The water temperature has definitely dropped. After peaking in August somewhere in the low to mid-60s and staying warm through much of September, October is the month where the temperature starts to fall. It doesn’t drop by many degrees, but once it gets into the lower 50s, it just feels different. It isn’t as frigid, of course, as it gets at the coldest point in the year. That’s in March where the temperatures dip down to the upper 30s.
The water temperature cycle is interesting because it typically lags behind the shift in air temperature. For example, sometimes peak water temperature happens at the beginning of September after a long, hot August. And, in March, the lowest temperatures tend to be after a chilly February. To that end, the change in temperature in October is not super dramatic, but it is the beginning of the decline.
As someone who likes to get in the water as often as possible all year long, I recently noticed the drop in temperature and was instantly jealous of the fish and other marine creatures that can withstand the cold without the aid or a wet or dry suit and stay submerged for long periods of time. There are, of course, people who are much tougher than me, including a friend who is an intrepid cold-water swimmer and goes every day throughout the year. But, for the most part, we humans are not well designed for the cold water.
Animals that live in the ocean, however, have some amazing adaptations that make living in Maine waters year-round possible. I was recently teaching a group of students about lobster migration and describing how they move further offshore into deeper water in the winter. These deeper waters are actually warmer in the winter than those at the surface that are in contact with the frigid air. This is less of a migration than a seasonal movement and is something that a lot of local fish and crustacean species do. Even the shellfish go deeper in the mud.
There’s something else about how Maine shellfish survive the winter, though, that I didn’t know until recently. Shellfish carbo-load ahead of the cold temperatures – much like someone might do ahead of a big game or race. They eat like crazy and build up stores of carbohydrates to sustain them through the winter when they basically hibernate.
During this time, they don’t filter feed much, so they need stored up energy to survive. They store this energy in the form of glycogen, a complex sugar, which is why shellfish taste so sweet in the fall when they are storing up for winter. Aside from providing sustenance, burning glycogen also helps to provide some degree of warmth and prevents the formation of ice crystals in animal tissues. This is much like glycol, another carbohydrate, which is added to water to prevent systems from freezing in the winter – something many of us in Maine know far too well.
Other types of animals, aside from shellfish, also store glycogen in their tissues, but it typically gets used up by the time we eat it. Shellfish are rare in comparison to most seafood because we eat it so quickly after it is killed, or even raw. After an animal dies, its stored glycogen is used up by the final twitches of muscle known as rigor mortis. So, the more quickly you eat something after it dies, the more glycogen will still be there.
All of this makes me wonder if I’d stay warmer if I ate a lot of shellfish this fall. It’s worth a try – and would also be a good way to celebrate National Seafood Month, which is October. As always, nature is impressive and the adaptations that have evolved to deal with challenging environmental conditions are complex. We are lucky that these adaptations make our seafood all the more sweet
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