Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Biological Science

First Advisor

Clifford A. Ochs

Second Advisor

Greg Easson

Third Advisor

Ryan Garrick


University of Mississippi

Relational Format



Zooplankton are important components of the food web of such lotic systems. Although capable of motility, they are weak swimmers and their distribution and community composition across a floodplain is strongly affected by patterns of water flow and hydrologic connectivity. However, there has been little research on the zooplankton dynamics of large rivers, such as the Lower Mississippi River (LMR). From morphological identification of zooplankton across the connectivity gradient, I assessed the degree to which hydrologic connectivity acts as an explanatory factor influencing spatial and temporal variation in zooplankton assemblage structure. Second, I compared the use of morphological identification to identification by molecular metabarcoding using Illumina sequencing of the cytochrome oxidase subunit I (COI) gene. Finally, I examined the spatial distribution of haplotypes of three zooplankton species (Anuraeopsis sp. 2017a, Diaphanosoma sp. 1, and Leptodiaptomus siciloides) and tested for evidence of cryptic species in two additional zooplankton species (Keratella cochlearis, and Brachionus calyciflorus). Rotifer assemblages across the sampling area were most correlated with combinations of dissolved nitrogen, turbidity, temperature, and chlorophyll a. Crustacean assemblages were most correlated with combinations of dissolved nitrogen, turbidity, temperature, chlorophyll a, and dissolved oxygen. Temperature was correlated with all beta diversity measures emphasizing a seasonal succession of zooplankton within the LMR. In general, barcoding assemblages is useful for defining patterns in zooplankton across connectivity as a large amount of data can be collected in a relatively short period of time compared to morphological identification. However, at this time, species abundance cannot be determined using Illumina sequencing data. Spatial distribution of haplotypes varied across the three species examined. Finally, one (Brachionus calyciflorus) of the two species tested for cryptic species shostrong agreement between the three methods used, while Keratella cochlearis had no agreement between methods. These results indicate that there may be either physiological limitations to cryptic species members morphologically identified as Keratella cochlearis from across the LMR catchment, causing those members to be excluded in the sample area, or that this region of the COI is relatively conserved across cryptic species of Keratella cochlearis within the sample area.



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