Utilization of Spartina- and Phragmites-Derived Dissolved Organic Matter by Bacteria and Ribbed Mussels (Geukensia demissa) from Delaware Bay Salt Marshes

Abstract

Phragmites australis has been invading Spartinaalterniflora-dominated salt marshes throughout the midAtlantic. Although, Phragmites has high rates of primary production, it is not known whether this species supports lower trophic levels of a marsh food web in the same manner as Spartina. Using several related photochemical and biological assays, we compared patterns of organic matter flow of plant primary production through a key salt marsh metazoan, the ribbed mussel (Geukensia demissa), using a bacterial intermediate. Dissolved organic matter (DOM) was derived from plants collected from a Delaware Bay salt marsh and grown in the laboratory with 14 C-CO 2 . Bacterial utilization of plant-derived DOM measured as carbon mineralization revealed that both species provided bioavailable DOM to native salt marsh bacteria. Total carbon mineralization after 19 days was higher for Spartina treatments (36% 14 CO 2 ±3 SE) compared with Phragmites treatments (29% ±2 SE; Wilcoxon-Kruskal-Wallis rank sums test, P<0.01). Pre-exposing DOM to natural sunlight only enhanced or decreased bioavailability of the DOM to the bacterioplankton during initial measurements (e.g., 7 days or less) but these differences were not significant over the course of the incubations. Mixtures of 14 C-labeled bacterioplankton (and possibly organic flocs) from 14 C-DOM treatments were cleared by G. demissa at similar rates between Spartina and Phragmites treatments. Moreover, 14 C assimilation efficiencies for material ingested by mussels were high for both plant sources ranging from 74% to 90% and not significantly different between plant sources. Sunlight exposure did not affect the nutritional value of the bacterioplankton DOM assemblage for mussels. There are many possible trophic and habitat differences between Spartina-and Phragmites-dominated marshes that could affect G. demissa but the fate of vascular plant dissolved organic carbon in the DOM to bacterioplankton to mussel trophic pathway appears comparable between these marsh types.

Effects of Spartina alterniflora invasion on the communities of methanogens and sulfate-reducing bacteria in estuarine marsh sediments

“…This abundant S. alterniflora -derived organic matter is hydrolyzed and fermented by heterotrophic microorganisms, which can release excess substrates for both methanogens and SRB. The higher abundance of methanogens and SRB in the S. alterniflora stands is also consistent with a report that identified higher TC mineralization capabilities of dissolved organic matter derived from S. alterniflora compared with P. australis -derived matter (Bushaw-Newton et al, 2008). Indeed, the enrichment of sediments with S. alterniflora detritus has been shown to fuel the activity of anaerobic microbial communities (Andersen and Hargrave, 1984; Kepkay and Andersen, 1985).…”

Lignocellulose-responsive bacteria in a southern California salt marsh identified by stable isotope probing

“…Lignocellulose-degrading and utilizing bacteria are ecologically important in any plant-dominated ecosystem ( McCarthy, 1987 ; Romani et al, 2006 ), and in salt marshes bacterial communities are thought to be largely supported by Spartina -derived carbon ( Bushaw-Newton et al, 2008 ). Recent SIP studies utilizing 13 C-labeled substrates have uncovered active microbial cellulose degraders or carbon utilizers in environmental samples ( Haichar et al, 2007 ; Bastias et al, 2009 ; Eichorst and Kuske, 2012 ).…”

Alginate Addition Influences Smooth Cordgrass (Spartina alterniflora) Growth and Macroinvertebrate Densities

“…While we observed a range of mussel sizes, we did not classify sizes, therefore the increased densities we observed likely occurred as a result of a combination of recruitment and migration. Although the increased S. alterniflora in the treatment plots could have provided a food subsidy (Broome et al 1975;Peterson and Howarth 1987;Lin 1989) and additional rhizome attachment sites (Bushaw-Newton et al 2008) for G. demissa, it is also possible that increased settlement in the high marsh could have been stimulated by chemical cues associated with alginate. In addition, S. alterniflora growth may have been further enhanced by the increase in G. demissa density (Bertness 1984;Levin and Talley 2002).…”

“…Increased biomass of S. alterniflora provides more plant surface area for deposition of detrital particles and growth of attached algae, increasing grazing area and habitat for L. irrorata (Stiven and Kuenzler 1979;Fierstein and Rollins 1987;Currin et al 1995). Spartina alterniflora can indirectly contribute to the diet of G. demissa because it is the preferred substrate for bacteria that G. demissa consume via filter feeding (Stiven and Kuenzler 1979;Bushaw-Newton et al 2008) and provides rhizomes for attachment (Bushaw-Newton et al 2008). Uca pugnax prefer to burrow in vegetated muddy sediment with abundant organic material (Teal 1958), and S. alterniflora roots help support crab burrows (Bertness and Miller 1984).…”