Nutrients. Plants love them - it helps them grow big and strong. You might think that an excess of nutrients in the waters of kelp forests would be a good thing for the kelp. Well, not necessarily.... In high nutrient conditions, algal turf is able to out-compete kelp. It quickly takes up any available space, and prevents new kelp growing. It's becoming a particular issue in areas such as southern Australia, where the kelp forests are known to be areas of high biodiversity. Stressors on any ecosystem rarely act totally independently, and there is one big stressor to the global ocean that has scientists particularly worried - rising carbon dioxide levels.
Laura Falkenberg and colleagues at the University of Adelaide, Australia sought out to discover if rising carbon dioxide and nutrient input interact with each other to impact algal turf growth. Their experimental research revealed that increasing carbon dioxide and nutrient inputs together created faster growth in algal turf than either nutrient or carbon dioxide separately. That's not good news, because our carbon dioxide emissions don't look like they are going to reduced significantly any time soon.
There is one possible glimmer of hope though. The research indicated that if nutrient inputs are stopped, then the turf declines by some 75% - despite carbon dioxide levels remaining elevated. Excessive nutrient input doesn't just affect kelp forests - check out my post on Google+ just a few days ago on agricultural pollution impacts on the Great Barrier Reef.
The question is, are we able to tackle nutrient pollution more successfully than carbon emissions? Image: Gazing upward in a giant kelp forest. California, Channel Islands NMS. Credit NOAA Photo Library (CC BY 2.0)