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The Southwestern Atlantic Ocean (SWA), is considered one of the most productive areas of the world, with a high abundance of ecologically and economically important fish species. Yet, the biological responses of this complex region to climate variability are still uncertain. Here, using 24 years of satellite‐derived Chl‐a data, we classified the SWA into 9 spatially coherent regions based on the temporal variability of Chl‐a concentration, as revealed by SOM (Self‐Organizing Maps) analysis. These biogeographical regions were the basis of a regional trend analysis in phytoplankton biomass, phenological indices, and environmental forcing variations. A general positive trend in phytoplankton concentration was observed, especially in the highly productive areas of the northern shelf‐break, where phytoplankton biomass has increased at a rate of up to 0.42 ± 0.04 mg m⁻³per decade. Significant positive trends in sea surface temperature were observed in 4 of the 9 regions (0.08–0.26 °C decade⁻¹) and shoaling of the mixing layer depth in 5 of the 9 regions (−1.50 to −3.36 m decade⁻¹). In addition to the generally positive trend in Chl‐a, the most conspicuous change in the phytoplankton temporal patterns in the SWA is a delay in the autumn bloom (between 15 ± 3 and 24 ± 6 days decade⁻¹, depending on the region). The observed variations in phytoplankton phenology could be attributed to climate‐induced ocean warming and extended stratification period. Our results provided further evidence of the impact of climate change on these highly productive waters. 

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 Ni˜na 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. 

The strong interaction between the Brazil Current and the adjacent shelf is clearly visible in satellite‐derived products (sea surface temperature, salinity, and chlorophyll‐a concentration). Assessments of circulation features and cross‐shelf exchanges from these products are, however, limited to the surface layer. Here we analyze the regional circulation and dynamics using the results of a suite of process‐oriented, high‐resolution numerical experiments. Passive tracers and Lagrangian floats characterize the exchanges between the shelf and the open ocean, identifying regions of high variability, and assessing the contribution of small‐scale eddies to the cross‐shelf mass exchanges. We estimate that 0.2–0.4 Sv of the shelf transport variability between 34°S and 25°S comes from ocean internal variability which represents ∼50%–70% of the total variability. Between 25°S and 21°S, internal ocean variability represents more than 90% of the shelf transport variability. We find that generation of cyclonic eddies is more frequent (>15% of the time) at the shelfbreak bights. The core of these eddies contains fresher, colder, and more nutrient‐rich shelf waters. Maps of satellite chlorophyll‐a concentration suggest that the horizontal and vertical exchanges of mass associated with these eddies are a critical element of the primary production cycle.

 

A high‐resolution ocean model is used to characterize the circulation and cross‐shelf exchanges in the Brazilian/Uruguayan portion of the southwestern Atlantic shelf. Cross‐shelf exchanges are strongly modulated by the bottom topography. There is ∼1.2 Sv of on‐shelf transport between 21°S and 25.2°S, and ∼1.6 Sv of off‐shelf transport between 35°S and 25.2°S. North of 25.2°S, the cross‐shelf exchanges show a two‐layer structure with an off‐shelf flow in the upper 50m and on‐shelf flow deep below. A Lagrangian diagnostic shows that ∼0.15 Sv of deep waters from the Brazil Current (z > 200 m) are injected into the shelf. Mixing with ambient waters produces a spicier (warmer and saltier) water mass, which is ejected into the open ocean in the southern region. Backward in‐time particle's trajectories analysis reveals that 95% of the southward shelf transport at 32°S originates in the open ocean at 22°S. Our model diagnostics show that there is a very limited connectivity between the shelf regions north and south of Cabo Frio. Correlation analysis shows no significant influence of El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) on the time variability of the cross‐shelf transport. Cross‐shelf transports, however, are significantly correlated with the local wind stress variability.

 

Studies on latitudinal patterns in plant defence have traditionally overlooked the potential effect that resource availability may have in shaping plant defence. Likewise, latitudinal patterns of tolerance traits have rarely been studied, yet they can be a critical component of plant defence. Therefore, the aim of our study was to examine latitudinal variation in the production of tolerance and resistance traits against herbivory along a latitudinal range and a natural gradient of resource availability from upwelling conditions.

North America (Canada, USA, Mexico).

Summer months of 2015.

The seagrassZostera marina.

We conducted experiments simulating macroherbivore (e.g., bird, fish) damage on the seagrassZ. marinaat 10 sites across the Eastern Pacific coast (Canada–Mexico) and Quebec and analysed several traits related to resistance and tolerance strategies against herbivory. In addition, we examined the effects of potential seagrass changes in defence strategies by performing a series of feeding experiments with mesoherbivores in a subset of sites.

We found that eelgrass resistance defences did not follow a linear latitudinal pattern but rather followed a bell‐shaped curve which correlated with bottom‐up control. In sites with higher nutrient availability, plants allocated resources to tolerance strategies and had lower resistance traits. Furthermore, seagrasses did not respond linearly to increased herbivory pressure; while they tolerated moderate levels of herbivory, they underwent a significant reduction in tolerance and resistance under high herbivory levels, which also made them more susceptible to consumers in feeding experiments.

Our results highlight the importance that nutrient availability has in shaping latitudinal patterns of plant defence against herbivory and show how these defences may not respond linearly to increased herbivory pressure in seagrasses.