Metamorphosis in response to bottom sediment was measured in two species of marine planktonic larvae. Ilyanassa obsoleta, a common mud-snail, and Capitella sp. I, a polychaete worm. A sediment control consisted of organic-rich sediment collected from Barnstable Harbor, Ma. One sediment treatment, termed muffled sediment, consisted of the sediment control heated at a high temperature in a muffle oven to remove all organic matter. A sharp decrease in percent metamorphosis was observed in larvae exposed to the muffled sediment condition compared to the sediment control. Results confirmed that settlement involves more than physical contact with the sediment and suggest that the metamorphosis-stimulating factor is probably a water soluble substance. The June 10, 1990, spilI of 7,500 gallons of No.6 fuel oil into Buzzards Bay, Massachusetts, provided oil contaminated samples of salt marsh sediment. Both the sediment control and muffled sediment were contaminated with the oil. The influence of oiled conditions on percent larval metamorphosis varied between species. Ilyanassa obsoleta showed no significant change (ANOVA ~=0.01) in percent metamorphosis between the oiled and unoiled conditions. In Capitel la sp. I, larval settlement rates on oiled sediment conditions were significantly lower than the control sediment. This trend suggests that the oil somehow altered the metamorphosis cue detected by larvae of Capitel la sp. I. However, the variability in results of both species support the need for further studies investigating the specific mechanisms of metamorphosis as wel 1 as the impacts of No.6 fuel oil on the development of marine invertebrate larvae.


Biology, general