COS 73-3 - Hydrology-mediated ecological function of a large wetland threatened by an invasive predator

Background/Question/Methods

Invasive species are one of the greatest threats to freshwater ecosystems, disrupting ecosystem function and leading to the collapse and extinction of native species. The Everglades ecosystem is the largest wetland system in the United States and is the focus of the largest and most expensive environmental restoration effort in history. Recovery of historical wading bird populations is a major goal of this restoration, and recovery of seasonally pulsed prey (fish, crayfish) is a trophic ecosystem function considered critical for their recovery. Non-native fishes have been found in the Everglades since the 1960s, but it was not until 2007 that Asian Swamp Eels (Monopterus albus/javanensis) were first found in Everglades National Park. While populations of many native fishes in the Everglades are intricately tied to the natural hydrological dynamics of the system, swamp eels are drought-resistant fish that opportunistically feed on many fishes and invertebrates. We used a 25-year dataset of aquatic animals in Taylor Slough of Everglades National Park to model relationships between common native species and hydrology prior to invasion and then assess changes in populations following invasion.

Results/Conclusions

Swamp eels were first detected at our long-term monitoring sites in Taylor Slough between 2012 and 2014. Since their arrival, swamp eels have become the most common large fish in the region, being more common than all other large fishes combined. Three years after the spread of swamp eels throughout the region, populations of two crayfishes and two fishes collapsed by ≥90%, two fishes had intermediate declines of 35–70%, and two fishes and grass shrimp remained unchanged. Species most strongly affected by swamp eels were reliant on predator-free habitats at the onset of the wet season, suggesting swamp eels have undermined ecosystem processes and trophic functions of the Everglades by disrupting the hydrology-mediated production of aquatic animals that are prey for many larger predators. Ongoing restoration is designed to restore hydrological conditions that support higher populations of crayfishes and small fishes, and nesting wading birds reliant on them. Water management and connectivity to canals may have facilitated the invasion of swamp eels, and as they continue to spread across the ecosystem there may be severe consequences for the trophic dynamics of, and expected restoration benefits for, the Everglades.