consumed more by the autumn spawning cohort, whereas fish was more frequently fed upon during austral winter and also by the spring spawning cohort. Cannibalism was also recorded more in austral winter months but, contrary to feeding on fish, was more prevalent in the autumn spawning cohort. Increased predation of Munida gregaria was observed in 2020 compared with 2001. This study is an important step towards improving the knowledge of D. gahi's two seasonal cohorts, providing data that can be used for future ecosystem modelling.

New epibiotic association in the deep-sea: the amphipod Caprella ungulina and the Patagonian lobsterette Thymops birsteini in the South-western Atlantic

AbstractThe present study reports for the first time the association between the decapod Thymops birsteini (Nephropidae) and the amphipod Caprella ungulina (Caprellidae). A benthic biodiversity survey was carried out to explore the Mar del Plata Submarine Canyon, off the Argentine coast, in the South-western Atlantic Ocean. A total of 205 caprellids (181 juveniles, 4 males and 20 not-classified individuals) were found attached to 7 specimens of T. birsteini caught between 1087–2212 m depth. The epibiotic parameters showed that the prevalence of C. ungulina on T. birsteini was 50%; the mean abundance was 14.64 and the intensity value was 29.29. In addition, specimens of C. ungulina were recorded mainly on mouthparts of T. birsteini (31.22%), followed by chelipeds (18.05%), cephalothorax (4.88%) and pereiopods (0.98%). Our finding of C. ungulina provides the deepest record until now; additionally, this epibiont is reported in a new host belonging to an infraorder and a family of crustacean that had not previously been found as basibionts. The potential mechanisms implied in the wide distribution of C. ungulina are discussed.