ANOTHER LIFE: The lengths to which dedicated Irish birders will go in pursuit of their hobby can be deeply intriguing, writes Michael Viney. Last month, in what has become a twitchers' August ritual, boat parties draped in bonoculars mounted 'pelagics' - long trips out to sea in the hope of glimpsing birds that rarely come within sight of land.
The prize this year was Wilson's storm petrel, Oceanites oceanicus, which breeds at antarctic latitudes but migrates as far as the North Atlantic in summer. Tick a Wilson's, and your twitcher's "life list" moves up a meritorious notch.
On one trip, four of the petrels were conjured up two miles off the Blaskets, gliding tirelessly over the swells on their dark little wings. And conjured up is exactly the term, since what fetched them was a teaspoonful of a volatile organic chemical, dimethyl sulphide, sprinkled on the sea.
DMS now promises to be a favourite "attractant" on such sorties, despite a concentrated potency that can saturate its users in an uninvited reek of garlic. Sulphur compounds are, indeed, what give garlic its pungency, but DMS is emitted by algal plankton and other marine organisms and is part of the smell of a freshly-caught fish.
A teaspoonful spilt on the sea can, it seems, be smelled up to one kilometre downwind and 70 metres high. Detected at infinite dilutions within the petrel's tubular nostrils, it suggests one thing - food. The same scent draws petrels to the disturbed wake of ships, in which animal plankton and small fish are churned to the surface, and to plankton upwellings where fish, dolphins and gannets assemble in frenzied banquets.
The use of "chum" - gory, oily fish-waste tipped over the stern - has been the more conventional attractant for pelagic birders, as for shark-anglers. Indeed, ethics would seem to demand that birds attracted by DMS should also be given some reward for their diversion: a feed of minced mackerel, at least.
Despite its noisome nature in laboratory concentration, dimethyl sulphide is a chemical that helps the life of the world go round. It figures notably in the writings of James Lovelock, whose inspirational theory of Gaia, a self-regulating, "living" Earth with infinite feedback controls, has now become almost respectable.
A central part of Gaian theory considers the rapid cycling and recycling of the elements essential to life, of which sulphur is one. Supplied originally from volcanic eruptions and the weathering of rock, it is as necessary to the growth of plants ashore as it is to those of the sea. There has to be some mechanism for returning the sulphur lost to the land in the run-off of rivers, and research stimulated by Lovelock's theory suggests that dimethyl sulphide emitted from algal plankton is the major carrier of sulphur from the sea to the land.
DMS bubbles up first as a gas, but oxidises in the air over the ocean to form tiny droplets of sulphuric acid. These droplets become the nuclei for the condensation of water vapours, to form clouds. Thus, algal plankton, in Lovelock's theory, helps control the climate of the Earth.
Where is the reproductive advantage to the algae? In other words, how could such a mechanism have evolved by natural selection? Such questions have put neo-Darwinian biologists among the strongest critics of Gaia. But some are now offering answers of their own: perhaps, for example, clouds and the surface winds they produce help to spread the spores of algae to seed fresh, nutrient-rich areas of ocean.
This has been an unusual year for the plankton off Ireland's Atlantic coasts. In the normal cycle of the sea's food-chain, the spring awakens an astronomical multiplication of plant diatoms and other microscopic algae (phytoplankton), followed by swarms of the microscopic animals that feed on them (zooplankton).
The production of phytoplankton is boosted locally at the boundaries of layers in the sea in which temperature changes sharply with depth. This layering process, called stratification, usually sets in as spring warms up and is fixed geographically by the middle of June. But when the Celtic Voyager, research vessel of the Marine Institute, made a tour of the west coast in July, it found a spring-like sea with very little stratification.
This turned out to be good news for the shellfish farmers of the west and south-west, whose livelihoods are often deeply affected by the growth and drift of plankton - in particular, the toxin-producing algae (dinoflagellates) that can close down their harvesting for months on end.
Stratification can produce concentrations of dinoflagellates that are then carried into our coastal bays and build up in the filter-feeding shellfish.
Thanks to our "extended" spring this year, most of what reached the coast were innocent diatoms.
Wind-driven water surging into the bays can produce a marked drop in temperature at the sea-bed, and this can be used as an early warning of a sudden change in plankton species. In July last year, for example, a shift of 3 degrees near the sea bed of Bantry Bay, Co Cork, was accompanied by an influx of toxic Dynophysis, a species that, eaten in mussels and other shellfish, can give humans "the runs".
The change was detected by an experimental array of undersea temperature-logging instruments giving hourly data to Marine Institute scientists. This summer, similar loggers have been running in a further 20 bays around the south and west coasts.
One might expect that the wind-driven water is all forced in from the west, but Bantry's harmful visitors often originate in the Celtic Sea south of Cork, and are swept around by winds that blow first from the east, then from the south-west. The more we learn about our coastal seas, indeed, the more complicated and "local" their patterns of life become.