Assessment of coastal pollutants and health status of Pacific oysters (Magallana gigas) in the Bahía Blanca Estuary and adjacent beaches (Argentina).

This study assessed the effects of pollutants on Magallana gigas along a coastal zone with different levels of human activity: a highly impacted zone in the Bahía Blanca Estuary and a less impacted zone on the adjacent sandy beaches. Oysters collected in 2021 were analyzed for various factors, including metals, polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, microplastics, oxidative stress and histology. Oysters of both environments exhibited detectable concentrations of all these pollutants in their tissues. However, the estuarine oysters showed higher concentrations of Zn, Cu and As and total PAHs than the beach oysters. Banned organochlorine pesticides were detected only in beach oysters. Estuarine oysters displayed morphological changes in their digestive gland including a reduction in the mean epithelial thickness of the tubule and elevated lipid peroxidation levels, indicating cellular damage. This study underscores the widespread presence of pollutants in M. gigas, indicating the need for effective strategies to safeguard coastal ecosystem health.

Biological and functional responses of the benthic surf zone community to different beach types.

In this study, we analyzed the biological descriptors and functional traits of the benthic community inhabiting the water/bottom layer in the surf zones of three sandy beaches: a tide-dominated flat, and two intermediate beaches, from tide-modified to wave-dominated. Samples were collected seasonally in the inner surf zone by hand-towing a benthic sledge equipped with two nets, one above the other, across transects parallel to the shore, capturing the benthic community in two levels, close to the seafloor. A total of 116 species were collected, with a total of 327,678 specimens. Arthropods were 99.63% of all individuals caught across the three beaches, mainly represented by peracarid crustaceans. An important species turnover was detected along the shore, with a significant change in community composition. The biological descriptors and some functional traits vary among beaches: the total density, the density of individuals of small (5-10 mm length) and very small sizes (<5 mm length), the density of larval forms, and the presence of colonial species were higher in the tide-dominated flat (sometimes also in the tide-modified beach). More arthropods and more mobile individuals were found in those beaches, while mollusks and sedentary individuals were found in high number in the wave-dominated beach. Stratification was present across the three studied beaches, with higher densities in the near-bottom layer. In the tide-dominated beach, there was also a higher richness in this layer, with a nested community between levels. In the wave-dominated beach, similar richness was registered between levels, with a different community composition (and some differences in functional traits), indicating that some species can maintain their position close to the bottom despite the turbulent conditions experienced on this beach. Differences in wave conditions among beach types could be an important factor driving the biological descriptors and functional traits of the benthic community in surf zone ecosystems. Therefore, acknowledging their role is crucial in deciphering global patterns in surf zone biodiversity.

First records of metal concentrations in the Pacific oyster (Crassostrea gigas) from a Southwest Atlantic estuary.

The Pacific oyster (Crassostrea gigas) is one of the world's most widespread bivalves and a suitable species for biomonitoring metals in coastal environments. In the present research, wild individuals were collected from an Argentinian estuary and the coastal beaches nearby. The concentrations of eight metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were quantified in the soft tissues of the Pacific oyster. Among the metals, Cu, Fe and Zn reached the highest concentrations in the soft tissues over the rest of the elements. The results showed the highest values to be estuary related, with the beach site achieving the lowest values. These results possibly lie on the impact of human activities surrounding the estuary, as well as streams and rivers that outflow within it. Higher Cu and Zn levels, both port related, were mainly found toward the outer estuary. On the other hand, high levels of Cr, Fe and Mn were found toward the inner zone of the estuary, an area with sewage sludge from the cities located on the margins of the BBE. Regarding the potential risk to public health, Cu and Zn levels found in C. gigas were above national and international safety guidelines in 100% and 11% of the samples, respectively.