Factors regulating composition and relative abundance in phytoplankton communities were investigated in an ancient lake with a highly endemic food web. Lake Matano has genera diversity (21) similar to tropical lakes, but low phytoplankton biomass (0.0162 µg/L). Vertical mixing physically limits primary production (42% Zeu:Zm); phytoplankton are moved below the euphotic zone. Macronutrient concentrations (0.30 µmol/L N, 0.13 µmol/L P) are low. Nutrient bioassays used N and P (30-320 µmol/L individually, 60:5-1920:160 µmol/L N:P combined). After 16 days, no significant (p > 0.05) changes in relative abundance and no biologically significant changes in phytoplankton biomass occurred. CHU-10 growth media cultivation, however, significantly increased chl-a. Analysis identified lakewater Cr (0.14 µmol/L) above a threshold to restrict algal growth (0.12 µmol/L) and Mo (0.0005 µmol/L) below requirements by most aquatic life (0.008 µmol/L). Therefore, physical (mixing) and chemical (toxicity, micronutrient) factors are concluded to limit composition and relative abundance of phytoplankton in Matano.

Amy completed her Bachelor''s in Environmental Chemistry from Sir Wilfred Grenfell College (Memorial University of Newfoundland) and her Master''s in Environmental Science (Chemistry and Toxicology) at the Great Lakes Institute for Environmental Research (University of Windsor). She now works as an Environmental Consultant in Toronto, Ontario.