Zooplâncton Gelatinoso no Atlântico Tropical Oeste: distribuição, estrutura populacional e ênfase em Pyrosoma

Abstract

Planktonic tunicates of the genus Pyrosoma are part of the gelatinous zooplankton and play a relevant role in the transfer of energy and matter in the ocean, yet they remain underestimated and understudied in the Tropical Atlantic, partly due to their fragility and the limitations of traditional sampling methods. Hydromedusae, another component of the gelatinous zooplankton, shared this history of scientific neglect, with taxonomic records still scarce for the Brazilian equatorial margin. This dissertation investigated, in two complementary chapters, the distribution and ecology of these groups in the Western Tropical Atlantic. Chapter II analyzed the spatial (horizontal and vertical) and temporal (day–night) structure of the genus Pyrosoma in the North and Northeast regions of Brazil, characterizing the physical and chemical variables of the water column (temperature, salinity, dissolved oxygen, turbidity, and fluorescence) and correlating them with colony density (CPUE; colonies·hour⁻¹) and size structure (length in mm). Data were obtained from three oceanographic surveys conducted aboard the R/V Antea , ABRAÇOS I (2015), ABRAÇOS II (2017), and AMAZOMIX (2021), using diurnal and nocturnal oblique trawls with a mesopelagic micronekton net. Analyses included comparisons among regions, depth layers, and time periods (Kruskal–Wallis, Wilcoxon), Spearman correlation, distance-based Redundancy Analysis (db-RDA), and Generalized Linear Models with a Gamma distribution. Chapter III reported the first records of the hydromedusae Leuckartiara octona and Calycopsis papillata (Hydrozoa: Filifera) for the Brazilian Equatorial Margin, based on samples collected during the AMAZOMIX survey. Morphological descriptions of the specimens, density data, vertical distribution, and the environmental conditions associated with the occurrence of each species in relation to the Amazon River plume were presented. Together, both chapters contributed to expanding the knowledge of gelatinous zooplankton diversity and ecology in the Western Tropical Atlantic, highlighting how regional physical-oceanographic gradients, particularly the contrast between the Amazon plume and the oceanic conditions of Northeast Brazil, modulate the distribution, abundance, and population structure of the studied groups.