Underwater Blooms
This past week (June 15-19), following our consideration of gardens as ecosystems, we began exploring underwater gardens all along the coast of Maine. This practice of underwater gardening is also known as aquaculture. We looked at mussel, oyster, salmon, cod, and kelp aquaculture methods, considering their potential impact on coastal ecosystems. Here are some questions we explored that invite research and critical thinking:
How do different methods of shellfish farming differently impact the environment? For example, we compared one method of seeding mussels on ropes suspended from rafts with the European method of seeding mussels on the ocean bottom, and then “dragging” the bottom to harvest them.
How might raising large numbers of fish in the ocean affect the levels of pollutants and nutrients in the water? Could this have a potential effect on algal blooms?
What is a potential effect of fish farming on the reproductive cycles of natural populations?
Our inquiries into the shellfish industry in particular led us to questions about red tide, which we all knew a little bit about, or at least had heard of.
What is red tide?
Red tide occurs when the population of certain kinds of algae known as dinoflagellates explodes, creating what's called an "algal bloom." When millions of these microscopic algae (phytoplankton) reproduce and cluster in one area of the ocean, they can change the color of the water. A rusty shade of red is often seen, though the color may range from pink or orange to brown or yellow. Most often in Maine, algal blooms occur invisibly. This makes regular red tide monitoring especially important here.
How does red tide cause toxic shellfish poisoning?
Through a process called filter feeding, oysters, clams, mussels and scallops draw water into their gills through syphons. Cilia in the gills trap phytoplankton and other food particles, which are then digested. Some species of phytoplankton, the same dinoflagellates responsible for red tides, are toxic for humans to consume in large quantities. Because the toxins accumulate in shellfish through filter feeding, humans can become poisoned by eating shellfish during red tide blooms. Red tide often results in outbreaks of paralytic shellfish poisoning (PSP) and amnesic shellfish poisoning (ASP).
Dinophysis, a common culprit in diarrhetic shellfish poisoning.
To learn more about red tide, shellfish poisoning, and the specific phytoplankton that cause it, we were lucky to welcome guest teacher Amber Wolf of the Community Environmental Health Lab (a program of the MDI Biological Laboratory). Amber’s work involves engaging students and citizen scientists in weekly phytoplankton monitoring. While the volunteer program is currently on hold due to the COVID-19 pandemic, Nature Links participants are definitely interested in getting involved when it's safe to do so!
Check out Amber’s presentation here:
