The Amazon River plume, a barrier to animal dispersal in the Western Tropical Atlantic

Abstract

The dispersal of marine organisms can be restricted by a set of isolation mechanisms including hard barriers or hydrological features. In the Western Atlantic Ocean, the Amazon River discharge has been shown to act as a biogeographical barrier responsible for the differences in reef fish communities between Caribbean Sea and Northeast Brazil continental shelves. Here, we compare the diversity of all Animalia phyla from biogeographic ecoregions along the Tropical Western Atlantic continental shelf to test the hypothesis that the Amazon River plume spatially structures species diversity. For that, we used beta diversity estimators and multivariate ecological analysis on a database of species occurrence of the whole animal kingdom including 175,477 occurrences of 8,375 species from six ecoregions along the Western Tropical Atlantic. Results of the whole animal kingdom and the richest phyla showed that the Caribbean Sea and Tropical Brazil ecoregions are isolated by the Amazon River Plume, broadening and confirming the hypothesis that it acts as a soft barrier to animal dispersal in the Western Tropical Atlantic. Species sharing is larger northwestwards, in direction of the Caribbean than the opposite direction. Beyond species isolation due to local characteristics such as low salinity and high turbidity, our results suggest the dominant northwestward currents probably play a major role in animal dispersion: it enhances the flux of larvae and other planktonic organisms with reduced mobility from Brazil to Caribbean and hinders their contrary movement. Thus, the Amazon area is a strong barrier for taxa with reduced dispersal capacity, while species of pelagic taxa with active swimming may transpose it more easily.

Identifying community assembling zones and connectivity pathways in the Tropical Southwestern Atlantic Ocean

“…The dispersal patterns and boundaries of the assembling zones we obtained consistently align with local and regional in situ spatial distribution and abundance patterns of organisms observed in previous studies conducted in the region (Neumann‐Leitão et al 1999, Krajewski and Floeter 2011, Santana et al 2018, Tosetto et al 2022a). These observed patterns encompass a diverse array of marine animal taxa with distinct life histories, ranging from holoplanktonic copepods to reef fish, as detailed in Box 1.…”

Cross-Hemispheric Genetic Diversity and Spatial Genetic Structure of Callinectes sapidus Reovirus 1 (CsRV1)

“…Prior reports of significant genetic differentiation of blue crab hosts between the Caribbean Sea and South America are not surprising due to the large geographic distance and biogeographic barriers between the two continents [ 47 ]. The Amazon River Plume acts as a soft barrier to blue crab larval transport and dispersal in the western tropical Atlantic, as the northwestward currents hinder the movement of larvae from the Caribbean to Brazil [ 76 ]. Coastal barriers to larval dispersal, such as river plumes, can affect population connectivity and gene flow, and may be common features in the ocean affecting a wide range of marine organisms with pelagic larval stages.…”

Community‐scale relationships between body shape and trophic ecology in tropical demersal marine fish of northeast Brazil

“…It is a western boundary current system under the influence of the North Brazil Undercurrent (Dossa et al ., 2022) characterized by a rather low stratification and deep thermocline (from ∼70 to ∼170 m) with warm (typically 26–29°C) and saline (typically 36.5–37.5) waters in the mixed layer (Assunção et al ., 2020). This oligotrophic region (Farias et al ., 2022) is characterized by a relatively high biodiversity (Eduardo et al ., 2018; Giachini‐Tosetto et al ., 2022).…”