macoma baltica


Shells of macoma baltica next to an illustration in the key to the book “Intertidal Bivalves” by Nora R. Foster.

When our mind seeks solutions to the problems of the day, it often takes a trip down memory lane. People remember things in different ways and often the memories are tied to certain items or images.

Recently, while strolling down a beach in Kalsin Bay, there were a large number of small seashells washed up in the tideline. My son picked one up to show me the striking pink layer on its inside.

Recognizing the shell as a small clam called macoma baltica, a flood of childhood memories started to play in my mind like a series of short movies. 

One summer when I was about 9 or 10 years old, my family took a vacation at the Baltic Sea coast in Denmark.

There is an image of my brother walking around for two days with a wet towel draped over his back after an encounter with a stinging jellyfish, which left him with a nasty rash.

I also have a memory of sitting peacefully in the sun-warmed sand playing with a collection of beautiful small macoma baltica shells, organizing them into pretty pictures, sorting them by colors and decorating sand castles with them.

I was always a bit of a dreamer as a child, easily absorbed in a pretty shell or the observation of an ant struggling across the sandy expanse of beach. Later, I would take the shells back to our vacation domicile, draw little butterfly bodies on a piece of paper and then glue on the shells for wings.

Macoma baltica is named after the Baltic Sea, which borders the countries of Germany, Denmark, Poland, Estonia, Latvia, Finland, Lithuania, Sweden and Russia.

Any species that lives in the Baltic Sea has to be tolerant of low salinity, because the Baltic Sea is an inland sea with only two connections to the rest of the world ocean and many rivers that empty their load of fresh water into it.

Thus, the Southern Baltic where the coasts of Germany and Denmark are, has a higher salt content carried in with water from the North Sea that enters through a channel called the Kattegat.

The further away one gets from that inflow, the less salty the water. Gradually, the North Sea species that are found near the Kattegat inflow become less abundant and smaller as they are trying to survive in the low salinity environment.

When vacationing at the Baltic Sea coast, one can eat local commercially caught fish, but the size of these fish would make our Kodiak fishermen laugh (or cry). Usually, a commercial-size specimen of Baltic Sea flat fish makes a meal for one person if served with potatoes and a side of salad or vegetables. 

The ability to thrive in low salinity water allows macoma baltica to populate river estuaries, and the species lives in temperate climates of the Atlantic and Pacific oceans.

The clam is less than 1 inch fully grown, has a life span of 8 to 10 years, and individuals of 8 to 10 millimeters are sexually mature.

From my childhood days, I remember them coming in pastel color shades of pink, blue, green, orange and yellow.

Here in Alaska, the colors seem less varied with most individuals showing pink and white or yellow.

While too small for commercial harvest, this clam is a key species in the food web and many juvenile crabs and millions of migrating birds depend on it.

The Copper River Delta Shorebird Festival in Cordova, with its annual spectacle of migrating birds feasting in the mudflats, happens thanks in part to macoma baltica and a lot of intertidal worms.

In the muddy estuaries of rivers, the sandy shores of the Baltic and the muddy intertidal areas from the North Sea coast to Cordova, billions of small clams use their long siphons to vacuum up the organic gunk on the ground around them and pump out dissolved nitrogen and phosphorous into the water.

Thus, like an earthworm in a compost bin, they process the dead organic materials and free plant nutrients for new growth.

Every spring the adults release gametes into the water from which fertilized eggs hatch into small larvae that disperse with the plankton.

After two to three weeks, the larvae settle, bury into the mud and grow their shells.

In some areas the tiny clams begin this growth state in very shallow water right at the edge of the water where you would wiggle your naked toes while going for a walk along the sandy beach. As the clams get bigger they migrate to slightly deeper water.

The Alaska Department of Fish and Game has some great pages with information on a number of local species published on their website.

While the site is missing many Alaskan species and is by no means complete, it is here that I found a great summary about macoma baltica in Alaska.

The author points out that there is little information about population trends of this important feeder clam, though one study found that climate change and the resulting higher temperatures in the spawning season caused a decrease in fertility.

Most of the information that is there comes from macoma baltica’s role as a bioindicator for biological toxins and oil.

Like all filter feeding shellfish, clams accumulate whatever they filter out of the water, including the toxins in some of their feeder algae and any pollutants dissolved in the water. 

Two days ago, I found a book on my shelf that I had forgotten was there.

The book has beautiful drawings of several common Alaska shells and its title is “Intertidal Bivalves” by Nora R. Foster.

Inspired by my find, I went for a walk on a beach in Middle Bay and collected all the different clam, mussel, scallop, cockle and jingle shells I could find.

Back home, I washed them, sorted them and tried using the key to find each one’s Latin and English name, then wrote the names on the inside of the shells in pencil.

I learned a lot about all the terms for different parts of the animals, and what to look for in identifying the species.

Every species has a different pattern of scars on the inside, where the muscles attached to the shell and a different lock to hold the two shells together.

Different families have concentric growth rings more or less visible, while scallops and cockles also have radial grooves. I admit I got so engrossed in my activity that time got away from me and dinner was late (no, we did not have clam chowder). 

Shell identification is not as easy as it would seem; there are many different species and some are difficult to tell apart, especially when the specimen at hand is not fully grown.

However, if you are looking for a great summer activity for yourself or with your kids, I recommend collecting, sorting and naming some shells from the beach.

Shells are a great way to combine science and art, hone observation skills and get into species identification just as deeply as you want.

If that is not your thing, you can always sort the shells and then come up with your own names for them. As a child I used to call macoma baltica the “butterfly shells,” but I have heard kids in Alaska use that name for the plates of a chiton, so if you make up names keep in mind that it complicates communication between people.

You may wonder why I would choose to write about an inconspicuous species we have little research on in a time when the world surely has bigger problems to deal with.

There are important research cruises that are canceled because of the effects and administrative handling of the COVID 19 pandemic, and a plethora of issues caused for fisheries, economics, management and research projects, the combined effects of which are still impossible to fathom.

The less conspicuous species, the always neglected research and the questions we don’t answer in times like this, will continue to keep us ignorant about the workings of our amazing ocean ecosystems.

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