When thinking of species that might define the environmental consequences of human activity on this planet there are many that come to mind. The blue whale, polar bear, giant panda or perhaps the organutan are all such examples; species that for variety of reasons seem to embody the damage caused by our activity on Earth. Typically large mammals, these species and sometimes even a single individual can attract large media interest. They are not only seen as important species in their own rights but symbols of the environmental future of this planet – to save or lose.
There are many other key species that arguably play a far greater role in the ecosystem of the Earth, whose loss could cause huge environmental repercussions on a world wide scale. One such example are phytoplankton – microscopic water based organisms which encompass thousands of different individual species. Phytoplankton are unlikely to be used as a poster-species for an environmental charity and yet phytoplankton are perhaps the most important group of organisms on the planet.
Phytoplankton are microscopic organisms capable of photosynthesis – a process that produces energy and oxygen whilst removing carbon dioxide from the environment just like terrestrial plants. Like their land-based equivalents phytoplankton are also vital in controlling atmospheric carbon dioxide levels. Phytoplankton are the oceans primary producers of the marine food chain – the first step that supports the entire marine ecosystem.
However a study published in Nature suggests that a decline of up to 40% of the world’s phytoplankton could have occurred in the last 50 years, triggering what could be one of the world’s largest environmental disasters.
Why the decline?
It seems at first glance almost contradictory. Warmer weather and increased carbon dioxide should provide optimal growing conditions for any photosynthesising organism – in fact the very term “greenhouse effect” derives from the greenhouses used in agriculture – where increased temperature and carbon dioxide levels are used to create a higher crop yield.
The natural world however is never quite that simple. Like all plants phytoplankton also need nutrients to survive. In the ocean most of these nutrients come from colder nutrient rich waters found beneath the surface layers. As global warming forces air temperature to rise the water near the surface heats up. This process increases thermal stratification – where the temperature difference between the warmer surface water and cooler nutrient rich deep water reduces mixing between the two layers. A paper in 2006 by Jef Huisman of the University of Amsterdam predicted a similar mechanism using computer models stating “A larger temperature difference between two water layers implies less mixing of chemicals between these water layers. Global warming of the surface layers of the oceans, owing to climate change, strengthens the stratification and thereby reduces the upward mixing of nutrients.” The net result is warm but nutrient poor surface waters resulting in decreased phytoplankton growth.
Phytoplankton reduction and the atmosphere.
Up till now the 2006 paper had been largely theoretical - but the newly published paper by marine scientists Daniel Boyce, Marlon Lewis & Boris Worm of Dalhousie University in Halifax could prove the theory chilling accurate and provide evidence for one of the worst environmental effects of global warming seen yet.
The paper compiled and researched nearly 450,000 different measurements of plankton levels and water clarity measurements that researchers have made between 1899 to 2008. Using historical data and satellite imagery the paper has suggested a that a decline of almost 1% per year of phytoplankton has occurred in recent years, totalling a 40% reduction in phytoplankton since 1899 with most of the decline occurring post 1950 – when carbon emissions began to increase dramatically.
The scientists completing the research made sure to use a long time frame to make sure they were witnessing an actual decline and not simply just any natural fluctuations that can occur in phytoplankton populations. Diminishing phytoplankton levels could have a dramatic effect on those who rely on fish for food or income.
“Phytoplankton is the fuel on which marine ecosystems run. A decline of phytoplankton affects everything in the food chain, including humans,” Dr Boyce, one of the paper’s authors, said.
The importance of phytoplankton cannot be overstated. A reduction in levels of phytoplankton could have far reaching and long term ecological consequences. Quite apart from a reduction of oceanic abundance and biodiversity it could also seriously effect the terrestrial environment. Reducing phytoplankton levels would diminish an important carbon sink, which would increase atmospheric carbon dioxide levels and exacerbate global warming creating a positive feedback loop with disastrous consequences. As the planet warms the oceans lose the ability to store carbon, which in turn contributes to global warming which further reduces the ocean’s ability to store carbon.
“Phytoplankton are a critical part of our planetary life support system. They produce half of the oxygen we breathe, draw down surface carbon dioxide and ultimately support all of our fishes” said Dr Worm, one of the paper’s authors “If this holds up, something really serious is underway and has been underway for decades. I’ve been trying to think of a biological change that’s bigger than this and I can’t think of one.”
Although more research is needed the paper could provide the glimpse at not only the largest change in the global ecosystem witnessed with a human time frame but potentially one of the most devastating.
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