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The deep-sea crab Chaceon notialis is distributed along the continental shelf and slope of the SW Atlantic Ocean, mainly in Uruguayan waters, supporting a male-only fishery of high commercial value since 1993. A long-term study of catch per unit of effort (CPUE), population structure and individual weight was carried out before and after the onset of exploitation. Some 23,000 individuals were collected at 300–900 m depth and between latitudes 35°00′ and 36°40′S during seven fishery-independent trap surveys. Additional data on weight and individuals with signs of molting were gathered from 1000 to 1600 m south to 37°00′S after the start of the fishery. Individual weight decreased markedly over time, particularly after the start of the fishery, and decreased with depth for both sexes, with opposite patterns with latitude. CPUE peaked at 900 m and 35°40′S and remained stable over time, suggesting that it does not reflect the condition of the stock. Ovigerous females were found between 300 and 500 m and in the northernmost edge of the distribution range (35°00′S–35°40′S). The number of females decreased exponentially with depth and linearly with latitude. Molting males and females followed opposite latitudinal patterns, with highest percentages of molting individuals found between 600 and 900 m depth. A spatial management framework is proposed, which includes closing areas to fishing where ovigerous females, juvenile crabs and largest males are concentrated. [ABSTRACT FROM AUTHOR]

Abstract: Spatial heterogeneity is a conspicuous feature in life history traits of the deep sea red crab Chaceon notialis in the Southwestern Atlantic Ocean. However, a quantitative assessment of its spatial distribution in Uruguayan waters is lacking. A fishing survey was conducted in 2005 between latitudes 35°00′S and 37°00′S, water depth ranging from 300 to 1600m. A likelihood-based geostatistical approach showed a persistent spatial structure of the red crab for both the whole population and the harvestable stock, with global biomass estimates of 55,054t and 34,870t respectively. Similar estimates were provided by the “effective fishing area” technique (53,800t and 36,400t, respectively). C. notialis showed clear large-scale patterns: (1) concerning latitude, the highest density and CPUE were found between 35°40′S and 36°20′S. Males were mainly concentrated between 35°20′S and 36°00′S, whereas the relative representation of both ovigerous and non-ovigerous females increased at the northern end of the study area. Male individual weight increased asymptotically towards higher latitudes, while females followed the reverse pattern. (2) Bathymetric analysis showed the highest density and CPUE at depths close to 900–1100m, coinciding with the highest representation of males. By contrast, females mainly occurred in shallower waters (300–500m), and ovigerous females only between 300 and 400m. Individual weight of males and females consistently decreased from 300 to 1600m. Proportion of molting males increased with latitude and depth, whereas molting females followed the reverse trend. Spatially explicit management tools are suggested, including fishing closures between 300 and 500m depth and between latitudes 35°00′S and 35°40′S (main spawning area with the highest proportion of females) and at depths>1200m (recruitment area). [Copyright &y& Elsevier]

Abstract: Deep-sea red crabs Chaceon ramosae and Chaceon notialis are commercially and ecologically important crustaceans in South Atlantic waters. With some overlapping occurring at the edge of the crabs’ distribution, the fisheries are managed separately in Brazil and Uruguay, with some differences in the regulations, although the stock is supposedly shared between the two countries. To assess genetic information on these two species, we examined the nucleotide sequence of the mitochondrial 16S rDNA and CO1 mtDNA genes in samples from the southern region. We also compared these data to sequences from other congeners. The genetic analysis revealed a clear separation between C. notialis and C. ramosae. In addition, we detected the existence of at least two different groups within the species that is currently recognized as C. notialis. This might indicate the existence of cryptic species, leading us to speculate about the presence of two different taxonomic entities, although further research is needed to resolve this issue. [Copyright &y& Elsevier]

The yellow clam Amarilladesma mactroides (Reeve, 1854) inhabits the intertidal zone of sandy beaches along the temperate Atlantic coast from Brazil to Argentina (24°-41°S). Over the past decades, there has been a noticeable decline in its abundance, underscoring the importance of understanding their reproductive strategies and phenotypic plasticity for conservation efforts. This study explored large-scale variations in the size at first sexual maturity (SL 50), the age at maturity (A 50), the vitellogenic oocyte area (VOA), and a reproductive age index (RAI) that combines A 50 and the lifespan of each clam population, in relation to local habitat characteristics (e.g., beach morphodynamics) and large-scale environmental variables, such as salinity, sea surface temperature (SST) and chlorophyll- a. Four sandy beach clam populations from Uruguay and Argentina (latitudinal range: 33°45′S - 38°56′S) were sampled monthly between June and August during the reproductive season. SL 50 increased linearly with the mean and maximum SST (SSTmean, SSTmax), while VOA and RAI decreased with tidal range and width of intertidal zone, respectively. In beaches that had higher SSTmean and SSTmax, yellow clams reached maturity earlier and spent more than 70% of their lifespan in reproduction. The yellow clam population at the lowest latitude showed the largest oocyte sizes and a shorter lifespan of 3.5 years, while the population at the highest latitude had a longer lifespan (7 years) and the smallest VOA values. Populations at intermediate latitudes showed delayed sexual maturity, a 50–60% investment of their lifespan in reproduction, the longest lifespan (up to 9 years) and intermediate VOA values. The influence of the Rio de la Plata and Bahia Blanca estuaries modified the expected latitudinal gradient in reproductive traits, but local habitat conditions prevailed over large-scale environmental variables as explanatory factors of the reproductive strategy of the yellow clam. Therefore, the species displays phenotypic plasticity in its reproductive aspects to ensure population success. • Sea surface temperature explained between-beach differences in yellow clam maturity. • Estuaries modified the expected latitudinal gradient in reproductive traits. • Local factors prevailed over large-scale environmental ones in reproductive strategy. [ABSTRACT FROM AUTHOR]

The red crab Chaceon notialis is endemic to the Southwestern Atlantic (Brazil, Uruguay and Argentina), occurring from 200 to 1600 m deep. The species belongs to the Geryonidae family and exhibits a K-strategist life cycle. Due to its increased exploitation over recent decades, this marine resource requires attention regarding its conservation and management. In this work, were analyzed red crab populations from the three countries that cover the species' entire distribution range, assessing diversity and differentiation through morphometric and genetic analyses. The evaluated morphometric measurements were length and width of the carapace; length, width and height of the chelae propodus; and female abdomen width. For genetic evaluation, the following mitochondrial DNA regions were used: the partial 12S gene and the entire Control Region (861 bp); and the partial Cytochrome c oxidase subunit I (1252 bp). The morphometric results showed two distinct phenotypic groups (one from Brazil/Uruguay and the other from Argentina), with significant differences in female abdomen width and chela size. Genetic analyses, however, revealed only a single panmictic population, with no genetic structuring among the analyzed stocks. These findings suggest that the management measures applied in each country will influence the population dynamics of the others, and that international cooperation is necessary for achieving sustainable fisheries of this valuable resource. Since commercial fishing of the red crab C. notialis is not conducted in Argentina, we propose that this area can act as a biological reserve for this species. Due to the commercial importance of this crab, knowledge of the species' diversity is of fundamental importance for its management, conservation, and to provide baselines for future biological and ecological studies. • Morphometric analyses identified two morphologically distinct red crab groups. • Chelae size and abdomen width are the main characteristics that separated groups. • Molecular analyses (mtDNA) identified a single panmictic population. • Planktonic larval distribution may influence the lack of genetic structure. • A coordinate fishery management between countries is suggested. [ABSTRACT FROM AUTHOR]