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174 Like plants, animals have adapted to the rigors of the tidal wetland environment. Resident sessile animals have to cope with whatever the environment brings their way. They must develop adaptations to flooding, varying salinities, alternating wetting and drying, temperature changes, and oxygen deficits (e.g., Levin and Talley 2000). Most wetland animals are mobile and can usually avoid undesirable conditions, returning when conditions improve. Some animals may visit these wetlands seasonally, at favorable tide conditions for food, for protection from predators, or to avoid adverse weather conditions (coastal storms). Most birds common to northern wetlands migrate south to avoid harsh winters. Terrestrial animals may frequent wetlands when not inundated. The salt marsh snail (Melampus bidentatus) and the marsh periwinkle (Littoraria irrorata, formerly Littorina irrorata) both climb the stems of smooth cordgrass (Spartina alterniflora ) during flood tides to avoid inundation and predation from fishes and crabs (Figure 6.1). Adults of the salt marsh snail may migrate within salt marshes to higher levels during spring tides and lower levels during neap tides (Price 1984). The ribbed mussel (Geukensia demissa) closes its shell at low tide to avoid exposure, and then opens it at high tide for feeding. The salt marsh ­ killifish or mummichog (Fundulus heteroclitus) can survive some out-of-water exposure by breathing air, allowing it to survive in tidal pools with oxygen ­ deficiencies (Halpin and 6 Tidal Wetlands as Wildlife Habitat Martin 1999). Mites may inhabit the hollow stems of grasses for protection. Prior to marsh flooding, fiddler crabs return to their burrows where they are virtually inactive under low oxygen conditions before emerging at low tide to feed (Vernberg and Vernberg 1972). Ants (e.g., Crematogaster ) may use their large heads to close the opening of their nests when tides flood the marshes (Mendelssohn and Batzer 2006). Some benthic animals of mud and sandflats (e.g., lugworms) can live in anoxic substrates by excavating U-shaped burrows and pumping water through the burrows at high tide, which stores enough oxygen to survive stressful conditions at low tide (Little 2000). Other animals have developed internal mechanisms that detoxify hydrogen sulfide, and some have symbiotic bacteria in their gills that can extract energy from hydrogen sulfide. Tidal wetlands serve many habitat functions . They may be feeding areas, resting or loafing areas, breeding grounds, refuges, or permanent homes. The vegetation and aquatic beds provide cover—refugia—for prey species and transient juveniles of predators (Zimmerman et al. 2000). The ebb and flow of the tides create quite varied and challenging environmental conditions. When flooded at high or spring tides, the wetland becomes an aquatic ecosystem providing fishes and marine invertebrates access to the riches of the marsh or swamp. At low tide, the wetland is exposed to air creating a more terrestrial habitat where spiders Tidal Wetlands as Wildlife Habitat   175 and insects may abound. Consequently, most tidal wetlands may be viewed as semi-aquatic, amphibious habitats, neither water nor land, but with properties of both depending on the moment. Food web interactions can be quite complex between aquatic and terrestrial organisms (Figure 6.2). Tidal flats are homes for benthic invertebrates and feeding grounds for fishes and waterfowl at high tide and for shorebirds and wading birds at low tide. Marshes are residences for some mammals and reptiles. While northern marshes are particularly important breeding and feeding grounds for many birds in summer, southern marshes offer year-round habitat. Tidal swamps are used by many species, much like their nontidal counterparts (forested wetlands), providing nesting habitat for colonial nesting birds, breeding habitat for a long list of migratory songbirds (neotropical migrants), and food and shelter for many terrestrial animals. In this chapter I introduce the use of tidal wetlands by various animals; more detailed treatments are found in other sources listed as citations or as additional readings. The absence of salt in the water makes tidal freshwater wetlands suitable habitat for many wildlife. Consequently, most of the frogs, toads, salamanders, reptiles, and mammals living in nontidal wetlands in the coastal zone can be found in tidal freshwater wetlands. The focus of this chapter will be on animals of salt and­ brackish marshes since tidal freshwater wetlands are habitats for thousands of animals typical of nontidal wetlands. Invertebrate Habitat Since tidal wetlands include nonvegetated flats, beaches, rocky shores, frequently flooded grasslands, and wet forests, they undoubtedly provide habitats for thousands of invertebrates. The environment, which is alternately flooded and exposed, creates Figure 6.1. Marsh periwinkles (Littoraria irrorata) climbing smooth...

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