Who cares about planktonic abundances and distributions' The stock answer is that phenologists, who study the timings of the seasonal activities of animals and plants, care, and so does the fisheries industry.
But should the common man care' He may have to. According to Martin Edwards and Tony Richardson, who made the claim in the August 20 issue of Nature, what lie beneath the waves are uniquely sensitive indicators of global climatic change.
Edwards and Richardson of the Sir Alister Hardy Foundation of Ocean Studies, substantiate their claim with compelling evidence that oceanic life has changed, extensively and rapidly, in the recent past.
The claim and the evidence are new. But they stem from a 73-year-old idea of Alister Hardy. Hardy realised the importance of knowing, in detail, about planktonic life and, being a professional oceanographer, built a simple instrument to study it. He enclosed the instrument in a rugged box, and had a ship that was sailing out of Plymouth harbour, in 1931, tow it out to sea. The data collected on that voyage gave him a glimpse of the teeming world that exists just seven meters below the ocean surface.
The voyage covered a minuscule part of the north Atlantic, but Hardy rightly calculated that Europe’s fisheries would be very interested in the data that his instrument, which he called the Continuous Plankton Recorder, would collect. Ever since then, people in the fishing industry have happily obliged any researcher who called on them for help in this area of ocean science.
But Hardy’s vision extended beyond the fishing industry, and beyond the vision of his colleagues, to the scientific importance of constructing a worldwide map of the abundances of the plankton species. He might not have lived to use, or even see, that map. But he was sure that future scientists would find it useful.
Plankton are microscopic, free-floating biota. They come in two types, the plant-like phytoplankton and the animal-like zooplankton. Both types are important. The phytoplanktons, which store 40 per cent as much carbon dioxide as all the land’s plants do, have the ability, unique to all earthly life, to harvest solar energy underwater. Without it oceanic life — as we know it — would be impossible.
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The zooplanktons eat the phytoplanktons. Their numbers, which are colossal, are distributed over many species. The combined weight of the single zooplankton subclass, protozoa, present in the southern oceans alone, is 1.5 billion tonnes; by contrast, all of the world’s penguins, seals and whales, weigh a mere 16 million tonnes.
Hardy’s instrument has gone far since 1931. Its successors have logged over two million nautical miles and captured over 200,000 samples of the creatures he set out to study. Starting from 1958, we now have monthly records of the abundances of 400 planktonic taxa, over wide swathes of the sea. No other continuous biological record is as big. None is as important.
Important to those in the fisheries industry, whose livelihoods depend on it, but also, as Edwards and Richardson have demonstrated, important to all of us.
For, when they analysed the total record in terms of five underlying functional groups: diatoms, dinoflagellates, copepods, non-copepod holozooplankton, and meroplankton, they found that the diatoms continued to bloom at the same time, year after year, from 1958 onward, but that the same constancy was absent for the zooplankton birthdays, all of which had advanced significantly, in one case by as much as 47 days!
Secondly, the growing mismatch between phytoplankton blooming times and zooplankton birthdays was accompanied by precipitate falls in zooplankton numbers; the numbers of some species decreased by as much as 70 per cent.
Thirdly, we expect the fall in numbers should affect the rest of the food chain. That is exactly what has happened. The numbers of cod and haddock caught every year have, for example, been falling. Everyone thought the falling numbers were due to over-fishing. But they were dead wrong. For climate change neatly explains how big changes can occur up the food chain, even when the single event on which all oceanic life rests, namely the phytoplankton blooming time, remains steady.
First of all, the phytoplanktons are plants. Like all plants, they respond to changes in light intensity, but are indifferent to changes in ocean temperature. But global warming cannot change the number of daylight hours. They have remained unchanged since 1958, so it is unsurprising that the blooming time of phytoplanktons has remained steady.
Secondly, global warming should affect the yearly life cycle of the zooplankton profoundly. In the normal course, those creatures are born the right number of days after the phytoplanktons bloom. Subsequently, the ones so born, develop at the right rate in order to eat enough of the plentiful plant food available to them.
Men began burning fossil fuels in a big way, around 400 years ago. Before then, zooey species that failed to develop in harmony with their phytoplankton food source perished. So, Darwinian evolution established a dynamic equilibrium, in which the numbers of all species remained steady, so long as the environment did not change. But global warming has upset that equilibrium.
Of course, the environment did change, naturally, long before industry began, for instance when the world racketed between its Ice Ages. Natural changes changed past oceanic populations. They will do so in the future. But the new question is “Are the marks of the industrial beast visibly present in today’s oceanic life, over and above the effects of natural causes”' The answer, for three robust reasons, is that such marks are indeed present.
First, the continuous plankton record shows that the numbers of zooplankton have fallen steadily over the whole period known to us. Secondly, we are sure that current global warming is, at least partly, due to fossil fuel burning. Thirdly, we expect ocean temperature and zooplankton numbers to be correlated because the animal-like zooplankton must be heat-sensitive. To appreciate this, just recall the familiar frog, and how dependent its life cycle is on the temperature of the surroundings.
Humans have changed the environment ever since they began to hunt the large mammals. But the early changes, even those due to agriculture, were small and confined, compared to those that came about due to the industrialisation of society.
Put that way, the outlook seems gloomy. Nevertheless, hopeful signs are also present. The new findings have brought more scientists together. Climatologists, who knew that physical and chemical changes in the world’s oceans would change the global climate system, know that they must take changes in their biology on board. On the other side, the phenologists are gearing up to face a couple of questions.
One of them is, “How does the ocean ecosystem adapt to a rapidly changing environment"' No one knows the answer to it, today. Nevertheless, the scene seems set to change. The other question stems from the enormous zooplankton mass. It asks how the life activities of those creatures have been integrated into the ecosystem. The question had remained unaddressed by ocean scientists, but Karin Beaumont, from Tasmania, kicked it into new life by focussing on the excreta the creatures produce.
People had assumed that the faeces must sink to the ocean bottom, thus not adding to the atmospheric carbon dioxide to which fossil fuel burning has hugely contributed, locking it up in the deep-sea sediments for thousands, maybe millions, of years.
But Beaumont focussed on the sizes of the zooplankton taxa. The smallest amongst them, the micro zooplankton, make up more than 90 per cent of the tribe, by weight. Beaumont found that their excreta floats on the surface of the oceans, so the carbon dioxide in it returns to the atmosphere.
The oceans are enormous, and enormously important. But ocean science is a low-priority affair. Most scientifically-literate people prefer the fashionable “deep mysteries”, particularly those coming from quantum cosmology, to those of the ocean’s deeps. As a result, few people go into ocean science. Their numbers are like the proverbial drop in the ocean, and one expects little from the efforts they make. Nevertheless, they have told us much that is of great importance.
Attitudes must change. A few figures may convince readers that change is imperative. As many as 120 billion tonnes of carbon dioxide have entered the atmosphere between 1800 and 1995. But even that large figure is only one third of what humans will ultimately send skywards, if things go on as before. The oceans have taken 50 per cent of the carbon dioxide that human activity has added to the atmosphere. But one half of that amount remains in a thin layer beneath the surface. It will stay there for at least a thousand years. It is wrong to see the oceans as the Great Carbon Sink, since carbon doesn’t go away. A molecule of carbon dioxide put into the air in a Calcutta street can go all the way to the air above the North Pole in a few years. But a molecule of the same gas put into the ocean will confined to a thin layer near its surface for a pretty long time. Though it will eventually go to the ocean deep, it will do so painfully slowly, for all living things.