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November 2011- Asian brackish water clam
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Article Content
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| Invasive Species of the month |
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Invasive species of the month- Asian brackish water clam, Corbular amurensis
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| What? |
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Primarily a filter feeding subtidal estuarine clam, C. amurensis is now a dominant benthic species in San Francisco Bay, with densities of 2,000–43,000 clams per square meter. Asian brackish water clams are a major biological disturbance, altering food availability, dominating community dynamics and food web assemblages, affecting habitat availability, contributing to the decline of soft-bodied mudflat species as well as negatively impacting the recruitment of juvenile fish that depend on zooplankton, and causing other ecological damages in places outside its native range. Ballast water, with its ability to inoculate a water body with numerous larvae at a time represents the pathway of primary concern for introduction, followed by occurrences of extreme hull fouling. Predators, such as diving ducks and sturgeon, that feed on clams in mudflats, may consume high levels of toxins that tend to accumulate in clams. The clam is thought to have contributed to the decline of commercial and recreational fisheries in San Francisco Bay. This species of clam is also known as the overbite clam, Asian clam, amur river clam, and brackish-water Corbula.
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| Where? |
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Native to Asia, specifically the North Pacific coasts of Russian, Korea, China, and Japan, the Asian brackish water clam has become well-established in San Francisco Bay, California since its introduction in 1986. C. amurensis is a primarily subtidal estuarine clam. It is considered a “highly tolerant” species as it can survive both high and low salinity waters (1–33 ppm in San Francisco Bay) as well as in near-tropical to colder temperate waters (0–28 degrees C in its native range). Although it prefers mixed mud/sand benthic habitats, it can occur across a wide variety of bottom types and even into the intertidal zone and has been found in hull-fouling assemblages. High reproductive success even in fluctuating salinities (corresponding to upstream flood and drought conditions) has also been seen in this species, opening up a wide variety of potentially suitable habitats in Oregon’s estuaries.
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| Lookalike? |
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May be confused with Corbicula, a non-native freshwater clam similar in shape (although not coloration—Corbicula are yellowy-green to olive drab) and name (also called “Asian clam”) that has been present in Oregon since the 1930s.
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