The effects of a water-soluble petroleum fraction on the neuroid electrical activity of the hydroid coelenterate Tubularia crocea

Abstract

Several properties of the excitable epithelium of the hydroid coelenterate, Tubularia crocea, are affected by a water-soluble fraction (WSF) of Platform Holly, Monterey Formation, crude oil (100% WSF= 20 ppm total hydrocarbons). In a flowing seawater system, 0·5 ml pulses of 1 WSF cause a significant increase in the epithelial pulse activity, while a 10·min exposure to 0·1% WSF produces a significant increase in the epithelial pulse frequency. Electrophysiological responses to the volatile and non-volatile subfractions are equal, but significantly lower than those to the whole WSF. Behaviorally, the 100% WSF elicits a more vigorous proximal tentacle closure than either its volatile or non-volatile subfraction. However, the closure response to the volatile subfraction exceeds that for the non-volatile component. Of the two epithelial neuroid pulse systems, the hydranth pulse (HP) system is affected to a greater extent than the neck pulse (NP) system. During 10 minutes' treatment with 100% WSF the amplitude of the neck pulses and hydranth pulses declined by 50% and 80%, respectively. The maximum 3H-toluene uptake from 100% WSF also occurs within this period, and sodium and calcium concentrations fluctuate rapidly. These results suggest that a rapid bioaccumulation of hydrocarbons by T. crocea alters membrane permeability, upsetting critical ion gradients which, in turn, alter the firing frequency of the epithelial conducting systems. This study demonstrates that concentrations of WSF approaching environmentally realistic levels (in areas of chronic pollution) alter the epithelial conducting systems that co-ordinate important elements of behavior in Tubularia. This system provides a sensitive neuroid-behavioral assay for aquatic contaminants.