Temperature Tolerance of the Isopod Saduria entomon  in Southwest Alaska

Temperature Tolerance of the Isopod Saduria entomon in Southwest Alaska

Todd A. Radenbaugh

Temperature Tolerance of the Isopod Saduria entomon  in Southwest AlaskaThis is part of Responses of Arctic Marine Ecosystems to Climate Change
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Abstract: The pan-arctic benthic isopod Saduria entomon is a euryhaline species that lives in northern oceans, bays, estuaries, and few large lakes connected to the sea. In arctic and subarctic regions, S. entomon is an important species in coastal food webs as an opportunistic predator and a detritus and carrion shredder. In southwest Alaska, the subarctic Nushagak Bay estuary is home to a large population of S. entomon, which has been observed feeding on the immense number of spawned out salmon and is found in abundance in waters influenced by salmon processing effluent. Because S. entomon is an opportunistic feeder and can easily change diet, it serves important functions in the estuarine food web. Given documented increases in arctic and subarctic water temperatures it is important to determine the ability of S. entomon to survive in warmer waters and continue its important ecological role at its southern distribution limits. To investigate temperature tolerances and preferences of S. entomon, specimens were collected from Squaw Creek, a small tributary that drains into the Nushagak Estuary. To equilibrate specimens to lab conditions, isopods were placed at 10°C for over 10 days, in water from Squaw Creek. Tolerance studies were conducted for three hour periods using a 2 m trough with a 0 to 20°C temperature gradient allowing isopods to choose their preferred temperature. Results indicated that the distribution of S. entomon collected at Squaw Creek were positively correlated to temperatures between 0 and 10°C and negatively correlated to temperatures above 15°C. Temperature loggers were placed at isopod collection sites to record temperature data in summers of 2007 and 2008. Ambient water temperatures in Squaw Creek fluctuated from 5°C (May) to 15°C (August). Higher water temperatures may limit the distribution S. entomon, considering that it prefers cooler water. More investigations are needed on temperature ranges of creeks and estuaries such as in the Nushagak. The upper temperature limit of S. entomon was determined to be 15°C suggesting that it could be used as an indicator of summer watershed temperatures.

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