SPIDER (ARANEAE) COMMUNITY STRUCTURE IN AN INTERTIDAL SALT-MARSH - EFFECTS OF VEGETATION STRUCTURE AND TIDAL FLOODING

The effects of vegetation structure and tidal flooding on the organization of a spider community were studied along an elevational gradient in an intertidal marsh. High marsh habitats were dominated by the grass Spartina patens (Ait.) Muhl., a species characterized by a low, matted profile and a complex layer of thatch. Another grass, Spartina alterniflora Lois., is more upright in structure, has a poorly developed thatch layer, and abounds in habitats that extend from the high marsh to much lower elevations. Along this elevational gradient, the structure of S. Alterniflora changes from a short form on the high marsh to a tall form on the low marsh, and the frequency and duration of tidal flooding increases. Although more robust in structure during the summer months, the tall-form habitat of S. Alterniflora is selectively destroyed and defaunated during the winter by shifting ice and storms and must be recolonized by spiders every spring from the more protected overwintering short-form habitat of S. Alterniflora on the high marsh. In all, 21 species of resident spiders were sampled from the two grasses. The community of spiders in S. Patens was less diverse than in S. Alterniflora and consisted mostly of hunting spiders (Lycosidae, Gnaphosidae, Clubionidae, Thomisidae, Philodromidae, and Salticidae), which were more abundant in this low-profile grass. Web-building spiders (Dictynidae, Linyphiidae, Araneidae, and Tetragnathidae), which were rare in S. Patens, occurred commonly in the more upright structured S. Alterniflora because of the abundance of sites for web attachment. Down the elevational gradient from short-form to tall-form S. Alterniflora, the abundance of most hunting spiders and several web-building species decreased and was associated with an increase in the frequency and duration of tidal flooding. Winter defaunation of tall-form S. Alterniflora contributed further to the depauperate spider community in this low marsh habitat. Thus, vegetation structure and elevational factors act in concert to influence the distribution, abundance, and community structure of spiders in intertidal marshes. © 1990 Entomological Society of America.