Biology subjects

Soerensen, A. L.

Publications and source records attributed to Soerensen, A. L..

4 recordsLinked to original sources

bioRxiv2025

The effect of Shifts in Fish Community Structure on PCDD/F temporal variability in common guillemot (Baltic Sea)

Persistent Organic Pollutants, specifically polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) (PCDD/Fs) threaten marine ecosystems through biomagnification and bioaccumulation in top predators. Following environmental legislation introduction in the 1970s, PCDD/F concentrations declined in the Baltic Sea biota. However, previous studies signaled that this decline plateaued from the 1990s onward in common guillemot (Uria aalge) eggs. This period coincides with shifts in Baltic environmental conditions and food-web structure, including guillemot prey species. Here, we hypothesize that temporal variability of PCDD/Fs in guillemot eggs was driven by changing environmental conditions and food-web structure affecting prey availability. We identified phases in the temporal dynamic of fish community structure, linked them to PCDD/Fs rate of change, and identified potential environmental and anthropogenic drivers of these phases. Three distinct phases emerged: cod and herring dominance (1976-1986), sprat dominance (1987-2001), and stickleback increase (2002-2021). PCDD/F concentrations declined sharply during the first phase (-6.4% y1), plateaued during the second (0.27% y1), and resumed a decline during the third (-3.8% y1). The transition to a sprat-dominated phase increased guillemots dietary exposure to PCDD/Fs, contributing to the second phase plateau. Conversely, stickleback rise as a potential key prey species during the third phase may have facilitated the post-2002 decline. Shifts in fish community structure were driven by changes in temperature, salinity, zooplankton size, and fishing pressure. We conclude that both bottom-up (environmental conditions) and top-down (fisheries food-web dynamics) effects have cascaded through the ecosystem, reshaping fish community structure and influencing PCDD/F concentrations in guillemot eggs.

ecology↗

bioRxiv2022

Abundance and expression of hgcAB genes and mercury availability jointly explain methylmercury formation in stratified brackish waters

Neurotoxic methylmercury (MeHg) is formed by microbial methylation of inorganic divalent Hg (HgII) and constitutes severe environmental and human health risks. The methylation is enabled by hgcA and hgcB genes, but it is not known if the associated molecular-level processes are rate-limiting or enable accurate prediction of MeHg formation in nature. In this study, we investigated the relationships between hgcA genes and MeHg across redox stratified water columns in the brackish Baltic Sea. We found that the abundance of hgcA genes and transcripts combined with the concentration of dissolved HgII-sulfide species were strong predictors of both HgII methylation rate and MeHg concentration, implying their roles as principal joint drivers of MeHg formation in these systems. In establishing relationships between hgcA genes and MeHg, we advance the fundamental understanding of mechanistic principles governing MeHg formation in nature and enable refined predictions of MeHg levels in coastal seas in response to the accelerating spread of oxygen deficient zones.

ecology↗

bioRxiv2020

Marine snow as a habitat for microbial mercury methylators in the Baltic Sea

Methylmercury (MeHg), a neurotoxic compound biomagnifying in aquatic food webs, can be a threat to human health via fish consumption. However, the composition and distribution of the microbial communities mediating the methylation of mercury (Hg) to MeHg in marine systems remain largely unknown. In order to fill this gap of knowledge, we used the Baltic Sea Reference Metagenome (BARM) dataset to study the distribution of the genes involved in Hg methylation (the hgcAB gene cluster). We determined the relative abundance of the hgcAB genes and their taxonomic identity in 81 brackish metagenomes that cover spatial, seasonal and redox variability in the Baltic Sea water. The hgcAB genes were predominantly detected in anoxic water, but some hgcAB genes were also detected in hypoxic and normoxic waters. Higher relative quantities of hgcAB genes were found in metagenomes from marine snow compared to free-living communities in anoxic water, suggesting that marine snow are hotspot habitats for Hg methylators in oxygen-depleted seawater. Phylogenetic analysis identified well-characterized Hg methylators such as Deltaproteobacteria in oxygen-depleted water, but also uncovered Hg methylators within the Spirochaetes and Lentisphaerae phyla. Altogether, our work unveils the diversity of the microorganisms mediating MeHg production in the Baltic Sea and pinpoint the ecological niches of these microorganisms within the marine water column.

microbiology↗

bioRxiv2018

Mercury-methylating bacteria are associated with zooplankton: a proof-of-principle survey in the Baltic Sea

Methylmercury (MeHg) is a potent neurotoxin that biomagnifies in marine food-webs. Inorganic mercury (Hg) methylation is generally considered to be conducted by bacteria associated with sediment or detritus, but endogenous methylation by the gut microbiome of animals in the lower food webs is another possible source. We examined the occurrence of the bacterial gene (hgcA), required for Hg methylation, in the guts of dominant Baltic zooplankters. A qPCR assay targeting the hgcA sequence in three main clades (Deltaproteobacteria, Firmicutes and Archaea) was used in the field-collected specimens of copepods (Acartia bifilosa, Eurytemora affinis, Pseudocalanus acuspes and Limnocalanus macrurus) and cladocerans (Bosmina coregoni maritima and Cercopagis pengoi). All copepods were found to carry hgcA genes in their gut microbiome, whereas no positive amplification was recorded in the cladocerans. In the copepods, hgcA genes belonging to only Deltaproteobacteria and Firmicutes were detected. These findings suggest that endogenous Hg methylation can occur in zooplankton and may contribute to seasonal, spatial and vertical MeHg variability in water column and food webs. Additional molecular and metagenomics studies are needed to identify bacteria carrying hgcA genes and improve their quantification in microbiota.

microbiology↗