Geomorphological determinants of nekton use of intertidal salt marsh creeks

Abstract

Spatial variations in nekton use are often attributed to differences in the configuration and composition of habitat. We predicted that differences in nekton use among intertidal creeks were related to certain geomorphological characteristics. We measured or derived 28 features at 8 inter- tidal creeks in the high salinity North Inlet Estuary, South Carolina, USA. Nekton were collected simultaneously from all creeks once each season for 2 yr. Spatial variations in total abundance and biomass were greater than seasonal variations. Differences of 3- to 30-fold in resident and transient taxa densities occurred among creeks on the same date. Relative use (ranks) was similar among sea- sons and years. In canonical correlation analyses, depth, steepness, flow, and location were primary factors for total nekton and many taxa. Creeks that were shallow, broad, and filled and emptied slowly supported the greatest use. Total nekton use was not related to creek size, amount of edge, or oyster bottom. Grass shrimp Palaemonetes spp., numerically dominant in 83% of the collections, responded most to creek shape. Mummichog Fundulus heteroclitus favored shallow creeks with low flow and low proportions of submerged bottom at low tide. Juvenile spot Leiostomus xanthurus and pinfish Lagodon rhomboides were associated with the same features throughout their seasonal per- iods of occurrence. Persistent differences in nekton use of adjacent intertidal creeks might be explained by behavioral selection for preferred conditions and reoccupation of selected creeks. Geo- morphological variations are significant among sites and must be considered when assessing factors affecting nekton use along salinity and other environmental gradients.