Spineless Wonders of Lake Merritt

…or, more technically, invertebrates…

Lake Merritt is justly famous for the many species of birds that overwinter on the lake . The occasional appearance of a sea lion or river otter makes headlines but did you know that the lake is also home to a great variety of micro-charismatic critters?

The most obvious (and perhaps least charismatic?) are the mussels that line the edges of the lake. They stick out in a low tide. Gulls love to feed on them — you may often see a gull with one in its bill. Gulls will also deliberately drop a closed mussel onto the pavement to open the shell and get at the meaty interior. Take a look inside an open mussel shell and there you will find yet other organisms.

Mussel inside

Less obvious but more important for the food chain is the plankton in the lake. Plankton consists of tiny critters that one needs a microscope to see and can include diatoms, protozoans, small crustaceans, and the eggs and larval stages of larger animals. The Nature Center (when we reopen again!) has microscopes that school groups and other visitors can use to get an idea of the diversity of life in the lake.

Microscope

The most “famous” invertebrate at the lake is a new kind of beach hopper discovered many years ago by a 14 year old boy, Jim Carlson, who went to great lengths to find out what it was.  (You can find his story at Bay Nature Magazine). Like most of the rest of the lake’s flora and fauna this “bug” probably was introduced on the hull of a ship. No one could identify this critter and it turned out to be a new species dubbed Transorchestia enigmatica. These beach hoppers may still be present on the small stretch of remaining beach near the bandstand. See if you can find one. You’ll find a more typical species of beach hopper along the channel.

enigmatica

My all time favorite invertebrate — seen at the lake back in 2015 — was a family of sea hares hanging out under the pedestrian bridge. Sea hares are related to octopuses and can eject a stream of ink to hide from potential predators.

Sea hare

Take a walk around the lake at low tide and see what you can find in the water.

— Dianne

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