Effects of surface and sunken crude oil on selected marine invertebrates

Abstract

The study deals with the toxicity and certain sublethal effects of surface and sunken crude oils on selected marine invertebrates. The first part comprises a general review of the state and sources of oil pollution of the seas, the fate of oil at sea, and methods used in combatting oil pollution. A resume of the current state of knowledge on the effects of oil on marine organisms is included, together with a review of the problems involved in assessing the impact of oil pollution on the marine ecosystem. Preliminary work in this study, on the suitability of weathered limestone powder as an oil sinking agent, suggests that it is a good oleophilic powder and that it is unlikely to release sunken oil and thus to cause re-pollution of surface waters. In comparing the emission of WSF from surface and sunken fresh crude oil, it is concluded that WSF are released less readily from sunken oil with silt mixtures, than by the surface oil. Toxicity studies on Artemia salina L, Paracentrotus lividus Lam., and Monodonta turbinata (Born), are carried out. WSF emitted from surface fresh crude oil have greater deleterious affects on the normal development of Artemia salina larvae, than WSF from same amounts of sunken fresh crude oil - as shown by reduced hatching of eggs, mortalities of exposed larvae and possibly, sublethal effects on the feeding activities of surviving larvae. High concentrations of WSF emitted by both surface and sunken crude oil can be tolerated by Paracentrotus lividus but not by Mondonta turbinata. The 96 hour LC50 value of WSF of surface oil for M.turbinata is found to be 3.17 mg/1, while that of WSF of sunken oil is 1.66 mg/1. When animals are exposed to surface crude oil such that direct physical contact with the undissolved oil is possible, P.lividus is again relatively resistent, while appreciable mortalities are recorded for M.turbinata. On direct contact with sunken oil both P.lividus and M.turbinata suffer significant mortalities. The possible causes of such mortalities resulting from direct contact with the sunken oil are discussed, and while ingestion of the sunken oil seems to be the cause of mortalities in P.lividus, contact toxicity resulting from some lethal chemical effect exerted by hydrocarbons of very low water solubility, cannot be ruled out in the case of M.turbinata. A number of sublethal effects of crude oil on the test species selected are reported. On exposure to WSF of surface and sunken oil, a reduction in the adhesive properties of tube feet and a decrease in the spine response to local mechanical stimuli are observed for P.lividus. On exposure to direct contact with sunken and especially surface fresh crude oil, a prolongation of the righting activity of the sea urchins is reported. Moreover P.lividus is found to be indifferent, i.e. neither attracted to, nor repelled from the presence of sunken oil in its immediate environment. It is however slightly repelled by the presence of surface crude oil. The most significant sublethal effect of crude oil on M.turbinata is found to involve an inversion reaction of exposed snails, so that they stand on their shell with foot fully extended without attempting to righten themselves up. While this 'inversion effect' is exhibited on exposure of WSF of surface and sunken crude oil, it is most evident when snails come in direct contact with sunken oil. On exposure of low concentrations of surface crude oil, the normal gregarious behaviour as well as the immersion-emersion activity of M.turbinata is greatly disrupted. Persistent fractions of crude oil are reported to be responsible for the latter effect. The behavioural response of M.turbinata towards the presence of crude oil is more complex than that of P.lividus.