California floater mussel
California floater mussel
California floater mussel, born and raised in San Francisco (photo by author)

After 7 years’ effort, there’s new evidence that native freshwater California floater mussels, reintroduced to Mountain Lake, are thriving. The mussels are a keystone species, vital to maintaining stable, healthy water conditions. Until now, the biologists responsible for restoring Mountain Lake’s habitat could only guess about how the mussels were doing. That is, until they put their heads underwater to get a more complete answer.

While we work the mussel, we meditate the hustle

Two biologists pull a net through the lake
Two biologists pull a net through the lake
Two Presidio field biologists and a net

Nature is gross

We dragged the net to shore. It was heavy with shanks of fibrous, dark green algae. Where strands of algae quivered, Presidio Trust biologists Jon Young, David Harelson and I (author/citizen scientist) reached in and grabbed at squirming, alien creatures. Then drop them into a white 5-gallon bucket. It’s an odd sensation.

Imagine holding a peeled hardboiled egg. Now imagine it’s slimy, writhing, and has a tail. That’s what holding a bullfrog tadpole is like. Along with Jon and David, I was grabbing as many of these oversized tadpoles as I could.

Other critters came up in the net. Threespine…

Western pond turtle’s face
Western pond turtle’s face
A riddle wrapped in an enigma packed into a bony shell (photo: National Park Service/public domain)

“So, what’s up with the turtles?”

I’ve been monitoring the Western pond turtle population at Mountain Lake for three years. 2017 was a mystery — where are the turtles? 2018 was a triumph — plenty of turtles. So, what about this year? The short answer? It’s complicated.

Until 2015, there were no Western pond turtles in San Francisco. They’d been eaten by ‘49ers and other new arrivals (when turtle soup was a thing in the US). Where their ponds weren’t filled in, the Western pond turtles found themselves competing with East Coast turtles that out-ate, out-grew, and out-bred* the Western…

How do you know when you’re doing it right?

The mergansers have returned to Mountain Lake in San Francisco’s Presidio. Mergansers haven’t been seen here for at least 20 years. But in December of 2018, a male and a small group of Hooded Mergansers visited Mountain Lake for a week. What changed? Why does it matter?

Male Hooded Merganser — Photo by Mike’s Birds

Ducks are generally omnivorous, eating whatever they come across — snails, tadpoles, algae, seeds, berries. Mergansers are a variety of duck that has gone carnivore.* They eat small fish, crayfish and aquatic insects. Their beaks are narrow, ideal for slashing through water after prey…

Natives Thrive at Mountain Lake

2018 was good year at Mountain Lake in San Francisco’s Presidio for habitat and native species restoration. Pacific Chorus Frogs and Three Spined Sticklebacks continue to thrive. Presidio biologists released more freshwater mussels and a new species, the endangered San Francisco Fork-tailed Damselfly. And the Western Pond Turtles came back in a big way.

Pacific Chorus Frog. They’re loud, they’re proud.

Sticklebacks are adaptable fish, living in both salt and freshwater, from Japan to Norway. So it’s not a big surprise that they’re doing well at Mountain Lake. Likewise, the chorus frogs will be demonstrating their numbers soon, when the rainy season starts. …

The Variable or Chalcedon Checkerspot (Euphydryas chalcedona)

March 2, 2018

The text came at 8:11 am. A week of late winter storms in Northern California had put the mission in jeopardy, but we had a window of clear weather. By 9:00, a squad of Presidio Trust naturalists and interns were rolling southbound in a van.

Behind the wheel, Jon Young, a Wildlife Ecologist with the Trust, announced that we were picking up Liam en route — Liam O’Brien, the go-to lepidopterist in the San Francisco Bay area. The mission sounded simple enough. Collect 200 caterpillars, and redistribute them in San Francisco’s Presidio.

The biologist E.O. Wilson called…

She got me up all night, all I’m singing is love songs

In the chilly, damp, Northern California winter, the young males gather at the water’s edge after dark. They sing, not quite in harmony, but loudly. Night after night, they get together and sing. And soon, the young females hear the love songs, and come to see who these performers are.

But this isn’t Outside Lands, or any of the dozens of outdoor concerts held in San Francisco. This is the beginning of mating season for the Pacific Chorus Frog, Pseudacris sierra.

These frogs are small, less than two inches long — about the size of a prune. They spend their…

A Western Pond Turtle basking. Image by By Yathin S Krishnappa

UPDATE: April 23, 2018

Recently, a group of scientists(1) published a paper detailing their progress in synthesizing genes(2) and successfully inserting their man-made chromosomes into yeast cells. In order to synthesize DNA, scientists write out a genetic blueprint for a gene, and predict how it will behave by modeling its behavior with computer software. Then the gene design is broken into smaller segments, and commercial DNA labs generate copies of these segments. The shorter segments are assembled into complete genes, and then inserted into living yeast cells. Their offspring are an extraordinary strain of common brewers yeast: Saccharomyces cerevisiae(3).

All living cells are loaded…

Yeast hard at work. photo courtesy barockschloss, flicker

How army of yeast transforms juice into wine, cider and beer

People have been enjoying the contribution of yeast and other microbes to create new foods for thousands of years. Evidence for wine and beer brewing date as far back as 8,000 years ago.[1]

The roots of turning juice into alcoholic beverages are not clear, but that should be no surprise. Any container of sugary liquid, like the juice of grapes or apples, is liable to ferment. There are obvious benefits to creating wine and cider from fresh fruit. Fermenting fruit juice allows you to preserve the harvest, and consume it at will. The alcohol in the liquids prevents further spoilage…

Zip Lehnus

Content designer, Urban artist, Community scientist. See more at

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