ABSTRACT: Estuarine habitats are characterized by environmental changes on many time scales. While certain physical parameters change on a regular, predictable basis, rapid environmental fluctuations can also occur as a result of stochastic events. For example, rainstorms are frequent, unpredictable events that can cause dramatic changes in the estuarine environment, in short periods of time. As a result of storm precipitation and terrestrial freshwater runoff, estuarine salinity can drop in excess of 20o/oo in 6 h. Our research focuses on the effects of these storm-induced salinity fluctuations on estuarine embryos and larvae in terms of growth, mortality, rate of development, and activity. We studied 2 species of estuarine invertebrates: the embryos and larvae of the mud snail Ilyanassa obsoleta and the larvae of the marine polychaete Arenicola cristata. In both species, greater reductions in salinity resulted in smaller larvae. Both the duration of salinity reduction and the age of embryos and larvae when exposed to a salinity reduction affected growth rates: longer and earlier (relative to embryonic or larval age) storms had a greater effect on growth rates, resulting in smaller larvae. Both species also exhibited changes in activity when exposed to salinity reductions: I. obsoleta larvae swam significantly less at 10o/oo, while A. cristata larvae displayed a delay in activities associated with the sequence of development from swimming trochophore, to crawling larva, to settled metamorphic juvenile. Our results show that stochastic events may have a significant impact on the growth and development of pre-settlement estuarine invertebrates, implying ecological effects on recruitment success.

KEY WORDS: Salinity . Larvae . Fluctuations . Growth . Activity . Mortality . Stoichiometry

Published in MEPS Vol. 133 (1996) on March 28
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996