Effect of Sargassum on the Behavior and Survival of the Earthworm Eisenia fetida

In the past decade, Sargassum natans and S. fluitans have massively reached the Mexican Caribbean shores. As a result, Sargassum confinement sites may be affecting the soil quality and health in coastal ecosystems and agroecosystems. The impact of Sargassum (e.g., polyphenols) on soil biodiversity has not yet been evaluated. Terrestrial ecotoxicological tests use the epigean earthworm Eisenia fetida as a model organism to assess the function of soil habitats. This study evaluated the behavior and survival of the earthworm E. fetida exposed to five Sargassum concentrations (0, 25, 50, 75, and 100 %) using two toxicological tests. The avoidance test showed that E. fetida repelled (>80 %) a diet with 100 % Sargassum. In contrast, the acute test recorded a low mortality; however, the growth of E. fetida was lower with increasing Sargassum concentrations. It is concluded that the ability to repel and E. fetida biomass are early warning bioindicators to predict the environmental risk of Sargassum in soil. Therefore, it is relevant to determine the potential risk of using earthworm compost and Sargassum leachates as biofertilizers in agroecosystems.