The microscopic algae known as phytoplankton are the foundation of most marine food chains, converting sunlight into organic matter that is then consumed by higher trophic levels. They also produce half of the oxygen we breathe and absorb vast amounts of CO2. Phytoplankton ultimately support all of our fisheries – they are ‘the fuel on which marine ecosystems run. A decline of phytoplankton affects everything up the food chain, including humans,’ explained the research’s lead author, Daniel Boyce of Dalhousie University in Nova Scotia, Canada.

The research team used ocean-transparency data from as far back as 1899 to assess fluctuations in phytoplankton populations. They calculated that the algae are declining at a rate of one per cent per year – a decline of 40 per cent since 1950.

The authors suggest that rising water temperature is the main culprit. As oceans warm, they become increasingly stratified, which limits the availability of nutrients located at the surface.

‘Climate-driven phytoplankton declines are another important dimension of global change in the oceans, which are already stressed by the effects of fishing and pollution,’ said study co-author Marlon Lewis.

‘We don’t know what happened before 1899 [when records began], and we’re not sure about what will happen in the future; but we absolutely need to monitor this worrying trend and watch how it is unfolding,’ added another co-author, Boris Worm.     

KARA MOSES
October 2010