Daphnia magna survival and body length differ over short-term and long-term exposure to different concentrations of cyanobacterial neurotoxin BMAA

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Subash Lamichhane, Biology, St. Norbert College, De Pere, WI and Carrie Kissman, Biology and Environmental Science, St. Norbert College, De Pere, WI

Background/Question/Methods
Cyanobacteria, blue-green algae, produces and releases cyanotoxins during harmful algal blooms (HABs) that cause ecological, economic and human and pet health concerns. The majority of cyanobacteria produce the neurotoxin beta-N-Methylamino-L-alanine (BMAA). Human exposure to BMAA may be an environmental cause of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson’s disease, and Alzheimer’s disease. The effect of BMAA on zooplankton has not been studied in depth. We investigated how ingestion of BMAA affects the reproductive and developmental behavior of Daphnia in the short- and long-term. We hypothesized that different concentrations of BMAA will affect the behavior of Daphnia associated with development and reproduction. We predicted that Daphnia would grow slower and produce fewer offspring in higher concentrations of BMAA. Daphnia magna were exposed to BMAA concentrations (0, 1, 10, 50, 100, 200 and 300 μg/L) for 96 hours at 22-24°C with a 16:8 light-dark cycle for the short-term exposure experiment and for 15 days with the same conditions for the long-term exposure experiment. The number of survivors, body length, the number of neonates produced and neonate length were measured. The data were analyzed using One way ANOVA, Kruskal-Wallis, and pairwise comparisons in SYSTAT 13.
Results/Conclusions
Short-term exposure experiment results indicated that BMAA affected the survival of D. magna since the survivorship of D. magna declined significantly as the concentration of BMAA increased. Results also showed D. magna body length did not differ among the survivors or dead with increasing BMAA concentrations, however, D. magna with larger body sizes had better survival as BMAA concentration increased. In the long-term exposure experiment, D. magna exposed to different concentrations of BMAA were larger than those in the control group. However, the survivorship of D. magna was not affected by the BMAA concentrations refuting the hypothesis. Previous studies suggest that the survival of zooplankton during HABs is enhanced by improved physiological resistance to ingested cyanobacterial metabolites, differences in competitive abilities, or by avoiding the ingestion of potentially toxic cyanobacteria via selective grazing. More studies are needed to better understand the mechanism by which the neurotoxin BMAA affects D. magna development and survivorship. A bioconcentration experiment to determine the toxicity uptake in each treatment will help to interpret the findings of our study. As frequencies of HABs increase, it is important to understand the mechanisms of cyanotoxins and their effects on ecological communities to help better control their occurrences.