which has exacerbated the invasiveness. Major Effects of Invasion
Hyacinth invasions around the world have many effects on the sur-
rounding ecosystem. However, unlike wolf eradication, these consequences are not neatly divided between abiotic and biotic effects on the environment. Eichhornia crassipes can greatly alter water quality in several ways including greatly decreasing dissolved oxygen content. This is a result of the leaf cover of hyacinths which prevent surface mixing, as well as shading primary producers (phytoplankton and native plants) subsequently preventing them from photosynthesizing and adding oxygen to the water (Villamagna & Murphy 2009). E. crassipes can also alter water nutrient levels because the plant has the ability to uptake and store greater levels of nutrients, like nitrogen and phosphorus, than it actually requires for future use in the event of nutrient shortages. The capability for nutrient uptake makes water hyacinths popular as waste water scrubbers, but can create imbalances in the nutrient levels of a normal freshwater ecosystem (Moran 2006). Villamagna and Murphy’s (2009) study investigates impacts on several aspects of the invaded ecosystem. Large hyacinth mats can negatively impact primary producers by out-competing them for space and sunlight. Decreases in production caused by competition are not always immediately seen because hyacinths may trap detritus that acts as an alternate food source for these producers. Both zooplankton and fish community structures act in highly variable ways dependent on preexisting populations, chemical conditions, predator presence, and season. Macroinvertebrates also show varying responses but it is largely thought that the novel habitat and shelter structure provided by the leaves and roots are beneficial to insect larvae, snails, and other larger invertebrates (Villamagna & Murphy 2009). Though research has not fully explored potential negative impacts on invaded ecosystems, continued research on E. crassipes is important in preventing potential harm to fresh water systems. 30
Excellence in Upper-Level Writing 2012