Marine ecology PhD student Daniel Boyce, one of the study’s authors, says phytonplankton are similar to plants like grass and trees.
“Phytoplankton are basically like microscopic little plants. They require sunlight and nutrients in order to grow,” he said.
“For phytoplankton in much of the ocean the nutrients are delivered to them from deeper ocean waters by mixing currents and turbulence.
“So what happens is as the ocean continues to warm the ocean becomes more stratified and more stable which limits the amount of mixing and limits the amount of nutrients delivered to phytoplankton at the surface and negatively affects their growth.”
He says phytoplankton are extremely important.
“Changes in their abundance will ultimately affect everything in the ecosystem, from tiny little zooplankton all the way up to fish and whales and ultimately humans,” he said.
“They can also have very strong climate affects, so they can affect the stability of our global climate and they can have affects on the sustainability of our fisheries.
“I think we should all be very concerned that phytoplankton have declined over this long time period and we should be looking to the future, you know, continually monitoring our global phytoplankton levels to ensure they don’t continue to decline.”
Another Dalhousie University study, also published in Nature, reports marine species could potentially die because of human impact and global warming.
The team of scientists mapped and analysed global biodiversity patterns for over 11,000 marine species, from tiny zooplankton to sharks and whales, living in “ocean hot spots”.
These are regions most damaged by climate change, pollution and over fishing.
The majority of hot spots were found in Indonesia, Japan, India, Australia and China.
Lead author and marine ecologist Derek Tittensor says diversity in the ocean was strongly linked with temperature for every group his team looked at.
“We looked at 13 different groups of organism, so there was really quite a consistent relationship there,” he said.
“We found that diversity patterns were different for groups of coastal species and for oceanic species.
“So whereas coastal species tended to have hot spots in around the tropics we found that oceanic species on the whole tended to have highest biodiversity in mid-latitude.
“What’s likely to happen is that as the oceans warm, species may move away from the equator, northwards and southwards to maintain their water conditions.”
He says a reorganisation of life in the ocean is likely, but depends on many factors.
“For example, you may have a species that moves north or south to stay in cool water but it may encounter predators that it has never run into before, for example,” he said.
“The consistent link with temperature suggests that we will see a reorganisation or a redistribution of marine diversity into the future as the oceans continue to warm.”