The microzooplankton community structure (species abundance, biomass, diversity) was investigated at a coastal marine station on the South-West Atlantic Ocean (34°23′S–53°45′W, Uruguay). This is a hydrographically complex site within the Subtropical Convergence zone of the SW Atlantic where knowledge of the microzooplankton is particularly scant. The main goal was to perform a first characterization of that community and evaluate its association to environmental drivers along an annual cycle. Oceanographic variables (temperature, salinity, irradiance, nutrients, chlorophyll-a) and ciliates (aloricate and loricate), and dinoflagellates were recorded monthly from July 2019 to June 2020. Over 100 microzooplankton taxa belonging to approximately 30 families and 40 genera were identified, including several subtropical and subantarctic species. Community structure followed wide transitions at the seasonal scale – particularly between summer and winter as subtropical taxa alternated with euryhaline taxa from colder subantarctic waters. The core environmental variables (temperature, salinity and dissolved inorganic nitrogen [DIN]) explained overall variance in microzooplankton community assembly. During summer, high temperatures (20.3, 16.3–22.4°C) and low nutrients (DIN: 3.5, 0.7–6.7 μM; PO4: 1.0, 0.8–1.5 μM) benefited the development of aloricate ciliates. A nutrient pulse in winter posed favourable stoichiometric conditions and the numerical abundance was dominated by dinoflagellates and loricate ciliates in the following months, while diversity remained highest (taxonomic richness: 36 [22–46]; Shannon–Wiener index: 2.5 [1.9–2.8]). Results suggested that the microzooplankton community at the study site is mainly structured by hydrographic variability linked to the seasonal replacement of offshore water masses that differed in thermohaline properties and nutrient levels, and local processes.

In South-western Atlantic waters, individuals of the southern right whale (SRW) Eubalaena australis spend part of the year (the austral winter and spring) in northern inshore waters where they breed and then migrate to southern feeding grounds during the summer. Mar del Plata (MDP) is located between two main reproductive areas (Península Valdés-Argentina and Santa Catarina-Brazil). The purpose of the present study is to report the presence of SRWs on their journey off the coast of MDP based on sighting records during the past half century. We carried out whale observations through systematic weekly coastal marine mammal surveys in different points of the MDP area from 1966 to 2016. The first SRW sighting was recorded in 1970; since then, sighting frequency has gradually increased, reaching a peak of 28 sightings (N = 63 whales) in 2016. These are unique long-term sighting records of SRWs in Argentina and the first on their journey off the shores of Buenos Aires province. We expect that these results will help local authorities to regulate tourism and other activities in the area and thereby contribute to the conservation of the species.

The historical and contemporary presence of southern right whales (SRWs; Eubalaena australis) around the Falkland Islands (Malvinas) has received little recognition. We assessed SRW occurrence in the Falklands via whaling records, a literature review, systematic surveys (boat, aerial and shore-based), and citizen science sightings. The combined data sources indicated a year-round (peaking in austral summer) presence of SRWs in pelagic areas around the Falklands. In contrast, most nearshore records originated in the austral late autumn and winter (May to August), including a marked increase in sightings along the north-east coast during 2017 compared with previous years. The data support spatio-temporal variation in the use of Falklands waters by SRWs. Pelagic waters appear to comprise summer foraging habitat, and may also be used by animals migrating between the Patagonian shelf and feeding grounds located further south and east. The peak numbers observed in nearshore waters occurred earlier in the winter (July) than those on the Argentinean or Brazilian calving grounds (Aug–Oct). Consequently, some whales may have continued migrating northwards to established breeding areas after departing Falklands waters. A component of the south-west Atlantic population could also be using the islands as a novel wintering destination, for mating and/or socializing (no calving has been confirmed to date). The importance of Falklands waters as a multi-use SRW habitat appears to be increasing. The region is important in the context of addressing current knowledge gaps regarding feeding grounds and migratory corridors highlighted in international SRW conservation and management plans for the wider South-west Atlantic.

Chondrichthyans are usually caught incidentally in fisheries for species of high commercial value and then discarded on board or landed as by-products. On the coast of Chubut province and adjacent waters (43°00′S–44°56′S) a bottom trawl fishery has developed targeted at the Patagonian shrimp (Pleoticus muelleri) and common hake (Merluccius hubbsi). Since 2005, this fishery has been monitored by the On-board Observers Program of Chubut province (POBCh). With the aim of advancing towards an ecosystem approach, POBCh not only collects information about target species but also about all the species caught by the trawl nets of the province fisheries. From the information collected by this programme it was possible to identify and record the chondrichthyan species vulnerable to the fishing gear used by the coastal fleet that operates from Puerto Rawson. The composition of the fleet catch was characterized according to the target species during the 2005–2014 period. In the analysis of 3786 hauls, 23 species of chondrichthyans (seven species of sharks, 15 species of batoids and a single species of Holocephali) were identified. Seven species showed a frequency of occurrence greater than 10% (Callorhinchus callorynchus, Discopyge tschudii, Mustelus schmitti, Sympterygia bonapartii, Psammobatis normani, Squalus acanthias and Zearaja chilensis). Species spatial distribution was evaluated and five areas of species assemblages were established. Besides the aspects related to bycatch, these analyses have contributed to the knowledge of the chondrichthyan biodiversity in the provincial coast where the fleet operates, a region with incomplete and mostly dispersed and outdated information.

Bycatch in longline fisheries is a major contributor to the global decline of albatrosses. Sexual segregation at sea often leads to unequal overlap with different fisheries, resulting in sex-biased bycatch, exacerbating the impact on a population level. In great albatrosses (Diomedea spp.), males (the larger sex) tend to spend more time at higher latitudes than females, attributed to competitive exclusion or differences in flight performance mediated by the pronounced sexual size dimorphism (SSD). Consequently, larger numbers of females are bycaught in pelagic longline fisheries in subtropical and temperate areas. Although this has been shown for Diomedea exulans, it has not been confirmed for all great albatross species. Here we examined the degree of SSD and developed discriminant functions to determine species and sex in D. epomophora and D. sanfordi; species that are often killed in several fisheries in the Southern Hemisphere. Based on a large sample of albatrosses bycaught off Uruguay, both species showed substantial SSD. Discriminant functions assigned species and sex to otherwise indeterminate individuals with 90–100% accuracy. Based on all birds identified (n=128), bycatch in the pelagic longline fishery was female-biased, indicating sexual segregation at sea. The discriminant functions presented enable species and sex to be identified, providing critical data for future bycatch assessments.

Three new species of paramunnid isopods are described: Pentaceration pleonarietis sp. nov., Neasellus argentinensis sp. nov. and N. bicarinatus sp. nov. The three species were collected off Buenos Aires province, the last one was also collected off Chubut province, Argentine Sea. The species belonging to Pentaceration represents the first record of this genus in the Argentine Sea. The diagnostic characters of the genus Neasellus are revised and besides the inclusion of the two new species herein described, a new combination for the species Pelagogonium oculatum Schultz, 1977 is proposed.

We analysed 267 zooplankton samples collected in the South Brazilian Bight (SBB; 23–27°S) to determine whether hydroids, typically benthic, are common components of the pelagic SBB. Two species, Clytia arborescens, recorded for the first time in the Atlantic Ocean, and Clytia sp. were identified. While these planktonic hydroids were frequent or relatively so in shallow shelf waters (~23% of the samples <50 m isobaths, and 5% of the samples >100 m), abundances were low (up to 61 hydranths m−3) suggesting a low trophic impact. Such colonies are probably fragments of benthic colonies detached by storms and/or tides. Given the good condition of the coenosarc, existence of gastric content, and presence of reproductive structures, development of these species appears to be normal in the pelagic environment. Existence in the plankton may increase their capacity for dispersion.

The interaction between baleen whales and longline fisheries is poorly known worldwide and likely underestimated. This article presents one of the most severe scenarios of this interaction; an incident that resulted in the severe mutilation of the entire fluke of a whale and probably lead to its death. Considering the characteristic of the fluke, we strongly suggest that the fluke belonged to a small balaenopterid, most likely a dwarf minke whale (Balaenoptera acutorostrata). The episode reported here seems to be the first in its nature involving a baleen whale entangled in longline fishing gear off the Brazilian coast, and so, it represents, at the very least, the need for further investigation into the magnitude of such interactions in the south-west Atlantic Ocean.

Five new species of Oncholaimellus are described. They were found in macrofauna samples from the continental shelf in the Potiguar Basin, north-east Brazil. Cuticular pores with a sclerotized outline associated with a gland were observed in some species. Oncholaimellus multiporus sp. nov. is differentiated from other species by the presence of cuticular pores of different sizes; the smaller pores are abundant and give an appearance of ornamentation. Oncholaimellus intersexus sp. nov. and O. distortus sp. nov. are similar, but differ in the size of the external labial and cephalic setae compared to the corresponding diameter, the presence of the cuticular pores and the tail shape. Oncholaimellus paulus sp. nov. and O. sineporus sp. nov. are similar, although features such as the external labial and cephalic setae size compared to the corresponding diameter and the cuticular pores differentiate between them.

We revised the zoogeographical distribution of mysids in the south-west Atlantic, from northern Brazil to Argentina (0° to 40°S), providing body length, and temperature and salinity range of occurrence for each species. All information concerning mysids from the south-west Atlantic was obtained from published/unpublished studies. Of currently 1128 mysids species described worldwide, only 31 were recorded in the south-west Atlantic which are distributed in 14 genera, 6 subfamilies and one family. This extremely low number of recorded species highlights the need for further studies focusing on mysids in the south-west Atlantic.

Global biodiversity declines and increasing rates of extinction necessitate the assessment and prediction of the vulnerability of species to extinction. Here, we examine the relationships between conservation status and ecological traits of reef fish species of the Brazilian biogeographical province. We used binomial tests and a logistic regression to address two questions. Do biological attributes differ between threatened and non-threatened fishes? Which combination of traits and impacts exerts greater influence on species threat status? Of the 559 species, 36 are categorized as threatened (compiled from global, national and local Red Lists). Three species are categorized as Critically Endangered, seven as Endangered and 26 as Vulnerable. Our analyses revealed that Elasmobranchii, sex-changing bony fishes and endemic species are the most vulnerable reef fishes in Brazilian waters. Body size and trophic category were identified as good predictors of the vulnerability of a species to extinction. Small-bodied species that are exploited by the ornamental trade and have complex reproductive strategies are also of concern. Such combinations of attributes could be of value in predicting which reef fish species elsewhere have a high risk of extinction.

This work provides the first information about the stomach contents of juvenile green turtles (Chelonia mydas) on the coast of Rio de Janeiro State, south-eastern Brazil (22°50′S–23°00′S). Between June 2009 and May 2010, we obtained 49 stomach contents of specimens that were stranded, of which 37 contained food items. Among food items, macroalgae stood out with 83.7% frequency of occurrence in the stomachs analysed and 37 species were identified. The most representative macroalgae in the stomach contents were: Sargassum vulgare, Ulva lactuca, Gelidiella acerosa and Pterocladiella capillacea. Teleosts and molluscs were also recorded in the stomach contents of the species in the region; however, with low representativeness. Analysis of stomach contents confirmed herbivory as the preferred dietary pattern of C. mydas.

The analysis of changes in benthic community structure using multivariate techniques has been successfully applied to the detection and monitoring of impacts caused by oil related activities. A survey to assess the status of the benthos was performed prior to a scheduled exploratory drilling at Banco Sarmiento, a shoal located off the eastern mouth of the Strait of Magellan (south-west Atlantic). The aims of this study are to provide baseline data about the composition and structure of the subtidal macrobenthic assemblages, to analyse the relationships between biodiversity and environmental variables, and to compare its benthic assemblages with those of neighbouring areas. Multivariate analyses classified the stations in two major groups, one composed of relatively shallow stations with coarse sediments dominated by filter-feeders, and the other consisting of stations with a high proportion of sand and mud dominated by deposit-feeders. Poorly sorted sediments had higher species richness than well sorted sediments. Shallow stations showed the lowest taxonomic distinctness due to the occurrence of a high proportion of bryozoans encrusting hard substrata. A five-fold increase in biodiversity can occur at scales of tens of km, suggesting that generalizations on regional biodiversity patterns should be made with caution because of the different gears used during the collection of samples, and should be based on a thorough knowledge about the physical environment.

This contribution reports the first record of intertidal reefs built by the sabellariid worm Sabellaria nanella in the lower intertidal at Monte Hermoso beach, Argentina (39°S). All previous records of S. nanella in the study area correspond to solitary individuals from shallow subtidal depths in coastal environments, while the present findings refer to well established reefs on stony rocks. Worms sort medium size sand grains to build the reefs, which contain higher amount of organic matter than the surrounding sediments. Size structure of worms shows multiple size cohorts that include recent recruits and mature adults. Many invertebrates, i.e. various annelids, arthropods, molluscs, nemerteans and nematodes, are the frequent organisms living within the reef, some of them already recorded in the area. The presence of intertidal reefs of S. nanella indicates that the species has plasticity to adapt to environments with different physical conditions (subtidal–intertidal areas).

In the present paper a specimen of the blue runner Caranx crysos, a thermophilic species commonly found in subtropical Atlantic waters, was newly reported from the Mar del Plata coast. The presence of the blue runner in Argentine waters could be explained by the warm drift theory.

The feeding habits of the Rio skate, Rioraja agassizi, from off Uruguay and north Argentina were evaluated using a multiple-hypothesis modelling approach. Relationships between number of preys and sex, maturity stage, body size, season and region were assessed by building generalized linear models. Rioraja agassizi fed mainly upon crustaceans (shrimps, crabs and amphipods) and teleosts, but also upon isopods, cumaceans, lancelets and polychaetes. Ontogenetic diet shifts were found: small R. agassizi consumed amphipods, cumaceans and isopods and large individuals on shrimps, crabs and teleosts. The consumption of crustaceans (amphipods, shrimps, crabs, isopods and cumaceans) was higher in the northern (34°–38°S) than in the southern area (38°–41°S). Rioraja agassizi consumed more teleosts in the cold season and preyed more on lancelets in the warm season. Prey size increased with increasing body size of R. agassizi, but large individuals also consumed small prey. Ontogenetic shifts may be related to body size rather than other life-history traits. Rioraja agassizi adapts its feeding habits in response to regional and seasonal changes.

An inventory of the main epibiont organisms on living specimens, on empty shells and on pagurized shells of Fusitriton magellanicus collected in Zygochlamys patagonica fishing grounds off Argentina is provided here. Additionally, considering that the presence of the thick, hairy periostracum could be an inhibitor of boring and encrusting species, we analyse the presence of a periostracum in living F. magellanicus in relation to the presence of epibionts. More than 70% of all shells bore encrusting organisms (of at least 30 taxa) but only a small proportion of shells was heavily fouled, the majority of living, empty and pagurized shells being lightly or moderately fouled. Polychaetes were the most common epibiont group (present on more than 60% of shells) while sponges and ascidians were responsible for the majority of the heavily fouled living gastropods. In general, specimens had a moderate level of encrustation and, simultaneously, a low or medium coating of periostracum. Hairy gastropods (only 14% of the sampled specimens) had few or no epibionts. A relationship between the size of the shell and the level of encrustation was only found in living gastropods. Fusitriton magellanicus is the second species in importance (after the Patagonian scallop) for the provision of a hard settlement substrate in the shelf-break frontal area of the Argentine Sea.

A morwong (Nemadactylus bergi) specimen was caught in May 2009 by a commercial trawler in Falkland Islands waters, outside its normal sub-tropical distribution. This extends its southwards range, possibly as a result of ongoing global warming.

The present paper reports the occurrence of Polyonyx gibbesi in Argentinean shelf waters and extends its distribution southwards in the western Atlantic. Forty-four specimens of P. gibbesi were found in stomach contents of the narrownose smoothhound shark Mustelus schmitti during November 2008.