What Plankton has to do with Your Scallop Dinner

Staff Writer: Maya Arruda

Email: marruda7@umassd.edu

On October 5th, the Department of Fisheries presented a seminar by John Zang about the relationship between phytoplankton and Atlantic Sea Scallops on the Northeastern U.S. continental shelf.

By using complex models, the behavior and characteristics of the phytoplankton on this shelf have been thoroughly examined. However, while phytoplankton might not be seen as important to the casual viewer (except for any Spongebob enthusiasts), phytoplankton directly impacts the production of scallops and other delicious commercial shellfish that can usually be found on the shelf.  

A picture of phytoplankton, originally from Wikipedia

Phytoplankton, the star of this story, do a lot more for the marine ecosystem than plotting to steal the Krabby Patty formula.

Phytoplankton are primary producers, which means they make energy out of some nutrients and the ultimate mutagen/death laser we call the sun. Of course, since phytoplankton photosynthesizes, they also produce good ol’ diatomic oxygen as a byproduct. Great for us aerobic organisms.  

In marine ecosystems, phytoplankton are the main producers of biomass (essentially aquatic grass in the ecosystem) and thus are what pretty much every other organism depends on to get their energy, either directly or indirectly.

Phytoplankton are heavily dependent on nutrient availability and temperature, resulting in spring and fall blooms for phytoplankton populations. However, nutrient availability and temperature have different peaks in the year, which limits phytoplankton population growth. 

Primary production of the ecosystem (when phytoplankton make food) usually occurs in the spring and summer, but mostly in the spring. Secondary production (when phytoplankton gets eaten) peaks in the summer due to high grazing and large phytoplankton populations to chow down on. Talk about suffering from success. 

Let’s focus on the location, now.

The Northeastern U.S. Shelf. This area includes the Gulf of Maine (not to be confused with the Gulf of Mexico) and the Mid-Atlantic Bight (the scallop’s natural habitat). It has great economic (and gastrointestinal) importance due to its abundance of delicious seafood. In this case, namely Atlantic Sea Scallops.  

This shelf has rapid warming and high seasonality. The regional climate smooths out any major differences in temperature or nutrient availability between years.

However, despite the climate, the resident animal populations (I.e., the phytoplankton and the tasty scallops) suffer because of the warming and seasonality every year. Especially the scallops.  

Enter the Atlantic Sea Scallop: that glorious, delicious, beautiful, picture-perfect shellfish that you see everywhere in the New England area. This tasty seafood staple feasts on phytoplankton and detritus (dead things). They predominantly live in the Mid-Atlantic Bight, a part of the Northeastern Shelf.  

In addition to being limited by their food supply (phytoplankton), scallops are strictly limited by the temperature of their environment. Warming really cuts into the scallop population. Not only does warming decrease the amount of scallop habitat (since they can only survive in lower temperatures), but warming also decreases the size of the scallop.  

The thing about scallops (and all organisms) is that they need to take in more energy than they lose in order to live. In the case of any heterotrophic animals, they need to eat other organisms to get that energy. However, only one-tenth of the energy in the eaten food gets transferred to the eater for use due to very low efficiency.

Ergo, the scallops would have to eat a lot of plankton to maintain population growth, especially with human and natural predation and other causes of mortality. 

By monitoring and modeling the phytoplankton population on the Northeastern Shelf with physical simulation models, graphical comparisons between NO3 and ChL levels, and measurements of the phytoplankton blooms, the phytoplankton population can be used to predict the population of Atlantic Sea Scallops

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