Local scientist shares years of experience in underwater environment
July 30, 2010
LAKE TAHOE, Calif. – Long-time local biologist Brant Allen first became involved in research scuba diving in 1985, after a missed trip to the Galapagos Islands.
“I wasn’t certified for research scuba diving,” said Allen, a research biologist for the Tahoe Environmental Research Center. “The next day, I went out and began the certification process.”
Since then, Allen, a North Tahoe resident, has conducted underwater research projects in an array of the Sierra Nevada’s alpine lakes and exotic locales such as Papua New Guinea.
But for the past 23 years, Allen has spent most of his time diving under Lake Tahoe’s cobalt surface, studying fish behavior, implementing experiments, identifying aquatic invasive species and helping visiting professors and scientists.
“I’ve been down in other pristine mountain lakes in the area,” Allen said. “But nothing surpasses the clarity of Tahoe.”
Allen said a view of Tahoe from beneath the lake’s surface is essential for scientists trying to understand its complex ecosystem.
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“Whether it’s by diving our just putting a mask on and snorkeling, you have to see what’s happening,” he said.
Allen said one of the most interesting things he encountered on his initial dives was the visible difference in the layers of the lake.
As he dove deeper, he said he could see the difference between the warmer, less dense layer of water on the surface and the colder, more dense water toward the lake bottom.
“It looked like pouring fresh water into a bucket of salt water and watching it mix,” he said.
However, Tahoe’s underwater landscape has changed in the past 23 years.
“One thing that stands out is the decrease in clarity,” he said. “When I’m working with a diving buddy, we have to stay closer – you can’t see fish from as far away and there is a general decline in sharpness of objects down there.”
Another pronounced difference, he said, is the presence of aquatic invasive species, which have affected local shifts in ecology.
Zooplankton – an organism that drifts through water bodies – is more prevalent in all areas of the lake, but particularly so in areas where Asian clams have established a stronghold, such as Marla Bay, Emerald Bay and the Round Hill Pines Beach and Marina.
“We used to see Zooplankton in the spring, but you would barely notice,” said Allen. “Now you see them virtually year round.”
Allen also said the increased presence of invasive aquatic plants has altered the underwater landscape, as the lake’s bottom used to be relatively desolate.
“There was some non-native aquatic vegetation here when I arrived, but it is surprising to see the large areas,” said Allen.
Now, Eurasian water milfoil and curly leaf pondweed have made significant inroads into portions of the lake, particularly near Tahoe Keys, Allen said. Large amounts of non-native fish like bluegill and large-mouth bass can be directly attributable to the presence of the plants.
“Bluegills like the plants for shade and their young use it for protection from predators,” Allen said. “These invasive species are benign for recreation purposes, but they can create severe ecological changes.”
Allen recently participated in a pioneering effort to curtail the population growth of Asian clams, which have procreated so heavily that clam beds in Marla Bay are visible from an airplane flying 800 feet above the surface, Allen said.
Early in July, a team of University of California, Davis, scientists rolled out a series of 100-foot by 10-foot rubber mats and spread them over a half acre of the bottom of Lake Tahoe in the vicinity of Round Hill Pines Beach and Marina, where Asian clam populations have grown in recent years. The barriers are a 45-millimeter thick pond liner that deprive organisms of oxygen.
Allen was on the principal dive team responsible for rolling out the barriers and securing them on the bottom of Tahoe.
“It definitely wasn’t easy,” Allen said. “I was pretty tired at the end of the day, but the UC Davis engineering team did a great job of making our job as easy as possible.”
Marion Wittmann, fellow UC Davis scientist, called the dive work “physically exhausting,” but said working with Allen helped.
“Brant taught me everything I know (about diving),” Wittmann said. “He is an excellent scientist and an excellent dive buddy. He has such a vast amount of experience, that I trust his judgment, and he also works really hard.”