Recolonization of sediment-associated microalgae and effects of estuarine infauna on microalgal production

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Abstract
Experiments were performed to determine the rate of recolonization of sediment-associated microalgae and effects of infauna on microalgal biomass and production. Estuarine sediment was defaunated and transplanted to the field and the laboratory. Recolonization of sediment by flora and fauna, relative to control sediment, was measured by chlorophyll a, gross primary production, community O2 uptake and infaunal abundance, sampled at days 1, 10 and 40. Microalgal colonization in the field was rapid with chlorophyll a, returning to control levels by day 10. Infaunal density returned to control levels within 40 d [day]. In the field experiment, the effects of the infauna on the microalgae may have been confounded both by the rapid rate of infaunal recolonization and by the import of microalgae. The laboratory experiment reduced these problems. Removal of infauna in the laboratory, primarily tanaids, increased sediment-associated microalgal growth. After 40 d, chlorophyll a was 4 times greater and gross primary production 2 times greater in the defaunated sediment than in the controls. Grazing of microalgae by infauna appeared to be the mechanism of control. Patterns of community O2 uptake were difficult to interpret and showed on simple relationship with infaunal density. These experiments indicate that estuarine infauna is one of the factors controlling sediment-associated microalgal biomass and production.

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