Impacts of dense crab populations on carbon exchanges across the surface of a salt marsh

Abstract

Laboratory mesocosm experiments were conducted to quantify the effects of 2 crab species, Sesarma catenata and Cleistostoma edwardsii, on carbon exchanges across the surface of a south temperate salt marsh. The grapsoid crab S. catenata was most abundant in the vegetated marsh flats, and the ocypodoid C. edwardsii In the unvegetated tidal creek. Replicate mesocosms of the marsh flats and tidal creek were incubated with and without crabs of the species dominant in that reglon. Both species enhanced the losses of carbon relative to uptake by the marsh, but they did so vla different mechanisms. In the tidal creek. C. edwardsii increased the net fluxes of total organic carbon (TOC) by 60 % (or 448 mg C m-' d-l), but had no significant impact on community net production (NP). (Bioturbation accounted for 95 %of the enhanced TOC fluxes, and excretion only 5 X). In the marsh flats, S. catenata had no measurable impact on the fluxes of TOC, but decreased community NP by 1132 mg C m-' d-l (Ninety-two percent of this reduction was caused through reduction in epibenthic NP through crab grazlng of mlcroalgae. Crab respiration accounted for only 8 % of the reduction). The crab effects were sufficient to determine whether, for a tide of a particular tlde elevation, the marsh functioned as a carbon source or sink. When crabs were absent, the marsh functioned as a carbon sink at all except the very hlghest tides that, in turn, accounted for only 3 %of all tides inundating the marsh. When crabs were present, the marsh functioned as a carbon source at 87 %, and all except the very lowest tides.

Movement of carbon among estuarine habitats and its assimilation by invertebrates

“…This makes the very restricted movement and assimilation of carbon by invertebrates among estuarine habitats shown by more surprising. There may be some difference simply due to the height of habitats in the intertidal zone (Taylor and Allanson 1995), but the influence of other environmental factors such as tidal regimes on carbon movement has not yet been determined. proposed a model in which estuarine invertebrates rely on autotrophic sources in their immediate surrounds.…”

Impact of fiddler crabs and plant roots on sediment biogeochemistry in a Georgia saltmarsh

“…The burrows generally extend from 3 to 25 cm into the sediment and may exceed abundances of 500 ind. m -2 (Taylor & Allanson 1993). The continuously changing spatial heterogeneity and physical conditions created by burrowing activities of fiddler crabs may affect the dynamics of organic matter decomposition in marshes.…”

“…sulfide). Fiddler crabs not only stimulate microbial activity and metabolism in the sediment (Taylor & Allanson 1993), they may also affect the partitioning between electron acceptors (e.g. sulfate vs Fe [III]) used by anaerobic bacteria in the terminal oxidation of organic carbon (Kostka et al 2002a).…”

Organic carbon fluxes between a high marsh and estuary, and the inapplicability of the Outwelling Hypothesis

“…Primary production of marsh epibenthic microalgae has been shown to be correlated with sediment moisture content (Sullivan & Moncreif 1988). The dry sediments of the marsh flats were heterotrophic, whlle the moister tidal creek sediments were autotrophic (Table 4) (Taylor & Allanson 1993). Because of the much larger area of the marsh flats, the sediments of the marsh as a whole were heterotrophic, channeling carbon to the atmosphere.…”

“…During these tides the vegetated marsh flats remained totally exposed. Even during tides that reached the average maximum tlde elevation of 1.0 m Allanson (1993) above MSL, only 0.5 ha of the vegetated marsh flats were inundated. Thus, for most tides, and for all periods between tldes, the marsh was exposed to the atmosphere, facilitating exhanges of gaseous carbon with the atmosphere rather than organic carbon with the estuary.…”