Graduation Year


Document Type




Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Ernst B. Peebles, Ph.D.

Committee Member

Christopher D. Stallings, Ph.D.

Committee Member

Steven A. Murawski, Ph.D.


deposit feeders, estuary fishes, hyperbenthos, phytoplankton, zooplankton


The ontogenetic movement of juvenile estuary-dependent fishes upstream in estuarine settings is a phenomenon observed around the world. These movements usually coincide with a shift in diet from smaller prey, such as calanoid copepods, to larger prey, such as mysids. However, the mechanism that drives this pattern has yet to be conclusively described. Prior to the current study, zooplankton/hyperbenthos (“zooplankton”), primary production, and water quality data were collected from the Caloosahatchee River estuary in two concurrent and coordinated studies over a two-year period. One of the products of these sampling efforts was a classification of primary-producer types at the sediment-water interface (“depositional states”) along the principal estuarine axis. Four depositional states were described: benthic microalgal dominance (i.e., little or no organic deposition), early phytoplankton deposition, late phytoplankton deposition and post-phytoplankton deposition. Using these classifications as a grouping factor, multivariate analyses were conducted to determine if there were distinct zooplankton communities associated with the four depositional states. An analysis of species indicator values identified the representative taxa for each sediment category. Using the top four returns from the species indicator value analysis for each deposition class, there was clear spatial seriation in zooplankton communities moving upstream from the river mouth: sediment category 1, defined as locations dominated by benthic microalgae that were growing in situ, was characterized by hooded shrimp, chaetognaths and estuarine copepods as its indicator taxa; sediment category 2, defined as locations dominated by early phytoplankton deposition, was represented by decapod zoeae, decapod mysis, percomorph fish eggs and postflexion Anchoa mitchilli larvae; sediment category 3, defined as locations dominated by late phytoplankton deposition, had indicator taxa that included two mysid species, a benthic isopod and a parasitic isopod; sediment category 4, defined as locations dominated by post-phytoplankton deposition (i.e., phytodetritus on bottom with little or no phytoplankton overhead), was associated with freshwater copepods, freshwater cladocerans and the freshwater larvae of the insect Chaoborus punctipennis. Based on these results, and with the knowledge that juvenile estuary-dependent fishes switch prey items as gape limitations change while they grow, I suggest the mechanism behind young fishes moving upstream as they grow is driven by increasing dependence on larger prey (notably mysids) that are supported by phytoplankton deposition. Depositional states where primary-producer cells exist both in the water column and on the estuary floor (such as sediment category 3) attract larger consumers such as mysids, which feed on both suspended diatom cells as well as phytodetritus, and are a preferred prey item for juvenile estuary-dependent fishes. Furthermore, the importance of fresh-water inflow management is highlighted, as this influences the presence and location of phytoplankton blooms.

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