Large-scale connectivity of the sandy beach clam Mesodesma mactroides along the Atlantic coast of South America, and climate change implications.

The yellow clam Mesodesma mactroides is a cool-water species that typifies sandy beaches of the Southwestern Atlantic Ocean (SAO), which embraces one of the strongest ocean warming hotspots. The region is influenced by the Rio de la Plata (RdlP), which represents a zoogeographic barrier that restricts its larval exchange. We investigated yellow clam larval connectivity patterns using an individual based model (IBM). The IBM combined outputs from a 3D hydrodynamic model with a clam submodel that considered salinity- and temperature-dependent mortality for the planktonic larvae. Connectivity across the RdlP estuary occurred only for larvae released in spring during a strong La Niña event. Mortality due to freshwater precluded larval transport across the RdlP, whereas larval mortality induced by warmer waters reduced connectivity, leading to self-recruitment in most areas. Warming acceleration in this hotspot could further restrict larval connectivity between populations in the SAO, with conservation implications for this threatened species.

Linking the scientific knowledge on marine frontal systems with ecosystem services.

Primary production hotspots in the marine environment occur where the combination of light, turbulence, temperature and nutrients makes the proliferation of phytoplankton possible. Satellite-derived surface chlorophyll-a distributions indicate that these conditions are frequently associated with sharp water mass transitions named "marine fronts". Given the link between primary production, consumers and ecosystem functions, marine fronts could play a key role in the production of ecosystem services (ES). Using the shelf break front in the Argentine Sea as a study case, we show that the high primary production found in the front is the main ecological feature that supports the production of tangible (fisheries) and intangible (recreation, regulation of atmospheric gases) marine ES and the reason why the provision of ES in the Argentine Sea concentrates there. This information provides support to satellite chlorophyll as a good indicator of multiple marine ES. We suggest that marine fronts could be considered as marine ES hot spots.

The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Satellite observations.

Satellite-derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf-open ocean exchanges in the western South Atlantic near 35°S. Away from the tropics, these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well-defined seasonal pattern of SSS during the analyzed period and of the location of the export of low-salinity shelf waters. In spring and summer, low-salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36°S to 37°30'S). In contrast, in fall and winter, low-salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low-salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low-salinity waters in the open ocean. KEY POINTS: Satellite salinity sensors capture low-salinity detrainment events from shelves SW Atlantic low-salinity detrainments cause highest basin-scale variability In summer low-salinity detrainments cause extended low-salinity anomalies.