We examined spatial variations in the biological descriptors of macrobenthic assemblage in relation to environmental parameters and metal distribution in the sediments along a channel of Bahía Blanca estuary affected by non-treatment sewage effluents. Along the channel, metal concentration values were higher than those in the internal estuary area, a sector considered as a reference site. The highest values of water turbidity and metal content in sediments were observed in the effluent discharge zone and at the site where sediments from dredging activities were deposited two years ago. The density of macrobenthic assemblages decreased towards the effluent discharge zone, but the richness and diversity reached to minimum values in both disturbed areas. Only two species of polychaetes were associated with these areas: Laeonereis acuta and Aphelochaeta sp.; the former being found in the effluent discharge zone, where Cd and Pb were most abundant, and the latter being the dominant species in the site characterized by dredging material and high concentrations of Cr and Ni. This study is the first approach to explore the impact of anthropogenic activities over the macrobenthic assemblage of the Bahía Blanca estuary, providing background data to use future management decisions.
The invasive ctenophore, Mnemiopsis leidyi, which had its first mass occurrence in Limfjorden (Denmark) . During that period, copepods and other mesozooplankton organisms were virtually absent while ciliates were a substantial part of the zooplankton biomass. In "pre-Mnemiopsis years", there seems to have been large variability in the grazing impact on zooplankton depending on the seasonal abundance of A. aurita. With the addition of the second carnivore M. leidyi, however, additional predation pressure caused the zooplankton stocks to be severely depressed throughout 2008 and 2009 when copepods and cladocerans no longer showed the high seasonal peaks in abundance typical of previous years.
The objective of this study was to characterize and evaluate morphological alterations and cell and tissue composition of the gill and digestive gland in Magallana gigasfrom urbanized areas with different degrees of human activity over one year. For that, the height of the plicas and filaments of the gill and the tubule epithelium area were measured, the ratio of cell-type and tissue composition analyzed of the digestive gland as well as alterations in the pattern of structural organization in these organs were assessed. The specimens were collected in November 2021, and February, May and August 2022 from two representative sampling sites of distinct anthropic pressures in the coastal area of Buenos Aires Province: Arroyo Parejas (AP, 38° 55’ S, 62° 04’ W) and Pehuén-Có (PC, 39° 01’ S; 61° 32’ W). The results of the morphological parameters, ratio of cell-type, tissue composition and histological alterations of Magallana gigas showed difference between the studied urbanized areas and seasons, suggesting a negative relationship between intense human activity and the health of the gills and digestive gland of the Pacific oyster. Understanding the gill and digestive gland morphology of Pacific oysters, as well as their response to varying levels of human activity in the study region, could help mitigate the impacts of this non-native species.
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