Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Deposition of terrigenous sediment on subtidal marine macrobenthos: response of two contrasting community types Technical Report

Lohrer, A.M., Thrush, S.F., Lunquist, C.J., Vopel, J., Hewitt, J.E., Nicholls, P.E.
Journal / Source
Marine Ecology Progress Series
Terrigenous sediment deposition, subtidal marine macrobenthos, disturbance, recovery
Changes in patterns of land-use have altered the regime of terrigenous material export from catchments to rivers and, subsequently, to estuarine and marine communities. This paper describes an experimental study on the impacts of terrigenous sediment in subtidal habitats. THREATS IDENTIFIED AND/OR DESCRIBED: Terrigenous sedimentation, land development SCOPE OF SPECIES, HABITATS AND ECOSYSTEMS IMPACTED: macrobenthic fauna SPATIAL EXTENT OF THREAT STUDIED: Kawau Bay and Mahurangi Harbour TEMPORAL EXTENT OF THREAT STUDIED: 30 days DATASETS USED IN THE ANALYSES: Benthic fauna, sediment characteristics METHODOLOGY USED TO IDENTIFY AND DETERMINE SEVERITY OF THREAT: Experimental deposition of terrigenous sediment into replicate plots at 2 subtidal sites, creating 3 treatment levels (magnitudes of terrigenous material addition). The persistence of the terrigenous deposits was tracked over time and macrobenthic communities were sampled at both sites to compare and contrast their responses relative to controls. Univariate and multivariate statistical techniques was used to characterise the response of macrofauna to the experimental addition of terrigenous sediment KEY FINDINGS OF THE ANALYSIS: The diverse coarse sand community outside the harbour site was more sensitive to terrigenous materials than that which lived in muddier sediments inside the harbour site: both the 3 and 7 mm treatments caused significant change at the site outside the harbour, whereas only the more severe 7 mm treatment caused significant change at site inside the harbour. The terrigenous sediments we added matched the grain size of sediments at the site inside the harbour better, and macrobenthic animals living in turbid tidal estuaries are probably better conditioned to cope with high suspended sediment concentrations and sediment deposition rates. However, beyond a critical threshold, terrigenous sediment had a negative influence on communities at both sites.