By Balma Sales Diaz INTRODUCTION The Great Barrier Reef is considered one of the seven wonders of the natural world and is considered the largest living organism on Earth. It is located in Australia. Its amazingly vivid corals and thousands of animals inhabiting it make up the beauty of this reef, making it one of the most touristic locations in the world. However, it will not last much longer if humans don’t act to stop the terminal stage the Great Barrier Reef is facing (Hoegh-Guldberg et al., 2009). This paper will discuss firstly the idiosyncrasy that forms Coral Reefs, and will continue by going into more detail about the Great Barrier Reef and what environmental causes have led it to a difficult terminal stage to recover from. CORAL REEFS Coral reefs are seen as immensely vast animals whose extension can reach hundreds of kilometers and provide habitat to a large number of organisms in tropical and subtropical areas. They are composed of coral polyps, which are tiny animals that produce a carbonate infrastructure for the reef where these organisms live. Their growth is affected by many factors such as light intensity, length, water temperature, plankton concentrations, and the deposition and removal of calcium carbonate (CaCO3); therefore, they are merely found in salinity warm seawaters where reefs can be built. On the other hand, corals’ light absorption occurs through zooxanthellae, which is a photosynthetic alga that lives in the corals tissue and provides them with a mutualistic symbiotic relationship. Turbidity can also affect the growth of corals depending on the levels of suspended sediment in the water column. The higher the levels, the lower the existence of reefs. Coral reefs, which reproduce asexually or sexually, compose the largest living creatures on Earth and even though there are many around the globe, the most popular one is located in Australia (Morrissey et al., 2018). THE GREAT BARRIER REEF (GBR) The Great Barrier Reef is an oceanic reef classified as the largest coral reef ecosystem in the world and the only living organism that can be seen on Earth from space (see Figure 1). It covers 360,000 square km, and the coral reefs stretch up to 2,575 km. Its waters can go over 2,000 meters deep and it encompasses 2,500 individual reefs. There are 400 different types of corals, 1,500 different fish species, 4,000 types of mollusk, and 240 different species of seabirds and many other organisms (UNESCO, 2017). Origin and Evolution The GBR found in Queensland’s continental shelf did not form until 6,000 years ago which is a relatively short period of time considering Earth’s history. During glacial and interglacial cycles, the area has been exposed to extreme conditions of sea levels rising and dropping which have enhanced the growth of these corals. Moreover, reefs are built mainly when sea levels rise indicating that the GBR was created during interglacial periods (Hoegh-Guldberg et al., 2009). Geomorphology The GBR is composed of three zones of reefs that go from fringing reefs to mid-shelf reefs and outer shelf reefs. All of them have major energy conditions in which the stronger these conditions are, the more different their zonation. Normally, coral reefs have a protectionist coral reef front which is steeper in high energy areas (see Figure 2). Afterwards, the reef crest appears and we can find a diversity of living organisms below the low spring tide area. It is then followed by a reef flat that contains the highest part of the reef and aligned, the densest area with coral colonies growing. At the back, there is the most vulnerable coral colonies growing in a slope of sand. Moreover, it is also important to highlight that the GBR does not only contain reefs and other organisms, but also some coral islands produced by the accumulation of sediments on the reef flat due to the action of waves. They can be classified by types of sediments and vegetation cover which includes from the unvegetated to highly abundant vegetation. The latter are important because they have different distribution patters. Vegetated islands exist on the far north and south but are absent on the central part of the Great Barrier Reef; nonetheless, unvegetated islands can be found along the entire GBR being less frequent on the center (Hoegh-Guldberg et al., 2009). HABITAT & ECOSYSTEM The GBR rises in a shallow continental shelf with a 75 km wide stretch of water located at the center, called GBR Lagoon where many reefs inhabit. This Lagoon absorbs nutrients and solids that are carried inshore after heavy rainfalls due to the force of rivers situated along the coast. At the Coastal Sea there are oceanic tides that also heavily influence some parts of the Great Barrier creating tidal nodes that end up forming a large number of tides in the area and strong currents. Along with sediment grain size, turbidity, depth and nutrients, all of these previously defined factors influence the habitat of coral reefs. Moreover, there are two major environments found in the Great Barrier Reef: the most common which represents 50% of the seabed and where we can find coarse sands, algae and benthos; and the less but more complex environment which is found in relatively less parts. Physical Factors Influencing the Ecosystem Mud is one of the most important factors found which conforms a great amount of the GBR’s length. Worms, shrimps and bivalves inhabit this inshore area even though there are still a few mobile animals which are included too. Offshore where turbidity is lower, muddy territory has the same fauna as inshore with a little bit more diversity. Moreover, muddy areas that are located further away from the shelf and which are quite sandy, support a wide range of surface biota such as starfish, crabs, fish and algae while supporting many bio habitats. On the other extreme there is Benthic Stress (BS) which is the cause of the largest tidal range in the GBR, provoking harsh currents that push sediments away to leave stones and rocks exposable to anything. As muddy territories, benthic stress also provides habitat to a large number of highly diversified fauna and moderated biomass. Upwellings play an important role as a physical factor when providing nutrients in deep clear waters. These areas have a moderate diversified fauna and biomass, and are located offshore out of the range of muddy and turbid areas, where light absorption is easier to reach the seabed (Hoegh-Guldberg et al., 2009). Development of Coral Reefs Corals in the GBR are supported by carbonated reefs and rock bases that geologically evolved over time. Fixing these carbonates to make them hard substrates in marine systems is a very important geological role for them (Morrissey et al., 2018). Besides carbonate ions, other factors affect the development of coral reefs: temperature and light availability. Firstly, temperature variations such as El Niño (or la Niña) cycle which can produce extreme hot and cold temperatures, can influence the stress coral reefs have to deal with (see Figure 3). On the other hand, light dependence is a major determinant to where coral reefs are located in order to obtain high rates of photosynthesis. Water columns sometimes block light absorption because of heavy particles they contain, and are the main reason why coral reefs are not located next to major rivers. Changes temporally can also influence light like tidal variations or periods of cloudiness over the water (Hoegh-Guldberg et al., 2009). Primary Productivity The GBR was defined by Charles Darwin as a “marine rainforest existing in an oceanic desert” due to the fact that coral reefs have a very productive ecosystem, but the ocean that surrounds them does not. Coral reefs have a manifestly efficient mechanism to photosynthesize and recycle nutrients provided by organisms such as blue green bacteria (Cyanophyta), seaweeds, phytoplankton and dinoflagellates. Their productivity depends on whether they’re found inshore or offshore, in a high or a low latitude and the location within the reef. Moreover, primary production is not only based on sunlight and CO2, but also on inorganic nutrients such as inorganic nitrogen and phosphorus. Their job is to breakdown waste of animals which have consumer other organisms and debris generated by predators. This nitrogen is supplied to coral reefs through a nitrogen fixation process which is quite important to coral reefs. As previously stated, there are consumers and producers in coral reefs; however, more producers currently exist than consumers do, consequently because of high inefficiencies in nutrients and energy transfer in trophic interactions. Coral reefs trophic levels range from primary producers at the bottom to herbivores, predators and apex predators at the top. Among them, some organisms have mutualistic symbiotic relationships with coral reefs which is a hallmark of coral reefs in the GBR. These have been a result of the low nutrient conditions that rule the advantages in the primary producer-consumer relationship. An example of these distinctive relationships are reef-building corals and dinoflagellate protists. The latter provide energy in large amounts to the coral which, in return, deliver access to inorganic nutrients. As a result, photosynthetic rates skyrocket and strengthen the process of calcification (Hoegh-Guldberg et al., 2009). Biodiversity: More than fish The Great Barrier Reef is commonly popular because of its status as the largest living organism on Earth, but also because of the richness of its biodiversity. Biota is highly diverse due to the diversity of habitat found within coral reefs that can sway from soft sediments to pelagic and coastal habitats. Furthermore, the highest number of organisms is found in the so-called “coral reef triangle” which is in line with Indonesia and the Philippines, even though these numbers are declining due to the major threat the GBR is suffering nowadays which will be discussed in a later section (Hoegh-Guldberg et al., 2009). Onwards, the Great Barrier Reef is home to a large extent of animals that range from the tiniest plankton to hosting one of the most important dungong populations in the world besides the overly popular fish. Some of these animals are the following:
THREATS TO THE GBR In the past 30 years the Great Barrier Reef ecosystem has been threatened by different factors that are not only limiting its growth, but destroying it slowly. Coral reefs are strong and have always faced disturbances to which they have adapted to survive. However, now those disturbances are damaging more than ever and action has to be taken (Hoegh-Guldberg et al., 2009). Human Impact The interaction of humans with the ecosystem of the Great Barrier Reef has greatly influenced the terminal stage the great wonder confronts these days. Even though humans play a significant role on the regenerative processes of coral reefs, their impact causes more harm than good. Overfishing has become a trend since there has been an increase in demand for seafood and more fisheries are being built. As a consequence, many species have been reduced, dangerously affecting the food web of the GBR and No Take Areas (NTA) where it is prohibited to fish, are increasing. It is important to highlight that due to this overfishing, dugongs have declined by 90% in the previous years (Australian Government, 2017). The use of land due to agriculture, urbanization and other disturbances have caused soil erosion and great amounts of sediments that flow into rivers to be taken to the GBR accumulating there and damaging coral reefs (Hoegh-Guldberg et al., 2009). This land run-off is the cause of poorer water quality that has increased the amount of sediments and pesticides in the marine water (Australian Government, 2017). Moreover, coral harvesting for personal pleasure, and human recreational activities such as fishing, also contribute to the damage when conducted excessively (Hoegh-Guldberg et al., 2009). However, one of the most important and popular human impacts that is affecting the environment worldwide too is climate change. Climate Change The increase of greenhouse emissions produced by deforestation and burning of fossil fuels by humans has greatly increased the earth’s overall temperature over thousands of years (see Graph 1). However, it is greatly impacting coral death in the GBR. Climate change has led to coral bleaching which is a phenomenon where corals feel stressed and they expel the zooxanthellae with which they had a mutualistic relationship (Anonymous, 2015). Corals change from brown to white as a result of the bleaching which is caused by rising sea level temperatures due to climate change. (Morrissey et al., 2018). Extreme weather conditions such as floods and cyclones are consequences of climate change too. Six cyclones of the highest category, number 5, have affected the GBR in the past decade (Anonymous, 2015). Increase in the turbidity and reductions on the levels of salinity can kill corals or create imbalances in the ecosystem due to over productivity caused by the increase of nutrients. (Australian Government, 2017) Greenhouse emissions of CO2 are expected to increase up to high levels that will exceed the conditions to which corals have always overcome; however, some researchers have found that some corals have symbiont relationships which can handle great thermal tolerance; hence, this can increase the probabilities resisting climate change if they adapt and create new symbiont relationships with new zooxanthella’s. (Morrissey et al., 2018). As a consequence of coral bleaching, pathogenic bacteria are increasing coral diseases, and although these diseases affect a low percentage of corals, it is still something to take care of (Hoegh-Guldberg et al., 2009). Ocean Acidification Out of all the impacts recorded and damaging the GBR, ocean acidification is the most significant one. Half of the CO2 that enters the atmosphere is absorbed by the ocean, and almost half of the CO2 created by humans (anthropogenic CO2) is found on 10% of the upper levels of the ocean. (Gangjian, et al., 2009). The main issue with ocean acidification is the damage of calcification rates in marine organisms. Its increase has produced large reductions on the Ph of the ocean, which produces calcification therefore increasing coral mortality rates (Gangjian et al., 2009). Coral reef building and habitat creation do not need high levels of acidification to be strongly affected; hence, the ongoing increase of CO2 levels in the water, can completely obliterate the GBR fauna and flora if greenhouse emissions are not reduced. (Australian Government, 2017). Path To Sustainability There are many reasons why the Great Barrier Reef needs immediate protection and action from everyone. Consequently, in 1975 the Great Barrier Reef Marine Park (GBRMP) was created to stabilize and protect it to ensure sustainability. This Marine Park was established in the coast of Queensland and it works cooperatively with the Australian government (Hoegh-Guldberg et al., 2009). The GBR is not only important because of the many species that provide such wonderful marine diversity in the largest coral reef ecosystem, but also because of the value and economic benefits it provides to Australia. It provides thousands of jobs for people and is one of the most visited touristic attractions of the world. Almost 2 million tourists visit it every year contributing on 90% of the economic activity of the large coral barrier reef (Australian Government, 2017). It can also influence human well-being of the community that relies upon it. Its beauty and the connection that many families living in Queensland have shaped over time with the natural wonder, contribute to a healthier environment. The Reef is not only a food source for numerous people, but a place to relax and enjoy the natural world that surrounds as well. In addition, it protects residents in the coast from extreme weather conditions that can result in strong wave actions (Australian Government, 2017). SUMMARY The Great Barrier Reef is the largest coral reef ecosystem in the world containing thousands of different species that make it unique. The Reef has always been faced with many disturbances from glacial to interglacial periods to which it has adapted in order to evolve and survive. However, in the last 30 years it seems that the reef’s adaptation to the extreme conditions that affect it nowadays is considerably challenging. Human impact has prompted the increase of climate change, consequently affecting ocean acidification and coral bleaching, which are the two main sources that are significantly damaging coral reef building and increasing coral mortality. Nevertheless, other more direct activities such as illegal fishing or water pollution from land based run-offs are critically impacting the ecosystem as well. The simplest solution to this problem is the reduction of CO2 absorbed in by the ocean. In order to implement it, international human interaction is essential. The Australian Government established the GBRMP to protect the Reef and sustain it to ensure its survival. The Marine Park can undertake as many actions as they’re capable of, but without the help of global cooperation to fight against global warming, these actions will be useless in the long-run. It is important to make people understand that if we want the future to survive climate change, first we have to start by saving the Earth and that implies the nature that makes us alive.
REFERENCE LIST
Anonymous. (2015). Judgement Day; Australia’s Great Barrier Reef. The Economist, 415, 38. Australian Government (2017, n.d). Australian Government: Great Barrier Reef Marine Park Authority. Retrieved from http://www.gbrmpa.gov.au Gangjian, W., Graham, M., Luhua, X., Malcolm, T. M., & Wengfeng, D. (2009). Evidence for Ocean Acidification in the Great Barrier Reef of Australia. Geochimica et Cosmochimica Acta, 73, 2332-2346. Hoegh-Guldberg, O., Hutchings, P., & Kingsford, M. (2009). The Great Barrier Reef: Biology, Environment & Management. Australia, New Zealand: CSIRO Publishing. Morrissey, J. F., Pinkard-Meier, D. R., & Sumich, J. L. (2018). Introduction to the Biology of Marine Life. Burlington, MA: David D. Cella. UNESCO (2017, n.d). UNESCO: World Heritage Convention. Great Barrier Reef. Retrieved from http://whc.unesco.org
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