Effect of suspended sediment on embryos and larvae of the cold‐water coral Lophelia pertusa

Abstract: The cold-water coral Lophelia pertusa (syn. Desmophyllum pertusum) provides importanthabitats in deep-sea ecosystems, allowing for a biodiversity similar to that of tropical coral reefs. Anthropogenic activities like bottom-trawling and drilling however leads to increased concentrations of suspended sediment, which can potentially cause various neg ative effects in all life stages of corals. The purpose of this thesis was to study the effects of suspended benthic sediments on embryos and larvae of L.pertusa. The embryos/larvae were exposed to one of four concentrations of sediment (control, 2.5 mg/L, 5 mg/L & 25 mg/L), during one or three days. Assessments were made on embryonic and larval sur vival, embryo development and larval swimming speed. Exposure of the embryos started at around 1 day of age (6-30h after spawning), while larvae were either 5, 9 or 12 days old. “Embryos” where exposure started > 6h after spawning appeared to survive the high est sediment concentration for 1 day. However, a large proportion of them were still in the oocyte stage, indicating that either fertilization or development was stunned. After three days of exposure, the embryos had decreased survival rate and were more likely to lack cilia with increasing concentration of sediment. They also often responded by falling apart into multiple smaller embryo parts. Meanwhile, the larvae were mostly, but not en tirely, unaffected in both their survival and swimming speed. These results suggest that the effect of suspended sediment depends on the age of embryos and larvae, the duration of sediment exposure, and the concentration of sediment. Future studies need to use more reliable techniques to be able to study large quantities of embryos, as well as other life stages of L. pertusa, to further understand the effects of suspended sediment. Knowledge gained on this topic can aid management decisions, to mitigate potential adverse conse quences on dispersal and deep-sea biodiversity.