Every summer, I look forward to seeing phosphorescence in the water. These are the tiny plankton that sparkle when disturbed. If you wave your hand or a paddle under the water, you can see them shimmer. I say “them” because they are individually so small that it takes a large number of them to put on a show. Many of these plankton are dinoflagellates, which are single-celled organisms that have two tails or “flagella” attached to a variety of “body” shapes. Up close, the variety of shapes and sizes is fascinating, but you need a good microscope to see anything beyond a teensy glowing dot. That’s because they are typically smaller than a millimeter and often less than a quarter of that!
Glowing plankton’s typically tiny size is why, on a recent night walk along the beach, I was in disbelief at seeing several individual glowing spots on the sand. While there are larger bioluminescent marine organisms including plankton-like jellyfish and also many deep sea creatures like fish and worms, these were small dots on the sand that looked as if someone had shaken out their soggy paintbrush. They were just below the line of seaweed and other tangled shells and creatures that the tide had left behind earlier in the day. At first, I thought that what we were seeing might be artificial, but when I picked one up, it wiggled a little in my hand and continued to glow. A second sample did the same thing.
A close-up of what the author thinks may be a beach or sand hopper that consumed bioluminescent plankton. Liliana Olcott photo
We carried one of the samples inside and put it safely in a teacup so as not to lose it, as it wasn’t so big that it couldn’t easily be lost. The little dot continued to glow and was quite bright when we took it into a totally dark room. Back under the light, under closer inspection, we puzzled at what this glowing creature could be. It was mostly translucent, or at least pale in color, and about the size of a standard earring backing. The shape was a little hard to discern, but it looked like it was possibly curled up. It definitely had an insect-like look to it but without a lot of clear definition. And I was pretty sure that of the standard glowing marine organisms, the insect-like type wasn’t among the most common.
After a bit of research, I found some reports of beachy insects that glowed as a result of consuming bioluminescent plankton. That’s true of so many living creatures — that they take on the color of their food. Think of flamingos that have pink feathers because of the pink shrimp they eat and the fact that even humans can start to look a little orange if they eat too many carrots.
In looking closely at our glowing critter, my best guess is that it is some kind of beach hopper or sand hopper, which are quite common, and we saw tons of them during the day. Beach hoppers are a type of crustacean, like shrimp and lobster. But they are in a category of crustaceans that do not have a carapace (the body section on the lobster). Instead, they have bodies that are segmented and are flattened side to side. There are multiple species of “hoppers,” and I am far from having the expertise to know which of these might be what we were seeing. And I could be completely wrong here.
I would welcome thoughts from any readers if they know what the specific identity of our glowing beach dots might be. Regardless, the ability of marine creatures to glow at night truly is magical and one of the seemingly inexplicable phenomena along the Maine coast.
Susan Olcott is the director of operations at Maine Coast Fishermen’s Association.
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