In situ depletion of phytoplankton by an azooxanthellate soft coral

Fabricius, Katharina, Gitai Yahel, Amatzia Genin

Limnol. Oceanogr., 43(2), 1998, 354-356 | DOI: 10.4319/lo.1998.43.2.0354

ABSTRACT: The in situ removal of phytoplankton by the soft coral Dendronephthya hemprichi was investigated by taking small-scale measurements of chlorophyll concentrations around colonies on a reef of the northern Red Sea. The chlorophyll concentration downstream of a 0.75-m-deep colony thicket was depleted by 6.4% (± 1.4% SE) compared with the water upstream. Neighboring organisms are thus exposed to water that is significantly depleted of phytoplankton. A 0.75 X 0.1 X 0.1-m passage of actively feeding colonies removed 34 mg of carbon per day from the water, equivalent to ~1.3 times their respiratory carbon demand. Rates of algae intake were also estimated by determining the decrease in gut fluorescence in starved colonies. The in situ depletion technique showed a three- to sixfold greater sensitivity compared with the gut fluorescence technique, and should be preferred as a technique for estimating feeding rates.

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