Marla Bay algae invasion is a mystery
August 4, 2008
It’s stringy. It’s bright green. And it’s slimy. Very slimy.
“It” is algae from the genus Zygnema, and people have found it in the shallow waters of Marla Bay at unprecedented levels this summer, surprising scientists and concerning residents.
“I was so shocked,” said Heidi Archdeacon, a longtime summer resident of Marla Bay. “It’s just grown incredibly.”
The algae’s growth also has surprised scientists at the Tahoe Environmental Research Center of the University of California, Davis.
“Occasionally, you see very small amounts (of Zygnema) in the water in the lake, but it usually tends to settle,” said Scott Hackley, a staff research associate with the center. “It’s just really striking to see that level of green.”
The algae bloom mostly has settled in the Marla Bay area, just south of Zephyr Cove, Hackley said, but what’s causing the bloom remains unknown.
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“It’s a very open question,” said research center Director Geoffrey Schladow, noting more research is needed to determine the cause of the unusual Zygnema growth.
Earlier this year, Schladow expressed concern about climate change halting deep-water mixing in Lake Tahoe over the coming decades. The phenomenon could increase the frequency of algae blooms in the lake. But Schladow doesn’t believe the Marla Bay algae bloom is part of that scenario.
Researchers hope to determine whether an unknown source of nutrients is sending nitrogen and/or phosphorus into the bay, fueling the growth of Zygnema.
High fecal counts registered in the water near Marla Bay during this year’s Water Quality Snapshot Day could be a potential source of food for the algae, said Dennis Oliver, spokesman for the Tahoe Regional Planning Agency.
Oliver speculated that the high counts could be from horse manure running into the bay or a possible sewer leak.
Researchers hope to examine a possible relationship between the algae and Asian clams, which also have been found in abundance in the area.
Asian clams have likely been in Lake Tahoe since at least 2002, according to an April research center study, which found the density of clams in the lake is higher than ever.
The clams could create pockets of water with relatively high calcium concentrations favorable to invasive mussel growth, Oliver said. The planning agency hopes to retrofit a boat this fall with an underwater vacuum to remove Asian clams from the lake.
A potential link between the clams and algae in Marla Bay remains unverified, though that doesn’t ease Michael Donahoe’s concerns. The Tahoe Area Sierra Club conservation co-chairman feels the issues reflect a bigger problem: inadequate management to prevent undesirable species from entering the lake.
“It’s just symptomatic of what’s going on around the lake,” Donahoe said. “We’re not winning this battle right now, and we don’t seem to have the collective will to address the issues.”
“I wouldn’t use these two things to mark the broad effectiveness of TRPA erosion controls and source-reduction programs,” he said. “All indications are the 10 years of EIP and some of the BMP compliance work in the basin has helped us turn the corner in terms of water quality and lake clarity.”
Despite the potentially larger debate, Marla Bay residents and visitors likely will have to deal with Zygnema’s uninvited guest appearance this summer.
Elana Wave, a lifelong resident of Marla Bay, said she has considered enlisting neighbors to help remove the algae with nets, and has changed some of her long-held habits in the meantime.
The algae has caused the Marla Bay resident to take showers after swimming in Lake Tahoe’s famously pure water, something she never has done before.
Wave hopes widespread concern about the algae growth will stop some of the “crazy development” at the lake from turning it into “pea soup” like some of the other bodies of water in the Sierra range.
“We used to drink the water,” Wave said. “Not now.”