Impacts of seasonality on mercury concentrations, polyunsaturated fatty acids, and stable isotopes: implications for the use of tetragnathid spiders as sentinels.

This article investigates the influence of seasonality on riparian spiders in the family Tetragnathidae, which are used as sentinels for bioavailable contaminants transferred from aquatic to terrestrial ecosystems via emergent aquatic insects. Sampling tetragnathid spiders fortnightly over an active season (April–October) at a site on the Stones River in Tennessee, USA, the study found that spider size, mercury (methyl mercury and total mercury), selenium, and arsenic concentrations varied significantly with season, particularly declining near the end of the active period. Carbon and nitrogen stable isotopes and polyunsaturated fatty acid biomarkers showed some seasonal variation but were generally stable, suggesting limited impact on trophic level assessments. The findings emphasize that timing of spider collection is critical for consistent contaminant monitoring, recommending sampling within the first 86% of the spiders’ active period to avoid seasonal biases in ecotoxicological studies.