Dynamic patterns of linkage between marshes and alligator ponds: Disturbance regime and refuge use by fishes in the Florida Everglades

Background/Question/Methods Disturbance can strongly influence linkages between habitats, especially when some habitats serve as refuge from harsh environmental conditions. In the Florida Everglades, alligator ponds exist as patches of relatively deep-water habitat embedded within the larger habitat matrix of the marshes and provide a source of refuge for aquatic organisms during seasonal droughts. Using an eleven-year record of hydrological conditions and fish abundance in 10 marsh sites and 34 alligator ponds dispersed among three regions of the Everglades, we sought to characterize patterns of linkage between marsh and alligator pond habitats. We quantified patterns of alligator pond use during non-stressful periods and episodes of drought in order to identify fish species that use alligator ponds as refuge, are resident in alligator ponds throughout the year, and to determine sources of variation in fish abundance within alligator ponds. Simultaneous measurement of fish and environmental conditions in surrounding marshes allowed us to determine if fish abundance and community structure in alligator ponds mirrored dynamics in the more spatially extensive, donor habitat. During the study, recovery time between disturbances decreased in all study areas, providing an opportunity to quantify the influence of disturbance regime on patterns of refuge use.

Results/Conclusions Fish abundance was positively related to recovery time between disturbance and as recovery times decreased during the study, abundances declined in the marshes of all three regions. Fish abundance in alligator ponds increased during seasonal declines in water level and was related to intensity of disturbance, size of refuge, and abundance in donor habitat. Assemblage structure in alligator ponds changed between the wet and dry season primarily because of immigration of large numbers of yellow bullhead and warmouth from the surrounding marsh during declines in water level. In portions of the Everglades landscape where recovery time between disturbances decreased the most during the eleven years of the study, declines in fish abundance and changes in assemblage structure in alligator ponds paralleled changes measured in the marshes.