Defense Date


Document Type


Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Jose Lopez, Ph.D.

Second Advisor

Lauren Krausfeldt, Ph.D.

Third Advisor

Matthew Johnston, Ph.D.


Lake Okeechobee, Microcystis, cyanoHABs, microbial community, cyanobacteria, blooms, freshwater ecosystems, high-throughput sequencing


The Lake Okeechobee (Lake O) watershed is a Floridian freshwater ecosystem that has been affected by the increased frequency and intensity of harmful cyanobacterial bloom (cyanoHAB) events occurring over recent decades. Lake O has several ecological and economic purposes such as providing habitats for various organisms and providing drinking water to urban communities surrounding the lake. Toxic cyanoHAB events are posing a threat to the ecosystem and economy of the lake due to the degradation of water quality. This study investigates how the microbial community structure within Lake O is affected by annual cyanobacterial harmful algal blooms over several years by assessing the dominant taxa, temporal patterns, and spatial patterns within the microbial communities and determining if cyanoHABs alter the microbial diversity in Lake O. Filtered surface water samples and public environmental data were collected from 21 routinely monitored sites within and connecting to Lake O from March 2019 to October 2021. DNA extraction, purification, and polymerase chain reactions on the V4 region of the 16S rRNA gene were used to create amplicon libraries for high-throughput sequencing on 541 samples, generating an average of over 40,000 reads per sample. After characterizing the dominant taxa within Lake O, the top four phyla include Proteobacteria, Bacteroidota, Cyanobacteria, and Actinobacteriota, which remained consistent across the sampling period. Microbial alpha diversity exhibited both spatial and temporal changes from year-to-year. The significant spatial differences observed across all three years suggested that there are stable biogeographical patterns within Lake O. Different environmental variables across the sampling period were found to drive beta diversity of the microbial communities in Lake O, with TN:TP ratio, turbidity, ammonia, total phosphate, nitrate + nitrite, dissolved oxygen, and pH remaining consistent in all years. Microcystis relative abundance was found to influence the alpha and beta diversity of the microbial communities, decreasing alpha diversity, and decreasing correlating beta diversity as well. Microcystis relative abundance also correlated with several environmental factors including temperature, total depth, and nitrate + nitrite concentrations. After observing such strong correlations to Microcystis, a co-occurrence network was created and has suggested that specific taxa may influence mutualistic or antagonistic relationships with Microcystis.



Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.