What's Living In Lake Merritt? A lot, it turns out.

Hedgpeth's Sapsucker, a photosynthetic sea slug that lives in Lake Merritt. Photo: Damon Tighe

"Come check out some cool Lake Merritt creatures!" 

It seems like a hard sell at first, given how much people watching there is to do at the Lake. Lake Merritt on a sunny weekend afternoon is packed with families and friends, joggers, bicyclists, drummers, dancers, ice cream vendors with their tinkling bells.  Still, curious folks come to our table  to see the shallow tubs we've set up - a PopUp Aquarium - which allows them to see and touch some of the Lake's lesser known inhabitants: tube worms, bubble snails, tunicates, hydroids, anemones... 

Reactions follow a predictable pattern: shock, followed by wariness, and then finally, amazement.

First people express disbelief that anything lives in the Lake. Long-time Oaklanders have not-so-fond memories of the Lake as smelly and full of trash. Since Measure DD funds were put to use water quality has improved and marine life has increased.  Large fish like bat rays, striped bass, and sturgeon have been seen in the Lake. In August,  a harbor seal was spotted in the Lake. Seals and other large marine animals feast on smaller fish and mollusks like the ones we are showing off in our PopUp Aquarium. 

"So these creatures come from the Lake?", people ask. I point to a spot near the shore where I had waded in, wearing my rubber boots. "I pulled this rock up right over there, and these anemones were on it!"

Orange-Striped Green Sea Anemone. Photo: Damon Tighe

Everything in the tanks is touchable, nothing will bite or sting enough to hurt a person. Still, it takes coaxing for folks to put their hands in the water. I pull out a compressible yellow-grey blob and place it gently in their hands. "What does it feel like?", I ask. "It feels like a sponge." That's because it is a sponge! Sponges are some of the simplest animals on Earth. They grow in small clumps on the docks along the Lake. 

After they connect with one creature, people become more comfortable. It's time to introduce the sea vase tunicate. The sea vase is a translucent cylinder with two translucent tubes arms branching from one side. When I pull one out of the tank, the tubes retract. Its surface is perfectly smooth and soft, like a peeled grape. Pressed gently, water squirts from the lower tube. This never fails to delight. Maybe you've heard the phrase "sea squirt"?  Weirder: of all the animals we are displaying- snails, shrimps, worms- the sea vase is the closest relative to humans. In its larval stage, the sea vase has a rudimentary notochord, a structure shared by all vertebrates. In human embryos the notochord becomes part of our vertebral column. Tunicates have no backbone. Their notochord is reabsorbed as the creature develops, leaving the adult a gelatinous, boneless glob.  Still, it's a glob that shares a common ancestor with us!

Sea Vase Tunicate. Photo: Damon Tighe

Within a few minutes, folks become believers. The fear of getting their hands wet is long gone. They notice incredible details of the structure and habits of the wildlife. "What's that? Why is it doing that? Is that a shrimp?" It dawns on them that Lake Merritt is full of amazing creatures, and it's been right here this whole time. People leave our table genuinely excited about what they've seen and learned. They continue their stroll or their jog with a newfound appreciation. All in all, a great afternoon at Lake Merritt.

We get lots of questions at our PopUp Aquariums. Here are a few common questions we fielded last week:

How did Lake Merritt form? During the last Ice Age, some 10,000 years ago, a channel was created that connected a low-lying area to the San Francisco Bay. Bay water flowed in and out with the tides, resulting in a salty marsh surrounded by mudflats. Human development in the last few centuries has dramatically impacted the landscape and ecosystem. Mudflats have been removed.  Nonnative species  have entered the waterway, often hitching a ride from distant lands via ballast water of international shipping tankers coming to the Port of Oakland.

Is Lake Merritt salty water or fresh? Both. Storm drains bring "fresh" water in the form of street runoff into the Lake. It's a mix of rain-water and all the nasty junk thats on the street (trash, dog poop, motor oil, plastic). If it's on the street, it flows into the Lake! Salt water comes in with the tides through the channel at the south end. Salinity in the Lake varies by time of year - less salty during the rainy season, saltier in the dry season. 

Are there fish in the Lake? Yes, I'm just not fast enough to catch them with my bare hands. There are lots of small bait fish living in the Lake. You can see brown pelicans dive-bombing from the air to catch them! Larger fish have been seen, too. Keep your eyes pealed.

Where did you get this stuff? We mostly collect samples from pier pilings and from rocks along the shore. Mussels and algae grow in clumps which act as a microhabitat for other organisms like worms, barnacles, tunicates and anemones. We try to return creatures as close as possible to where we found them. 

What kind of shellfish did the Native Americans eat?  Ohlone people lived along the marshy banks for thousands of years. They ate clams, mussels, and oysters and amassed the shells into massive heaps known as shellmounds.  Hundreds of shellmounds were documented around the Bay, including one at Lake Merritt. Some of these were also sacred burial places and ceremonial sites. For more information about shellmounds, check out the fight to preserve the West Berkeley Shellmound.

Is the Lake getting cleaner? Yes. The restoration of Lake Merritt is ongoing. The Lake Merritt Weed Warriors meet each month to plant and maintain native saltmarsh plants, which restore habitat and nutrients for other Lake dwellers. You can join them at a work day!