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Solution Holes in the Rocky Glades Region of Everglades National Park: Sources or Sinks for Non-indigenous Fishes?

Bradley E. Dunker1,2, Shawn E. Liston1,2, Kristine J. Dunker1,2, Jennifer S. Rehage1,2 and William F. Loftus1
1U.S. Geological Survey - Everglades National Park Field Station, Homestead, FL, USA
2Audubon of Florida, Tavernier Science Center, Tavernier, FL, USA

The Rocky Glades region of Everglades National Park (ENP) is a remnant of a large, karstic, short-hydroperiod habitat that separates Shark River and Taylor Sloughs. Historically, solution holes in this region provided dry-season refuge for aquatic animals, and likely provided a source of fish colonists upon re-flooding of the marsh surface. Management of the Everglades has substantially affected Everglades hydrology, decreasing overland sheet flow and reducing hydroperiods in the Rocky Glades. Since 2000, the incidence and relative abundance of non-indigenous fishes in solution-hole refuges in the Rocky Glades have increased markedly, especially Hemichromis letourneuxi (African jewelfish), Cichlasoma bimaculatum (black acara), and C. urophthalmus (Mayan cichlid). It is unclear whether, under current water-management practices, solution holes act as sources of fish colonists upon wet-season re-flooding. If so, there is potential for non-indigenous fishes to affect the ecology of wet-season Rocky Glades marshes.

In this study, we compared the community structure and abundance of fishes in solution holes at the end of the dry season with communities from adjacent marshes immediately upon re-flooding. We sampled weekly in 2002-04 (1) in solution holes during the dry season using 3-mm, wire-mesh minnow traps, and (2) on the marsh surface during the wet season in drift fences with embedded 3-mm, wire-mesh minnow traps. Although the community structure of shallow (≤ 40-cm max. depth) and medium-depth (41 to 80-cm max. depth) holes at the beginning of the dry season was similar to the community found on the marsh surface (dominated by native species), those holes dried annually, resulting in 100% mortality. As water levels receded during the dry season, dissolved-oxygen levels decreased dramatically, providing an increasingly adverse environment for fishes. Communities that survived through the end of the dry season in deep solution holes (≥ 80-cm max. depth) were dominated by H. letourneuxi and C. urophthalmus, which are relatively tolerant of poor water-quality. Comparisons of community structure in solution holes and marsh habitats showed substantial inter-annual variation, related to inter-annual hydrologic variation. During the 2002-03 dry season, water levels remained relatively high, resulting in similar overall fish-community structure in dry-season solution holes and wet-season marshes. In contrast, the 2003-04 dry season was severe, had significantly lower water levels, and as a result, all but two solution holes dried completely. The community structure of those solution holes at the end of the dry season was significantly different from that on the marsh surface upon re-flooding. Solution holes currently appear to serve as sinks for the entire fish community; the few that remain wet are dominated by non-indigenous fishes. Everglades restoration plans include increased water deliveries to this region, but it remains unclear how that will affect the non-indigenous fishes established there.

Contact Information: William F. Loftus, U.S. Geological Survey, Florida Integrated Science Center, 40001 State Road 9336, Homestead, FL 33034, Phone: 305-242-7835, FAX: 305-242-7836, Email: bill_loftus@usgs.gov


(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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