Miranda, L.E., and D.J. Dembkowski. 2024. Fish size structures in lakes of the Mississippi River floodplain. Freshwater Biology 69:1390-1398. https://doi.org/10.1111/fwb.14313
Abstract
The Lower Mississippi River has a floodplain that includes more than 1,350 permanent lakes carved by shifts in river courses and other hydro-fluvial processes over eons. Notwithstanding their similar provenances, these bodies of water exhibit an immense variety of morphologies and successional stages that illustrate their natural transformation from aquatic to forested wetlands. A result of this geographical, morphological, and temporal diversity is dynamic and varied fish communities. Our goal was to examine how size structures of fish communities in these floodplain lakes were associated with key in-lake and off-lake environmental drivers. In a sample of 30 lakes, an abundance of smaller fish was typically associated with increasing levels of turbidity, chlorophyll-a, phycocyanin, and surrounding agriculture, with the latter likely influencing the preceding three variables. Typically, shallow, hypereutrophic floodplain lakes associated with agricultural landscapes and reduced connectivity experienced harsher physicochemical environments. These conditions appeared to hinder the formation of sustained fish communities but may confer a survival advantage to juveniles or small short-lived species. Conversely, larger fish were associated with increasing lake depth, water clarity, connectivity, and extent of surrounding forests-wetlands. Enhanced stability and size structure was observed in communities residing in deeper and clearer lakes, suggesting that these conditions facilitated the development of longer-lived species spanning multiple age groups. The enhanced connectivity that facilitates this increased stability also permitted the presence of larger itinerant species. Size structure assessments can serve as a valuable ecological and biodiversity indicator in floodplain lakes. These assessments could further supplement, or even supplant, conventional taxonomic analyses that would facilitate enhanced surveillance of this enormous natural resource.