The effects of the water soluble fractions of No. 2 fuel oil on the survival and behaviour of coastal and oceanic zooplankton

Abstract

Acute effects of water-soluble fractions (WSF) of No. 2 fuel oil both coastal and oceanic zooplankton were studied and their LC 50 for various exposure times (1 to 72 h) compared. Coastal zooplankton seemed to be more resistant to the WSF than oceanic zooplankton. This difference was probably caused mainly by the dissimilar species composition of the two zooplankton populations under investigation. The evidence from this study indicates that, on a species or taxon basis, there are some species in coastal waters more vulnerable to oils than among oceanic zooplankton and it is strongly recommended that further studies of the tolerance of both populations to various petroleum hydrocarbons be carried out at the same time. A vital staining method was used to distinguish the dead from the immobile forms. Expected variations both in the curves of mortality compared with time and in the curves of mortality compared with concentration of oil are explained and a possible method to decrease variability is suggested. Change of behaviour of coastal zooplankton due to the WSF of No. 2 fuel oil was also observed during the first hour of exposure.