Effects of sediment-bound endosulfan on survival, reproduction and larval settlement of meiobenthic polychaetes and copepods

Abstract

Endosulfan-contaminated muddy sediments were collected from a tidal creek bottom after rain runoff from an agricultural watershed and tested for their effects on larval settlement/growth, survival and reproduction of cultured meiobenthic polychaetes and copepods. Endosulfan (ES) strongly inhibited larval colonization and early juvenile growth of the cosmopolitan, euryhaline polychaete Streblospio benedicti. In laboratory microcosms, ES concentrations as low as 50 μg·kg−1 sediment significantly reduced the number of larval colonists by >50% relative to ES-free control sediments. Higher concentrations closer to actual field levels suppressed Streblospio benedicti colonization completely. Early growth of newly metamorphosed juveniles was depressed 36 and 40% relative to controls at ES concentrations of 50 and 100 μg·kg−1, respectively. In contrast, when the common benthic harpacticoid copepod Pseudobradya pulchella was chronically exposed to sediment ES as high as 200 μg·kg−1, survival and egg production were unaffected despite many examples of high ES toxicity to other crustaceans. Of more than 1,600 Pseudobradya pulchella tested, more than 95% survived ES concentrations of at least 200 μg·kg−1, and over 98% of 1,200 females produced normal clutches of eggs. Similarly, survival of another common benthic copepod, Nannopus palustris, was not significantly affected below a threshold concentration of 200 μg·kg−1 ES. At 200 μg·kg−1, however, Nannopus palustris' survival was significantly reduced relative to control and 50-μg·kg−1 ES treatments.