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May 172010

From Green Right Now Reports

Photo: Nevada Division of State Parks

Photo: Nevada Division of State Parks

Lovers of California’s picturesque Lake Tahoe long have lamented development’s effect on the lake’s legendary deep blue water and high transparency. Now, a study by Miami University’s Global Change Limnology Laboratory suggests that the change may be a threat to native fish species, too.

According to the group, maintaining high ultraviolet (UV) transparency may be the key to reducing invasion of warm-water fish, such as bluegill. The study, led by Andrew Tucker, doctoral student in zoology at Miami, is published in the March issue of the journal Ecology.

The study examined how underwater UV radiation (UVR) can regulate warm-water fish invasion. Changes in the UV transparency of the waters of the sub-alpine lake have allowed warm-water fish species to invade and spread. Transparency has decreased over the past several decades, and a number of nonnative warm-water fish species have established populations in some portions of the lake.

“For example, invasive bluegill can only nest successfully when human disturbance such as shoreline development reduces UV transparency,” said Craig Williamson, Ohio Eminent Scholar in Ecosystem Ecology and head of the Global Change Limnology Lab. “This creates a UV refuge, an ‘invasion window,’ which enables the bluegill to spawn in the surface waters where the temperatures are warm enough for survival of its embryos and larvae.”

The study indicated that dissolved organic carbon (DOC) and chlorophyll were important regulators of variation in the UVR in near shore areas of Lake Tahoe. Regulating chlorophyll and “DOC inputs” or runoff could help stem future declines in UVR transparency and in turn help reduce invasion of nonnative fish.

An understanding of the mechanisms underlying UVR transparency in Lake Tahoe could “enable us to better understand how regional and global environmental changes related to the factors that mediate UVR transparency could, in turn, affect habitat invasibility in the large, highly transparent lake,” Tucker said. “We suspect that this framework and our results could be directly relevant to other transparent lakes.”

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