Monday, June 10, 2013

The Underestimated Epidemic: Coral Reef Destruction

By Cori Brant

Mark Conlin/Alamy

Since the industrial revolution carbon dioxide levels in the ocean have sky rocketed. Currently around 22 million tons of carbon dioxide are absorbed into the oceans every day. This is causing disastrous affects on all ocean life, especially coral reefs. Coral reefs around the world aren’t able to regrow as fast as they are eroding away, and are suffering from massive bleaching. Ocean acidification is fast growing and increases daily, without fast change all coral reefs and their inhabitants will be gone forever.
Many people have heard of ocean acidification and coral bleaching but don’t know exactly what affects they have on coral reefs. Ocean acidification is the rise in pH levels when carbon dioxide
This is a diagram of how CO2 breaks down when 
combined with H2O to cause ocean acidification
is absorbed into the water. The increase of carbon dioxide in the atmosphere is due to the burning of fossil fuels for human uses. When carbon dioxide reacts with water it forms carbonic acid, which releases a hydrogen ion. When there is a significant increase in hydrogen ions, the pH of water decreases causing it to become more acidic. Since the industrial revolution the pH of the oceans has decreased by .1 units and by the end of the century the pH is predicted to be another .4 units lower (2). While this change sounds small and insignificant this will heavily impact many species of marine life.Rob Dunbar provides an in-depth look at ocean acidification and its affects on our planet in a TedTalk video, which can be found at the bottom of the page.
Coral bleaching is a major issue facing coral reefs. Coral bleaching is a stress response to many abiotic and biotic factors such as increased
water temperature and change in water chemistry (acidification). Coral has a symbiotic relationship with zooxanthellae, a unicellular organism that lives within corals tissues and preforms photosynthesis, when coral is placed under an environmental stress the coral stops supplying the zooxanthellae with the
nutrients it needs to preform photosynthesis. This leads to the release or death of the algal symbionts and in turn causes the coral host to parish (1).  Along with being in a symbiotic relationship coral also provides an important recycling system to the ecosystem. Healthy coral produces calcium carbonate, and in turn is taken into the new skeleton base for the new growing coral. But since the coral isn’t producing enough calcium carbonate, it cannot replace its self as fast as it is eroding away. This also affects species that depend on that calcium to produce shells.
With a rise in CO2 levels, this new environment may increase and benefit plants such as photosynthetic algae and the sea grasses. But this increase in acidification also affects calcifying species in an extremely negative way. “The main effect of the symbionts on host calcification is supposed to be mediated by the removal of CO2 for their photosynthesis”(1). The acidification causes a shift in the equilibrium of the carbonate chemistry in seawater; this leads to a decrease in carbonate ions that are available for calcifiers to use for their skeletons. Animals such as oysters, clams, sea urchins and pteropods are a primary part of the food chain that rely on the carbon ions to produce their calcium skeletons. Pteropods or “sea butterfly” are small creatures that feed many marine animals. Sea butterflies use carbonate ions to create their calcium shells. Orr et al., 2005 conducted a test that increasing the pH of the water to the predicted level by the year 2100.  Within 45 days the shell of the sea butterfly had dissolved over 50%. Without being able to sustain a long lasting shell, their populations will decrease, which in turn will cause a decrease in many marine animals food supply. It is clear that CO2 levels will impact the health, function and activity of many marine invertebrates (5). Losing keystone species like these will have devastating affects on not only the marine food web but also on many villages and tribes that rely on these fish and muscles for food. 
The shell above is a sea butterfly after the pH level had
 been increased to the predicted level of 2010.
National Geographic Image
It’s reported that 75% of coral reefs are threatened from ocean acidification and bleaching. On these coral reefs live 25% of all fish species in the ocean. These species depend on those ecosystems for food and protection. Coral reefs hold the most diverse fish populations in the entire world. The two largest coral regions are the Indo-pacific and the tropic western Atlantic, neither of these reefs overlap. Each contains its own unique fish fauna. If either of these reefs were wiped out we would lose many endemic fish (3). Many reef fish have adapted their physical appearance to survive specifically in certain parts of coral reefs. The symbiotic relationship the reef has with many different species makes it impossible to try and relocate these creatures. Removing just one of these species can cause drastic changes to the reef. Along with providing unique living conditions for many species, reefs also provide numerous benefits such as protecting shores from wave impact, delivering food resources and medicines for humans.   
To combat the loss of coral reefs, artificial reefs are being installed to help sustain the diversity. Artificial reefs are man-made structures that are placed near other reefs to encourage marine life growth and to support local diversity (4). These structures range from sinking old ships to carefully made statues. The General Hoyt S. Vandenberg was an old missile-tracking ship that was sunk a few miles off Key West in early 2009. This ship, like many others has filled with fish and other marine life, as can
National Geographic Image
be seen in the picture to the left. These structures are placed in such a way that when the water hits the vertical structure a plankton-rich upwelling occurs bringing in sardines and minnows. These smaller creatures then attract larger predators. After this, other marine life seeks out shelter from the open water and begins to overtake the small holes and openings, such as snapper, squirrelfish and eels. Smaller predators like barracuda will come reside in these structures for easy prey. It may take several months to a year for algae, sponges, hard coral and soft coral to begin growing (6). Projects like the Reefmaker design specialized reefs as unique habitats, wave attenuation, oyster restoration and estuary enhancement.  Many of these reefs are made from a natural soft rock, which encourages growth better then cement and brick (7). Reefmaker creates basic structures like large hallow pyramids but many artists have taken it upon themselves to create art at the bottom of the ocean. The picture on the right of the lion surrounded by columns is just one of
Willfredo Lee
many artistic reefs that are being put in place. While these artificial reefs may provide a home for the diverse population of fish and other species, these reefs do not provide a magical solution to the loss of coral.  While the fish may be able to find a temporary home in these reefs, the shell species that require carbon ions to create there shells will still be at a loss. There are few quick solutions to ocean acidification and coral bleaching but steps to reduce carbon out put and the burning of fossil fuels is the only way to truly save our beautiful and diverse oceans.

Rob Dunbar TedTalk: The Threat of Ocean Acidification


1.     Erez, Jonathan. Reynaud, Stephanie. Silverman, Jacob. Schneider, Kenneth. Allemand, Denis. “Coral Calcification Under Ocean Acidification and Global Change.” Coral Reef an Ecosystem in Transition. 2011, p. 151-171.
2.       Meron, Dalit. Rodolfo-Metalpa, Riccardo. Cunning, Ross. Baker, Andrew. Fine, Maoz. Banin, Ehud. “Changes in Coral Microbial Communities in Response to Natural pH Gradient.” The ISME Journal. 6. 2012, p.1775-1785.
3.     Plaisance, L. Caley, Mj. Brainard, RE. Knowlton, N. ”The Diversity of Coral Reefs: What Are We Missing?” PLoS ONE. 6(10): e25026. doi: 10.1371/journal.pone.0025026 
4.     Rilov, Gil. Benayahu, Yenuda. “Rehabilitation of Coral Reef-fish Communities: The Importance of artificial-reef” Bullet of Marine Science. 70(1). 2002, p. 185-197.
5.     Widdlcombe, Stephen. Spicer, John. “Predicting the Impact of Ocean Acidification on Benthic Biodiversity: What Can Animal Physiology Tell Us?” Experimental Marine Biology. 366. 2008, p. 187-197
6.     Stephan Harrigan(Febuary 2011). Artificial Reefs. National Geographic (online).
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