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Abstract
Along the southeast continental shelf of Brazil, the Paraiba do Sul River (PSR) plays a fundamental role in sediment and nutrient transport. This study focuses on the contribution of the PSR and its effect on the benthic macrofauna. Physical and chemical analyses of the sediment were conducted, and the macrofauna were identified and counted. Multivariate analyses were used to compare the distribution patterns of the benthic assemblages related to the depth gradient over two sampling periods. The principal component analysis showed that shallow waters assemblages are mostly influenced by the environmental descriptors temperature, salinity and chlorophyll a, whereas pheophytin, degree of sediment sorting, total carbonate and organic carbon were correlated with benthic assemblages at greater depths. The high organic enrichment reflected an increase in surface and sub-surface deposit feeders such as the polychaetes Spiophanes sp. and Prionospio cristata and the crustacean Phtisica marinain the deeper stations, with a corresponding decrease in other trophic groups. This study provides evidence of differences in organic matter sources, from primary production in shallow waters to detritus in deep waters. These sources provide different niches for the corresponding macrofaunal assemblages along the continental shelf adjacent to the PSR, with species richness and abundance of benthic populations related to the river output.
Highlights
Depositional organic matter (OM) is a significant source of energy and elemental raw materials for most benthic communities, so sedimentary OM dynamics exert strong control over marine benthic biodiversity
This study focuses on the contribution of the Paraíba do Sul River (PSR) and its effect on the benthic macrofauna
The principal component analysis showed that shallow waters assemblages are mostly influenced by the environmental descriptors temperature, salinity and chlorophyll a, whereas pheophytin, degree of sediment sorting, total carbonate and organic carbon were correlated with benthic assemblages at greater depths
Summary
Depositional organic matter (OM) is a significant source of energy and elemental raw materials for most benthic communities, so sedimentary OM dynamics exert strong control over marine benthic biodiversity. An increase in the amount and quality of OM can lead to an increase in the biomass and density of the benthic organisms and to dystrophic events, such as episodes of hypoxia or anoxia, which can cause massive reductions or elimination of the benthic fauna. Such phenomena are frequent and well documented in the northern Adriatic Sea (e.g., Ambrogi et al 1990, Crema et al 1991, Moodley et al 1998). Field studies (Wijsman et al 1999, Akoumianaki et al 2013) have provided supporting evidence that sedimentary processes in coastal areas that are influenced by smaller rivers are related to the distance from riverine sources
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