Fish Community Colonization Patterns in the Rocky Glades Wetlands of Southern
Florida
William F. Loftus, Robert M. Kobza, and Delissa Padilla
U.S. Geological Survey, Center for Water and Restoration Studies, Miami, FL
Joel C. Trexler
Florida International University, Miami, FL
As part of a larger effort to assess the role of aquatic refuges and subterranean habitats in system restoration, we began collecting baseline data on the ecology of constituent aquatic communities of the Rocky Glades in the wet season of 2000.
The Rocky Glades is a threatened, short-hydroperiod habitat that remains intact structurally only within Everglades National Park (ENP), but even there its hydrology has been adversely affected by drainage. Pre-drainage accounts indicate that this region once had higher water levels that likely provided a richer habitat for aquatic species. Little has been published about the species composition of animals that survive below-ground through the dry season, their community patterns once above-ground, and their movements back into holes as water recedes in autumn. The highly eroded landscape offers dry-season refuge to aquatic animals in solution holes, which also allow them access to groundwater. As soon as rains flood the area in the early summer, fishes and invertebrates immediately appear on the wetland surface. We are investigating whether recolonization of the surface is a function of survival in local refuges, results from rapid, long-distance dispersal, or a combination of both.
In the early 1990s, we observed mass, early wet-season fish movements in the
Rocky Glades, which sparked this study of the fish communities and dispersal. In the first project year, we tested methods designed to detect directional dispersal by using drift fences and funnel traps along a hydroperiod Figure 1. Drift-fence Arrays 1-13 in ENP.

gradient. Several questions arose from these preliminary observations of dispersal in the Rocky Glades: How rapidly do different species appear in the arrays? Are the movement patterns of animals related to water flow?; Do the animals disperse from the main sloughs to recolonize the Rocky Glades or, Are the Rocky Glades acting as a source of animal colonists for the sloughs?; Do roadways act as barriers to movement?; How do composition, size-structure, and recruitment of aquatic animals change during the flooding period?
In 2000, we erected four x-shaped drift-fence arrays (Arrays 1 to 4: fig. 1), with
12 m wings made of black plastic cloth, along the main park road of ENP. The wings of the fences directed animals into traps that face the compass directions
(fig. 2). When the wetlands flooded in June, we made daily collections for the first two weeks, reduced the frequency to twice weekly for three weeks, and to weekly collections until drydown. We identified, weighed, and measured all animals in the lab. In
2001, a more spatially expansive study was implemented
Figure 2. Trap retrieval at Array 4.
The number of animals in each trap on a particular day seemed to be related to the water flow and depth, with the highest number taken during the highest flows.
Most animals dispersed rapidly after the wetlands flooded. Preliminary assessments of the data indicated that the direction and degree of rheotaxy varied by species. Fishes and crayfish often reappeared in the traps on the same day that the wetlands flooded, supporting the case for local subterranean refuges.
However the largest numbers of fishes appeared within two weeks of flooding
(fig. 3). It remains unclear whether they may have been able to disperse for tens of kilometers across the heavily vegetated wetland landscape from Shark Slough and its estuarine creeks in that time. Hypotheses about dispersal patterns will be tested in 2003-2004 using methods such as stable isotope and otolith microchemistry analyses, and radio-tracking of larger species.

20
Everglades pygmy sunfish
Array 4, 2001
Golden topminow
Tadpole madtom
15
10
Spotted sunfish
Dollar sunfish
Warmouth
Mayan cichlid
Largemouth bass
Bluefin killifish
Bluegill
Taillight shiner
5
Sheephead minnow
Sailfin molly
Pike killifish
Black acara
Least killifish
Flagfish
Marsh killifish
Mosquitofish
0
0 1 2 3 5 10 15 20 25 30 35
Week of Inundation
Figure 3. Appearance of fish species by week of sampling at Array 4 in 2000 and 2001.
Subsequent sampling provided data on community-succession patterns as new species appeared in the traps and relative abundances changed. Size-structure data have been used to document the onset of reproduction. Most fishes emerging onto the surface were adults that began reproducing with one or two weeks.
Small juveniles appeared in the traps within a month of flooding.
The study of ecological interrelations between surface and subterranean habitats will help determine how human management has affected this region and what benefits can be anticipated by the restoration of natural hydrology. The temporal dynamics of the use of Rockland habitats in relation to hydrology have just begun to be described. This project will provide data important to simulation models, such as whether solution holes in the Rockland function as sources or sinks for fishes and how hydropattern affects trophic structure and the composition of aquatic animal communities in this landscape .
This research was funded through the Critical Ecosystem Studies Initiative by agreement between the U. S. Geological Survey (USGS) and the U. S. National
Park Service.
Bill, Loftus, U. S. Geological Survey, 40001 State Road 9336, Homestead,
Florida, 33034, Phone: 305-242-7835, Fax: 305-242-7836,
Bill_Loftus@usgs.gov
, Ecology and Ecological Modeling