Living benthic foraminifera and organic matter compounds as proxies to characterize the trophic state in an impacted hypersaline environment: Araruama Lagoon - Brazil

Abstract

Recognizing the tolerance levels of foraminifera species towards organic matter components is a crucial aspect of biomonitoring in diverse coastal environments, including hypersaline ecosystems. Despite the importance of this information, there remains limited knowledge about the biodiversity and ecological relationships of these organisms in hypersaline environments, hindering their application in biomonitoring studies. This study aimed to assess the impact of organic components on the distribution of living benthic foraminifera in the Araruama Lagoon, utilizing a comprehensive approach involving biopolymer concentration, physical-chemical parameters, and sediment grain size analyses. The results revealed a high richness of foraminiferal fauna in the lagoon, comprising 44 living species. These organisms exhibited responses indicative of anthropogenic impact, including reductions in density, diversity, and alterations in assemblage composition. Statistical analyses demonstrated that foraminiferal distribution was influenced by grain size, salinity, and organic matter concentration. Bioindicators of highly impacted areas included Ammonia tepida, Ammonia parkinsoniana, Bolivina translucens, Bolivina striatula, Elphidium excavatum, Cribroelphium gunteri and Fursenkoina pontoni. Quinqueloculina milletti and Quinqueloculina seminulum were associated with sandy areas characterized by high hydrodynamics, while Discorbis bertheloti and Valvulineria rugosa were associated to hypersaline conditions. The foraminifera distribution allowed the identification of four distinct regions within the Araruama Lagoon, each exhibiting different trophic conditions. The Environmental Quality Standards (EQS) proved effective in delineating the most environmentally compromised areas of the system. However, it was not as efficient in the characterization of the most hypersaline areas of Araruama lagoon.