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

Abstract

Multiple stressors in estuaries can cause declines in native species and impairment of ecosystem goods and services. In contrast, one stressor -the introduction of non-native speciesactually leads to higher local richness. We examined the changes in ecosystem function associated with introductions into Willapa Bay, Washington, USA, a relatively undeveloped estuary with 45 documented exotic marine species. The replacement of native oysters by 2 new bivalve species has increased secondary production of harvested suspension feeders by 250% over peak historic values (3.3 × 10 5 vs. 0.9 × 10 5 kg dry wt yr -1), based on >150 yr of records of harvested biomass. Key aspects of aquaculture -particularly planted area -have remained constant over time, so we attribute much of the altered secondary production to higher growth rates of non-native species. The addition of 2 tracheophytes has increased primary production on the tideflats by > 50% (5.3 × 10 7 vs. 3.5 × 10 7 kg dry wt yr -1 ), which we calculated by scaling up local measurements of plant growth to the total area occupied by each species. These changes in production are also associated with altered detritus, water filtration, and biogenic habitat. Because other stressors are largely absent from Willapa Bay, the addition of particular exotic species has dramatically enhanced system production, while fundamentally reshaping the ecological character of the estuary. These strong ecological impacts of introduced species have rarely been measured at whole-ecosystem scales, and they occur in part because new species occupy habitats where similar native species were not present.

Temperature- and light-dependent growth and metabolism of the invasive red algaeGracilaria vermiculophylla– a comparison with two native macroalgae

“…For example, G. vermiculophylla can smother sessile oyster communities and have negative effects on seagrasses, particularly at high temperatures (Martinez-Luscher & Holmer, 2010;Höffle et al, 2011). However, other studies suggest that the introduction of G. vermiculophylla into habitats with little substratum suitable for macroalgal attachment, may increase species diversity (Ruesink et al, 2006;Nyberg et al, 2009;Thomsen et al, 2010;Thomsen, 2010).…”

Quantifying the historic contribution of Olympia oysters to filtration in Pacific Coast (USA) estuaries and the implications for restoration objectives

“…For example, the filtration capacity of the historic O. lurida population in Willapa Bay has been previously conservatively estimated, using oyster abundance extrapolated from harvested biomass statistics, to filter 0.8 % of the estuary within its residence time (Ruesink et al 2006). We estimate an order of magnitude greater filtration in this study, with the historic population estimated to be capable of achieving *12 % of full estuary filtration, and the estimated pre-commercial exploitation population *36 % of full estuary filtration.…”

Density-dependent effects of an introduced oyster, Crassostrea gigas, on a native intertidal seagrass, Zostera marina

“…The second largest estuary along the open west coast of the USA, Willapa Bay covers 35000 ha at mean high water but has a large tidal prism (60% of the area exposed at low tide) , and is subject to strong seasonal variations in oceanic input due to wind-driven upwelling and downwelling events, as well as periodic freshwater influxes from the Columbia River plume (Hickey & Banas 2003). It is a major site of shellfish aquaculture production, primarily oysters and clams (Ruesink et al 2006). Crassostrea gigas was introduced from Japan in 1928 and is currently cultivated on-bottom (averaging 20% cover) or in clusters on longlines suspended above the tideflats; C. gigas also has established reefs where it recruits naturally.…”

“…Crassostrea gigas was introduced from Japan in 1928 and is currently cultivated on-bottom (averaging 20% cover) or in clusters on longlines suspended above the tideflats; C. gigas also has established reefs where it recruits naturally. Nearly 10% of the USA's total oyster harvest comes from Willapa Bay (Ruesink et al 2006), and about 21% of the bay's intertidal area is farmed and managed for oysters ). The bay also contains extensive beds of Zostera marina (3400 ha) at elevations of −1.0 to + 0.6 m relative to mean lower low water (MLLW) (Ruesink et al 2010).…”