Bryozoans and ocean acidification

Oceans are becoming more acidic due to increased levels of carbon dioxide (CO₂) in the atmosphere. Tiny marine animals called bryozoans may help monitor the impact of ocean acidification on the marine ecosystem.

Ocean acidification has the potential to affect many marine organisms that make shells and skeletons out of calcium carbonate. Associate Professor Abby Smith and the Carbonate Geochemistry and Sedimentology research group at the University of Otago are investigating bryozoans as a way to monitor the impacts of ocean acidification. Bryozoans may be the ‘canary in the coalmine’ for our oceans.

Understanding ocean acidification

The world’s oceans currently absorb as much as one-third of all CO₂ emissions in our atmosphere. This causes the pH to decrease, resulting in the ocean becoming more acidic. Scientists have long understood that an increase in carbon dioxide in the atmosphere will result in higher levels of dissolved CO₂ in seawater. However, a relatively recent discovery is that even small changes in water pH can have big impacts on marine biology. Ocean acidification is a worldwide issue. However, as CO₂ is more soluble in colder water, it is of particular concern in New Zealand’s temperate oceans.

The effect of ocean acidification on marine ecosystems

Many marine species rely on calcium carbonate to build a shell or skeleton. One of the effects of ocean acidification is a reduction in the availability of carbonate. This means that any animal that produces a calcium carbonate skeleton will find it much more difficult to do so as CO₂ levels in the atmosphere rise and oceans become more acidic. Organisms could grow more slowly, their shells could become thinner or they might dispense with shells altogether.

Many of these organisms, such as bryozoans, may no longer be able to form thickets that currently provide an important shelter and nursery area for other marine animals such as sea stars and many fish species. It is difficult to predict the overall impact on the marine ecosystem, but many scientists fear that ocean acidification has the potential to decrease marine biodiversity on a very large scale. Climate change, overfishing and pollution also threaten the health of our marine ecosystems, and ocean acidification is likely to increase vulnerability to these pressures.

Bryozoans can help monitor ocean acidification

Abby Smith is a biogeochemist who leads the Carbonate Geochemistry and Sedimentology group at the University of Otago. Abby and her students investigate carbonate sediments in temperate waters and geochemical signals in shells and skeletons. A major focus of their work is New Zealand’s bryozoans – their identification, classification, growth and production, ecology and geochemistry. With growing concern over ocean acidification, the work with bryozoans is becoming more important. This is because bryozoans have the potential to act as environmental indicators and provide information about the effects of ocean acidification.

Part of Abby’s research involves working on different bryozoan species and investigating how they respond when they are placed in solutions with different pH levels. The results have shown that a decrease in pH affects the skeletons of bryozoan species differently, depending on what they are made of and the shapes formed by their colonies. These results mean that some species of bryozoans have the potential to act as ‘a canary in the coal mine’ and provide early warning signs for areas that are at greatest risk from ocean acidification.

Ocean acidification has caused Abby to change some of her views and approaches to scientific research. Over the past couple of years, she has started to collaborate more with researchers in other fields and work harder on the practical applications of her science research, rather than just focusing on the intellectual challenge. As part of her role as a scientist, Abby is now becoming involved in things like policy, government response and advocacy.