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. 2011;6(10):e27065.
doi: 10.1371/journal.pone.0027065. Epub 2011 Oct 28.

Sedimentary environment influences the effect of an infaunal suspension feeding bivalve on estuarine ecosystem function

Hannah F E Jones  1 , Conrad A Pilditch, Denise A Bruesewitz, Andrew M Lohrer
Affiliations

Sedimentary environment influences the effect of an infaunal suspension feeding bivalve on estuarine ecosystem function

Hannah F E Jones et al. PLoS One. 2011.

Abstract

The suspension feeding bivalve Austrovenus stutchburyi is a key species on intertidal sandflats in New Zealand, affecting the appearance and functioning of these systems, but is susceptible to several environmental stressors including sedimentation. Previous studies into the effect of this species on ecosystem function have been restricted in space and time, limiting our ability to infer the effect of habitat change on functioning. We examined the effect of Austrovenus on benthic primary production and nutrient dynamics at two sites, one sandy, the other composed of muddy-sand to determine whether sedimentary environment alters this key species' role. At each site we established large (16 m(2)) plots of two types, Austrovenus addition and removal. In winter and summer we deployed light and dark benthic chambers to quantify oxygen and nutrient fluxes and measured sediment denitrification enzyme activity to assess denitrification potential. Rates of gross primary production (GPP) and ammonium uptake were significantly increased when Austrovenus was added, relative to removed, at the sandy site (GPP, 1.5 times greater in winter and summer; ammonium uptake, 8 times greater in summer; 3-factor analysis of variance (ANOVA), p<0.05). Denitrification potential was also elevated in Austrovenus addition plots at the sandy site in summer (by 1.6 times, p<0.1). In contrast, there was no effect of Austrovenus treatment on any of these variables at the muddy-sand site, and overall rates tended to be lower at the muddy-sand site, relative to the sandy site (e.g. GPP was 2.1 to 3.4 times lower in winter and summer, respectively, p<0.001). Our results suggest that the positive effects of Austrovenus on system productivity and denitrification potential is limited at a muddy-sand site compared to a sandy site, and reveal the importance of considering sedimentary environment when examining the effect of key species on ecosystem function.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Location of sites (indicated by a star) in Tauranga Harbour, New Zealand.
Sd  =  Sandy site, Ms  =  Muddy-sand site.
Figure 2
Figure 2. Austrovenus stutchburyi abundance and biomass.
Mean (+ 1 SD; n = 3) Austrovenus abundance (A) and biomass (B) in Austrovenus addition (+AS; grey fill) and removal (–AS; no fill) plots as a function of site and season.
Figure 3
Figure 3. Macrofauna (excluding Austrovenus stutchburyi) abundance and biomass.
Mean (+ 1 SD; n = 3) macrofauna abundance (A) and biomass (B) in Austrovenus addition (+AS) and removal (–AS) plots as a function of site and season.
Figure 4
Figure 4. O2 fluxes and gross primary production (GPP).
(A) Mean (+ 1 SD; n = 3) O2 fluxes in light (no fill) and dark (black fill) chambers in Austrovenus addition (+AS) and removal (–AS) plots, as a function of site and season. Positive values represent an efflux out of the sediment, and negative values represent an influx into the sediment. (B) Mean (+ 1 SD; n = 3) normalised GPP (light minus dark chamber O2 flux) in +AS (grey fill) and –AS (no fill) plots, as a function of site and season.
Figure 5
Figure 5. NH4 + fluxes and uptake.
(A) Mean (+ 1 SD; n = 3) NH4 + fluxes in light (no fill) and dark (black fill) chambers in Austrovenus addition (+AS) and removal (–AS) plots, as a function of site and season. Positive values represent an efflux out of the sediment, and negative values represent an influx into the sediment. (B) Mean (+ 1 SD; n = 3) NH4 + uptake (dark minus light chamber NH4 + flux) in +AS (grey fill) and –AS (no fill) plots, as a function of site and season.
Figure 6
Figure 6. NO3 − and PO4 3 − fluxes.
Mean (+ 1 SD; n = 3) NO3 − (A) and PO4 3− (B) fluxes in light (no fill) and dark (black fill) chambers in Austrovenus addition (+AS) and removal (–AS) plots, as a function of site and season. Positive values represent an efflux out of the sediment, and negative values represent an influx into the sediment.
Figure 7
Figure 7. Sediment DEA (denitrification enzyme activity; i.e. denitrification potential).
Mean (+ 1 SD; n = 3) DEA in Austrovenus addition (+AS; grey fill) and removal (–AS; no fill) plots as a function of site and season.
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