MEPS 254:69-80 (2003)  -  doi:10.3354/meps254069

Effects of the invasive, nonindigenous seagrass Zostera japonica on nutrient fluxes between the water column and benthos in a NE Pacific estuary

Scott T. Larned1,2,*

1Coastal Ecology Branch, United States Environmental Protection Agency, 2111 SE Marine Science Drive, Newport, Oregon 97365, USA
2Present address: National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand

ABSTRACT: The effects of Z. japonica on dissolved nutrient fluxes between the water column and the benthos in Yaquina Bay, Oregon, USA were examined. Nutrient fluxes in Zostera japonica habitats were compared to those in adjacent unvegetated sediment in warm and cool seasons, and in daylight and darkness. In daylight, Z. japonica habitats were net sinks for nitrate (NO3), ammonium (NH4) and dissolved reactive phosphorus (DRP) in the warm season, and for NO3 and DRP in the cool season. At night in the warm season, Z. japonica habitats were net sinks for NO3 and NH4. Unvegetated sediments were net sources of NH4 to the water column in daylight in both seasons, and net sinks for NO3 at night in the warm season. On a diel basis, Z. japonica habitats habitats were net sinks for NO3 and NH4, and unvegetated sediments were net sources of NH4. Porewater NO3 and NH4 concentrations in unvegetated sediments were twice those in Z. japonica habitats. Nutrient fluxes in abutting monospecific patches of Z. japonica and the native seagrass Z. marina were also compared. Both species were sinks for NO3, NH4 and DRP. NO3 influx rates per unit above-ground biomass were higher in Z. japonica habitats, but areal rates of NO3 influx were higher in Z. marina habitats, reflecting the latterŒs higher biomass. The data demonstrate that Z. japonica invasions alter water column-benthos nutrient fluxes. These alterations may in turn affect pelagic primary production. At current biomass levels, Z. japonica is estimated to remove 50 to 60 mole dissolved inorganic nitrogen (DIN) h-1 and 0.2 to 2.2 mole DRP h-1 from the Yaquina Bay water column, and continued expansion of Z. japonica in the estuary could lead to substantial reductions in nutrient availability.

KEY WORDS: Estuary · Invasion · Nonindigenous species · Nutrient flux · NE Pacific · Porewater · Seagrass · Sediment · Zostera japonica

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