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

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 (NO 3 ), ammonium (NH 4 ) and dissolved reactive phosphorus (DRP) in the warm season, and for NO 3 and DRP in the cool season. At night in the warm season, Z. japonica habitats were net sinks for NO 3 and NH 4 . Unvegetated sediments were net sources of NH 4 to the water column in daylight in both seasons, and net sinks for NO 3 at night in the warm season. On a diel basis, Z. japonica habitats habitats were net sinks for NO 3 and NH 4 , and unvegetated sediments were net sources of NH 4 . Porewater NO 3 and NH 4 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 NO 3 , NH 4 and DRP. NO 3 influx rates per unit above-ground biomass were higher in Z. japonica habitats, but areal rates of NO 3 influx were higher in Z. marina habitats, reflecting the latter's higher biomass. The data demonstrate that Z. japonica invasions alter water columnbenthos 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.

A Comparison of Bulk Estuarine Turnover Timescales to Particle Tracking Timescales Using a Model of the Yaquina Bay Estuary

“…2) is a macro-tidal drowned-river estuary located on the central Oregon coast of which about 60 % of the area is intertidal (Larned 2003). The estuary area is roughly 11.5 km 2 in a drainage basin about 445.6 km 2 reported by multiple sources (Choi 1975;Sigleo and Frick 2007).…”

The Invasive Species Challenge in Estuarine and Coastal Environments: Marrying Management and Science

“…To date, only a handful of studies have measured the effects of invasive species on the cycling and storage rates of carbon and nitrogen in coastal systems (e.g., Larned 2003;Ruesink et al 2005Ruesink et al , 2006Tyler et al 2007;Williams and Smith 2007 for introduced seaweeds). Examples from the invasion of Spartina (see above) have shown that Spartina can significantly affect macroalgal production, increase storage of carbon and nitrogen in plant detritus, and cause a shift from a net autotrophic to a net heterotrophic system (Tyler and Grosholz, in review).…”

Changes in productivity associated with four introduced species: ecosystem transformation of a ‘pristine’ estuary

“…In addition, Willapa's introduced engineers probably also affect biogeochemical cycles. In another coastal estuary, introduced Zostera japonica serves as a sink for water-column nutrients (Larned 2003), and bivalves can store nutrients in biodeposits (Chapelle et al 2000), or, at high densities, enhance nutrient release (Bartoli et al 2001). Furthermore, oyster expansion has occurred at the expense of burrowing shrimp and other infauna, undoubtedly causing changes in sediment porosity and bioturbation and further affecting biogeochemistry (Webb & Eyre 2004).…”