EFFECTS OF NUTRIENT ENRICHMENT AND GRAZING BY AN INVASIVE FILTER-FEEDER ON PHYTOPLANKTON BIOMASS

BRUSCHETTI, C.M.; ADDINO, M.; LUPPI, T.; IRIBARNE, O.O

mar del plata

Conferencia; 2nd World Conference on Biological Invasions and Ecosystem Functioning; 2011

Invasive species may exert strong effects on structure and function of marine ecosystem. Top-down effects of invasive predators and bottom-up effects related to resource availability can be important in determining community structure and function. In estuaries, filter-feeders can counteract the production of phytoplankton and regulate the abundance of primary producers. However, nutrient enhancement can increase microalgal biomass and productivity. In this context, the objective of this work was evaluate the effect of the invasive polychaete Ficopomatus enigmaticus on phytoplankton biomass, the increase of nutrients on pelagic primary productivity of the Mar Chiquita coastal lagoon. In order to evaluate this objective an experiment with mesocosms (n=4) was performed, and consisted in 4 treatments: T1) with nutrients, T2) with reefs and nutrients, T3) with reefs and T4) without reefs and nutrients (control). Samples of water (500 ml) were obtained from mesocosms in order to determinate in vivo Chlorophyll a concentration (Chla), turbidity and nutrients concentration (NO3-, PO43- and NH4+). The experimental nutrient enrichments (T1 and T2) successfully increased nutrient concentration above control treatments and ambient concentration. However, the concentration of nutrients was higher in the treatment with reefs of Ficopomatus and nutrient addition (T2) during all sampling days. Nutrient supply increased the Chla concentration inside mesocosms, but when we added reefs the concentration of Chla decreased. In conclusions, the nutrients increased the pelagic primary producers but grazing by reefs of Ficopomatus counteracts these increments. We conclude that top-down and bottom-up processes can be important joint determinants of primary production in this lagoon.