In a new paper in the science journal PNAS the long known role of seabirds is reported anew. Seabirds flock to plankton blooms and in doing so their presence is more than just as consumers of the plankton though indeed they do consume. But of course like all life only a portion of what goes in stays in and the seabirds are shown in this paper to be very important to the blooms by their fertilizing efforts. Like any caring farmer the seabirds give back to the bloom and in doing so nurture and sustain it.
The birds have something else to contribute other than the obvious nitrate and phosphate component of their waste guano. The Southern Ocean is far from large dusty land masses, and is very low in iron, which arrives almost exclusively as dust in the wind. Krill, a favourite food of seabirds, are rich in iron, but birds can absorb relatively little iron — so the rest is excreted back into the ocean, promoting more plankton growth.
Iron as the most vital plankton micro-nutrient, actually a nano-nutrient, has more than a million times the potency of better known fertilizing agents like nitrates and phosphates. A flock of a thousand seabirds and their nitrogenous guano are, from the iron nano-nutrient plankton bloom sustaining point of view, like flock of a billion birds. Nature and her birds are not merely there as dumb agents of consumption, they have evolved a vital and powerful synergy of give and take.
Tragically as the ocean pastures continue to die as a result of our CO2 they take with them their partners the birds, fish, and whales. Replenishing a little of that dust gone missing from the wind brings the ocean pastures back to life.
This new paper goes on to present the case for plankton blooms which produce a gas named DMS (dimethyl sulfoxide). Seabirds benefit from being able to detect this gas from great distances as they flock to the blooms.
An additional role for DMS in regulating climate as was proposed by Robert Charlson, James Lovelock, Meinrat Andreae and Stephen Warren in the 1980s. According to the CLAW hypothesis, warming oceans lead to more growth of green phytoplankton, which in turn release a precursor to DMS when they die. Rising levels of DMS in the atmosphere cause cloud formation, and clouds reflect sunlight, helping to cool the planet. It’s a negative feedback loop to control the planet’s temperature while feeding all of ocean life.
Savoca and Nevitt who wrote this recent paper looked at 50 years of records on seabirds’ stomach contents, combined with Nevitt’s experimental results of which species use DMS to forage. They found that species that respond to DMS overwhelmingly fed on krill, which graze on phytoplankton.
On land, there are several known examples of plants that respond to attack by insects by producing chemicals that attract predators that eat those insects. Nevitt and Savoca propose the same thing happens in the open ocean: when phytoplankton come under attack by krill, the DMS released as they die attracts predators that eat the krill.
We observed the seabirds coming to our bloom in 2012 in the NE Pacific. Where before the bloom we created began we would observe only a few seabirds each day when the blooming was going strong thousands of seabirds arrived. In the morning just as the sun came up our research ship which had bright lights was surrounded by vast swirling flocks of storm petrels. Their bird song in the morning was so cacophonous that it almost drowned out the roar of the ships engines. It was a sight to behold.
With seabirds above the bloom tending to it they are joined by the whales below which are like giant earthworms plowing through the bloom eating and spreading whale manure. Both bird and whale are not merely “freeloaders” or “predators” they have a very important job that they do with earnest intent that being as farmers and stewards of their ocean pastures.
To every thing there is a season, and a time to every purpose under the heaven:
A time to be born, and a time to die; a time to plant, a time to reap that which is planted;
Here’s the recently passed Pete Seeger singing this truth and knowledge.
We will miss you Pete. Thanks for your gifts of song to us all.
PS. Yes, as some have pointed out there is a version of this sung by the Byrds, but you’ll have to listen to it on Youtube.