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
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.
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.
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
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.
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/).
This is Jim Fiorendino, your host for On the Ocean.
Did you know that some phytoplankton are thieves? Phytoplankton are microscopic marine organisms that make their own food through photosynthesis. Photosynthesis is a chemical reaction that requires light, carbon dioxide, and water. Photosynthesis occurs in special structures within phytoplankton cells known as plastids. Without plastids, phytoplankton cannot photosynthesize.
There are some phytoplankton that lack plastids of their own, yet still depend on photosynthesis for survival. They accomplish this by eating other phytoplankton and stealing their plastids. Typically, these predatory phytoplankton will digest their prey, but preserve their prey’s plastids. In some cases, the entire prey cell may be maintained for a short time. This behavior is known as kleptoplastidy. Phytoplankton that engage in kleptoplastidy are mixotrophic, since they both photosynthesize and feed on other phytoplankton.
Once acquired, the plastids that mixotrophic phytoplankton steal from their prey continue photosynthesizing and producing food. The plastids will last for several days or weeks, but must eventually be replaced. Some species of phytoplankton can replicate captured plastids, extending their lifespan. Interestingly, plastids that have already been stolen can be passed to another mixotrophic plankter. The toxic bloom-forming alga Dinophysis ovum obtains its plastids from the marine ciliate Mesodinium rubrum. Mesodinium rubrum does not create its own plastids, instead stealing them from a tiny strictly photosynthetic phytoplankter.
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.
This is Jim Fiorendino, your host for On the Ocean.
Mixotrophic organisms get their food from both autotrophic and heterotrophic pathways. For marine phytoplankton, this means both photosynthesizing and consuming other marine microbial organisms. Scientists have recently come to appreciate the importance of mixotrophy within marine microbial communities, as well as larger marine ecosystems. In addition to offering a potential competitive advantage over non-mixotrophic phytoplankton, mixotrophy may be an important factor in the development of harmful algal blooms, or HABS.
HABs occur when phytoplankton populations grow to densities capable of causing deleterious effects to humans or ecosystems. In areas where human activity is loading marine environments with excess nutrients, such as coastal cities, the risk of HABs is especially great. This input of excess nutrients is known as eutrophication, and can stimulate the growth of potentially harmful or toxic species of plankton.
Mixotrophs are unique because eutrophication can promote their growth both directly and indirectly. Eutrophication encourages the growth of phytoplankton directly by increasing the abundance of important nutrients needed for phytoplankton to grow. Mixotrophs may also benefit indirectly from eutrophication if organisms they like to eat become more abundant. Strictly photosynthetic phytoplankton do not share this additional benefit.
The mixotrophic phytoplankter Dinophysis ovum is known to form HABs in the Gulf of Mexico. This species produces toxins that accumulate in shellfish like oysters and cause diarrhetic shellfish poisoning. Scientists at the Texas A&M University Department of Oceanography are currently attempting to catch and grow Dinophysis ovum in a laboratory so it can be studied. Ultimately, through laboratory experiments, scientists hope to be able to predict the occurrence of blooms of this species and prevent human illness.
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. The above image shows a single Dinophysis ovum cell taken by the Imaging Flow Cytobot (IFCB) in Port Aransas, Tx during a bloom in early 2014. More images of marine plankton taken by the IFCB can be viewed here