Environmental factors shaping microbial community structure in salt marsh sediments

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 × 10 3 , range: 0.1 to 9.3 × 10 3 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 × 10 9 ; range: 0.6 to 16 × 10 9 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 Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 399: [15][16][17][18][19][20][21][22][23][24][25][26] 2010 derived carbon appeared in meiofauna within 1 h of the addition of 13 C bicarbonate; bacteria incorporated the labeled carbon within several hours (Middelburg et al. 2000). These and other observations suggest that algal-derived carbon is channeled through 2 discrete pathways: (1) directly to herbivorous metazoan meiofauna, or (2) through bacteria to the microbial food web (van Oevelen et al. 2006). However, exchanges between these trophic pathways also occur. For example, diatoms were ingested by both protists and meiofauna (Epstein 1997a) and ingestion of bacteria by meiofauna and microinvertebrates has been observed (Kemp 1987). Additionally, the linkages between bacterivorous microbenthos and meiofauna (Epstein & Gallagher 1992, Hamels et al. 2001a) indicate that the 2 major routes of carbon flow in benthic environments, at least at times, intersect.The processes regulating the abundance and activity of bacteria in sediments are especially important as sediment bacteria play a significant role in benthic metabolism and geochemistry by transforming carbon, nitrogen, and sulfur compounds (revi...

Ecosystem engineering by large grazers enhances carbon stocks in a tidal salt marsh

“…Our results imply that because we can manage livestock grazing in many ecosystems, it being a well-used management tool in European marshes (Dijkema 1990, Esselink et al 2009, we can manage and enhance carbon stocks in mature marshes and potentially in other terrestrial ecosystems (Sjögersten et al 2012). However, the balance between indirect and direct effects due to grazers needs to be determined in each individual ecosystem independently.…”

Cordgrass Biomass in Salt Marshes

“…Below-and above-ground biomasses are key functional traits that play very important roles in the ecological behavior of cordgrasses. Thus, Spartina biomass influences on the carbon content of marsh sediments (Tanner et al, 2010), the marsh carbon stock (Wieski et al, 2010), marsh methane emissions (Cheng et al, 2010), salt marsh microbial community (First & Hollibaugh, 2010;Lyons et al, 2010), grazing (Burlakova et al, 2009), sediment dynamic (Neumeier & Ciavola, 2004;Salgueiro & Cacador, 2007;Li & Yang, 2009), etc. Cordgrass biomass affects the emergent of the habitat structure, facilitating succession development by providing a base for habitat development (Castellanos et al, 1994;Figueroa et al, 2003;Proffitt et al, 2005;Castillo et al, 2008b).…”

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“…The ciliates could also be consuming bacteria, but flagellates are a more likely food source, and presumably a more "attractive" one for ciliates in view of the much greater nutritive value of each cell and the coarser filter required (Fenchel, 1988;ElSerehy and Sleigh, 1993;First and Hollibaugh, 2010). The filter-feeding ciliates in waters of the Ras Mohammed protectorate are numerous enough during spring to filter the whole water body four times a day, and the ciliate population could therefore surely catch enough flagellates during this time to provide for ordinary growth and maintenance of the population.…”

“…The food chain of bacteriaflagellates-ciliates may consume about 60-70 % of primary production in the water column (Pomeroy, 1974 andAzam et al 1983). Although the existence of the microbial loop has been known for some time, the precise nature of the linkages and the rates of the processes involved in the microbial loop are still being studied and are only now close to being fully understood by biological oceanographers (JoaquimJusto et al, 2006;First and Hollibaugh, 2010). This "loop" may really be an almost closed circuit, with little energy passing to the larger zooplankton such as copepods and indeed, might be seen as a parallel food chain to the conventional "grazing" chain of phytoplankton-zooplankton-fish.…”