Stop marine pollution to protect kelp forests

The researchers have found a combined effect on kelp forests from nutrient pollution and higher CO₂, which could have a devastating impact on Australia's marine ecosystems.

"When we manipulated CO₂ and nutrient levels in an experimental marine ecosystem we found the effect of both of them together was greater than the sum of their individual impacts," says Dr Bayden Russell, of the University's Environment Institute and Senior Lecturer in the School of Earth and Environmental Sciences.

The project, by PhD student Laura Falkenberg, found that removing the nutrients from the water removed the combined effect, improving the environment for kelp growth.

Kelp forests are one of the most productive marine ecosystems in colder waters and form the basis of food webs for many fish and other marine life. "They are the coral reefs of colder waters," Dr Russell says.

"Increased nutrients from agriculture, wastewater discharge and stormwater on urban coasts are already causing damage to kelp populations in our coastal waters but our research shows that, as CO₂ rises the impacts will be much worse and we could lose these really important marine habitats," says Dr Russell.

The researchers grew kelp in experimental tanks floating in the North Haven Boat Harbour with different combinations of added nutrients and CO₂. They measured the growth of turf algae which is a precursor to kelp forest loss. As the turf algae grows it displaces the kelp.

"When we removed the nutrients but kept the CO₂ high we found that after six months we'd reduced the turf algae by 75% -- we'd removed that synergistic effect," says Dr Russell.

"As we face a future of climate change and higher CO₂ levels, there is considerable evidence that our marine ecosystems are going to be severely impacted. We won't be able to manage those global factors at the local level, but what we can manage is local nutrient pollution into our seas from urban areas," he says.

"This work has shown that by reducing the nutrients we should be able to substantially reduce the impact of rising CO₂. The bottom line is that we need to reduce the nutrient pollution now."

The research is continuing with larger tanks, known as mesocosms, set up at West Beach and in natural marine areas where CO₂ seeps into the water from seabed volcanic activity in New Zealand.