PLANKTON AND WHALE POOP
Spring ushers in a great diversity of biological life to the shallow seas of the Gulf of Maine. Productivity peaks when the longer days of spring sunlight interact with nutrient rich meltwater from the land to create conditions leading to a phytoplankton bloom in surface waters. These single cell plants are the foundation of the marine food web and they feed small shrimplike crustaceans and fish larvae known as zooplankton. In the shallow edges and banks of the Gulf, to the saltmarshes and mudflats, this concentration of protein attracts fish of all sizes, seabirds, and ultimately, marine mammals.
Small zooplankton called copepods feed on the primary producers and diatoms. They can also be carnivorous, preying on protozoans and small zooplankton.1As waters warm, the phytoplankton bloom is sustained by regenerated nutrients produced by the feeding animals themselves. Their waste products are excreted, taken up by the smallest organisms to keep the transfer of energy going across the food web, from producers making food from sunlight to various levels of consumers and scavengers. A final boost comes from decomposers, such as bacteria, which release the nutrients that sustain the cycle. This process is called a trophic cascade, where trophic refers to food or feeding activity that leads to energy transfer.2
Fish are found at various times and places in the Gulf of Maine depending on where the algal blooms appear. Bottom feeders like cod gather at the West side of the Gulf while pelagic (open water fish like tuna) cruise the upper water layers of the East side of the Gulf. This separation reflects the various mixing regimes caused by the still little-known current movements. Many of the teachers and students featured on this site have contributed to increased knowledge of these currents by building, launching, and tracking ocean drifters over the last several years.
Later in the season as surface water cools, grows heavier, and sinks, it helps to restore conditions for plankton growth by bringing nutrients left over from the earlier feeding frenzy. A convection current forms which actually rolls over the water layers somewhat like turning over the soil in a garden to rebalance the nutrients.3Large animals like whales aid in this process by feeding at greater depths but releasing their waste or “poop” at the surface. In doing this they help to control their food supply by bringing nutrients from the lower layers where it is too dark to photosynthesize up to the fertilized waters (by whale poop) in the photic zone. thus renewing the energy transfer by feeding again.
As phytoplankton volume has been declining with rising sea temperatures, studies begun in the late 70's indicated that the decline of plankton was highest where marine mammals were hunted. When they die, plankton take their carbon with them. So at historical population levels, whales may have had a small, but significant effect on lowering CO2 levels. Could this be considered a benign form of geoengineering based on whale poop?
Sources: 1. Thurston, Harry, The Atlantic Coast: A Natural History, Greystone Books, Vancouver, BC Canada, 2011 2. Monbiot, George, "Everything is Connected" in Monbiot How Did We Get in This Mess?Versa Publishers, London, 2016
John Halloran is the Director of Science for GOMI and a member of the GOMI Guide Team. John’s interests focus on the ocean environment where he pursues educational adventure travel, research, and recreation by sail, paddle, and scuba.John is the founder and director of Adventure Learning, Newburyport, MA, which has been involved with educational outreach in area schools and recreational programs for teens and adults since 1980. A long-time educator, John was at the forefront of the experiential education movement in the U.S. for 36 years, he taught natural science in the Newburyport Public Schools.