When the growth of much of what is on land slows during the winter, the opposite is surprisingly true for some things that grow in the ocean. Maine seaweeds have gotten a fair amount of attention as seaweed aquaculture is a rapidly growing industry, but the rapid growth of seaweeds themselves during the winter months is not always front and center.

It is during the quiet months of winter that many species of Maine seaweed do their speediest growing. This is particularly apparent to those that farm seaweed in Maine was they can easily measure the growth from “seeding” to harvesting. Of the myriad seaweed species that grow in Maine, a few varieties of kelp have emerged as the most common ones. Sugar kelp (Saccharina latissima), so named because you can find a white powdery substance on its surface when it dries that looks like sugar, is perhaps the most common. It has a lovely long frond that has plenty of surface area for absorbing sunlight and a thin stipe that it attaches to a hard surface — a rock in the wild, for example, or a rope in a cultured situation. Other commonly farmed kelps included winged kelp (Alaria esculenta) and skinny kelp (Saccharina latissima forma angustissima).

Seaweed farmers David Leith, left, and Stewart Hunt haul in a line of kelp for harvesting, on April 29, 2021, off the coast of Cumberland. Robert F. Bukaty / AP file photo

Kelp is a common choice to farm because it grows quickly, with “seeding” typically happening in December and harvest in April. That short wintry period can result in a crop around 10 feet in length. It is grown on aquaculture leases, permitted by the Maine Department of Marine Resources, that consist of a series of submerged ropes. A farm starts with a seed string that has been seeded with spores by a culturing lab. That rope is rolled up onto a spool that a farmer can buy. Then, they can unroll it at their site and run more lines through it to increase the surface area for the spores to grow on. Although the lines are submerged, you can tell where a farm is by looking for the “Sea Farm” buoys that mark a lease site’s perimeter. These are used for other aquaculture types as well, but many of those have structures at the surface like oyster cages, for example.

So, what makes kelp grow so quickly in the winter? Kelp are cold water species that thrive when the water is coldest. As photosynthesizers, they, of course, rely on sunlight. But they also rely on nutrients in the water. Nitrogen is one of the most critical nutrients they need for growth and its levels are higher in the winter months. While you might think that sunlight would be limiting in the winter, the water clarity is higher, which means the kelp fronds can absorb more of the sun’s rays. Kelp also likes wave action, which tends to pick up with winter storms and winds. Finally, because all of the other things that live in the ocean, some of which like to munch on or grow on and weigh down kelp, are around in smaller numbers in the winter.

When it comes time for the spring harvest, you might wonder what happens to all this kelp. Some of it turns into seaweed salads, seasonings and other products. And, if you’re not a seaweed lover, you can find it in fertilizers and pet food as well as in soaps and lotions. There are many great Maine companies both growing seaweeds and making innovative products. The Maine Seaweed Council has a list of many of them on their website at seaweedcouncil.org/maine-seaweed-companies. Or if you’re just interested in learning more about the seaweeds themselves, Maine Sea Grant has a great resource page at seagrant.umaine.edu/maine-seafood-guide/seaweed.

Regardless, it is heartening to know that there is thriving life in Maine waters at this time of year when much of the other life in and around the waterfront goes dormant until spring.

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