Interactions between contaminants and the trophic ecology of two seabirds in a coastal lagoon of the Gulf of California

TL;DR

This study examines how pollutants like mercury and pesticides interact with the diet and feeding habits of two seabird species in a Mexican coastal lagoon.

Contribution

The study provides new insights into contaminant concentrations and their relationship with trophic ecology in tropical seabirds.

Findings

Laughing Gulls had higher levels of certain pesticides, while Magnificent Frigatebirds had elevated mercury and other pesticide isomers.

Pollutant concentrations in Laughing Gulls were linked to diet and habitat use, showing biomagnification.

Sex-related differences in isotopic signatures in Magnificent Frigatebirds did not correlate with pollutant accumulation patterns.

Abstract

Monitoring the dynamics of contaminants in ecosystems helps understand their potential effects. Seabirds have been used as biomonitors of marine ecosystems for this purpose. However, exposure and vulnerability to pollutants are understudied in tropical species, and the relationships between various pollutants and the trophic ecology of seabirds are poorly understood. In this study, we quantified mercury (Hg), lead (Pb), cadmium (Cd), and organochlorine pesticide (OC) concentrations in the blood of Laughing Gulls and Magnificent Frigatebirds breeding in Bahía Santa María, México. Using carbon and nitrogen isotopic ratios (δ13C and δ15N), we examined the interaction between contaminants and trophic ecology. Laughing Gulls exhibited higher concentrations of dichlorodiphenyltrichloroethane and its metabolites (ΣDDTs), endrins (ΣDrins), and chlordanes, while Magnificent Frigatebirds had elevated levels of Hg and hexachlorocyclohexane isomers (ΣHCHs). Both species displayed temporal and sex-related variations in isotopic signatures. Some blood pollutant concentrations in Laughing Gulls were explained by diet: ΣOCs in plasma were directly related to trophic levels, indicating biomagnification, whereas higher Hg levels were associated with changes in habitat use. In contrast, the differences in sex-related isotopic signatures in Magnificent Frigatebirds did not reflect pollutant accumulation patterns, possibly due to their opportunistic feeding habits.

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