Tropicalization of demersal megafauna in the western South Atlantic since 2013

Abstract

Temperatures in the southwest South Atlantic Ocean have increased over recent decades due to changes in Brazil's Current dynamics affecting marine ecosystems. However, the effects of ocean warming on demersal fauna in the region are poorly understood. Here, we analyse megafauna species composition, and changes in biomass of species with warm- and cold-water affinities for 29,021 commercial demersal catches landed in the harbours of Santa Catarina state, Brazil, between 2000 and 2019. We find evidence of megafauna tropicalization in the Brazilian Meridional Margin during this period. The mean temperature of catches has increased sharply since 2013, with the averaged optimal temperature preferences of all species in commercial catches in one year increasing at a rate of 0.41 °C yr−1. These changes in the mean temperature of the catch correlate well with model-based bottom water temperatures (with 0 and 1-year time-lag) and transport volumes of the Brazil Current (with 3 and 4-year time-lag).

Report of the Workshop to Finalise the Review of the Franciscana (Curitiba, Brazil, 4-5 June 2022)

“…Recent samples analysis from franciscana diet indicated mainly whitemouth croaker (Micropogonias furnieri) and king weakfish (Macrodon ancylodon) as prey. However, new tropical fishes are being observed in diet analysis, suggesting vague niches or the tropicalisation of the southern region of Rio Grande do Sul, southern Brazil (FMA III) as has been observed of commercial demersal catches in the area (Perez and Sant'Ana, 2022).…”

A blueprint for integrating scientific approaches and international communities to assess basin-wide ocean ecosystem status

“…Such changes may trigger oscillations such as those seen in the biologically diverse communities associated with cold-water corals off western Scotland, which switch between cooler and warmer water affinities according to the state of the North Atlantic Oscillation 62 . In the South Atlantic, widespread declines in catches of cooler water species of groundfish on the Brazilian Meridional Margin 63 and cooler water species of large migratory pelagics throughout the South Atlantic may also be related to positive thermal anomalies, although the effects of fisheries pressure cannot be discounted and may be synergistic.…”

Poleward catch displacement of blackfin tuna Thunnus atlanticus in the southwestern Atlantic Ocean: Possible effect of increasing water temperatures

“…Distribution shifts of marine fish are related to climate change worldwide (Cheung et al., 2013; Last et al., 2011). In the southwestern Atlantic Ocean (SWAO), ocean warming is presumably responsible for a poleward shift of several essential fish stocks (Franco et al., 2020; Gianelli et al., 2023; Perez & Sant'Ana, 2022), increased sensitivity of commercially critical species (Gianelli et al., 2023), and long‐term replacement from cold‐water to warm‐water species in industrial fisheries of Uruguay (Gianelli et al., 2019). Evidence suggests that the Brazil Current is intensifying and shifting southwards, thereby causing intense ocean warming along its path, the South Brazil Bight, and in the Río de la Plata (Franco et al., 2020).…”