Microscopic marine algae which form the basis of the ocean food chain are dying at a terrifying rate, scientists said today.

Phytoplankton, described as the ‘fuel’ on which marine ecosystems run, are experiencing declines of about 1 per cent of the average total a year.

According to the researchers from Dalhousie University in Canada the annual falls translate to a 40 per cent drop in phytoplankton since 1950.

The research into phytoplankton comes as a separate report today offered evidence that the world has been warming for the past 30 years.

The reduction in the amount of algae in the seas could have an impact on a wide range of species, from tiny zooplankton to marine mammals, seabirds, fish and humans.

If confirmed, the decline of the phytoplankton would be a more dramatic change change to nature’s delicate balance than the loss of the tropical rainforests, scientist said.

The research, published in the journal Nature, said the declines were linked to rising sea-surface temperatures and changes in the conditions of the ocean, particularly close to the equator.

Most of the declines were seen in polar and tropical regions and in the open ocean, where most phytoplankton are produced.

The scientists suggested that in warmer oceans there was less movement between the layers of the sea, reducing the amount of nutrients delivered from deep water to the surface ocean.

As phytoplankton need both sunlight and nutrients to grow, the limits on the amount of nutrients in the upper layer of the sea affects production of the algae.