AMSTERDAM - Fish and invertebrate animals are much more affected by the consequences of warmer and more acidic seawater than previously thought. That is the conclusion of a study led by marine biologist Katharina Alter, based on a new analysis method published in the scientific journal Nature Communications. 

Lead author Katharina Alter from the Royal Netherlands Institute for Sea Research (NIOZ) explains why it is important to summarize and analyze published studies on the impacts of climate change. 

"To better understand the overall global impact of climate change, marine biologists calculate the effect on all fish or all invertebrate animals together. But the effects revealed by different individual studies may cancel each other out. If invertebrate animals such as snails benefit from a certain change in the environment, while other invertebrates such as sea urchins suffer, the average effect for mollusks is set to zero, while both groups are affected differently." 

It is even the case that snails eat more due to climate change and sea urchins eat less. Alter: "Both effects are important and also have a cascading effect: seaweed, the food for sea urchins, grows more while the growth of kelp, the food for snails, decreases. The difference in feeding of the two invertebrates causes a shift in the ecosystem from a kelp-dominated ecosystem to a seaweed-dominated ecosystem, changing the habitat for all other animals living in this ecosystem." 

Ecological Shifts 

Together with colleagues from Wageningen University and twelve other research institutions from the US, France, Argentina, Italy, and Chile, Dr. Alter developed the new research method that no longer negates seemingly conflicting results but uses both to determine the consequences of climate change on animal fitness. 

Before this method was used, it was known that ocean warming and more acidic seawater had a negative effect on fish and invertebrate animals in three general ways: their survival chances decrease, their metabolism increases, and the skeletons of invertebrate animals become weaker. 

Using the new method, the international group of marine researchers discovered that climate change has negative effects on other important biological responses of fish and invertebrate animals: physiology, reproduction, behavior, and physical development. 

Alter: "Because this can lead to ecological shifts that affect the structures of marine ecosystems, our results suggest that climate change is likely to have stronger consequences than previously thought." 

Affected 

Increasing carbon dioxide levels in the air have been causing warmer and more acidic seawater for decades, a trend that is expected to continue in the future. But the speed and extent are unknown. 

Alter and her colleagues calculated the consequences of three expected scenarios of carbon dioxide increase, and thus ocean warming and acidification: extreme increase, moderate increase at the current rate, and - through possible measures - lower increase. 

Alter: "Our new approach shows that if ocean warming and acidification continue according to the current trend, up to 100 percent of the biological processes in fish and invertebrate species will be affected, while previous research methods found changes in, respectively, only about 20 and 25 percent of all processes." 

Furthermore, the research shows that measures to reduce carbon dioxide concentrations in the atmosphere will help reduce changes in biological processes: in the low carbon dioxide concentration scenario, 50 percent of the responses in invertebrates and 30 percent in fish will be affected. 

Hidden Consequences 

According to Alter, the major advantage of the new method is that more details are known about the effects of climate change on species. "The new calculation method weighs the significant deviation from the current state, regardless of its direction - favorable or unfavorable - and counts it as an influence of seawater warming and acidification. With our new approach, you can take the widest range of measured responses into account and detect effects that remained hidden in the traditional approach."