Toxin Production and Population Dynamics of Gloeotrichia echinulata with Considerations of Global Climate Change

Global climate change has been identified as a driver for increasing cyanobacteria blooms world-wide. Blooms of the cyanobacterium, Gloeotrichia echinulata, (hereafter, G. echinulata) have been observed in Silver Lake (Oceana County, MI), often forming dense surface scums. This organism is known to produce the hepatotoxin, microcystin- LR, and its growth is linked to phosphorus accumulation from sediment and temperature. A series of experiments at ambient and elevated temperatures (+2° and +6°above ambient) with sediment from four locations in Silver Lake with varying phosphorus concentrations were conducted to examine the effect of these variables on G. echinulata growth. These experiments were designed to examine the effects of global climate change and sediment phosphorus concentrations on G. echinulata blooms. Initially, colonies were incubated to induce akinetes. Akinetes then were incubated in growth chambers at three different temperatures (17°C, 19°C, and 23°C) for 30 days in test tubes filled with 30 mL of filtered lake water and 5mL of sediment from one of the four locations. On alternate days, 25 mL of lake water was withdrawn from each test tube, placed into a scintillation vial, and preserved with Lugol’s solution until enumeration. Withdrawn water was replaced with 25 mL of filtered lake water. At the end of the incubation period, settling chambers were used to enumerate filaments germinated by each colony. The concentration of microcystins was examined three times throughout the sampling season, using 500 washed and filtered pelagic colonies, and analyzed by LC-MS. Lastly, time-to-event statistics were performed on temperature and phosphorus treatment data. The results showed that G. echinulata colonies produced low levels of microcystin-LR and microcystin-RR in Silver Lake (0.17 μg/l and 0.09 μg/l, respectively). Results showed that it was possible to induce early akinete development in G. echinulata by approximately four days using lowered incubation temperatures and shorter periods of light availability. Results of various temperature and phosphorus treatments showed a significant difference in temperature and phosphorus treatments. A high temperature produced earlier germination, regardless of phosphorus concentrations (χ2 = 0.2, df = 1, p = 0.622). However, at low temperatures, phosphorus concentrations became important in germination times (χ2 = 7, df = 1, p = 0.01)