TITLE:
Interactive Effects of Temperature, Nitrogen, and Zooplankton on Growth and Protein and Carbohydrate Content of Cyanobacteria from Western Lake Erie
AUTHORS:
Deepesh Bista, Scott A. Heckathorn, Thomas Bridgeman, Justin D. Chaffin, Sasmita Mishra
KEYWORDS:
Cyanobacteria, Great Lakes, Harmful Algal Blooms, Nitrogen, Temperature
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.6 No.12,
September
25,
2014
ABSTRACT: Harmful
algal blooms (HABs) in freshwater ecosystems, especially of cyanobacterial
species, are becoming more frequent and expanding geographically, including in
Lake Erie in North America. HABs are the result of complex and synergistic
environmental factors, though N or P eutrophication is a leading cause. With
global mean temperatures expected to increase an additional 2°C - 5°C by 2100,
cyanobacterial blooms are predicted to increase even more, given their
typically-high temperature optimum for growth. We investigated how increases in
temperature and nitrogen, singly or in combination, affect the growth, food
quality, and herbivory of Lake Erie cyanobacteria. Algal community samples
collected from Lake Erie, and isolated non-N-fixing (Microcystis aeruginosa) and N-fixing (Anabaena flos-aquae) cyanobacterial species, were cultured at 20°C, 25°C, or 30°C, and at 5, 50, 150, or 250 μM N, and then analyzed for growth and (for isolates) content of total
protein and non-structural carbohydrates (NSC). Temperature and N both affected
algal growth, and there were temperature × N interactions, which were sometimes
affected by presence/absence of zooplankton. For example, cyanobacteria (but
not green algae) growth increased with both temperature and N, especially from
25°C to 30°C, but N and
herbivore presence increased cyanobacterial growth primarily only at 30°C. In general, temperature and N had little
consistent effect on NSC, but increasing temperature and N tended to increase
protein content in Microcystis and Anabaena (temperature effects mostly at
higher N levels). In Anabaena,
increases in N did not increase growth or protein at 20°C or 25°C, but did increase both at 30°C, indicating that N fixation is damaged at
high temperatures and that high NO3 can overcome this damage. These
results indicate that future global warming and continued eutrophication will
increase cyanobacterial growth, as well influence algal herbivory and
competition between N-fixing and non-N-fixing cyanobacteria.