Popup Aquarium at Lake Merritt: Questions and Answers

We ran our first popup aquarium today at the Madison Street dock in Lake Merritt. Lots of folks dropped by and learned about the many invertebrates that live in this estuary at the heart of Oakland. Though we tried to answer as many questions as we could, we couldn’t answer them all without some research. With the power of the Internet, though, we gave it a try. Not really sure why so many of these are about barnacles. People love barnacles? Who knew.

How long do barnacles live?

It varies by species. One of the barnacles that lives in Lake Merritt, Balanus amphrite, usually lives between 1-2 years, but even that varies based on location. Balanus balanoides, a European species that doesn’t occur in the SF Bay, can live up to 8 years.

What’s the biggest barnacle?

This one’s a bit tough because the data isn’t readily available. Wikipedia will tell you that it’s Balanus nubilus, and cites a magazine article that claims that species can reach a diameter of 300 mm (~1 ft), but Morris et al.'s Intertidal Invertebrates of California, an older but more authoritative source (in our opinion), states that B. nubilus maxes out around 110 mm, while the similar Menesiniella aquila reaches a diameter of 130 mm. Both of these sources are only concerned with California, which leaves out barnacles from everywhere else on Earth, so this question remains unanswered.

Do barnacles growing on whales benefit the whale in any way? Do whales try to remove them?

First, yes, barnacles live on whales, and usually different species of barnacles live on different species of whales. Here’s a great article on this subject, which suggests that the barnacles on whales probably don’t help them in any way, but might provide some advantage when males fight each other over females. Seems like just a theory, though. As to whether or not they remove them, still researching... [Update: we talked to our marine biologist friends at the California Academy of Sciences and they'd never heard of whales intentionally removing barnacles. Doesn't mean it doesn't happen, but it doesn't seem like anyone's observed it.]

How do different organisms attach to things?

This is a pretty big and important question that we might have to punt on… for now, pending further research, but here’s a link to whet your appetite: http://museumvictoria.com.au/discoverycentre/infosheets/how-do-barnacles-cement-themselves-to-rocks. Also, that article about whale barnacles has a kind of horrifying picture of how barnacles attach to whales. *shudder*

How healthy are the fish populations in Lake Merritt and is anybody monitoring them?

As far as we know at CCNH, no one is performing ongoing monitoring of the fish populations in Lake Merritt, so it’s unlikely that anyone could really answer this question. In fact, the only people we know of who have been performing long-term monitoring of environmental conditions at the Lake are the high school students at the Environmental Science Academy of Oakland High School, led by the heroic teacher Katie Noonan (though please correct us if we're wrong about this!). To read more water quality at the Lake and some of Katie’s efforts, check out this East Bay Express article.

What did arthropods evolve from?

Arthropods are animals with a body divided into discrete segments that usually have a hard exoskeleton, like crabs, bees, spiders, but also things like barnacles and horseshoe crabs. They go way back to the Cambrian era, 500-600 million years ago, but what, exactly, the first arthropods really looked like is a matter of some debate, which, frankly, Wikipedia seems to have done a fairly good job of covering. All we’ll add is that humanity doesn’t really know the answer to this question! Maybe you could be the one to figure it out.

Is Lake Merritt “healthy”? What makes a healthy ecosystem?

This is a pretty big question that hinges on what you mean by “healthy.” Healthy for who or what? According to the aforementioned East Bay Express article, dissolved oxygen has remained low since the 12th street culvert was day-lit and the Lake has received more water from the Bay, but anecdotally biodiversity seems to be increasing, with sightings of more bat rays, striped bass, and even a river otter. Again, though, to our knowledge, no one is performing rigorous monitoring of these organisms in Lake Merritt.

What do the birds at Lake Merritt eat? 

Many of the inverts and plants we had at the pop-up aquarium are on the menu for some bird or another, but the answer really depends on the type of bird. Different species are adapted to eat different kinds of organisms, and different parts of the Lake, depending on the depth of the water, or distance from the shore, have different kinds of vegetation and animal life. Birds go to where their preferred food source is.

Mallards Ducks (Anas platyrhynchos) are “dabblers”. They stay mostly at the surface of the water and munch on vegetation and occasionally small critters (like insect larvae and small invertebrates) floating there. Greater and Lesser Scaup (Aythya marila and Aythya affinis), on the other hand, are diving ducks, and feed mostly on clams and other bivalves in the mud at the bottom of the Lake. Coots (Fulica americana) can submerge themselves below the water and eat a wide variety of the things they find there, mostly vegetation, but also insects, snails, and other aquatic invertebrates. Double-crested Cormorants (Phalacrocorax auritus) dive and swim under the water and catch fish pretty much exclusively, but maybe shrimp and other inverts. Brown Pelicans (Pelecanus occidentalis) dive from the air and catch schooling fish. Great Egrets (Ardea alba)  stand in the shallow water at the lake’s edge, and snap unsuspecting fish and inverts with their long bills.

Most of this information comes from The Sibley Field Guide to Birds of Western North America, a fantastic bird guide if you’re looking for one, but http://www.globalbioticinteractions.org is also a cool source for this kind of data, and it was created by fellow Oaklander Jorrit Poelen! That said, this kind of data is often very localized: ducks might eat one thing in one place and another in a different place, or eat one thing in Spring, but something else in the Fall. You can actually help people learn about these local details by taking pictures of birds eating stuff and posting them to citizen science websites like eBird and iNaturalist!