Narrated by George Monbiot, this video by Chris Bryan and Maggillivray Freeman of Sustainable Human (sustainablehuman.me) explores the vital role of whales and their diving behaviour in providing “trophic cascades”–key mechanisms–for ocean ecosystem health and in affecting changing climate.
“One of the most exciting scientific findings of the past half century has been the discovery of widespread TROPHIC CASCADES…” A trophic cascade is an ecological process that starts at the top of the food chain and cascades down the trophic levels to affect all life. Trophic cascades occur when predators in a food web suppress the abundance or alter the behaviour of their prey; this releases the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore).
Whales eat fish and krill. Some misinformed non-ecologists suggest that killing whales will boost the krill and fish population. However, as the great whales declined, so did the krill and fish populations. This supposed counter-intuitive result is easily explained when the entire system and the whale’s role in it is considered; how it feeds and how its feeding behaviour affects the entire ecosystem and its supporting life.
Whales feed in the dark depths of the ocean, then return to the photic zone at the surface, where there is enough light for photosynthesis to occur. Whales then release fecal plumes (of poo; called poo-namies in the video). Rich in nutrients (such as iron and nitrogen) and often scarce in surface waters,
these fecal plumes are used by the microscopic plant-like plankton, which, in turn, are food for fish and krill. The diving also stirs the waters, vertically mixing and redistributing plankton and nutrients where they are needed.
So, more whales means more plankton, which means more krill and fish.
Phytoplankton also takes up carbon dioxide, causing a carbon sink as they die and decompose on the ocean floor. This contributes to climate control.
“The return of the grey whales–if they are allowed to recover–could be viewed as a benign form of geo-engineering; it could undo some of the damage done both to the living systems of the sea and the atmosphere.”–How Whales Change Climate