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# Seasonal trophodynamics of bacterioplankton and heterotrophic microflagellates in Southampton Water

Antai, Ekpo Eyo (1989) Seasonal trophodynamics of bacterioplankton and heterotrophic microflagellates in Southampton Water. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

## Abstract

The trophodynamics of the heterotrophic microplankton population in the Southampton Water estuary was investigated over almost two seasonal cycles. Water samples were collected from two sites, Netley buoy in the mid-estuary and at Calshot buoy at the mouth of the estuary. Bacterioplankton abundance, 3H thymidine uptake rates, bacteria secondary production and microflagellate abundance were routinely measured at both sites at approximately two weekly intervals. Bacterioplankton abundance (determined from epifluorescence cell counts) and carbon prodution (estimated by 3H thymidine uptake rate) ranged from 0.27 to 19.4 x 109 cells l-1 and 0.06 to 19.0 μg C l^-1 hr^-1 respectively with specific growth rates of 0.02 to 0.2 hr^-1. These estimates suggested that bacterial production required a substantial input of dissolved organic carbon into the estuary which is at least in part supplied by phytoplankton primary production in the estuary. The temporal and spatial distribution of bacterial parameters covaried with phytoplankton biomass (determined by chlorophyll a concentration). Heterotrophic microflagellate abundance determined by epifluorescence microscopy ranged from 0.5 to 9.8 x 10^6 cells l^-1. The estimated grazing rates were consistent with bacterial growth rates which suggests these organisms to be the dominant bacteriovores in the estuary. In a second phase of this study, the bioenergetics and physiology of a heterotrophic microflagellate (identified as colourless Chrysomonad, diameter, 8 - 12μm) isolated from Southampton Water were studied in batch cultures grown at 10, 15, and 20oC. The results indicated that the isolated phagotrophic microflagellate can effectively ingest bacteria at rates between 1 and 220 bacteria flagellate-1 hr-1 depending on the initial bacteria concentration and growth temperature. The growth rates, clearance rates and ingestion rates of the Chrysomonad isolate were determined at each temperature using a mixed bacterial culture as a food source. Measurements of the microflagellate respiration and ammonium excretion rates were determined using a combination of differential filtration and inhibitor. Rates of ammonium excretion and respiration of the microflagellate showed an increase over the range of growth temperatures used. Estimates of ammonium excretion rates were consistently higher in cultures of microflagellates with added prokaryotic inhibitors than those with active' bacterial cells. The differences were attributed to bacterial uptake of excreted ammonium. Results from this study have established that bacteria can form an important component of the plankton in productive estuaries and seasonal changes in their abundance and secondary production are correlated with phytoplankton biomass. The bacterioplankton were actively grazed by heterotrophic microflagellates at rates consistent with bacterial growth rate. The possible role of these microflagellate bacteria grazers in the estuarine plankton is discussed with reference to the flow of energy to higher trophic levels through the microbial loop'.

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## More information

Published date: 1989

## Identifiers

Local EPrints ID: 461971
URI: http://eprints.soton.ac.uk/id/eprint/461971
PURE UUID: 3bcb190d-2d9a-42e7-a144-5ce89165266e

## Catalogue record

Date deposited: 04 Jul 2022 18:59
Last modified: 04 Jul 2022 18:59

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## Contributors

Author: Ekpo Eyo Antai

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