Whales!
Our friend Monbiot (my emph.):
http://www.monbiot.com/2014/12/12/everything-is-connected/
[T]he natural world is even more fascinating and complex than we had imagined. And we are only just beginning to understand just how rich and strange ecological processes might be.
I promised whale poo, and whale poo you shall have. Studies in the 1970s proposed that the great reduction in the large whales of the southern oceans would lead to an increase in the population of krill, their major prey. It never materialised. Instead there has been a long-term decline. How could that be true? It now turns out that whales maintain the populations of their prey.
They often feed at depth, but they seldom defecate there, because when they dive the stress this exerts on the body requires the shutdown of some of its functions. So they perform their ablutions when they come up to breathe. What they are doing, in other words, is transporting nutrients from the depths, including waters too dark for photosynthesis to occur, into the photic zone, where plants can live.
In the southern oceans, iron is a limiting nutrient, without which the plant plankton at the bottom of the food chain cannot reproduce and grow. By producing their poonamis – sorry, faecal plumes – in the surface waters, the whales fertilise the plant plankton on which the krill and fish depend. This effect, known as the “whale pump†has been hypothesised for several years. But now there is some experimental evidence to support it. A team of scientists at the University of Tasmania collected some pygmy blue whale poo (who knew that marine biology was so rich with possibility?) and grew plankton in water containing varying concentrations of it. They found that the richer the mix, the greater the productivity. No surprises there.
Separate research, in the Gulf of Maine, estimates that whales and seals, by defecating at the surface and recycling nutrients there, would, before their numbers were reduced by hunting, have been responsible for releasing three times as much nitrogen into those waters as the sea absorbed directly from the atmosphere. The volume of plant plankton has declined across much of the world over the past century, probably as a result of rising global temperatures. But the decline appears to have been been steepest where whales and seals have been most heavily hunted. The fishermen who have insisted that predators such as seals should be killed might have been reducing, not enhancing, their catch.
But it doesn’t end there. Plant plankton, when they die, slowly descend into the abyss, taking with them the carbon they have absorbed from the atmosphere. It is hard to quantify, but when they were at their historical populations, whales are likely to have made a small but significant contribution to the removal of carbon dioxide from the atmosphere. The recovery of the great whales, which were reduced by between two thirds and 90%, but whose numbers are slowly climbing again in some parts of the oceans, could be seen as a benign form of geo-engineering.
This should not be the only, or even the main, reason why we should wish them to return, but the way in which whales change the composition of the atmosphere provides yet another refutation of the idea that we can manipulate the living world with simple, predictable results.
(Goto link for his refs)
Wasn’t rewilding the prairies supposed to be really good for carbon sequestration? (Though not as good as leaving fossil fuels in the ground and/or ending the industrial age admittedly.)
cheers,
I
