Spatial patterns in planktonic cnidarian distribution in the western boundary current system of the tropical South Atlantic Ocean

Abstract

In marine western boundary systems, strong currents flowing coastward spread oceanic water masses over the continental shelves. Here we propose to test the hypothesis according to which oceanic cnidarian species may dominate western boundary system regions even in coastal waters. For that purpose we use a set of data collected above the shelf, slope and around oceanic seamounts and islands in the Western Tropical South Atlantic. Samples were acquired with a plankton net with 300 μm mesh size over 34 stations during an oceanographic cruise carried out in October 2015. Results reveal a diverse cnidarian assemblage in the area, extending the known distribution of many species. In addition, the Fernando de Noronha Chain and most of the narrow continental shelf presented a typical oceanic cnidarian community, dominated by holoplanktonic siphonophores. In this western boundary system, this condition was likely driven by the strong currents, which carry the oceanic tropical water and associated planktonic fauna toward the coast. A specific area with reduced influence of oceanic currents presented typical coastal species. The pattern we observed with the dominance of oceanic plankton communities up to coastal areas may be typical in western boundary systems characterized by a narrow continental shelf.

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

“…The situation is slowly changing as the number of studies on marine biodiversity increased in the recent years in northeast e.g. 34 – 36 and north Brazil e.g. 37 – 39 .…”

First record of Cnidocodon leopoldi Bouillon, 1978 (Cnidaria: Anthoathecata) in the Atlantic Ocean

“…In this particular area, the strong western boundary currents that flow coastward South America, which transports warm and salty water and its associated planktonic fauna over the continental shelf, have its influence reduced due to interactions with bottom topography. Thus, oceanward transport of coastal water is observed in this area (Dossa et al, 2021;Tosetto et al, 2021a). This hydrographic configuration has significant implications in the structure of cnidarian community and possibly the entire ecosystem (Tosetto et al, 2021a).…”

“…Thus, oceanward transport of coastal water is observed in this area (Dossa et al, 2021;Tosetto et al, 2021a). This hydrographic configuration has significant implications in the structure of cnidarian community and possibly the entire ecosystem (Tosetto et al, 2021a). Historically, planktonic cnidarian biodiversity from tropical areas in the western border of the Atlantic Ocean were understudied comparing to subtropical and temperate provinces.…”

“…Historically, planktonic cnidarian biodiversity from tropical areas in the western border of the Atlantic Ocean were understudied comparing to subtropical and temperate provinces. With recent progress in oceanographic research in Northeast Brazil this situation started changing not only for cnidarians (e.g., Farias et al, 2020;Tosetto et al, 2018Tosetto et al, , 2020Tosetto et al, , 2021aTosetto et al, , 2021b but also for other marine animals (e.g., Eduardo et al, 2018Eduardo et al, , 2020Alves-Jr. et al, 2019. Thus, the current report contributes not only to the understanding of local biodiversity, but also for an adequate comprehension of regional and global biogeographic and diversity patterns.…”

Rich and underreported: First integrated assessment of the diversity of mesopelagic fishes in the Southwestern Tropical Atlantic

“…This region holds distinct biodiversity and includes several Marine Protected Areas and Ecologically or Biologically Significant Marine Areas (EBSAs) that, by definition, are special places of fundamental importance for biodiversity and life cycles of marine species (CBD, 2014). Moreover, the SWTA includes different biogeographic provinces with contrasting thermodynamic features, current systems, and water-mass properties, leading to shifts in biodiversity and ecosystems (Bourlès et al, 1999;Pinheiro et al, 2018;Assuncão et al, 2020;Costa da Silva et al, 2021;Dossa et al, 2021;Tosetto et al, 2021;Silva et al, 2022).…”