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Marine Ecology Progress Series

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MEPS 399:15-26 (2010)  -  DOI:

Environmental factors shaping microbial community structure in salt marsh sediments

Matthew R. First1,2,*, James T. Hollibaugh1

1Marine Science Building, Department of Marine Science, The University of Georgia, Athens, Georgia 30602-3636, USA
2Present address
: Woods Hole Oceanographic Institute, Woods Hole, Massachusetts 02543, USA

ABSTRACT: We examined benthic microbial communities in 3 contrasting subtidal salt marsh sediments over the course of a year to investigate the relationship between environmental conditions and benthic microbial community structure. Samples were collected monthly from a high-energy sandy beach, a tidal creek bed, and a Spartina alterniflora marsh border. The concentrations and biomasses of benthic microalgae (BMA), total and potentially active bacteria (measured by an enzyme-activated fluorogenic compound), heterotrophic protists, and metazoan meiofauna were measured at each location. Sediment grain size and porewater pH explained most of the variability in biomass distributions; variations in benthic biomass did not correlate well with temperature. There was a seasonal shift from a BMA-dominated community in the spring and summer months to bacteria-dominated communities in autumn at all locations, when inactive bacteria were most abundant. When normalized to sediment porewater volume, benthic protists concentrations were not significantly related to sediment porosity. Benthic protist porewater concentrations (mean: 3.4 × 103, range: 0.1 to 9.3 × 103 protists ml–1) were comparable to protist concentrations in the water column. In contrast, bacteria were several orders of magnitude more concentrated in the sediments (mean: 4.2 × 109; range: 0.6 to 16 × 109 bacteria ml–1) than the water column. Low abundances of protists relative to bacteria appear to contribute to long bacterial turnover times, especially in fine-grained sediments. We hypothesize that both grazing by meiofauna and low anaerobic growth efficiency lead to relatively low biomass of bacterivorous protists.

KEY WORDS: Marine sediments · Salt marsh · Microzoobenthos · Protists · Bacteria · Biomass

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Cite this article as: First MR, Hollibaugh JT (2010) Environmental factors shaping microbial community structure in salt marsh sediments. Mar Ecol Prog Ser 399:15-26.

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