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publications > paper > seasonal fish community variation in headwater mangrove creeks in the southwestern Everglades: an examination of their role as dry-down refuges
Seasonal fish community variation in headwater mangrove creeks in the southwestern Everglades: an examination of their role as dry-down refuges
Jennifer S. Rehage and William F. Loftus
Addresses: (J.S.R.) Nova Southeastern University, Oceanographic Center, 8000 North Ocean Drive, Dania Beach, Florida 33004-3078. (W.F.L.) U.S. Geological Survey, Florida Integrated Science Center, Everglades National Park Field Station, 40001 State Road 9336, Florida 33034. Corresponding Author: (J.S.R.) Email: <email@example.com>.
By comparison, the connectivity between fish communities in mangrove regions and upstream freshwater habitats has received much less attention. A reason for this is that in many mangrove systems, the freshwater influence is small, and the contribution of freshwater fishes to the estuarine community is limited (Pinto and Punchihewa, 1996; Laroche et al., 1997; Kuo et al., 1999; Nordlie, 2003; Hindell and Jenkins, 2004). In the Greater Everglades Ecosystem, shallow vegetated freshwater marshes transition into an extensive region of tidal mangrove forests (up to 15 km in width, over 60,000 ha of mangroves), which dominates the landscape along the southwest Florida coast (Smith et al., 1994). At the ecotone, mangrove-lined creeks drain upland marshes into a network of interconnecting estuarine rivers, bays, and mangrove forests. The ecosystem is rainfall-driven, marked by strong seasonality (high rainfall in the summer and fall, low in the winter and spring), which greatly influences the spatial extent of inundation of freshwater marshes, as well as the salinity regime of this broad estuarine region (Gunderson and Loftus, 1993).
As in other estuarine systems, salinity levels play an important role in structuring the plant and animal communities of the Greater Everglades Ecosystem (Montague and Ley, 1993; Serafy et al., 1997; Ley et al., 1999; Lorenz, 1999; Faunce et al., 2004). Historically, large volumes of freshwater reached estuarine areas, particularly during the wet season (Fennema et al., 1994). Today, drainage, channelization, and impoundment of marshes have greatly diminished the freshwater inflow into estuarine areas, resulting in substantially higher and more variable salinity regimes (Smith et al., 1989; Montague and Ley, 1993; Light and Dineen, 1994; McIvor et al., 1994). Fish community response to the natural and the anthropogenically-derived variation in freshwater inflow and salinity has been relatively well-studied in the southern and eastern parts of the ecosystem, namely, Florida Bay and Biscayne Bay (Thayer et al., 1987; Montague and Ley, 1993; Serafy et al., 1997; Ley et al., 1999; Lorenz, 1999; Serafy et al., 2003; Faunce et al., 2004; Lorenz and Serafy, 2006); but remains understudied along the southwest region (but see Green et al., 2006), where the mangrove zone is substantially more extensive than in the southern and eastern parts (Smith et al., 1994). Mangrove creeks along this area also drain generally longer hydroperiod marshes than the southern and eastern regions (Fenema et al., 1994). These marshes (Shark Slough) support more diverse and abundant fish assemblages than southern marshes (Taylor Slough) (Trexler et al., 2001; Chick et al., 2004; Green et al., 2006); thus high connectivity between the mangrove and freshwater fish communities may be expected.
In this study, we examined variation in the fish community of headwater mangrove creeks in response to seasonal fluctuations in freshwater flow and salinity in the southwestern region of Everglades National Park (ENP). In particular, we explored the role of low-order, ecotonal mangrove creeks as dry-season refuges for freshwater fishes. As marsh water levels drop, fishes are forced into deeper habitats such as alligator holes, solution holes, canals (Kushlan, 1974; Nelson and Loftus, 1996; Chick et al., 2004; Kobza et al., 2004; Rehage and Trexler, 2006), and presumably headwater creeks. We sampled the fish community in the uppermost stretches of creeks, where habitat may be most suitable for freshwater species because of proximity to marshes and low salinity regimes. A secondary goal of this study was to compare sampling efficiency among gears. Sampling with electrofishing and gill nets targeted large fishes, whereas minnow traps targeted small fishes. Sampling focused on two regions: Rookery Branch (RB) and the North and Watson rivers (NW) (Fig. 1). Headwater creeks in the RB region link the main freshwater drainage of the southern Everglades (Shark Slough) to Tarpon Bay, and the Shark and Harney rivers. Creeks in the NW area are headwaters of the North and Watson rivers which flow into Whitewater Bay. In neither system have the fish communities in the oligohaline reaches received enough attention to describe their seasonal and long-term dynamics beyond surveys that provided inventory data (Tabb and Manning, 1961; Odum, 1971; Loftus and Kushlan, 1987), despite their historical importance as a prey source for wading birds (Ogden, 1994) and their key role in the mangrove food web (Odum, 1971).
SOFIA Project: Role of Marsh-Mangrove Interface Habitats as Aquatic Refuges for Wetland Fishes and Other Aquatic Animals
U.S. Department of the Interior, U.S. Geological Survey
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