Ecological Impacts of Hydrilla

Hydrilla poses a serious threat to the ecological health of the areas it infests. 

It has several adaptations that allow it to be so successful:

1. It can tolerate lower light conditions than most aquatic plant species, which allows it to begin photosynthesizing earlier in the morning, giving it an advantage. 
2. It spreads efficiently through both tubers and turions. 
3. There are no native predators that eat hydrilla, and so their growth is not checked.

These adaptations allow hydrilla to out-compete other plants for space to grow. In fact hydrilla is so successful it can double its biomass every two weeks during the summer, and can fill the entire water column up to 20 feet deep, therefore creating a monoculture- a term used to describe areas dominated by a single species, as opposed to a regular ecosystem that contains many species. Monocultures can be harmful when they limit the ability of animals in the area to find food or habitat and by preventing the growth of native plants, effectively reducing biodiversity. 

Although hydrilla can provide habitat for fish, it unbalances the predator-prey relationships of some fish. Some predator fish (like sunfish and bass) attack their prey by ambushing them, and benefit from the additional cover provided by hydrilla. However in the long-term this can lead to an overall decline in the fish population, and eventually even the fish that prefer cover cannot hunt when hydrilla becomes too dense.

Hydrilla also harms fish because it depletes oxygen levels of the water. Hydrilla, like all plants, gives off CO2 and uses oxygen during the night time (although the opposite is true during the day), which can bring oxygen levels to dangerously low levels for fish. Additionally an increase of hydrilla can cause an increase in released nutrients from sediments that cause algae blooms, again depleting oxygen levels.

Bird populations are affected by declines in fish population, and can also be harmed by toxic blue-green algae that grows on hydrilla leaves.

(The California Department of Food and Agriculture Hydrilla Eradication Program Annual Progress Report 2010)

Last updated November 1, 2016