Seabirds, are tied both to the health of the ocean ecosystem and to global climate regulation

When phytoplankton are eaten by grazing zooplankton like copepods and krill, the krill release a chemical signal that calls in seabirds. At the same time, this chemical signal — dimethyl sulfide, or DMS — forms sulfur compounds in the atmosphere that promote cloud formation and help cool the planet.

Tiny Storm Petrel recovering in my pocket having collided with boat rigging. This little guy along with tens of thousands of his kind showed up at our restored ocean pasture blooming with plankton in vast abundance.

I witnessed this seabird plankton connection in our 2012 ocean pasture restoration project. As our ocean pasture bloomed with revived abundance tens of thousands of seabirds arrived.

The same seabirds consuming the zooplankton are performing work to help sustain their ocean pastures. Their guano fertilizes and sustains the phytoplankton most importantly with vital iron, which is scarce in the vast Southern Ocean. The work was published March 3, 2014  in the Proceedings of the National Academy of Sciences.

“The data are really striking,” said Gabrielle Nevitt, professor of neurobiology, physiology and behavior at UC Davis and co-author on the paper with graduate student Matthew Savoca.

Seabirds and humpback whales feeding together in a plankton bloom

This shows that seabirds are more than just consumers, they are caretakers of their ocean pastures and vitally important in climate regulation.  Although even with this potent role they are left out of climate models, Nevitt said. But the dark side of this story is that seabird populations are declining as ocean pasture plankton blooms are in a cataclysmic state of collapse.

“In addition to studying how these birds are responding to climate change, our data suggest that more attention should be focused on how ecological systems, themselves, impact climate. Studying DMS as a signal molecule helps make the connection,” she said.

Nevitt has studied the sense of smell in ocean-going birds for about 25 years and was the first to demonstrate that marine grazers use climate-regulating chemicals for foraging and navigation over the featureless ocean. DMS is now known to be an important signal for petrels and albatrosses, and the idea has been extended to various species of penguins, seals, sharks, sea turtles, coral reef fishes and possibly baleen whales, she said.

Phytoplankton are the plants of the open ocean, absorbing carbon dioxide and sunlight to grow. When these plankton die, they release an enzyme that generates DMS.

Noone other than James Lovelock, Mr. Gaia, et al proposed this same DMS plankton bloom mechanism as one of Nature’s ways for managing climate change in the 1980s. According to his CLAW hypothesis, warming oceans lead to more growth of green phytoplankton, which in turn releases a precursor to DMS when they die. The CLAW hypothesis morphed with Lovelock’s popularization of Gaia, the Earth as a single living entity.

DMS in the atmosphere helps cause cloud formation, and clouds reflect sunlight, helping to cool the planet. It’s a negative feedback loop to control the planet’s temperature. However, in today’s world, plankton blooms are in cataclysmic decline.  With less DMS, it is projected that fewer clouds will form over the vast oceans to block out the Sun’s warming rays.

Katharina Six, Max Planck Institute for Meteorology, has a paper published in Nature Climate Change ‘Global warming amplified by reduced sulphur fluxes as a result of ocean acidification’ explains and projects that reduced cloud cover due to lower concentrations of DMS could will raise projected global average temperatures about 0.4 to 0.9 degrees Fahrenheit (0.23 to 0.48 degrees Celsius).

Savoca and Nevitt 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 heavily fed on krill, which in turn graze on phytoplankton.

Whales also recycyle vital nutrients back to the ocean pastures where they graze. Link to our post “Whales are worms” to learn more.

The seabirds have something very important to contribute. They really do give a shit about their ocean pastures.

The Southern Ocean lacks large land masses from which minerals can wash or blow into the ocean and is thus very low in iron. Krill accumulate and are rich in iron, but birds can absorb relatively little of it — so the rest is excreted back into the ocean, promoting plankton growth.

The work suggests that by linking seabirds and phytoplankton — the top and bottom levels of the food chain — their favorite chemical DMS plays an important role in the ocean ecosystem, which affects climate by taking up carbon, as well as a physical role in generating clouds, Nevitt said.

“Studying how seabirds use scent cues to find plankton blooms and forage has shown us a mechanism by which the seabirds themselves contribute to climate regulation. That’s not what we expected, but I really think our results will have global significance,” she said.

At the same time, numbers of these birds are declining, with almost half of species listed as vulnerable, endangered or critically endangered. The newly discovered links between seabirds and the base of the ocean food web mean that a decline in seabirds could have a significant effect on the marine productivity.

The work was funded by the National Science Foundation.

Journal Reference: M. S. Savoca, G. A. Nevitt. Evidence that dimethyl sulfide facilitates a tritrophic mutualism between marine primary producers and top predators. Proceedings of the National Academy of Sciences, 2014

‘Global warming amplified by reduced sulphur fluxes as a result of ocean acidification’ Six K.D., Kloster S., Ilyina T., Archer S.D., Zhang.K, Maier-Reimer E., Nature Climate Change, doi:10.1038/nclimate1981, 2013  “Our results indicate that ocean acidification has the potential to exacerbate anthropogenic warming through a mechanism that is not considered at present in projections of future climate change.”