Abstract

This study examined sediments and foraminiferal assemblages on the inner continental shelf adjacent to Ponta Negra Beach, an important tourist destination in northeast Brazil. Eighteen sediment samples were collected in October 2013, nine each at depths of 5 m and 10 m. The predominance of sandy textures (64–99%), the very limited amounts of organic matter (<4.3%), and minimal differences in surface and bottom temperatures and dissolved O2 concentrations, indicate that hydrodynamics, including waves and currents, are major influences on the sedimentary environment. Foraminiferal species richness was very low; only 11 species were identified in the most species-rich sample and the median for the 18 samples was 5 species. The dominant species were Ammonia tepida, Quinqueloculina angulata, Q. atlantica, Textularia gramen, Bolivina translucens and Pseudononion atlanticum, which are common nearshore shelf taxa. At the 5 m stations, A. tepida and Q. angulata dominated, while at the 10 m stations, T. gramen dominated. Principal Components Analysis revealed four major factors: sand, depth, % gravel and % silt and clay; % gravel correlated positively with % carbonate and % total organic matter in the sediments. Cluster analysis of the foraminiferal data produced two distinct groups corresponding to the 5 m and 10 m stations. In a multidimensional-scaling plot, each group spread along a linear trend from low to higher % carbonate, with slightly higher organic matter in the 10 m samples. Ammonia tepida, an opportunistic and hypoxia-tolerant species, was most dominant near the outlet of the heavily urbanized Potengi River.

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