Fri, 21 May 2010 3:19p.m.
By Fiona Hodge
Staring Bryozoans as the Canary-In-The-Mine in “THE SOURING OF THE OCEANS”
Some of the most beautiful filter feeders in our oceans are the bryozoans (watch them here). Bryozoans are a diverse looking lot. Some look like tiny stiffened feathers (e.g. Pterocella scutella), whilst others form exquisitely patterned crusts (eg Membranipora membranacea). What they share is a common threat from the oceans souring. The souring of our oceans may sound a lot like a science fiction dystopia. However, the oceans have already soured since the industrial revolution, and are set to sour further.
Ocean acidification, the proper name for this souring, is a result of increased carbon dioxide in the atmosphere. Since the industrial revolution carbon dioxide has increased by 40 percent in the atmosphere. Oceans absorb carbon dioxide from the atmosphere. When atmospheric carbon dioxide dissolves in water it changes the chemistry of the sea water, reducing the concentration of carbonate ions and making it more acidic (the pH of seawater has decreased by 0.3 units since the industrial revolution). Watch this video for a brief outline of ocean acidification.
So what does this mean for bryozoans? Bryozoans produce their skeletons from a range of calcium carbonate compounds. Their ability to secrete and maintain these skeletons is likely to be affected by ocean acidification. The diversity in morphology and skeleton composition suggests bryozoans will have a broad range of vulnerability to ocean acidification.
Membranipora on kelp (Photo: Dr Abigail Smith)
Otago University researcher Dr Abigail Smith is interested in the mineralogy of skeletons. Dr Smith has used information of the diverse mineral composition and morphology of bryozoan skeletons to create a ‘canary in the mine’ system to monitor small scale ocean acidification. This ‘canary in the mine’ system aims to allow scientists to use the skeleton morphology of different bryozoan species in an area to determine the local extent of ocean acidification.
Research into the implications of ocean acidification is generally finding that it can affect species with calcium carbonate skeletons. These include some of the plankton, tube worms, echinaderms like kina and sea dollars, molluscs like snails, crustacea like crabs and crayfish, corraline algae, and corals. It can also affect the development of the larvae, the tiny tadpole-like babies, of some species. Research on one species of pteropods, a group of planktonic sea snails, found their shells began to dissolve within just two days of exposure to sea water with the chemistry predicted for 2100.
We need more ocean acidification studies on a broader range of species. The studies should be long term and incorporate natural environmental conditions. The interactions between the losers and the few winners are currently hard to predict, and also require more study. For example pteropods (the planktonic sea snails) make up greater than 60 percent of the juvenile pink salmon diet. Will all the pteropods begin to dissolve in 2100 conditions like the species mentioned above? What will happen if they do? Will the salmon be stubborn or flexible in their dining choices? If flexible, what will their new prey be? How will this affect other species? Etc etc…
The only thing that is clear is the urgent need to reduce our carbon dioxide emissions. These anthropogenic emissions drive both ocean acidification and climate change. It is economically far more rational to act now to reduce ocean acidification and climate change, than to attempt to mitigate their effects in the future.