Influence of Marsh Flooding on the Abundance and Growth of Fundulus heteroclitus in Salt Marsh Creeks.

Abstract

Like many other estuarine fish and crustaceans, Fundulus heteroclitus (mummichog) regularly makes use of the marsh as a foraging area, nursery habitat, and refuge from predators. Mummichogs are known to follow flooding tides onto the intertidal marsh to forage (1, 2). Through this behavior, they provide an important trophic link between salt marsh and open estuary (3). Previous research indicates that access to the intertidal flooded marsh has significant effects on the growth rate of F. heteroclitus. Weisberg and Lotrich (4) showed that foraging exclusively on subtidal food sources was not sufficient to support normal growth rates of mummichogs. Javonillo et al. (5) found that mummichogs denied access to the marsh had lower growth rates than those that were allowed entree to the marsh surface. Both of these studies employed caging techniques on a relatively small scale. Our goal was to examine the importance of marsh flooding to mummichog growth and abundance in a natural environment without enclosures. Tidal creek flooding onto the marsh determines the vegetation in the area surrounding the creek. Spartina altemijora grows on the marsh adjacent to the creek that floods on every high tide, whereas S. patens grows on the higher marsh that floods less frequently. We measured the length from the creek edge to the transition between S. altemijlora and S. patens at increments along the creek. The mean of these measurements multiplied by the length of the creek was considered the area of marsh accessible to mummichogs at high tides. This area is equivalent to the area of marsh adjacent to the creek covered by S. altemijora. A comparison of the regularly flooded area in the 5 tidal creeks that were part of our study is shown in Figure la. We measured the abundance and growth of F. heteroclitus in tidal salt marsh creeks of the Rowley River in the Plum Island Estuary in northeastern Massachusetts (42”44’ N X 70’50’ W).