Climate Change and Its Effects on Coral ReefsBrian Pollak

Ross School, January 2010

Mission: Coral reefs are complex ecosystems which host a rich abundance of life. The goal of this project is to educate others about the need to protect these natural resources through increased awareness about the impact human activities have on reef health. The research presented here outlines the general ecology and biology of reef systems, the impact that climate change is having on their health, and the possible consequences of their decline. A survey of Tres Palmas, a coral reef in Puerto Rico, is featured as an example of how education and awareness can offer hope for the longevity of these rich habitats. Objectives:Understand the biology and ecology of coral reefsUnderstand and appreciate the impact that anthropogenic activities are having on coral reef healthCoral Reefs:Coral reefs are one of nature’s most diverse and intricate living communities, yet they are also one of the most fragile. There are many reasons for the recent destruction of coral reefs. Two forces that have contributed to coral reef destruction are climate change and over-fishing. Coral reefs serve many purposes on this planet and destruction of the coral reefs will put many other aspects of nature at risk.

The Importance of Symbiosis on the Reef:“It is this fusion of polyps with their tiny captive algae which has allowed reef life to become so rich and diverse: the widespread symbiotic relationship has become one of the fundamental ecological characteristics of the coral reef community.” (Sheppard, 2002)

Definition of Symbiosis: A mutually beneficial relationship between organisms.The relationship between the coral reefs and the fish is amazing. The concept of symbiosis is when two species mutually benefit from each other. The reason why it is a symbiotic relationship is because both the fish and the reefs benefit mutually. From the reef, fish receive protection, hunting grounds and areas where they can safely spawn and leave their young for development. In return, the fish act as cleaning agents, removing the seaweed that covers the Zooxanthellae as well as helping to fertilize the reef substrate. Also, other animals such as sea cucumbers filter the waste from the water, which keeps the reefs clean and healthy. Another form of symbiosis has to do with the process of photosynthesis. Photosynthesis occurs on the reefs when the Zooxanthellae, the algae living within the reef skeletons, convert light energy into chemical energy, which becomes food for the reef. When the fish eat the plants that live off of the food that the microalgae manufactured through photosynthesis, energy is released and recycled. The reason that this is a symbiotic cycle is because within coral reefs there is a lack of nutrients and without this process the corals would starve. The coral polyps are able to consume tiny particles such as plankton, but more than two thirds of the corals nutrients come from the sun. This is why it is very important that the Zooxanthellae manufacture the nutrients necessary to keep the coral reefs alive.

Case Study: Rincón, Puerto RicoAs part of my study, I visited and dove a coral reef on the northwest coast of Puerto Rico. The reef was part of the Tres Palmas reserve and is considered to be one of the best-developed reef systems in this area. I was able to access the reef directly from the beach, as the reef begins almost immediately at the water’s edge. The reef begins as a tide pool area and then gradually drops off to an eight-meter depth. This site is not only known for its beautiful display of elk-horn coral, brain coral, star coral and fan coral, but it also creates a beach barrier that sets-up Puerto Rico’s most famous big wave surf spot. I dove the reef 5 times over the course of a week, and was able to get a sense of the both the reef’s diversity and overall health. As I mentioned previously this reef is part of the Tres Palmas Reserve and thus is protected from fishing, spear fishing, littering or taking anything from the reefs, such as rocks, pieces of coral or fish. From my research, I was anticipating seeing some signs of stress, perhaps areas of bleaching. When I arrived, I had the opportunity to interview a local reef expert, Leon Richtor, who not only helped to plan my dives but also gave me information about the nature of this reef. The Tres Palmas reef is a fringing reef system, which means that it is directly attached to the shore. Richtor stated that this reef is a healthy and vibrant, crediting its success to the fact that Puerto Rico protects it as a natural resource. They are aware that the reef’s continued health ensures a robust eco-tourism industry. I was amazed by the impressive size of the corals. In particular I was struck by the vibrancy of one species of brain coral, Platygyra lamellina, which seemed to be illuminated by its neon green color. The Elkhorn coral dominated the reef landscape providing feeding and cleaning stations for the reef fish. Sea urchins and turtles were also plentiful in this ecosystem. Urchins play a great role in protecting fish. The razor sharp, poisonous spines give shelter to smaller fish that live within the reef. The hardground areas, or flat coral reef beds, were pocketed with tiny craters where water pooled, which is where the urchins seemed to gather. This area, slippery with green and dark red seaweed, dropped off into the sea. I was attuned to assessing the health of the reef for myself, and as such did notice a few areas where bleaching seemed to be occurring. These spots were all located in the shallows closer to the beach where some development has taken place. Although this proximity could be a factor in the bleaching, there is no substantive proof. As Richtor had noted in our interview, this reef is a protected resource and as such is carefully monitored. The beauty, size and the apparent biodiversity of this reef system impressed me. The hope would be that other countries would also try to minimize the impact that human interactions have on reef systems. Tres Palmas could act as a model in this case: We need to take more of an active role to educate the public about both the fragility and beauty of these underwater jungles.

Climate Change:Climate change has been happening for a long time, it is part of the earth’s natural cycle. The problem that we are faced with is that recently, in comparison to the earth’s age, there has been an excess use of greenhouse gases, which have trapped heat inside our atmosphere. Eleven of the past twelve years are among the twelve warmest years since 1850 (Baldwin, 2009). The Industrial Revolution, which occurred in the mid 1800’s, started the human reliance on fossil fuels as a primary energy source. Since then, our dependence on fossil fuels has exasperated the climate change dilemma. Temperature changes on the planet also increase the average temperature in the world’s oceans.

Climate Changes: Threats on Coral ReefsTemperature Change:Climate change is a factor in the widespread death of coral reefs. Coral reefs are very vulnerable to temperature changes. Coral reefs can only thrive in a narrow temperature range and a two degree Celsius change can burn off the Zooxanthellae. When the temperature gets too high in the water, the algae disintegrate shutting down photosynthesis. When photosynthesis ceases, the coral starves, turning a ghostly white color. This act is referred to as coral bleaching. Coral bleaching does not only occur when the water is too warm. Temperature changes affect many other aspects of the ocean. Due to climate change, many of the ice caps have been melting. The reason why this is harmful is because it raises the volume of the ocean. When the ocean levels rise, the corals are covered by a greater volume of water making it harder for the Zooxanthellae to obtain sunlight and feed the reef.

Ocean Acidification:Ocean acidification is another huge factor in the destruction of coral reefs. “Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained”(Hoegh-Guldberg, Mumby, et al, 2007).

The production of carbon dioxide is in direct relation to the acidification of the ocean. It is well known that the ocean has functioned, as a “carbon sink” for the planet, and up until recent times was able to buffer this impact. However, with the increased use of fossil fuels the balance has been tipped. Simply put, the amount of carbon dioxide dissolved in the ocean has increased at an alarming rate: “Since the Industrial Revolution, the oceans have become 30 percent more acidic (from 8.2 pH to 8.1 pH).” (European Science Foundation, 2008). When the ocean becomes too acidic, the corals have difficulty absorbing carbonate ions from the water column in order to build their skeletons. The full impact of this change is still largely unknown thus representing an area of study that scientists are just beginning to research. The question is though, how much time remains before the effects are irreconcilable? The one fact that all scientists agree upon is that carbon dioxide emissions must be cut dramatically.

Coral reefs reproduce sexually and asexually. When the coral reef reproduces sexually, fertilization can be either internal or external. During internal fertilization, the eggs are brooded by the polyps for days to weeks, depending on species. After this stage, free-swimming larvae are released into the water and settle within hours. Externally fertilized eggs develop while adrift. Given a few days, the fertilized eggs mature into free-swimming larvae. Calm waters represent the best times for spawning. Spawning relies on chance and the less water movement, the easier it is for the sperm to fertilize the egg. After the egg is fertilized, a low tide will drain the water and carry the egg far from the reef it came from to create a new coral reef. The way that corals reproduce asexually is by coral budding. Coral budding occurs when the polyp pinches off of to create a new polyp, actually cloning itself. The newly-formed polyp is the daughter polyp. During growth a mouth, tentacles and coelenterons are created. Coelenterons are the central cavities of the coral, around which the exoskeleton forms. This newly formed daughter polyp essentially has two cell layers, the ectodermis and gastrodermis. As this new polyp grows, it continues to develop its feeding apparatuses: tentacles and mouth. This process allows it to function independently of the parent polyp. Fragmentation is another form of asexual reproduction. In this case, a piece of the colony can actually be broken off and “replanted”. Again, this type of reproduction creates a clone of the original, thus limiting biodiversity. However, fragmentation has important implications for the preservation of reef systems. In Fiji they are using the concept of fragmentation to create coral farms. The success of this process provides hope for the future.

Coral Reproduction: (Kazlev, 2003)

(Surfrider Foundation, 2008)

Coral Reefs of the World(Coral Reef Info, 2008)

(Stephan Goldman, Cayman Islands. 2001)

(Roy, 2008)Works Consulted

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