Invasive Myriophyllum spicatum and nutrients interact to influence algal assemblages
Eutrophication and invasive species are widespread stressors that have the potential to interact and alter the biodiversity and productivity of aquatic ecosystems. We conducted a two-way factorial mesocosm experiment testing interacting effects of nutrient loading and presence of the invasive macrophyte Myriophyllum spicatum on the composition, biomass, and productivity of attached and suspended algal assemblages. Chlorophyll a concentrations, a proxy for suspended algal biomass, were an average of 75% higher on all sampling dates in high nutrient treatments than in low nutrient treatments. By the end of the 30-day experiment, biovolume of attached algae suspended in the water column (e.g., Bulbochaete sp. and Cladophorasp.) was 35 × higher in treatments containing M. spicatum than in those that did not and 11 × higher in high nutrient treatments than in low nutrient treatments. This increase in attached algae was associated with changes in ecosystem productivity, including a 10% increase in dissolved oxygen saturation during the day and 1.3–2.4 × higher rates of gross primary production in high nutrient treatments with M. spicatum. NMDS analysis revealed major taxonomic shifts in the algal assemblage as the experiment progressed, including a loss of large diatoms and an increase in cryptomonads, planktonic chlorophytes, and attached chlorophytes. Nutrient enrichment may be critical in affecting rates of overall ecosystem productivity, but the structure of the assemblage contributing to that productivity may be influenced by interactions between nutrient enrichment and the presence of rooted macrophytes.
Ortiz, J. E.,
Juneau, K. J.,
Invasive Myriophyllum spicatum and nutrients interact to influence algal assemblages.
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