For decades, numerous studies have reported that natural underwater environments are being eroded by land development, the addition of non-native species, the changing climate and more. This news has alarmed thousands of environmentalists, fishermen and more, who fear that this change could have a problematic impact on local habitats and fish populations. Now, a report from the University of Florida has used underwater cameras to determine exactly how an invasive plant species is affecting the number of fish in Florida’s natural fish habitats.

Fish need cover and shelter to help them survive. Normally, this need is met by underwater plants, rocks and other objects on the floor of the lakes, rivers, and other waterways they call home. When these fish habitat structures are lost or destroyed, however, fish have no place to seek protection, search for mates, or find food, which can cause the population to diminish. For this reason, many municipalities and private landowners use artificial fish structures, called fish attractors, to simulate natural cover and concentrate fish in certain areas. However, certain ponds in Florida have a different problem: bodies of water in the Kissimmee Chain of Lakes have been taken over by an invasive plant called hydrilla, which creates dense coverage for the lake floor. While this may sound positive, researchers have long speculated that the introduction of non-native plants could drastically change water chemistry, oxygen levels and habitat structures, causing a similar loss in population.

Now, a study from the University of Florida, published in the journal Marine and Freshwater Research, has illustrated a way to study this relationship: the research team found that underwater video cameras can penetrate even dense fish habitat structures like hydrilla, allowing researchers to count the number of fish in the environment. To test the effectiveness of the technique, the research team spent 13 weeks counting fish with the underwater cameras before draining the ponds to obtain the actual fish densities. This verified the effectiveness of the new counting method, in spite of the dense hydrilla in these ponds.

Researchers have used underwater cameras in the past to document fish behavior and count fish in relatively clear areas, but this study is the first to study fish populations in thick vegetation and verify their numbers. Now, the research team hopes that their information may be used to study how species react to invasive fish habitat structures, which could lead to improvements in how artificial fish habitat structures are introduced.

Hydrilla is a problematic presence throughout Florida, Central America, South Africa and Australia. Experts estimate that the state of Florida spent up to $14 million per year during the early 2000s to manage the plant, while the United States as a whole spent $100 million in that same period on invasive plant species during this same period.