Will Sponges Bulldoze Coral Reefs Faster in an Acidic Ocean?


Wisshak M., C.H.L. Schonberg, A. Form, A. Freiwalk. 2014. Sponge bioerosion accelerated by ocean acidification across species and latitudes? Helgol Mar Res68(2): 253-262.

‘Cause I Know That It’s Delicate.

Taylor Swift knows all about how delicate relationships can be, much like the delicate relationships in an ecosystem. If that balance is disrupted, it could alter the way an ecosystem functions and impact those who rely on it. Nothing is more delicate than the relationship between coral reefs and sponges, and we may be helping to tip the scale in the wrong direction.

A Bustling Underwater Metropolis.

A coral reef ecosystem is one of the most beneficial and diverse ecosystems on the planet. A coral reef is made up of colonies of coral polyps that use calcium in the water to build hard, skeleton structures. Microscopic algae create a home within the tissue of the coral polyps and provide food for the coral as it photosynthesizes. As the physical structure grows, an ecosystem is created around the reef that supports an extensive variety of marine life by providing food and shelter. Coral reefs support about 4,000 species of fish, 800 species of hard corals, and hundreds of other species. In fact, scientist think there may be another 1-8 million undiscovered organisms living in and around the reefs that we don’t even know about yet!

This biodiversity helps to support the fishing industry; the US makes $100 million in commercial fishing, and Australia makes $1.5 billion in fishing and tourism. The reefs also provide new drugs for medical research of various ailments, including cancer, arthritis, human bacterial infections, viruses, and other diseases. Lastly, coral reefs protect those living along the shoreline by buffering wave action. Coral reefs may provide goods and services worth $375 billion a year, which is astounding since their ecosystem covers less than 1% of Earth’s surface!

May I Have This Dance?

Enter the delicate tango between coral reefs and sponges. While coral reefs are building up their underwater cities, sponges are working to tear them down! Sponges are marine animals that use an acidic chemical to break down dead coral and make their homes in the excavated reef. This erosion is a natural process, as the sponges remove dead material and recycle the calcium for new coral or oyster reefs to use.

Tipping the Scales.

So, what’s the problem? The issue lies in the rate that corals form new reefs, and sponges erode old ones. If sponges erode reefs faster than corals can build them, there may not be enough real estate left to support these highly productive underwater cities. To make matters worse, humans are causing the ocean to become more acidic. The more carbon dioxide (CO2) we pump into the atmosphere, the more COdissolves into the ocean, which lowers the pH and increases acidity. As ocean acidification worsens, sponges may not need to work as hard to break down coral because the water will already be acidic! This could tip erosion rates above building rates – and upset the delicate, natural balance of the coral reef ecosystem.

Scientists wanted to see if human-caused ocean acidification was tipping the coral reef ecosystem to an unhealthy state. Wisshak and colleagues exposed corals and sponges (C. celata) from the North Sea to present day ocean conditions, moderately elevated acidity, and strongly elevated acidity. Their goal was to determine if sponges would erode corals faster under more acidic conditions. Not surprisingly, they found that sponges eroded corals the fastest under the strongly elevated acidic conditions. The rate of erosion under strongly elevated acidity was three times higher than present day conditions!

The team compared their results with the findings of other scientists and realized the pattern was widespread. Other species of sponges from all over the world were eroding corals faster under more acidic conditions. Ocean acidification affects the ocean as a whole, and since sponges and reefs are found globally, it is clear that this problem is on a global scale! Tipping the balance against corals would have dire consequences for not only their existence, but could spell trouble for those species who rely on their ecosystem for survival, including us.


“Importance of Coral Reefs” Biodiscovery and the Great Barrier Reef, Queensland Museum, https://www.qm.qld.gov.au/microsites/biodiscovery/05human-impact/importance-of-coral-reefs.html.

“Importance of Coral Reefs.” Corals, NOAA National Ocean Service Education: , 6 July 2017, www.oceanservice.noaa.gov/education/kits/corals/coral07_importance.html.

Wisshak M., C.H.L. Schonberg, A. Form, A. Freiwalk. 2014. Sponge bioerosion accelerated by ocean acidification across species and latitudes? Helgol Mar Res68(2): 253-262. https://doi.org/10.1007/s10152-014-0385-4

Ocean Acidification. National Oceanic and Atmospheric Administration, Nov. 2013,www.noaa.gov/education/resource-collections/ocean-coasts-education-resources/ocean-acidification.

“Structure, Classification and Function of Corals” Biodiscovery and the Great Barrier Reef, Queensland Museum, https://www.qm.qld.gov.au/microsites/biodiscovery/03sponges-and-corals/structure-classification-function.html.

“Why Are Sponges so Toxic?” Biodiscovery and the Great Barrier Reef, Queensland Museum, www.qm.qld.gov.au/microsites/biodiscovery/03sponges-and-corals/why-are-sponges-so-toxic.html.

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Nick Iraola

Nick has a Master of Science in Marine Science from UNC Wilmington. His master's thesis research pertained to eutrophication and nutrient cycling within an urban blackwater lake in Wilmington, NC. Currently, Nick works for the Cape Fear Public Utility Authority testing drinking and waste water for safe consumption and discharge (respectively!!). Nick also works as a part-time research scientist at UNCW's Center for Marine Science in the Aquatic Ecology Laboratory and the Nutrient Analysis Core Facility. When he's not sciencing, Nick enjoys running, swimming, cooking, sailing, and catching up with friends and family. His favorite candy is Reese's pb cups, because what is there not to like!?

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