A few years ago I had the opportunity to teach a marine science class for teachers in Rye, New Hampshire. It was an excellent experience for me. The teachers were enthusiastic, and the coastline was fascinating and beautiful. We spent several hours exploring and collecting along the rocky shore, looking for any unusual algae or marine animals that might appear, or wash up on the beach.
On one of our trips we encountered a very interesting brown alga known as the sea colander (Agarum cribosum). Using a long-handled dip net and bucket, I scooped the alga out of the water, carefully balancing myself on the slippery rockweed. When you first examine this alga it looks like an animal has been chewing on the blade, leaving large holes, hence the common name sea colander. I've also heard it referred to as the Swiss cheese alga.
The blade is fan-shaped and up to a foot wide. The holes or perforations are due to its growth habit and the effects of waves, and not the munching of numerous herbivores. It is usually found in colder, deeper water, and is often attached at the end of jetties with its strong root-like holdfast.
At a time when invasive species tend to dominate in many areas, it is always exciting to locate a species that is not frequently seen. I have collected this alga on Cape Cod occasionally, but it is more common in the colder waters of northern New England. Its appearance is so different that it always gets noticed when it appears.
The teachers enrolled in my class taught grades ranging from kindergarten to twelve grades, yet they all shared my thrill at finding Agarum in an environment dominated by rockweed. We tried making a pressed specimen for our coastal herbarium and collection, but the alga is too thick, and it warped on the paper. Still, we were able to study it in detail back in the classroom and could appreciate it for its interesting features.
One of the lessons I am always conveying to my students, young and otherwise, is that the marine environment is a dynamic, ever-changing system. You never know what you may find. You can visit a particular beach or marsh several times, and each time it will be different. Sometimes these differences are subtle and small, such as when a sea colander washes ashore. It is those moments that enhance one's visit to these special places.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.