Assessment of the ecological quality status of the Sepetiba Bay (SE Brazil): When metabarcoding meets morphology on foraminifera

In recent years, the region surrounding Sepetiba Bay (SB; SE Brazil) has become a hub of intense urban expansion and economic exploitation in response to ore transport and industrial and port activities. As a result, contaminants have been introduced into the bay, leading to an overall worsening of the environmental quality. The present work applies for the first time a foraminiferal morphology-based approach (M) and eDNA-based metabarcoding sequencing (G), along with geochemical data to assess the ecological quality status (EcoQS) in the SB. Principal component analysis shows that the eDNA and morphospecies diversity as well as most of the taxa relative abundance decline in response to the environmental stress (ES) gradient related to total organic carbon (TOC) and metal pollution. Based on ecological indices, Exp(H'bc) (G), Exp(H'bc) (M), foraminifera ATZI marine biotic index (Foram-AMBI), Foram Stress Index (FSI), and geochemical indices (TOC and Potential Ecological Risk Index), the lowest values of EcoQS (i.e., bad to moderate) are inferred in the innermost part of the SB. Despite minor discrepancies among the six EcoQS indices, an agreement has been found for 63% of the stations. To improve the agreement between the ecological indices, it is necessary to fill the gap in species ecology; information on the ecology of many species is still unknown. This work reinforces the importance of molecular analysis and morphological methods in environmental impact studies and confirms the reliability of foraminiferal metabarcoding in EcoQS assessment. This is the first study evaluating the EcoQS in the South Atlantic by using combined foraminiferal eDNA metabarcoding with morphological data.

Inferring the ecological quality status based on living benthic foraminiferal indices in transitional areas of the Guanabara bay (SE Brazil)

Using benthic foraminifera, we evaluate the ecological quality status (EcoQS) of transitional waters of the Guanabara Bay (SE Brazil) by applying the diversity-based index exp (H'_bc) and the sensitivity-based Foram-AMBI for the first time in South America. The Guanabara Bay was selected for this study as it is one of the largest transitional ecosystems in the State of Rio de Janeiro and has been severely impacted by anthropogenic activities. Concentrations of potentially toxic elements (PTEs) were assessed by sequential chemical extraction in three phases (i.e., dissolved in water, adsorbed on organic matter, and Mn oxy-hydroxides). Total organic carbon, total nitrogen, and stable isotope (δ¹³C and δ¹⁵N) signatures of organic matter were analyzed to trace environmental stress. The Ammonia/Elphidium ratio suggests hypoxic conditions at most of the sampled sites. Principal component analysis identifies the first component as environmental stress underlying organic matter and PTE enrichment (in all three phases), which is positively related to Foram-AMBI and negatively to exp (H'_bc). The exp (H'_bc) and Foram-AMBI indices reveal that stations near the Governador Island and Niterói margin have the worst EcoQS, showing medium to extreme pollution. Additionally, Foram-AMBI and exp (H'_bc) provide a congruent EcoQS classification for ∼64% of the sites. Although these results are promising, they suggest that a significant effort should be made to obtain better knowledge of foraminiferal ecological requirements to employ benthic foraminifera as a biomonitoring and management method.

Unraveling Anthropocene Paleoenvironmental Conditions Combining Sediment and Foraminiferal Data: Proof-of-Concept in the Sepetiba Bay (SE, Brazil)

The Sepetiba Bay (SB), located in the state of Rio de Janeiro (SE Brazil), is a transitional ecosystem highly anthropized. Because of its great environmental, economic, and social importance, the SB has been the target of several studies to investigate the sources of pollution and their environmental impact. However, studies on the response of foraminifera to pollution are rare. This study applies for the first time in the SB the Ecological Quality Ratio (EQR) based on the biotic index exp(H’bc), related to foraminiferal diversity, coupled with granulometric, mineralogical, and geochemical data and a robust age model (based on 210Pb and 137Cs activity). This study aims to evaluate the paleo-ecological quality status (PaleoEcoQS) along core SP5, collected in the inner central region of the SB. In the sedimentary record of the first half of the 20th century, no foraminifera were found, and the moderate enrichment in lithogenic elements was probably related not only to weathering and erosion of rocks but also to mining activities in the region. From the second half of the 20th century, the study area was under higher marine influence. Progressive siltation took place because of anthropogenic interventions in river courses, eutrophication, and metal pollution. Weak hydrodynamic conditions favored the accumulation of fine-grained sediments and organic matters. In the same period, low diversified benthic foraminiferal assemblages, including mainly opportunist species, were developed. Paleo-ecological conditions inferred by the biotic index exp(H’bc) were poor around 1970 and worsened after the metal spill released by Companhia Ingá Mercantil (a zinc ore processing plant). After that, progressively recovery has led to good ecological conditions in 2015. This study shows how benthic foraminiferal methods could represent a very useful tool to track changes in the evaluation of PaleoEcoQS.

Heavy metals bioconcentration in Crassostrea rhizophorae: A site-to-site transplant experiment at the Potengi estuary, Rio Grande do Norte, Brazil

In this study, we analyzed the bioconcentration of Cd, Cr, Cu, Pb, Ni, and Zn in the soft tissue of transplanted oysters in two sites in the Potengi estuary for six months. Native oysters collected before and after the transplantation experiment provided the background for statistical analyses. Cd, Cr, and Ni showed a strong inverse correlation with oyster weight in both sites. Transplantation upstream of the estuary presented increasing concentrations of Zn, Cu, and Pb and condition index (CI) and decreasing trends for Cd and Ni, whereas Cr oscillated significantly. In the downstream transplantation, Cu, Pb, and Zn and the CI tended to decrease, whereas for Ni, Cd, and Cr, the concentrations increased. Spatiotemporal principal component analysis correlated these results mainly with proximity to the polluting source, seasonality, and previous exposure to heavy metals. These results helped interpret the responses provided by these biomonitors to environmental changes, whether they are natural or anthropogenic.