Photo Credit: Peter Roopnarine, Joe Roman, James J. McCarthy
And this liquid fecal matter, rich in nutrients, has a huge positive influence on the productivity of ocean fisheries, Roman and his colleague, James McCarthy from Harvard University, have discovered.
Their discovery, published Oct. 11 in the journal PLoS ONE, is what Roman calls a “whale pump.”
Whales, they found, carry nutrients such as nitrogen from the depths where they feed back to the surface via their feces. This functions as an upward biological pump, reversing the assumption of some scientists that whales accelerate the loss of nutrients to the bottom.
And this nitrogen input in the Gulf of Maine is “more than the input of all rivers combined,” they write, some 23,000 metric tons each year.
It is well known that microbes, plankton, and fish recycle nutrients in ocean waters, but whales and other marine mammals have largely been ignored in this cycle. Yet this study shows that whales historically played a central role in the productivity of ocean ecosystems — and continue to do so despite diminished populations.
Despite the problems of coastal eutrophication — like the infamous “dead zones” in the Gulf of Mexico caused by excess nitrogen washing down the Mississippi River — many places in the ocean of the Northern Hemisphere have a limited nitrogen supply.
Including where Roman and McCarthy completed their study: the once fish-rich Gulf of Maine in the western North Atlantic. There, phytoplankton, the base of the food chain, has a brake on its productivity when nitrogen is used up in the otherwise productive summer months. (In other parts of the ocean, other elements are limiting, like iron in some regions of the Southern oceans.)
“We think whales form a really important direct influence on the production of plants at the base of this food web,” says McCarthy.