Ocean Acidification

Ocean Acidification

I’m McKensie Daugherty, your host for On the Ocean. This month we are talking about ocean acidification and its impacts on coral reefs. All across the world, the ocean and atmosphere exchange gasses and even microscopic particles. Atmospheric oxygen, hydrogen, dust, carbon dioxide, and more are constantly interacting with the earth’s oceans. This means that when humans burn fossil fuels for energy, the excess carbon dioxide introduced into the atmosphere gets directly and indirectly absorbed into the ocean. When carbon dioxide interacts with ocean water, it reacts to form carbonic acid. So each carbon dioxide molecule introduced into the ocean forms an acidic molecule in the water column. This is the phenomenon known as ocean acidification. Since the industrial revolution, ocean acidification has been happening on such a massive scale, that the ocean’s overall pH levels are actually decreasing in response, becoming more acidic over time. Even though ocean waters are still slightly basic, the acidity of the earth’s oceans has increased by 30 percent since the industrial revolution. This is the largest and fastest change in ocean chemistry that has occurred in millions of years. This change in oceanic pH has many negative impacts on ocean life, especially on ecosystems that are already vulnerable to changes, like coral reefs. Researchers at Texas A&M University and across the globe are studying ocean acidification in an effort to better understand the impacts this change will have on coral reefs and other marine ecosystems. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Contributing Professor: Dr. Katie Shamberger

 

week 1_Shamberger et al 2011_calcif vs omega

This graph shows that the growth (i.e. calcification rate) of coral communities in laboratory experiments (open symbols) and of real coral reef ecosystems (solid symbols) slows as CO2 increases and aragonite saturation state (Omega ar) decreases.  Omega ar is a measure of the stability of aragonite (what coral skeletons are made of) in seawater.  From Shamberger et al. 2011.

week 1_co2_time_series_12-17-2014

This graph shows the correlation between rising levels of carbon dioxide (CO2) in the atmosphere at Mauna Loa in Hawaii with rising CO2 levels in the nearby ocean at Station Aloha in the north Pacific. As CO2 accumulates in the ocean, the pH of the ocean decreases. Modified after R. A. Feely, Bulletin of the American Meteorological Society, July 2008. Image created by, and posted with permission from, NOAA PMEL Carbon Group (http://www.pmel.noaa.gov/co2/).

Coral Reefs

I’m McKensie Daugherty, your host for On the Ocean. One of the world’s most diverse, and potentially most fragile ecosystems is directly impacted by ocean acidification. Coral reefs are often referred to as the “rainforests of the ocean”, but some coral reefs hold even more diversity of life than rainforests. Coral reefs are made up of incredible animals, all built on an animal backbone. That’s right, corals are actually animals. What you see on coral reefs are calcium carbonate skeletons built by coral polyps. Each polyp is its own animal, which looks like a tiny sea anemone. Colonies of millions of polyps form massive skeletons that make up the three dimensional reef structure that provides habitat for a myriad of marine organisms. The process of creating calcium carbonate skeletons is called calcification. But the reef structure is harder to build and can be dissolved if there is too much acid in the water. This corrosion of the coral skeleton makes coral reefs more susceptible to erosion from waves and storms, and also bioerosion from clams and tube worms that break down the reef. The calcification of coral reefs has been in decline over at least the past 40 years, caused by global warming, overfishing, pollution, and ocean acidification. This decline in reef health threatens incredibly important ecosystems and economies. Coral reefs serve as storm barriers for coastal communities, and support tourism and fishing trades that are the lifeblood of many island nations. Coral reef research is also leading to the development of new pharmaceuticals for revolutionary solutions to many medical problems. Coral reefs are under direct threat from ocean acidification, and scientists are working toward understanding when and how these reefs will react to the increase in ocean acidity. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Contributing Professor: Dr. Katie Shamberger

week 2_Drenkard et al 2013_baby coral

These image show a baby coral, approximately 3 weeks old, with a single polyp with short tentacles on the right and its calcium carbonate skeleton on the left.  This single polyp would eventually make copies of itself in a process called “budding” and grow into a large coral colony.  From Drenkard et al. 2013.

week 2_Drenkard et al 2013_ambient and high CO2 unfed

These images show the calcium carbonate skeletons of baby corals grown at different CO2 levels for three weeks. The top image shows a healthy coral skeleton grown at today’s CO2 levels and the bottom image shows a smaller, less developed coral skeleton grown at CO2 levels expected for the end of this century. From Drenkard et al. 2013.

Great Barrier Reef

I’m McKensie Daugherty, your host for On the Ocean. The Great Barrier Reef in Australia is the largest coral reef system in the entire world. Scientists who study the effects of ocean acidification on coral reefs have used this system to understand the direct impacts the increase in acidity of seawater has on these fragile ecosystems. One such study was performed on One Tree Reef on the Great Barrier Reef by Texas A&M researchers in collaboration with the Carnegie institution for science in Stanford and Woods Hole Oceanographic Institution. In this study, scientists measured how fast One Tree reef calcifies, or grows, at current pH levels, and at less acidic pH levels that mimic what the ocean was like before we began burning fossil fuels for energy. To measure calcification and acidification, scientists measured seawater chemistry on the reef by putting oceanographic sensors on the reef and by taking water samples and analyzing them chemically in the lab. What they found was that when they added a basic compound to the reef water to make it less acidic than it is now, the reef grew faster than it normally does at today’s ocean pH levels. This is the first direct evidence that ocean acidification impacts are happening now, and have likely already slowed the growth of real coral reefs. This is bad news for coral reefs around the world that are also in danger from global warming, pollution, and overfishing. To help coral reefs survive we need to stop ocean pollution, including carbon dioxide pollution. Anything you can do to use less energy and to use energy sources that don’t produce carbon dioxide will help coral reefs all over the world. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Contributing Professor: Dr. Katie Shamberger

 week 3_Albright et al. 2016_Fig 1(2)week 3_Albright et al. 2016_Fig 1(1)

a) Map of Australia and an aerial photograph of One Tree Reef with the study area shown in the orange box. b) and c) Cross-sections of the reef along the yellow line in a) showing high tide (b) and low tide (c) and how water flows in one direction across the study area at low tide. d) Schematic of the study area showing sampling sites (blue circles) and the plume of low CO2, high pH water flowing across the reef at low tide. From Albright et al. 2016.

 

week 3_Katie_One Tree Reef

Dr. Katie Shamberger securing a conductivity (measures salinity), temperature, and depth (CTD) sensor to the reef at the study site on One Tree Reef. Photo credit: Ken Caldeira, Carnegie Institution for Science.

Palau

I’m McKensie Daugherty, your host for On the Ocean. Scientists want to understand the impacts of ocean acidification on coral reefs today and in the future. A good place to learn about the effects of future acidification caused by humans are areas in the ocean where high levels of acidification occur naturally today. The Palau Rock Islands are an excellent location to study the effects of natural ocean acidification on coral reefs. The Rock Islands are a group of small islands that form a maze like system of bays and inlets, with beautiful coral reefs. It takes a long time for seawater to flush out of the Rock Island bays and carbon dioxide accumulates in the water as coral reef organisms breathe and grow, increasing acidification levels. Scientists at Texas A&M University in collaboration with Woods Hole Oceanographic Institution and the Palau International Coral Reef Center, measured the biological diversity of coral reefs in Palau at different acidity levels. They found that Palau is the only area of natural acidification with healthy, highly diverse coral reefs.  However, like other naturally acidified coral reefs, Palau’s Rock Island reefs are much more susceptible to bioerosion by organisms like clams and tube worms that bore into and break down the reef. Researchers are also measuring the temperature, salinity, currents, nutrients, densities, depth, and the amount of oxygen in the water to look for any answers to why Palau’s coral reefs are surviving so well under acidification. This study is ongoing, and scientists hope they can discover answers about ocean acidification and coral reef resilience. It seems likely that as ocean acidification continues, we will see more and more bioerosion breaking down coral reefs. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Contributing Professor: Dr. Katie Shamberger

week 4_Shamberger et al 2014_Fig 1

Satellite image of the main islands of Palau showing sampling locations (yellow circles). Inset shows aragonite saturation state (Omega ar) with high Omega ar, high pH, and low CO2 in blue and vice versa in red. Low pH Rock Island Bay sites can be seen in red.  From Shamberger et al. 2014.

week 4_Uchelbeluu_highpH

A healthy coral reef community at a low CO2, high pH barrier reef site in Palau.  From Shamberger et al. 2014.

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A healthy coral reef community at a high CO2, low pH Rock Island Bay site in Palau. From Shamberger et al. 2014.

Dr. Katie Shamberger with an automated water sampler (Remote Access Sampler by McLane Laboratories) at a high CO2, low pH Rock Island Bay site in Palau.  Photo credit: Pat Lohmann, Woods Hole Oceanographic Institution.