Abrasive effects of Mount Saint Helens ash upon epidermis of yolk sac larvae of Pacific herring Clupea harengus pallasi

Abstract

Larval Pacific herring Clupea harengus pallasi were exposed for 24 h to suspensions of estuarine sediment and volcanic ash from 0 to 8000 mg/litre. The effects of these suspensions on the epidermis of the yolk sac larvae were determined using light and scanning electron microscopy. Examination of the epidermis at specific locations on dorsal and ventral body surfaces showed that the effects were apparent with increasing concentrations of both sediment and ash. The effects of volcanic ash, however, occurred at lower concentrations and were of greater magnitude than those of sediment. Examination of the epidermis of these larvae under the scanning electron microscope revealed puncture-type damage associated with volcanic ash but not estuarine sediment. Thus, in addition to the possible effects of smothering which may occur with fine particulates, the ash particles result in direct mechanical damage to the delicate early larvae. The concentrations where effects were noted were greater than those likely to be observed in the lower Columbia River estuary where the larval herring occur. In upriver locations characterized by higher suspended particulates, delicate larvae of other species may suffer epidermal damage.