The full moon this week led to some seriously high tides, creating mirror-like expanses reflecting the newly barren trees and dusty colored marsh grasses. This is a lovely late fall scene. On the flipside, when all that water goes out, there is a great swath of mud that is uncovered. And here in Brunswick, we have a lot of intertidal that is muddy. I find the shiny exposed mud just as lovely, particularly when you can see the lacey patterns on its surface that the water leaves as it trickles slowly out. But then there is the smell. The fresh fall breezes of high tide turn sour smelling as they blow over the mud. While this would at first seem to indicate death and decay, there is, in fact, a lot of life under that mud. I’ve written many times about the shellfish that burrow underneath and are an important coastal resource. You can see the holes in the surface of the mud where their siphons reach up to filter out food from sea water. But, there is a lot more life down below than just clams.
In addition to being hard to find because they are buried under some thick, stinky mud, those living things are also very tiny. Their name, microbe, is short for “microscopic organism,” meaning that they cannot be seen without magnification. These can include bacteria, viruses, fungi and protozoa (the infamous types of protozoa cause toxoplasmosis and malaria). These may seem like dangerous and unhealthy forms of life, but many of them serve positive roles, including breaking things down like food in our digestive system or decomposing things in nature that have died and recycling their nutrients for new life. Microbes are one of the most diverse forms of life, coming in just about every shape and size, rather than just being the plain, tiny specks you might imagine. Although their forms are diverse, their color is pretty bland. When scientists look at them under a microscope, they often stain them so that they can better see their details. It is worth looking up pictures to see the range of types.
Microbes can live in a wide array of habitats and conditions. In the ocean, some live near the surface of the water where they use sunlight, or photosynthesize, to make energy. Others are found in some seemingly inhospitable places — places where there is little or no oxygen. These “anoxic” conditions, ironically, are found in some of the deepest and some of the shallowest places in the ocean: the deep sea and the intertidal.
If you think about it, in a mudflat, it makes sense that clams stick their siphons way up to reach out into the oxygen once you realize that there isn’t much oxygen down underneath. Instead, there is a lot of sulfate — the favorite food of many types of microbes. Most organisms we are familiar with get their energy through “aerobic” respiration, meaning they breathe air. These mucky microbes use “anaerobic” respiration, which means they break down sulfuric compounds to get their energy. The byproduct is the sulfides that we smell coming off of mudflats.
This stinky smell is one of the reasons I think the muddy intertidal sometimes gets a bad rap. Unlike the lovely rocky intertidal with its glistening tidepools and draped fronds of kelp, it appears both pretty boring as well as not smelling so nice. But if you understand the importance of these scrappy microbes in revitalizing the mud and appreciate their tolerance for suffocating conditions, the mud seems a little shinier and complex. It’s also particularly shimmery in the low light of these short days — a different kind of beauty when the tide is out.
Susan Olcott is the director of operations at Maine Coast Fishermen’s Association.
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