Citation:

JANOUSEK, C. N., C. FOLGER, AND H. LEE, II. Tidal wetland plant and algal assemblages in Oregon: spatial patterns of composition and vulnerability to climate change. Presented at Hatfield Marine Science Center weekly seminar series, Newport, OR, April 19, 2012.

Impact/Purpose:

Tidal wetlands support important ecosystem functions along the coast of the Pacific Northwest such as primary production and nutrient transformation.

Description:

Tidal wetlands support important ecosystem functions along the coast of the Pacific Northwest such as primary production and nutrient transformation. Sea-level rise (SLR) and elevated salinity due to climate change may affect the abundance, distribution, and diversity of plants and algae in these ecosystems, potentially altering their function. To better understand potential climate change effects, we quantified spatial patterns of plant and algal composition and diversity in four Oregon estuaries. Our future work involves merging species data and SLR projections in order to identify species and types of wetlands most vulnerable to change. Plant and algal composition differed only modestly among estuaries, even though the sites we studied differ substantially in their relative degree of freshwater inputs. Composition varied more strongly within estuaries (among habitat classes and along environmental gradients). Tidal elevation was a key factor for both groups of primary producers. Macroalgal abundance and diversity and benthic chlorophyll a peaked in low marsh. In contrast, plant diversity was greatest in high marsh. Low marsh was often dominated by halophytes such as Sarcocornia and Triglochin whereas taxa such as Deschampsia cespitosa and Juncus balticus tended to characterize high marsh. Salinity also appeared to affect primary producer composition, though many common species occurred across a wide salinity gradient. Plant composition differed markedly between low marsh (the most saline habitat) and palustrine tidal marsh (the freshest habitat). Fresher marshes tended to have less macroalgae and chlorophyll a than more saline wetlands and had plant taxa such as Carex obnupta, Galium and Phalaris arundinacea (reed canarygrass, a non-indigenous species). Linking spatial patterns of composition in the wetlands to likely climate change impacts suggests the following preliminary conclusions: (i) SLR (without compensatory sediment accretion) will likely increase available habitat for low-marsh halophytes, reduce overall plant diversity, and shift ratios of algal versus plant productivity, and (ii) elevated salinity may not substantially alter plant and algal composition in more saline regions of estuaries, but may impact species restricted to fresher tidal wetlands. Although it is likely that SLR will affect the distribution of tidal wetland primary producers, it is unknown how climate change may affect species physiologies or ecological interactions and thus, ultimately, shape wetland ecosystem function.

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