Purple varnish clam, dark mahogany-clam • Nuttallia obscurata
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Kelly Fretwell
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Identification
This introduced species is named for the shiny brown coating (periostracum) on the exterior of its shell (which peels off like old varnish) and the purple colouring of the interior. The periostracum is worn away to white at the hinge, and sometimes smaller shells will have some purple on the exterior. The shell reaches 7 cm long, is thin, relatively flat, and fairly oval in shape. This clam has long, unfused siphons.
Habitat & Range
Native to Japan, Korea, and China, the purple varnish clam was introduced to the Pacific Northwest in the 1980s, likely via ballast water. Since its introduction it has spread through the Strait of Georgia, Puget Sound, and Juan de Fuca Strait (collectively known as the Salish Sea), and south along coastal Washington and Oregon. It is also now established in Barkley Sound on the west coast of Vancouver Island. While its distribution is commonly noted as extending no further north than southern BC, there is one record from the North Coast, and the empty shells pictured above were found on the Central Coast near Calvert Island.
This invasive clam is found buried up to 20 cm deep in muddy or sandy to sand-gravel or cobble substrates. It is most common and abundant in the mid to high intertidal, especially near freshwater seepage areas, though it may also be found lower in the intertidal.
Similar Species
Other clams may have shiny brown periostracum, however this combined with the purple interior and fairly regular oval shape make this species easy to identify.
Intriguing Info
Trial harvests and marketability studies have been conducted on this species, with somewhat favourable results, however there are issues that make consistent harvest of this species tricky. A major issue is that purple varnish clams over a certain size often host a native species of pea crab, and there currently is no method for purging these crabs from their host. In addition, this clam can store the toxin that causes paralytic shellfish poisoning (PSP), and therefore is subject to red tide warnings and closures.
iNaturalist
https://www.inaturalist.org/taxa/430211-Nuttallia-obscurata
This introduced species is named for the shiny brown coating (periostracum) on the exterior of its shell (which peels off like old varnish) and the purple colouring of the interior. The periostracum is worn away to white at the hinge, and sometimes smaller shells will have some purple on the exterior. The shell reaches 7 cm long, is thin, relatively flat, and fairly oval in shape. This clam has long, unfused siphons.
Habitat & Range
Native to Japan, Korea, and China, the purple varnish clam was introduced to the Pacific Northwest in the 1980s, likely via ballast water. Since its introduction it has spread through the Strait of Georgia, Puget Sound, and Juan de Fuca Strait (collectively known as the Salish Sea), and south along coastal Washington and Oregon. It is also now established in Barkley Sound on the west coast of Vancouver Island. While its distribution is commonly noted as extending no further north than southern BC, there is one record from the North Coast, and the empty shells pictured above were found on the Central Coast near Calvert Island.
This invasive clam is found buried up to 20 cm deep in muddy or sandy to sand-gravel or cobble substrates. It is most common and abundant in the mid to high intertidal, especially near freshwater seepage areas, though it may also be found lower in the intertidal.
Similar Species
Other clams may have shiny brown periostracum, however this combined with the purple interior and fairly regular oval shape make this species easy to identify.
Intriguing Info
Trial harvests and marketability studies have been conducted on this species, with somewhat favourable results, however there are issues that make consistent harvest of this species tricky. A major issue is that purple varnish clams over a certain size often host a native species of pea crab, and there currently is no method for purging these crabs from their host. In addition, this clam can store the toxin that causes paralytic shellfish poisoning (PSP), and therefore is subject to red tide warnings and closures.
iNaturalist
https://www.inaturalist.org/taxa/430211-Nuttallia-obscurata
References
Harbo, R.M. (1999). Whelks to Whales: Coastal marine life of the Pacific Northwest. Madeira Park, BC: Harbour Publishing. p. 96.
Lamb, A. and Hanby, B. (2005). Marine Life of the Pacific Northwest [electronic version]. Madeira Park, BC: Harbour Publishing.
Meacham, P. (2017). Nuttalia obscurata (Purple varnish clam,varnish clam, or dark mahogany clam). Washington Department of Fish & Wildlife: Conservation. Accessed 25/07/2017.
Mills, C.E. (2002). Nuttallia obscurata, the purple varnish clam or the purple mahogany-clam. Accessed 25/07/2017.
Nuttallia obscurata Reeve, 1857. In Klinkenberg, Brian. (Ed.) E-Fauna BC: Electronic Atlas of the Fauna of British Columbia. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. Accessed 25/07/2017.
Authors and editors of page
Kelly Fretwell (2017).
Harbo, R.M. (1999). Whelks to Whales: Coastal marine life of the Pacific Northwest. Madeira Park, BC: Harbour Publishing. p. 96.
Lamb, A. and Hanby, B. (2005). Marine Life of the Pacific Northwest [electronic version]. Madeira Park, BC: Harbour Publishing.
Meacham, P. (2017). Nuttalia obscurata (Purple varnish clam,varnish clam, or dark mahogany clam). Washington Department of Fish & Wildlife: Conservation. Accessed 25/07/2017.
Mills, C.E. (2002). Nuttallia obscurata, the purple varnish clam or the purple mahogany-clam. Accessed 25/07/2017.
Nuttallia obscurata Reeve, 1857. In Klinkenberg, Brian. (Ed.) E-Fauna BC: Electronic Atlas of the Fauna of British Columbia. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. Accessed 25/07/2017.
Authors and editors of page
Kelly Fretwell (2017).
