Invasive species are among one of the more pressing issues when it comes to ecosystem health. Specifically, invasive species have a negative impact on biodiversity, which has been shown to be a marker of ecosystem stability. In order to try and lessen the impact of invasive species on an ecosystem, we need to understand why and how invaders affect the environment in which they are found.
Although much research has been conducted on invasive species, not much research has been produced on the effect of invasive species in aquatic systems. This is important because according to Carey and Wahl -the two researchers- invading species are: “implicated in the decline of %70 of the fish species listed as threatened or endangered under the US Endangered Species Act”. Researchers at the University of Illinois try to mend this gap by studying the effect of an invasive species on native species of fish. The invader who’s affect they studied was the common carp, see picture below.
The researchers chose to use 1325L mesocosms (think huge fish tank) to study 6 native species of fish, and the carp’s affect on native fish growth, plankton volume and total metabolism. Metabolism is a measure of how much oxygen is dissolved in a given volume. In the mecososms, either 0,1,3 or 6 species of native fish were placed. Carp were either added in on top of the current native fish, or replaced native fish to keep the total mass the same.
Researchers found that more diverse fish populations (with 3 or 6 difference species) lessened the effect of invasive species on the environment. It was found that carp reduced native fish growth. This was pronounced more in the groups with less species of fish compared to the more biodiverse groups. Oddly enough, bluegill fish seemed to be affected the most by invaders. The researchers were not able to explain this phenomenon. However, they hypothesized that the native species grew less because of resource competition. They theorized that the carp were more efficient predators and thus out-competed the native species.
As aforementioned, the researchers also measured the affect of invaders on plankton and other small organisms. It was found that the groups with invaders had lower levels of zooplankton and rotifers than the groups without invaders. This is important because both of these organisms are food sources for fish and with lower counts, ecosystem health suffers. Further, it was found that chlorophyl count (representing plant biomass) increased with the presence of invaders. This might be due to carp eating more organisms than plants. Lastly invaders did not affect net metabolism.
As a reader, you might be wondering at this point in the article how this research relates to real ecosystems. It is worth mentioning that the researchers tried to mimic the environment as much as possible. They did this by conserving native fish species ratios, and introducing the same food sources as found in the wild.
Invasive species have been found to negatively impact the ecosystem in not only terrestrial environments, but aquatic environments as well. This study presents information that might help in the recovery of ecosystems with invasive species. It is very important that we put efforts into conserving ecosystem health for many reasons, among them, our own survival. We now know that a good approach to lessoning the impact of invaders is to ensure a high level of biodiversity.
Carey, Michael P., Wahl, David H. 2010. Native fish diversity alters the effects of an invasive species on food webs. Ecology 91:2965–2974, 2010. http://www.esajournals.org/doi/full/10.1890/09-1213.1
Written by: Alex Ciccone