Freshwater Ecoregions of the World
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123: Oregon & Northern California Coastal

Author

Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA. Additional text provided by Jennifer Hales.

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Biodiversity
Species Richness
# of Endemic Species
Threats
Description

Major Habitat Type

Temperate coastal rivers

Countries

United States

Boundaries

This ecoregion extends along the Pacific Coast of Oregon and California to the northern shore of San Francisco Bay, including the western portion of the San Francisco peninsula south to Santa Cruz. In southern Oregon and Northern California, the ecoregion reaches further inland, encompassing the western drainages of the Klamath and Siskiyou Mountains.

Drainages flowing into

Pacific Ocean

Main rivers or other water bodies

Important rivers include the Umpqua, Mad, and Klamath. The ecoregion contains several lakes, including Upper Klamath Lake in southern Oregon. 

Topography

This ecoregion has plentiful water resources because of its location on the slopes of four mountain ranges—the Cascades, the Coastal Ranges, the Klamath Mountains, and the Siskiyou Mountains.

Climate

This ecoregion’s mild maritime climate and abundant rainfall have made it a haven for terrestrial and aquatic species. The climate is characterized by cool dry summers and mild wet winters with average annual precipitation ranging from 760 mm to over 3000 mm (McNab & Avers 1994).  

Freshwater habitats

Characteristic freshwater habitats of the ecoregion include coastal headlands, tidal rivers, estuaries, floodplains, wetlands, streams and rivers. Along the Oregon coast rivers have cut steep dendritic drainages, with many of the large rivers terminating in sizeable estuaries (McNab & Avers 1994). These coastal estuaries contain high and low salt marshes, as well as freshwater marshes (Vander Shaaf et al. 2006). The northern California coast is characterized by relatively slow streams and rivers in alluvial channels that terminate primarily in brackish estuaries (McNab & Avers 1994).

Terrestrial Habitats

Temperate coniferous forests make up a majority of the ecoregion, with dominant species including Douglas fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) in the coastal mountains, and Sitka spruce (Picea sitchensis) in a narrow band along the coast (Vander Shaaf et al. 2006). Redwood (Sequoia sempervirens) forests are unique to the northern California coast, and are among the biggest, tallest, and oldest trees in the world. Broadleaf species such as black cottonwood (Populus trichocarpa) and red alder (Alnus rubra) replace the otherwise ubiquitous conifers along the many rivers and streams of the Pacific Northwest (Ricketts et al. 1999).

Fish Fauna

The Oregon and Northern Californian Coastal ecoregion is the southernmost habitat for many of the Pacific Coast anadromous species, including coho salmon (Oncorhynchus kisutch) and cutthroat trout (O. clarki). Stream capture, the process by which the headwaters of a drainage basin are naturally diverted to a neighboring one, has contributed species to this ecoregion that were originally found in more inland systems.

Description of endemic fishes

While this ecoregion contains no endemic mussel or crayfish species, roughly a quarter of its fish species are endemic, including the Umpqua squawfish (Ptychocheilus umpquae), the Klamath smallscale sucker (Catostomus rimiculus), the Klamath largescale sucker (C. snyderi), two sculpins (Cottus princes and C. tenuis), three lampreys (Lampetra folletti, L. minima and L. similis), two suckers (Chasmistes brevirostris and Deltistes luxatus), two chubs (Gila coerulea and (Oregonichthys kalawatseti), and Umpqua dace (Rhinichthys evermanni).

Other noteworthy aquatic biotic elements

The ecoregion includes a number of restricted range freshwater mollusks and crustaceans, including the Great Basin rams-horn (Helisoma newberryi newberryi) (Frest & Johannes 1995) and species of endemic syncarid shrimp (Syncaris spp.). Many unusual aquatic invertebrates also occur in the region.

Evolutionary phenomena

The Oregon and Northern Californian Coastal ecoregion is noted for its higher taxonomic endemism in fish and amphibians (Abell et al. 2000). The region contains one endemic fish genus (Deltistes), two near-endemic fish genera (Oregonichthys, which it shares with the Columbia Unglaciated [121], and Eucyclogobius), and one near-endemic salamander genus (Hydromantes).

Justification for delineation

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).

References

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