MEPS 479:25-45 (2013)  -  DOI: https://doi.org/10.3354/meps10206

ABSTRACT: To test the interacting effects of hard clams Mercenaria mercenaria and bottom shear stress on nutrient- and ecosystem dynamics, we performed a 4 wk experiment in six 1000 l shear turbulence resuspension mesocosms (STURM). Three tanks each contained 50 hard clams (RC set-up), and 3 tanks had no clams (R set-up). All tanks contained defaunated muddy sediment and estuarine water and had similar water column turbulence intensities (~1 cm s^-1), energy dissipation rates (~0.08 cm² s^-3), and tidal cycles (4 h mixing on and 2 h off). The same high instantaneous bottom stress (0.35 to 0.4 Pa) was applied to all tanks during the mixing-on cycles. Hard clams in interaction with high bottom shear stress initially destabilized the sediments and increased seston levels to ~200 mg l^-1 in the RC tanks during the mixing-on cycles. Over time, seston concentrations declined in the RC tanks until they reached levels similar to the R tanks of ~60 mg l^-1. Bivalve feeding in the RC tanks significantly reduced phytoplankton biomass and shifted the phytoplankton community structure to Chlorophyceae/Prasinophytes. Nutrient (particulate phosphorus, nitrogen, and carbon, dissolved inorganic nitrogen, nitrate + nitrite, phosphate) concentrations were significantly enhanced in the RC tanks, mediated by high sediment resuspension and bivalve excretion. A brown tide organism, Aureococcus anophagefferens, bloomed in 2 of 3 RC tanks. Bivalve feeding and light limitation reduced microphytobenthos biomass in the RC tanks. Microphytobenthos biomass was low overall but significantly higher in the R tanks. Phytoplankton abundance, microphytobenthos biomass, seston concentrations, and nitrogen dynamics were significantly affected by interactions between hard clams and bottom shear stress.

KEY WORDS: Mercenaria mercenaria · Bivalve · Bottom shear · Experimental ecosystem · STURM · Destabilization · Benthic flux · Scaling

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Cite this article as: Porter ET, Mason RP, Sanford LP (2013) Effects of shear stress and hard clams on seston, microphytobenthos, and nitrogen dynamics in mesocosms with tidal resuspension. Mar Ecol Prog Ser 479:25-45. https://doi.org/10.3354/meps10206 Export citation Share:    Facebook - - Bluesky - linkedIn