EFFECTS OF NO. 2 FUEL OIL ON CHEMICALLY-EVOKED FEEDING BEHAVIOR OF THE MUD SNAIL, ILYANASSA OBSOLETA

Abstract

ABSTRACT Chemically-mediated feeding responses of the mud snail, Ilyanassa obsoleta, were evaluated after exposure to various fractions and concentrations of No. 2 fuel oil in a continuous flow-through seawater system. This type of feeding response involves chemical perception of and movement toward a point source of food followed by feeding through an extended proboscis. To investigate the effects of oil on this behavior, two types of bioassays were employed. In the first, arousal was used as a criterion to document effects on initial perception of food (olfaction or distance chemoreception). This initial phase of the feeding response is particularly susceptible to disruption by oil, with significant inhibition occurring after 48 hours exposure to concentrations as low as 0.015 ppm of an oil-in-water dispersion (OWD) and 0.43 ppm of the water-accommodated fraction (WAF). In the second bioassay, extension of the proboscis was used as a criterion to document effects on subsequent tasting or contact chemoreception. This later phase of feeding is less sensitive to oil, with significant inhibition occurring only after one month exposure to 0.49 ppm WAF, or after 48 hours exposure to concentrations in excess of 1 ppm (1.45 ppm OWD and 5.97 ppm WAF). Other, more obvious effects, including mortality, were observed at these two higher dose levels. This work illustrates the ability of extremely low levels of petroleum hydrocarbons to impair vital behavioral processes in marine organisms.