Zooplankton can amplify changes resulting from physical forcing associated with climate change at interannual and longer time scales, so multi-year time series data for the pelagic assemblage can provide useful information about climate-ecosystem interactions. Zooplankton biomass and taxonomic composition were analyzed for the region over the southern Patagonian shelf (SPS) for March 1994 to 2012 to describe interannual patterns of variation, determine the spatial consistency and dominant scale of temporal variability, and examine their relation to the regional hydrography. The biomass of selected taxa, including primarily copepods, amphipods, and euphausiids, decreased in 2003 and remained low until 2012. These patterns were associated with a moderate increase in sea surface temperature. Our observations could not establish the causal mechanisms, but the observed biomass decrease might be related to variation in northward current flow over the SPS, which is driven by large-scale climatological forcing and would result in reduced cold-water availability over SPS. Understanding the drivers of interannual variability in zooplankton composition and biomass of this ecosystem is essential for prediction of impacts of climate change on the pelagic ecosystem, including important commercially fished species.

On the southern Patagonian shelf (Argentina, 47 degrees-55 degrees S) phyto- and protozooplankton are key structural and functional components of a complex trophic web that sustains commercially important species. During late summer 2004, spatial structure, assemblage species and their association with environmental characteristics of water masses were studied for the 2-200 mu m phyto- and protozooplankton communities. Ultraplankton 2-5 mu m was the most abundant size-fraction (90%), followed by the lower nanoplankton 5-10 mu m (7.5%), the larger nanoplankton 10-20 mu m (1.5%), and microplankton 20-200 mu m (1%). Several of the 319 morpho-species found are potentially toxic taxa (the dinoflagellates Alexandrium tamarense, Protoceratium reticylatum, Dinophysis acuminata, Prorocentrum cordatum, Karenia and amphidomataceans and the diatom genus Pseudo-nitzschia), and this is important since the area sustains significant fisheries. A ultraphytoeukaryotic coccal cell (probably chlorophyte/prasinophyte) (3 mu m), P. cordatum, and a microplankton naked ciliate were the morpho-species with the highest abundance and occurrence. Abundance and biodiversity patterns indicated that the plankton community structure was heterogeneous vertically, cross-shelf, and along-shelf, suggesting shifts in community structure over the region. Five areas with dissimilar plankton assemblages were defined, each corresponding to different environments. Depth, bathymetry, latitude and temperature were the most explanatory variables for the assemblage distribution patterns observed. This south Patagonian region possesses important fisheries and, considering expected environmental changes, our results help to understand the spatial structure of plankton communities over a broad size spectrum.

The first data on the biological features of the Southwestern Atlantic were the result of European expeditions of the eighteenth to nineteenth and early twentieth centuries. Around the 1920s to 1940s, European-born specialists and their local disciples started playing a central role, and locally produced knowledge grew consistently. Early surveys centered on inventorial and distributional aspects of the flora and fauna, in particular mollusks and fishes, followed by community-level investigations including causal relationships with oceanographic settings (water masses, temperature, salinity, nutrients), red-tide outbursts, prospection of fishing grounds, etc. In Argentina, logistical support for the oceanographic cruises was historically associated with the Naval Hydrographic Service and in Brazil with the Brazilian Navy and the Universities of São Paulo and Rio Grande do Sul. As of 2017, in both these countries, there are >30 teaching and/or research institutions totally or partly dedicated to marine studies. Presently, knowledge of the taxonomy and biogeography of the plankton of the Southwestern Atlantic varies greatly among taxa, but several aspects (e.g., vertical distribution patterns, seasonal and especially multiannual variations, life histories, and many others) have received very little attention. Despite limited financial support and adequate floating platforms and equipment, lack of coordinated efforts, and political turbulences, the scientific output of Argentina, and especially Brazil, has grown in the last two decades, doubling from ~1.2% of the world total in 1996 to ~2.4% in 2016.

ABSTRACT Although Serratosagitta tasmanica is widely distributed, there is little information on how hydrology affects its distribution, abundance and demography. In this study we analyzed the distribution, carbon content and population structure of S. tasmanica in the Southwestern Atlantic Ocean. Samples were collected at 34°–39°S (Northern Argentine Continental Shelf in winters of 1999 and 2000) and at 47°–55°S (Southern Argentine Continental Shelf in spring 2005, summer 2006 and winter 2006). The analysis of more than 8500 individuals showed that its dominance decreased spatially from south to north, whereas biomass (mgC/m2) increased temporally by three orders of magnitude between spring (4.06) and summer (12.7). In the southern area the presence of all maturity stages in all seasons suggests year-round reproduction, with maximum reproductive activity in winter. Body length increased with increasing latitude and decreased with temperature. We detected differences in the morphology of seminal vesicles and ovary length between mature specimens. In the northern area all individuals exhibited short-type ovaries whereas in the southern area individuals had either short or long ovaries, suggesting that some individuals of the latter area had been advected from the Southern Pacific Ocean through the water discharged from the Magellan Strait.

The marine cyclopoid Oithona similis sensu lato Claus, 1866, is considered to be one of the most abundant and ubiquitous copepods in the world. However, its minimal original diagnosis and the unclear connection with its (subjective) senior synonym Oithona helgolandica Claus, 1863, may have caused frequent misidentification of the species. Consequently, it seems possible that several closely related but distinct forms are being named O. similis or O. helgolandica without explicit and accurate discrimination. Here the current situation concerning the correct assignment of the two species is revised, the morphological characters commonly used to identify and distinguish each species are summarized, and the nomenclatural implications of indiscriminately using these names in current taxonomic and ecological practice is considered. It is not intended to upset a long-accepted name in its accustomed meaning but certainly the opposite. "In pursuit of the maximum stability compatible with taxonomic freedom" (International Commission of Zoological Nomenclature), we consider that reassessment of the diagnostic characters of O. similis sensu stricto cannot be postponed much longer. While a consensus on taxonomy and nomenclatural matters can be attained, we strongly recommend specifically reporting the authority upon which the identification of either O. similis s.l. or O. helgolandica s.l. has been accomplished.

[This corrects the article DOI: 10.3897/zookeys.552.6083.].

With the aim of studying population aspects of Themisto gaudichaudii, samples from 12 research cruises carried out in different seasons were analyzed. Abundances and biomass were among the highest recorded for the species throughout its distribution range. These parameters showed a strong seasonal variation with the highest values recorded during spring-summer (maximum at the end of the period: 16.6 ind. m-3 and 20 mg m-3), and minimum values in winter (0.9 ind. m-3 and 1.7 mg m-3). The highest concentrations were located between 50° S and 52° S in the Bahia Grande. These biomasses would be developed by adaptations to local environmental conditions, particularly to high food availability and temperature. The population of T. gaudichaudii analyzed presents a more extended reproductive period (spring-summer), a larger number of cohorts (two main cohorts) and a smaller size at maturity (~ 10 mm) than other populations at similar latitudes. These adaptations would favor a larger population of T. gaudichaudii placing the ecosystem of the southern Patagonian shelf among the most favorable for the development of the species throughout its global distribution range. † Dr. Hermes W. Mianzan passed away on July 9, 2014.

Surveys conducted during spring, summer and late winter in 2005–2006 over the southern Patagonian shelf have allowed the seasonal distribution of mesozooplankton communities in relation to water masses and circulation to be investigated. In this system, most of the shelf is dominated by a distinct low salinity plume that is related to the runoff from the Magellan Strait (MSW), while the outer shelf is highly influenced by the cold and salty Subantarctic water (SAW) of the boundary Malvinas Current. Separating these two, the Subantarctic Shelf water mass (SASW) extends over the middle shelf. Correspondingly, the structure of the MSW and SAW mesozooplankton communities was found to be clearly different, while the former and the SASW assemblages were barely separable. This relatively fresh water mass is actually a variant of Subantarctic water that enters into the region from the south and the shelf-break, and hence its mesozooplankton community was not significantly different from that of the SAW water mass. Dissimilar species abundance, in turn associated with different life histories and population development, was more important than species composition in defining the assemblages. Total mesozooplankton abundance increased about 2.5-fold from the beginning of spring to late summer, and then decreased at least two orders of magnitude in winter. Across all seasons copepods represented >70–80% of total mesozooplankton over most of the shelf. Copepod species best represented through all seasons, in terms of both relative abundance and occurrence, were Drepanopus forcipatus and Oithona helgolandica. Although seasonal differences in abundance were striking, the spatial distribution of mesozooplankton was largely similar across seasons, with relatively higher concentrations occurring mainly in Grande Bay and surroundings. The well defined spatial patterns of mesozooplankton that appear from our results in conjunction with the southward wide extension of the shelf and the predicted current path and speed suggest that plankton production is locally enhanced in the Grande Bay area and has the potential to be exported downstream.

The copepod community structure, with special emphasis on small-sized species, was studied over the southern Patagonian shelf in late summer 2004, applying the first plankton sampling in the region with a fine-mesh (66 μm) net. The key role of the copepods Drepanopus forcipatus and Calanus australis was confirmed, but also the high abundance and frequency of occurrence of the microcopepods Oithona helgolandica and Microsetella norvegica and of the medium-sized copepod Ctenocalanus vanus were revealed. Copepod community structure was nearly homogenous over the entire study area. Drepanopus forcipatus, O. helgolandica and M. norvegica were identified as the typical species of the region, although secondarily C. australis and Oithona atlantica also contributed significantly to community similarity across the area. The study of interspecific relationships of dominant copepods indicated that D. forcipatus and C. australis were associated positively with O. helgolandica, while C. vanus, and M. norvegica constituted a separate assemblage with Clausocalanus brevipes and O. atlantica. The importance of fine-mesh-size nets for collecting the smaller size fractions of mesozooplankton and for accurately portraying the mesozooplankton assemblage structure in the area is stressed by this study.

Drepanopus forcipatus and Calanus australis are key planktonic copepods on the southern Patagonian shelf. Their feeding and reproductive patterns and population status were investigated during late summer, when environmental conditions may be critical. The presence of food in the gut and food-pellet length were recorded in adult females and the most abundant copepodite stages. Diet composition was also studied in adult females. Female reproductive status was evaluated by gonad staging. Despite generally low feeding conditions and decreasing seasonal temperature, both copepods fed to some degree. The most numerous copepodites and adult females of both species showed similarly low feeding activity. About half of the adult females of the two species and C5s of C. australis contained food in their guts, but the proportion of fed C4-females of D. forcipatus was much lower. All copepods were generally feeding at low or intermediate levels. Gonad stage distribution and population structure showed low but still ongoing reproduction in both species. Gut content findings suggest a preference for smaller nanoplanktonic particles, especially dinoflagellates by D. forcipatus, and for autotrophic prey, particularly large diatoms by C. australis. The feeding and reproduction patterns of the two copepods were likely influenced by the distributions of potential food resources and temperature.

We investigated the spatial distribution of the abundance, biomass and size of zooplankton (nauplii, calanoids, cyclopoids and appendicularians) in relation to the distribution of first-feeding larvae and eggs of Engraulis anchoita across the frontal system of Peninsula Valdés. Twelve samples of zooplankton and ichthyoplankton were taken with small Bongo (67 μm) and Pairovet (200 μm) nets during the spring of 2004 along two transects. The total abundance of zooplankton and the chlorophyll a concentration were higher in homogeneous waters, while total biomasses were higher in stratified waters. Temperature was negatively correlated with biological variables and was the main factor affecting the zooplankton distribution. In both transects, abundance peaks of first-feeding larvae were detected at coastal stations along with the smallest fraction of zooplankton ( < 500 μm), while the largest fraction was dominant at the external stations, coinciding with the highest egg abundance. The physical structure of this front generates different levels of food availability for first-feeding larvae. Calanoids (southern transect) and cyclopoids (northern transect) are predominant followed by nauplii and appendicularians. The biomass of zooplankton preys contributes to the carbon transfer to the upper trophic levels and is probably important for the survival and growth of anchovy larvae in this frontal system.

A strong interest in the southern Patagonian shelf has emerged in recent years, along with the increasing recognition of its high biological productivity. Knowledge of the pelagic food web structure that supports the richness of this system is still developing, but there are indications that mesozooplankton occupy a pivotal position, as consumers of smaller plankton and as vital prey for fish and squid. All plankton communities in the size 2μm–20mm, total and size-fractioned chlorophyll a (Chl a), nutrients and hydrology were surveyed simultaneously in October 2005 between 47°S–55°S. Picoplankton, nanoplankton and microplankton were taxonomically and functionally (autotrophs, heterotrophs) sorted within each size fraction. Plankton data and trophic relationships were examined through multivariate statistics. At that time fairly homogeneous thermal conditions prevailed over most of the shelf but weak saline horizontal gradients were evident. N/P ratios indicated no N or P limitation for phytoplankton. Surface concentrations of total Chl a were particularly high in the Grande Bay area at ca. 51°S near shore (28.6mgm−3) and at ca. 47°S on the shelf-break (7.7mgm−3). At both locations the contribution of the Chl a>5μm fraction was remarkably high. The dinoflagellate Prorocentrum minimum (10·106cellsL−1) and the diatom Thalassiosira cf. oceanica (1.3·106cellsL−1) were respectively blooming at these sites. Otherwise <10μm plankton prevailed overall. Copepods largely dominated the >200μm fraction. Three mesozooplankton assemblages typical of the inner, middle, and outer shelf were identified. The inner and middle shelf assemblages overlapped slightly but were spatially separated from the outer shelf community. Adults and late copepodids of Drepanopus forcipatus were typical of the inner shelf assemblage. Middle-shelf species included the copepod Ctenocalanus vanus, the amphipod Themisto gaudichaudii and the chaetognath Sagitta tasmanica, while an assortment of taxa characterized the outer sector. Latitudinal patterns in mesozooplankton community composition were less noticeable than cross-shelf patterns. No clear distribution of phytoplankton and protozooplankton assemblages was apparent when the whole <200μm plankton community structure was considered. In contrast, communities in the optimal size food for copepods (>10–200μm) were slightly different across shelf. Overall, spatial patterns of mesozooplankton and food availability matched weakly, suggesting a poor coupling between consumers and their prey communities at the time. Significant correlations were found particularly with large autotrophs and heterotrophs.

Three representative copepods occurring in the southern Patagonian shelf, i.e., Calanus australis, Drepanopus forcipatus and Oithona helgolandica were sampled by the first time with paired nets of 66 and 150µm mesh size. The stage-specific estimates of abundance of their populations were statistically analyzed to assess differences in the catchability by both plankton nets. Differences between nets were significant only for smaller developmental stages and species, with higher catchabilities by the 66µm net, while no differences were detected for most of the stages of the medium and large size species. A significant effect of the spatial distribution on the estimates of abundance was detected for the majority of the species and stages but the interaction between mesh size and spatial distribution was not significant. This means that differences between both nets were maintained across the latitudinal gradient. Our results strongly suggest the convenience of using the 66µm plankton net to estimate the abundance of the three copepods' populations. Furthermore, we propose a correction factor to adjust past estimates of abundances from 150µm mesh collections.

The copepods Drepanopus forcipatus and Calanus australis are key species in the mesozooplankton community over the southern Patagonian shelf. Their population abundance, stage composition and vertical distribution within the region were studied during late summer 2000. Individual size of adult females was also examined. Maximum abundances of D. forcipatus were recorded in outer waters of Grande Bay at ca. 51°S and decreased noticeably towards the northern and southern parts of the study area. Calanus australis was much less abundant but rather uniformly distributed over the entire study area. Highest numbers were recorded in the inner area of the Grande Bay and lowest in shelf waters offshore. Both populations were also differently distributed in the water column. Drepanopus forcipatus were concentrated mainly within the upper layers down to ca. 50 m, whereas C. australis were deeper close to the bottom. Late copepodids were dominant in both populations over most of the shelf. Size variation of adult females was much larger in D. forcipatus than in C. australis. Overall, these preliminary data suggest that both copepod species have developed different life-cycle strategies to contend with the suboptimal food conditions that typically follow the spring net-phytoplankton bloom in high latitude ecosystems.

The marine calanoid Calanoides carinatus s.l. (Krøyer, 1848) is a dominant species in productive coastal upwelling regions on the western coast of Africa, the east coast of South America and off Somalia in the Indian Ocean. However, its first description is very short and based on a single female specimen collected in the south-western Atlantic with ambiguity as to the type locality. As a consequence, it appears that closely related, but undescribed, species are still being identified as C. carinatus. We re-describe and illustrate the adult female and male of C. carinatus s.s. from specimens collected from Brazil. We currently restrict the distribution of this species sensu stricto to the coast of Brazil. Nevertheless, it may be distributed along the whole east coast of South America but confirmation of this conclusion awaits genetic evidence. Additional information is presented on the morphology of C. macrocarinatus (Brodsky, 1972) from off the coast of New Zealand, and Brazilian specimens of C. carinatus are compared with C. macrocarinatus. We discuss the status of Calanoides from other localities and consider the availability of names for species we predict may be differentiated from C. carinatus s.s. in the future.

When formulated in mathematical terms, the problem of zoning a protected natural area subject to both box and spatial constraints results in a combinatorial optimization problem belonging to the NP-hard class. This fact and the usual dimension of the problem (regularly in the tens of thousands order) suggest the need to apply a heuristic approach. In this contribution we describe a quantitative method for zoning protected natural areas based on a simulated annealing algorithm. Building upon previous work by Bos (1993), we introduce three main innovations (a quadratic function of distance between land units, a non-symmetric matrix of compatibilities among uses, and a spatial connection constraint) that make the approach applicable for ecological purposes. When applied to solving small-size simulated problems, the results were indistinguishable from those obtained via an exact, enumerative method. A coarse-scale zoning of Talampaya National Park (Argentina) rendered maps remarkably similar to those produced by subject area experts using a non-quantitative consensus-seeking approach. Results are encouraging and show particular potential for the periodical update of zoning of protected natural areas. Such a capability is crucial for application in developing countries where both human and financial resources are usually scarce but still critical for updating zoning and management plans.

This paper provides an overview of the research being carried out at the moment by a group of Argentinean scientists working on the subjects of marine biodiversity and oceanography.When the idea of the Census of Marine Life (CoML) was proposed following the Symposium held during the IAPSO-IABO conference in Mar del Plata in October 2001, there was a wide response from the marine scientific community.Information about current research projects, as well as plans for future work in the context of the CoML, were then obtained from about 70 scientists (Appendix I) belonging to 12 institutions located along the Argentinean coast (Appendix II, Figure 1).This has been used to illustrate what is currently being pursued in marine biodiversity in Argentina and which subjects are considered as priority for future research in the area.This paper is, thus, not an historical update of the knowledge of marine biodiversity, but it attempts to give an idea of the current situation and what is planned for the future.The development of an extensive database of what is known on marine biodiversity in the region is considered to be a necessity, but it constitutes a complete project on its own; as such it is included in the proposals for future work (see Future Work in this paper).It is emphasised that this synthesis is not exhaustive in the content of the topics being studied or in the number of researchers working in marine biodiversity in the country.It is, though, considered to be a representative sample of the knowledge in marine science in Argentina today.This is a starting point for the CoML project in South America and it is hoped that, as it develops, it will be improved by the active participation, advice and experience of many other scientists in the region.