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147 contEnts Tidal Marsh Invertebrate Study Rocky Intertidal Invertebrates Invertebrate Diversity Invertebrate Distribution Invertebrates as Food Resources Synthesis and Future Directions i ntertidal habitats present a harsh physical environment for resident invertebrates. Twice-daily tides subject terrestrial invertebrates to the risk of drowning and aquatic invertebrates to the risk of desiccation. Inundation periods and sediment properties vary across the intertidal gradient, and environmental conditions change rapidly with inundation and exposure. Physical and biological conditions change over small spatial scales, as slight changes in elevation translate to large changes in hydrology, geomorphology, and vegetation (Collins et al. 1986; Pennings and Callaway 1992). The distribution of rocky intertidal invertebrates varies over both large and small spatial scales as a result of differences in dispersal, recruitment, and response to changes in microhabitat among species (Underwood and Chapman 1996). The small-scale zonation of rocky intertidal invertebrates results from a combination of physiological limitations and ecological interactions (Tomanek and Helmuth 2002). Within tidal marshes, distinct subhabitats— from large, high-order channels to small, loworder channels, to marsh plain and natural levee—are found adjacent to each other along the tidal gradient, sometimes changing abruptly from one meter to the next. Marsh invertebrate communities vary by subhabitat, with many species showing a preference for particular elevations , vegetation zones, or substrate types (Teal 1962; Davis and Grey 1966; Levin and Talley 2000). Invertebrates constitute much of the secondary productivity in tidal marshes (Teal 1962) and play a critical role in transferring primary productivity up the food web, forming a substantial part of the diet of many resident marsh vertebrates (Grenier and Greenberg 2005). As there are few seeds and fruits in the marsh available for terrestrial vertebrates to forage on (Greenberg et al. 2006), the distribution and diversity of invertebrates largely determines the food resources available for secondary consumers and influences their foraging behaviors. Invertebrates constitute a substantial portion of the diets of many common marsh fish species as well (Visintainer et al. 2006). This chapter provides original data on the distribution of macroinvertebrates across a tidal gradient and reviews what is known about the diversity, distribution, and abundance of intera Case stuDy of China CamP state Park, marin County April Robinson, Andrew N. Cohen, BrieLindsey, and Letitia Grenier invertebrates chaPtEr tEn 148 Ecology: organisMs tidal invertebrates at China Camp State Park in Marin County, California, a National Estuarine Research Reserve site. Data from two studies, one of tidal marsh invertebrates and the other of rocky intertidal invertebrates, are presented here (Robinson et al. 2011). Most of the previously available invertebrate data from China Camp focus on predation of invertebrates (Dean et al. 2005; Visintainer et al. 2006) rather than on their diversity and distribution. The implications of invertebrate distribution and diversity on the behavioral ecology of their predators is also briefly discussed. The data presented in this chapter demonstrate the unequal distribution of invertebrates across intertidal subhabitats at China Camp State Park in San Francisco Bay. Relatively few species made up the majority of the invertebrate biomass in the tidal marsh, and the majority of both the rocky intertidal invertebrates and the tidal marsh invertebrates identified to species were exotic. The strong association of certain invertebrate groups to specific subhabitats suggests that predators with different feeding specializations may forage primarily in one part of the marsh or another. tidal Marsh invErtEbratE stUdy Invertebrates at China Camp marsh were collected from the channels, marsh plain, and natural levees as part of a food web study reported in greater detail by Grenier (2004). Invertebrates were collected to investigate which taxa were available as potential prey items for the San Pablo song sparrow (Melospiza melodia samuelis), a tidal marsh obligate, and other marsh vertebrates and to determine how macroinvertebrates were distributed across the tidal gradient. Because no single method was sufficient to account for all invertebrate locomotion types and habitat preferences , multiple trapping methods were used. The study was conducted in a 3.3 ha plot within the portion of the marsh that has accreted since the mid-1800s, characterized by the simple, less sinuous channels typical of a rapidly formed marsh. Sampling was conducted at low tide from May to July 2001 and consisted of five capture methods: pit trap, sweep net, snail count, mud core, and sticky trap. Equal sampling effort was expended along high-order and low-order channels . For each channel type, random sampling locations were stratified across three subhabitats: within the channel, on the natural levee adjacent to the channel, and on the...

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