Spatial patterns of epifaunal communities in San Francisco Bay eelgrass (Zostera marina) beds

Seagrass beds play a vital role in estuarine systems worldwide by providing substrate, food, refuge from predation, and nursery habitat for a diverse assemblage of associated organisms (Williams & Heck 2001). Mesograzers, mobile epifaunal invertebrates, are important components of seagrass communities, serving as a link in the food chain from primary producers to higher-order consumers (Kikuchi 1974; Edgar & Shaw 1995). Additionally, by grazing epiphytic algae that compete for light, mesograzers can increase seagrass growth by up to 200% (Duffy et al. 2001). Because mesograzers are important in seagrass ecosystem structure and function, community composition and species distributions have been well documented in a wide variety of locations (Orth et al. 1984; HellwigArmonies 1988; Gambi et al. 1992; Thom et al. 1995; Bostrom & Bonsdorff 1997; Mattila et al. 1999; Duffy et al. 2001; Arroyo et al. 2006). Epifaunal species play different roles in the structure and functioning of eelgrass systems (Duffy et al. 2001); evaluating patterns in their distribution and abundance aids in the assessment of their functional importance. Epifaunal species generally show large seasonal fluctuations in community structure and relative abundance (Dugan & Livingston 1982; Edgar 1990; Arroyo et al.