July 09, 2018
Photos by Evan Krape and Jessica Stella, GRBMPA
The University of Delaware’s Danielle Dixson has been awarded a National Science Foundation (NSF) Faculty Early Career Development Award to explore how climate change will affect the symbiotic relationship between clownfish and the sea anemones they call home in the Indian and Pacific oceans.
Until now, most climate change studies have focused on understanding the effect that one aspect of climate change has on a single species, for example, how temperature affects coral. By considering the relationships and interactions between animals rather than looking at one species in particular, Dixson hopes to better understand the interactive effect, as well as the individual effects themselves.
Armed with $750,000 in funding over five-years, Dixson specifically will focus on the effects of temperature and ocean acidification on the marine organisms’ mutualistic relationship under future predicted climate change scenarios.
“The world is getting hotter because of carbon dioxide, and carbon dioxide is causing ocean acidification, so it makes sense to think of these things collectively,” said Dixson, an assistant professor in the College of Earth, Ocean, and Environment’s School of Marine Science and Policy.
Studying the mutualistic relationship
Clownfish, the more common name for anemonefish, are found exclusively in the Indo-Pacific. They are symbiotic animals that only live in sea anemones, a close relative of corals that don’t have a hard outer shell. The anemone provides a home and protection for the clownfish, while the clownfish provides food and protection for the anemone.
In the lab, Dixson will use a carbon dioxide and temperature adjustment system to test anemonefish, with and without their anemones, under future predicted climate change scenarios. The system will allow Dixson to measure each marine organism’s response to physical stressors such as bleaching, a phenomenon that causes anemones to expel the algae living inside its tissues and turn white.
If a bleaching event goes on too long, anemone can starve from lack of nutrients typically provided by the algae. But Dixson wonders whether the outcome might be different if the anemone and the anemonefish remain together despite the bleaching.
In particular, she is curious whether the clownfish can sufficiently augment the food the anemone loses when the algae are expelled and whether anemone with fish will recover from bleaching quicker than anemones that don’t have this extra food source. She also questions whether the anemones with fish will experience delayed bleaching compared to anemones without the fish present.
“It may be that if the anemone bleaches it’s potentially harmful for the fish to remain in the anemone because the fish’s colorful exterior becomes more visible to predators,” Dixon said. “But it could be that being with your ‘friend’ or staying in the ‘home’ you know during a crisis may lower your stress level and help you cope with challenges more easily, so the two species might be somewhat buffered to the effects of climate change because they have each other.”
Focusing on habitat specialists
Dixson’s doctoral research was the first to identify that fish would be affected by climate change. Previously, fish were overlooked because the scientific community understood that higher order animals like fish and humans, have the ability to buffer their blood chemistry.
“It’s a catch-22. The reason fish aren’t affected by drops in pH is because they can change their internal chemistry, but by changing their internal chemistry the fish also change some their brain functions and it causes cognitive and behavioral problems, such as taking more risks or being attracted to predators,” which equates to increased mortality, Dixson said.
For the project, Dixson will conduct a combination of lab research at the Hugh R. Sharp campus in Lewes, Delaware, and fieldwork in Papua New Guinea and Australia. The study will focus on two species of clownfish that are under the greatest threat of climate change: Amphiprion latezonatus and Premnas bioculeatus.
Amphiprion latezonatus is already located at the southernmost range of where anemones are found, and while it can live in more than one type of anemone, the species will not be able to migrate south if water temperatures become too hot or if its anemone species bleach. By contrast, Premnas bioculeatus is the most habitat specialized anemonefish and can only live in the bubble tip anemone, giving it no other option if its home is threatened.
Dixson plans to mimic the natural fluctuation of pH and temperature that the ocean experiences over a 24-hour period in the lab in order to monitor the cumulative effects these animals would normally experience in the wild. For example, while the average ocean pH might remain at 7.8 throughout the day, within a reef this pH may fluctuate, peaking around 5 p.m. and sinking to its lowest around 5 a.m., due to the photosynthetic activity of plants and animals.
“This will help us get a more realistic idea of the impacts of climate change on these animals,” Dixson said. “These peaks and lulls might show that their behavior isn’t as affected as we’ve been predicting when they are held in a static condition, or maybe it’s worse because they are constantly coping with different fluctuations. We don’t know.”
Dixson says the anemone-anemonefish is a model organism for understanding systems that have a tight coupling of a photosynthetic habitat and animals that live inside it, such as fish and kelp forests or fish and coral. She also will test temperature alone and pH alone to try to piece together where the breakdown might occur.
“When there are multiple stressors on a system, they don’t add up like 1+1=2,” Dixson said. “Instead they create a synergistic effect where in 1+1=5, for example, which means that while a fish or anemone may be okay with temperature fluctuations, when you add ocean acidification the organism just can’t handle it.”
Educating children about climate change
Dixson takes a special interest in communicating science to young audiences. As part of the award, Dixson will continue to develop storybooks about her research for children age 3 to 7 years old. She began creating storybooks while conducting field research on coral reefs in Fiji, where she noticed children littering. To help the children understand how littering affects marine life, Dixson wrote a story about a shark that ate a soda can and got a stomach ache. Once the children understood the effect of their actions, they stopped littering and even began taking ownership of keeping the local beach environment clean.
Today, Dixson is the author of a science-based children’s series called Sea Stories. So far, there are two published books in the series with more on the way. In 2017, she also developed an undergraduate course called Science Through Storybooks with faculty colleagues in art and psychology to help college students make marine research more accessible to the public.
“The earlier we educate children, the more likely we can help them, and maybe even their families, establish good behaviors from the start in terms of climate change,” said Dixson.