Long-term time series based on repeated ecological sampling and the continuous collection of biological, environmental, and associated metadata are essential for understanding community dynamics over time. In Argentina, the Patagonian scallop (Zygochlamys patagonica) fishery started in 1996, and the monitoring of the benthic community was one of its main management objectives. This study provides a long-term study of the composition and diversity of the benthic invertebrate community in two Fishing Grounds (FG D and FG E) of the Patagonian scallop fishery located in the shelf break front of Argentina in the SW Atlantic Ocean. A total of 254 samples were studied from six stock assessment surveys conducted between 2015 and 2022, using a non-selective dredge. Ninety epibenthic taxa were recorded. No species loss or decrease in biodiversity indexes was detected. The highest biomass and species richness were recorded at FG D, where Porifera dominated, with smaller contributions of Ophiuroidea, Echinoidea, and Ascidiacea. In FG E, Ophiuroidea dominated, and Echinoidea, Porifera, and Polychaeta were the other most important groups depending on the year. Biodiversity, benthic community composition, and species associations only showed small variations. The main assemblages—composed of the Patagonian scallop, Porifera, three Ophiuroidea species, the sea urchin Sterechinus agassizii, and the cnidarian Alcyonium sp.—persisted over time. The lack of significant differences in diversity and biomass values can be interpreted as evidence of ecological stability and resilience, and of the capacity of this benthic community to maintain or recover key properties over years to decades, highlighting that the ecosystem-based management approach applied is being effective.

The Argentine shelf-break front is of high ecological and economic importance and supports diverse benthic communities and key life-history processes of several commercial species. This study provides the first comprehensive synthesis of reproductive traits among benthic invertebrates inhabiting this area of the southwestern Atlantic Ocean (80-120 m depth). Information was compiled for 126 epibenthic species belonging to Porifera, Cnidaria, Annelida, Mollusca, Brachiopoda, Echinodermata, Arthropoda, Bryozoa, and Chordata (> 1 cm) from published sources, aiming to identify the dominant reproductive strategies that sustain populations persistence over time. Species-specific reproductive data were available for only 47% of the taxa, and for only five species (~ 4%) such information derived from specimens collected at the shelf-break front itself. Despite data gaps and the need for extrapolation from related taxa or regions, this synthesis reveals predominant reproductive patterns among benthic invertebrates and provides essential baseline knowledge for ecosystem-based management. Approximately 68% of the species are gonochoric, although most sponges and all ascidians are hermaphroditic, while 43% can reproduce asexually or have the ability of regeneration. Internal fertilization predominates (71%), while all bivalves and polychaetes reproduce by external fertilization. Parental care, defined as any kind of protection of embryos through incubation or encapsulation, occurs in 61% of the species, being universal among crustaceans and frequent in gastropods (89%). Indirect development characterizes 82% of the species, of which 59% produce lecithotrophic larvae and 33% planktotrophic larvae. Understanding reproductive modes and dispersal capacities is crucial to assess connectivity, resilience, and vulnerability of benthic communities in the Argentine shelf-break front.

Marine Protected Areas (MPAs) aim to preserve species, habitats, and the Nature Contributions to People they support. In the sub-Antarctic MPAs Namuncurá - Burdwood Bank I and II, the primary conservation features are the rich and abundant benthic assemblages across two distinct habitats: the plateau and the slope of the bank. Currently, these MPAs face significant threats from anthropogenic CO2 emissions, which drive climate change and ocean acidification processes. Here, we establish an ecological baseline by analysing the diversity and structural patterns of benthic assemblages to evaluate MPA effectiveness, monitor climate change impacts, and inform management strategies. Comparisons were performed across three areas: the MPA, the Beagle Channel, and the Atlantic shelf of Tierra del Fuego, and between zones and habitats within the MPA. Sampling was conducted at depths of 90-710 m using bottom trawls, with megafauna identified to the lowest possible taxonomic level. Uni- and multivariate analyses revealed marked differences across areas. A total of 236 taxa were distinguished, but only 16 were shared among all the three areas, while 167 were unique to the MPAs. The habitats were characterized by different biotas, with sponges (mainly Demospongiae) dominating shallower environments and calcifying taxa, such as corals and echinoderms, predominating in deeper habitats. High β-diversity turnover within the MPAs suggests that the current zonation may inadequately protect benthic habitats, which is further exacerbated by ocean acidification predictions. Our findings highlight the biodiversity and conservation value in two opensea sub-Antarctic MPAs, providing a basis for effective management and the assessment of ecological responses to environmental change.

This study presents the first in situ images of benthic invertebrates and fishes inhabiting the shelf break front of Argentina, in the SW Atlantic Ocean. Obtained over a soft-sandy substrate, these images represent the first live visual records of several species of invertebrates and fish commonly found in this area, where the Patagonian scallop (Zygochlamys patagonica), the Argentine hake (Merluccius hubbsi), and the Argentine squid (Illex argentinus) fishery fleet operate. These images reveal the structure of these very rich benthic communities, in which echinoderms, mainly ophiuroids, are one of the dominant groups.

In this study, we assessed the diversity and distribution of sponges of the Order Poecilosclerida from the Burdwood Bank (BB), including the Namuncurá–Burdwood Bank Marine Protected Areas I and II, considering samples collected during two expeditions onboard the RV ARA “Puerto Deseado” in 2016 and 2017. Additionally, a comparative analysis of species richness and composition between BB and adjacent regions in Patagonia (Tierra del Fuego, Malvinas/Falkland Islands) and the Scotia Arc (South Georgias and South Orkney Islands) was made, employing information from bibliographic sources. A total of 53 species were recorded at BB, including 44 species recorded during the present study and 9 other older records from bibliographic sources. These results doubled the known richness of sponges of this order for the region and provided the most complete and updated checklist. Furthermore, new records and updated information on the distributional and bathymetric ranges of Amphilectus fimbriatus, Amphilectus rugosus, Clathria (Clathria) microxa, Guitarra sigmatifera, Iophon roseum, Lissodendoryx (Ectyodoryx) antarctica, Lissodendoryx (E.) diegoramirezensis, Lissodendoryx (E.) patagonica, Mycale (Carmia) gaussiana, Myxilla (Myxilla) basimucronata, and Stelodoryx argentinae are here provided. Poecilosclerida richness at BB was similar to that found in the Malvinas/Falkland Islands and South Georgias Is., with species composition being more similar among these areas than to Tierra del Fuego (TF). These findings significantly enhance the knowledge of sponge diversity in the region and highlight the relevance of the BB and their MPAs as a hotspot of diversity in the SW Atlantic Ocean.

The contribution of sponges to benthic communities in three areas of the Argentine continental shelf and slope (North, Central and South), between 34° and 55° S and between 47 and 551 m, is presented here. Sponges were recorded as components of the invertebrate by-catch in 51% of the studied sites (133 hauls). On average, sponges constituted 18.01% of the benthic community (47.91 kg/mn2, in terms of density), reaching more than 90% of the by-catch and more than 500 kg/mn2 at some particular sites. A total of 34 sponge taxa were recorded. Tedania spp., Clathria (C.) microxa and Callyspongidae (Siphonochalina fortis + Callyspongia sp.) were the only taxa shared among the three sampled areas. Sixty percent (60%) of the sponge species were recorded only at one or two sites.

The phenomenon of subtidal organisms arriving, accumulating, and depositing onto the beach is not unusual, although they have been seldom documented in South America, especially regarding marine invertebrates. In this study twelve major events that happened at the Atlantic South American shorelines between 35 degrees and 38 degrees S during the austral summer of 2022-2023 were investigated. The arrivals were mainly composed by egg capsules of the gastropod Pachycymbiola brasiliana and by colonies of the hydroid Amphisbetia operculata. Prior to these events, persistent winds from the north/northeast quadrant that promoted moderate to strong currents toward the coastline were recorded. The compilation of other historic events reveals that the 2022-2023 are probably the largest and best documented events involving these species. Great mortality of recruits of the gastropod Pachycymbiola brasiliana may have consequences for the species as well as other members of the local assemblages and food webs. Contrarily, to established populations of the hydroid Amphisbetia operculata, these events pose minimal biological or ecological threats. Unpleasant subsequent conditions for tourists at the beaches are caused by the wrack. This contribution also draws attention to the lack of legislation in Argentina regarding how this wrack should be removed from the beaches.

In this study the finding of the sponge Clathria (Clathria) unica in coastal waters of Mar del Plata city (38 degrees 14 ' 24 '' S, 57 degrees 27 ' 30 '' W), Argentina, at the formation called 'Banco de Afuera', is reported. This record constitutes the northernmost record of the species, which was known until the present study only from its type locality in San Antonio Oeste, R & iacute;o Negro province. Additionally, the bathymetric range of the species is updated from intertidal to 20 m. Other two common sponge species, Cliona aff. celata and Spongia (Spongia) magellanica, were also recorded in this environment for the first time.

In the present study we update the distributional, bathymetric ranges and taxonomic characters of the carnivorous sponge Asbestopluma (Asbestopluma) magnifica Lopez, Bravo & Hajdu, 2011 providing new records for Argentinian jurisdictional waters in the SW Atlantic Ocean, including the Marine Protected Area Namuncur & aacute;/Burdwood Bank. The shallowest bathymetric range is now changed to the upper bathyal (289 m depth). We also amend the original description after re-examination of type materials, when markedly different micrometric values were observed for their subtylostyles and acanthotylostrongyles. We noticed a remarkable similarity between Asbestopluma (Asbestopluma) sarsensis Goodwin, Berman, Downey & Hendry, 2017 and A. (A.) magnifica and we suspect they may be synonymous, but we refrain from taking a formal decision pending revision of all materials reported for the younger taxon or a genetic analysis.

The South Orkney Islands (SOI) is a poorly studied Antarctic archipelago located in the Scotia Arc. In this study, we added 25 Demospongiae species to the SOI known sponge richness, which was previously represented by only 16 species. Of these, 22 species represent new records for SOI region, although they were previously recorded from other Antarctic sectors. Samples were collected during two Argentinean Antarctic Research Cruises onboard RV Puerto Deseado. The most frequently collected species were Artemisina apollinis, Iophon gaussi, I. unicorne, Lissodendoryx (E.) ramilobosa, Myxodoryx hanitschi and Tedania (T.) tantula. Data and illustrations of some rare or uncommon species are provided: Iophon gaussi, Lissodendoryx (E.) anacantha, Microxina charcoti, Raspailia (H.) hentscheli, Haliclona spongiosissima, Haliclona (G.) cf. cucurbitiformis. Although the present results increase substantially the previously known information on sponge species, this is still an underestimation of total richness because certain orders (Tetractinellida, Suberitida, Biemnida, Polymastiida) and classes were not studied during the current investigation, although previous records were included.

A detailed analysis of the richness and abundance of invertebrates associated with three common sea fan species at Burdwood Bank is provided. Samples were acquired during a research cruise on board the RV Puerto Deseado (Argentina) in 2017. Thouarella sp., Dasystenella acanthina, and Bayergorgia vermidoma were frequently encountered octocoral species and found to provide habitat to at least 65 associated taxa. The majority of the recorded associate fauna consisted of filter or suspension feeders. Polychaetes and ophiuroids were the most frequently observed associated organisms, followed by bryozoans, bivalves, and brachiopods. We also report the presence of acariids on B. vermidoma and foraminifers on both Thouarella sp. and B. vermidoma. Dasystenella acanthina and Thouarella sp. have a complex three-dimensional structure. This increases the available substrate area for other organisms, thereby increasing the seafloor heterogeneity, which is demonstrated by the high richness and abundance registered here. In this sense, they act as habitat and niche multipliers, which led them to contribute structurally and functionally to the studied marine animal forests.

The world's oceans designated under marine protection have increased recently. Most marine protected areas (MPAs) target vulnerable, keystone, charismatic, and/or endemic species. In the sub-Antarctic, ocean protection is associated with oceanic islands, except for the MPAs Namuncura-Burdwood Bank I and II (MPA N-BB; similar to 53-55 degrees S, similar to 56-62 degrees W), which are associated with a submarine plateau and a southern deep slope, respectively. We present the first analysis of the predator-prey network for the MPA N-BB, applying a topological network approach to characterise the complexity and structure of the food web and to identify the species' role. The MPA N-BB food web consists of 1788 interactions and 379 species, with a connectance of 0.01. Almost half of the consumers feed at more than one trophic level (0.48), and the network displays a small-world pattern (short path length, high clustering of compartments). This network pattern suggests that the ecosystem might be vulnerable to perturbations targeting highly connected species, although some properties might provide resilience and resistance, resulting in a rearranged structure that preserves its original functions. Several species arise as being important in trophic structure and functioning and response to perturbations. Generalist species, mainly fishes, play a crucial role in the bentho-pelagic coupling and should be considered as relevant energy transfer agents for the ecosystem. We argue that the diversity of species, including both the benthic and pelagic habitats, is responsible for securing the connectivity within the food web to withstand perturbations, thereby contributing to the structure and stability of the ecosystem.

The Parapaguridae comprises hermit crabs that inhabit deep-water environments. In these environments, shell availability can be limited, mostly consisting of small and fragile-shelled gastropods. Thus, different strategies have evolved to mitigate this limited shell supply. Sympagurus dimorphus (Studer, 1883) lives in association with a zoanthid cnidarian that creates a pseudo-shell that grows with the hermit crab. In contrast, Oncopagurus gracilis (Henderson, 1888) inhabits small, calcified gastropod shells. Therefore, we selected these two species as models to test sexual dimorphism and shape patterns of their chelipeds and cephalothoracic shield, due to their different shelter acquisition methods. We photographed the animals and digitized the images to employ comparative geometric morphometric techniques. We tested the differences in shape between the sexes within each species, and also tested sexual size dimorphism based on centroid size. For O. gracilis, we found shape differences for the chelipeds and cephalothoracic shield, however, we observed sexual size for the For S. dimorphus, an inverse pattern was found, in which females presented more robust chelipeds, and sexual size dimorphism was present in which males were larger. These differences can be reasonably explained by their shelter acquisition methods, in which O. gracilis depends on small shells that limit growth, while S. dimorphus grows with its cnidarian pseudo-shell. The robustness found in the shape patterns may also be related to their behaviors, e.g., in addition to competition for shells, they also fight during mating. However, we emphasize that future studies with other populations of these species are needed for comparative purposes.

There has been confusion regarding the specimens identified as "Dendrilla membranosa (Pallas, 1766)" in Antarctic and subantarctic waters, considering that the original description corresponded to specimens from the Indian Ocean. In this study, we clarified the identification of the specimens collected in Argentinian waters, SW Atlantic Ocean, that should be identified as Dendrilla antarctica Topsent, 1905, updating its distributional range and considering the new records reported in the present study.

The invertebrate by-catch of the Argentinean squid Illex argentinus collected by bottom trawls off San Jorge Gulf during an expedition performed in December 2020 was employed to characterize the bottom assemblages of the area, with special emphasis on sponges. According to the results, sponges were conspicuous and abundant components in these benthic communities, representing up to 40% of the total invertebrate by-catch (average: ~130 kg·nm2 per site). Tedania (T.) mucosa was the dominant species. Other recorded species were T. (T.) charcoti, T. (T.) murdochi, Isodictya verrucosa, Iophon proximum, Clathria (C.) microxa, C. (C.) discreta, Haliclona bilamellata, Siphonochalina fortis, and Myxilla (M.) mollis. The results of this study contribute to filling in the gaps in the distribution records of sponges in the continental shelf of Argentina in a previously poorly studied area.

In this study we report the presence of the soft coral Verticillata castellviae at 947 m deep, off Buenos Aires Province, Argentina, which constitutes the northernmost record for this species. The specimen was collected as a bycatch species with a troncopyramidal trap during an experimental cruise devoted to the study of the red crab Chaceon notialis and the Patagonian lobsterette Thymops birsteini.

The Argentinian 2012 Summer Antarctic Expedition took place in the austral summer of 2012. One of its goals was the study of the benthic communities, considering the biodiversity and the distribution of the species around the Antarctic Peninsula and neighbouring islands. Samples were mainly collected by bottom trawling at eight locations. Sponges were sorted from the total catch, photographed, labelled, and frozen onboard, while identification was carried out using the classical methodology at the Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP, Argentina). In this preliminary study, we provide data on sponges belonging to the Demospongiae Class. A total of 34 samples were collected, and at least 24 morphospecies were identified. The most represented Order was Poecilosclerida with 18 taxa (Isodictya erinacea, I. lankesteri, I. cf. verrucosa, Mycale (Oxymycale) acerata, M. (M.) cf. tridens, Phorbas glaberrimus, P. acantochela, Lissodendoryx (Ectyodoryx) anacantha, L. (E.) ramilobosa, L. (L.) flabellata, Artemisina apollinis, Myxodoryx hanitschi, Clathria (Axosuberites) nidificata, Tedania (Tedaniopsis) charcoti, Iophon unicorne, I. cf. aceratum, Myxilla (M.) mollis, and Kirkpatrickia aff. coulmani), followed by Haplosclerida with 5 taxa (Haliclonissa verrucosa, Haliclona sp., Calyx cf. arcuarius, Microxina charcoti, and Hemigellius cf. pilosus). The most frequently recorded species was Mycale (O.) acerata followed by species of the genera Isodictya and Lissodendoryx. Some of the recorded taxa such as Phorbas glaberrimus, Myxodoryx hanitschi, Phorbas cf. acanthochela, and Raspailia (Hymeraphiopsis) hentscheli have only scarce records in this region. The results of this study greatly contribute to the knowledge of the distribution and biodiversity of Antarctic sponges, a very important component of the benthic communities.

Tehuelche scallop, Aequipecten tehuelchus , is a commercially exploited species in Northern Patagonia, Argentina. Without genetic differentiation at the species level, A. tehuelchus presents three morphotypes: tehuelchus , madrynensis , and a non-common variant felipponei . The main goal of this study was to analyze the shell shape variation of Tehuelche scallop to differentiate and identify the phenotypic stocks. The shape differences between and within the two main morphotypes ( tehuelchus and madrynensis ) were assessed using geometric morphometrics in nine localities. The shell shape presented variability at geographic scale, with the morphologic traits that maximized the differentiation among localities between the tehuelchus and madrynensis morphotypes. Scallops from madrynensis morphotype presented higher and circular shell discs with smaller auricles than those from tehuelchus morphotype. Morphometric differentiation was also detected among localities of each morphotype, wherein most of the variability was related to the disc circularity and the symmetry of the auricles. The presence of morphologic variation in San Matías and San José gulfs, wherein a single genetic pool is shared, evidenced the plastic nature of the species. Given the distribution of this resource in distinct provincial jurisdictions, the differentiation of phenotypic stocks has relevance in the context of fishery management, especially if zoning and rotational strategies are implemented.

Two nor-diterpenes, 9,11-dihydrogracilin A (1) and the previously unreported 9,11-dihydrogracillinone A (2), were isolated from the sponge Dendrilla antarctica. The sponge was collected by trawling at a depth of 49 m, from the research vessel Puerto Deseado, near the coast of Tierra del Fuego, farther north than the reported habitat for this species. Since these compounds were particularly abundant and the sponge was free from epibionts, both 1 and 2 were included in soluble-matrix paints and tested for antifouling activity in the ocean. The results obtained from these experiments clearly indicated a potent antifouling activity for both compounds against a variety of colonizing organisms, and established a probable role as natural antifoulants for these abundant secondary metabolites and other structurally related compounds previously isolated from Dendrilla spp.