Differences in the benthic-pelagic particle flux (biodeposition and sediment erosion) at intertidal sites with and without clam (Ruditapes philippinarum) cultivation in eastern China.
An annular flume or flux system (AFS) was deployed to measure the biodeposition and sediment resuspension processes at four stations in the mid-shore and low-shore zones along both natural and Manila clam (Ruditapes philippinarum) farming transects in Xuejiadao intertidal area located in Jiaozhou Bay, eastern China. The results showed that there was a significant correlation between biodeposition rates and the density (r=0.984, P<0.05) and biomass (r=0.977, P<0.05) of the suspension feeding Manila clam. The effect of biodeposition at the farming transect was more intensive than at the natural transect where the biodeposition effect was lower than that resulting from natural sedimentation. In contrast, the biodeposition rate at the culture site with the high density of Manila clams was four times the sedimentation rate. Following the addition of Manila clams to increase their density in natural sediments, there was a marked increase in both clearance and biodeposition rates at all four sites. At the site with the highest natural bivalve biomass, the biodeposition rate increased 1.5-fold, while at the site with the least bivalve biomass, it increased by 40 times compared with the biodeposition rate by natural biota. The mean clearance rate of Manila clam was 0.90+/-0.34 l h(-1) ind.(-1) and the biodeposition rate was calculated to be 0.06+/-0.01 g h(-1) ind.(-1). The critical erosion velocities of intertidal sediment at Xuejiadao were from 17.4 to 20.4 cm s(-1). Relationships describing suspended particulate matter (SPM) vs. current velocity were analysed by linear regression following log transformation of the SPM. Statistical analysis of the slopes of the regression lines revealed that there were distinct differences between the low-shore and mid-shore (P<0.05) at both transects, respectively. There was also distinct difference between the two mid-shore stations (P<0.05) possibly due to differences in the densities of bioturbators (e.g. Macoma incongrua etc.), however, there was no significant difference between the two low-shore stations (P>0.05). Furthermore, it was found that the site differences in sediment erodibility were not significantly correlated with measured physical properties of sediments and biota factors such as total macrofauna biomass, total abundance and macrofauna densities, Chl-a and Ph-a (P>0.05). However, there was a significant correlation between sediment erodability and both median grain size (P<0.01) and the density of the bioturbator M. incongrua (P<0.05). There was also evidence of a slight increase in sediment stability after 3 h of air exposure, but the effect was not overcome following the addition of Manila clams. It is hypothesised that the lower stability of sediments at the mid-shore level was probably associated with higher densities of bioturbators and with disturbance by shrimp farming near the high-shore.
Jie
H
H
Ocean University of Qingdao, Qingdao 266003, Shandong, People's Republic of China
Zhinan
Z
Z
Zishan
Y
Y
Widdows
J
J