MEPS 619:85-96 (2019)  -  DOI: https://doi.org/10.3354/meps12951

ABSTRACT: Coastal areas are affected by freshwater runoff that carries terrigenous sediments and reduces salinity, both of which can have deleterious effects on early life stages of marine organisms. The aim of this study was to experimentally assess the combined stress of low salinity and suspended or deposited sediments on larval and post-larval development of the sea urchin Evechinus chloroticus. Larvae were exposed to low salinity (28, 32 ppt) and suspended sediments (40, 80 mg l^-1), in a fully factorial design, for 4 d, then returned to control conditions (36 ppt, 0 mg l^-1). Four weeks later, competent larvae from every treatment were placed in bowls under control conditions to allow them to settle. To assess additional effects of deposited sediments on settlement, the bottoms of half of the bowls were covered with fine sediments. Seven days after fertilisation, larval development was reduced in the lowest salinity and suspended sediment treatments, but these differences were no longer visible by Day 21. Larval survival was not affected by the treatments. However, settlement success and juvenile development were reduced both by larval exposure to the lowest salinity and in the presence of deposited sediments. At 28 d post-settlement, there were no surviving juveniles that had been exposed either to the lowest salinity or to the highest level of suspended sediment early in larval life. Our findings suggest that even short exposure to runoff during early development can have strong consequences for later larval settlement and juvenile performance, which could compromise recruitment to adult populations.

KEY WORDS: Latent effects · Multiple stressors · Runoff · Larval development · Settlement · Evechinus chloroticus