Habitat use patterns of the mummichog,Fundulus heteroclitus, in New England. I. Intramarsh variation

Although studies of intertidal habitats have contributed greatly to the field of ecology, the processes governing the use of these areas by highly mobile animals such as fish remain poorly understood. In particular, although large-scale patterns of estuarine fish abundances are well known, fine-scale patterns of habitat use have been largely overlooked. Here, I examine among and within habitat use patterns of the mummichog,Fundulus heteroclitus, in a New England salt marsh. Using minnow traps I sampled changes in mummichog habitat use among closely spaced sites within creeks, mudflat, and channel over 2 yr. The general pattern of mummichog captures was consistent among years, showing peaks in summer months and lows in winter. Use of specific habitat types was also seasonally dependent. For most of the year (fall, winter, spring) mudflat capture rates were lower than creek capture rates in the summer; however, densities in the mudflat equal or exceed those in creeks. In most months channel habitats did not differ significantly in use from either creek or mudflat habitat. Consistent patterns also occur within induividual marsh habitats.F. heteroclitus concentrate in the uppermost portion of creeks. Additionally, mudflat capture rates (August 1990) declined with increasing water depth. Diurnal habitat use is heavier than nocturnal use for all habitats. These findings demonstrate that mummichogs are restricted to areas representing a very small proportion of total available habitat and that their patterns of habitat use are strongly seasonal. Only careful experimental work can determine the relative advantages of these habitats for estuarine fish. Further comparative work is required to reveal how biological and physical parameters affecting habitat use may vary geographically.