Spring is a time for sprouting. Everywhere you look, buds are forming, and tiny green shoots are emerging from the newly softened ground. I often go on walks to places with sunny southern exposures to look for the first crocus or daffodil to poke through. More light and more warmth.
Less easy to see is the new growth that occurs on the shore. The bright green new blades of eelgrass pushing through the mud may be the exception. Harder to notice are the changes occurring in the seaweed that blankets the intertidal rocks. It isn’t exactly as if it is going to burst into flower, but there are more subtle indications of growth.
One of the most common species of seaweed on our coast is rockweed (Ascophyllum nodosum). This is a type of brown algae that lays its long spindly blades over the rocks when the tide retreats, keeping them moist and cool for the animals that live underneath. When the tide comes back in, they swash back and forth, reaching up to the sunlight to make food. It keeps its spot by attaching with a remarkably strong holdfast to just about any surface.
One of the things it does while waving in the water in late spring is to reproduce. Because rockweed is in the ocean and also because it is not a plant but rather an algae, it doesn’t reproduce through pollination like the spring flowers we eagerly watch for. Instead, it has little knobs on the ends of its fronds called receptacles. These look a little different than the other knobs that are along its stem, or stipe, that are filled with air and help keep the rockweed to float. It is for these air filled knobs or knots that rockweed is also sometimes called knotweed. In the late spring or early summer, these receptacles get bigger and more yellow in color. They also develop raised dots on their surface when they become mature and fill with sperm and eggs. Then, when the water temperature gets warm enough, these receptacles burst, releasing sperm and eggs into the water column that combine and produce new little rockweed zygotes that find their way to settle on a surface and start to grow.
Because of its prevalence and its important role in the intertidal ecosystem in providing shelter as well as nutrients and oxygen, rockweed has been chosen by Maine Sea Grant as one of the species in its “Signs of the Seasons” program. This is a community science effort to help scientists gather information on more than twenty native species to study the effects of climate change. Rockweed is the only coastal species in this program. Along with the other species included in the program, rockweed is considered an indicator species. This means that it serves to alert scientists to changes in environmental conditions that could also impact other species.
As a part of the program, volunteers along the coast look for changes in color and texture in the receptacles as well as when they burst open and then fall off after reproduction. They also measure growth from year to year. Rockweed is typically 20-30 inches long but can grow as long as ten feet and live for 8-10 years. Sea Grant offers training and equipment for those interested in participating in the program. There is more information as well as an instructional video on their website: extension.umaine.edu/signs-of-the-seasons/.
There are myriad opportunities to officially participate in community science efforts along the coast. But, whether you become involved in one of these projects or not, they all offer resources and information that can help you to learn how to be more observant and to appreciate the small changes that occur each season.
Comments are not available on this story.
Send questions/comments to the editors.
