Plankton will suffer as oceans warm

Phytoplankton off the coast of SW England: Warmer oceans will leave less available to feed fish
Plankton will suffer as oceans warm
Alex Kirby, September 8, 2013 climatenewsnetwork.net

One effect of the warming of the oceans will be to depress the growth of plankton, with consequences for fish and other species that depend on it.

LONDON, 8 September – Researchers at two UK universities have found that rising temperatures in the world’s oceans will affect the development of the plankton on which most marine life feeds.

The research team, from the universities of East Anglia and Exeter, has demonstrated that the increasing warmth caused by a changing climate will upset the natural cycles of carbon dioxide, nitrogen and phosphorous.

This will affect the plankton, making it scarcer and so causing problems for fish and other species higher up the food chain. There are also likely to be implications for climate change, but just what they will be, the team leader says, is far from clear.

Plankton play an important role in the oceanic carbon cycle by removing half of all CO2 from the atmosphere during photosynthesis – the process during which plants and other organisms convert light, usually from the Sun, into energy.

The carbon then falls deep into the ocean and ends up on the sea bed, where it remains safely isolated from the atmosphere for centuries.

But the novel point about the team’s work, published in Nature Climate Change, is their discovery that water temperature has a direct impact on maintaining the plankton’s delicate ecosystem. This means the effects of oceanic warming will affect plankton and drive “a vicious cycle of climate change”.

Researchers from UEA’s School of Environmental Sciences and the School of Computing Sciences investigated phytoplankton – microscopic plant-like organisms which rely on photosynthesis to reproduce and grow.

The lead researcher, Dr Thomas Mock, says: “Phytoplankton, including micro-algae, is responsible for half of the carbon dioxide that is naturally removed from the atmosphere.

“As well as being vital to climate control, it also creates enough oxygen for every other breath we take, and forms the base of the food chain for fisheries, so it is incredibly important for food security.

“Previous studies have shown that phytoplankton communities respond to global warming by changes in diversity and productivity. But with our study we show that warmer temperatures directly impact the chemical cycles in plankton, which has not been shown before.
Higher nitrogen ratio

“We found that temperature plays a critical role in driving the cycling of chemicals in marine micro-algae. It affects these reactions as much as nutrients and light, which was not known before.”

Team members from Exeter developed computer-generated models to create a global ecosystem model which took into account world ocean temperatures, 1.5 million plankton DNA sequences taken from samples, and biochemical data.

As temperatures warm, marine micro-algae appear not to produce as many ribosomes as they do in cooler water (ribosomes join up the building blocks of proteins in cells and are rich in phosphorous).

If their numbers fall this will produce higher ratios of nitrogen compared with phosphorous. The result, says Dr Mock, would be lower plankton productivity, with implications for the marine carbon cycle. He told the Climate News Network: “There will be consequences both for climate change and for marine food webs.

“The oceans may retain less CO2, though other factors, like the stratification of the water layers under the influence of temperature and salinity, may counteract that.

“But warming the oceans and increasing the amount of nitrogen they contain could equally well mean that they can store more CO2 than they do now.

“So there’ll certainly be an effect on climate change, but the ultimate outcome is really difficult to predict. With food webs it’s much easier: we know there will simply be less plankton available for higher species.”