Environmental projects with PADI Course Director Garth Schumann.

LIFE OF THE CORAL REEF

Coral reefs, also known as Sea Gardens, are structures consisting of coral skeletons built upon coral skeletons. They grow in tropical seas in the photic zone, where there is mild wave action, not so strong to tear the reef apart yet strong enough to stir the water and deliver sufficient food and oxygen. Coral reefs also need nutrient-poor, clear, warm, shallow water to grow. The limestone cups house coral polyps.

Coral reef biology

The building blocks of coral reefs are the generations of reef-building corals, and other organisms that are composed of calcium carbonate. For example, as a coral head grows, it lays down a skeletal structure encasing each new polyp. Waves, grazing fish (such as Parrotfish), Sea -urchins, Sponges, and other forces and organisms break down the coral skeletons into fragments that settle into spaces in the reef structure. Many other organisms living in the reef community contribute their skeletal calcium carbonate in the same manner. Coralline algae [i.e zooxanthelate, filamentous algae] are important contributors to the structure of the reef in those parts of the reef subjected to the greatest forces by waves (such as the reef front facing the open ocean). These algae contribute to reef-building by depositing limestone in sheets over the surface of the reef and thereby contributing to the structural integrity of the reef.

Reef-building or hermatypic corals are only found in the photic zone (above 50m depth), the depth to which sufficient sunlight penetrates the water for photosynthesis to occur. The coral polyps do not photosynthesize, but have a symbiotic relationship with single-celled algae called zooxanthellae; these algal cells within the tissues of the coral polyps carry out photosynthesis and produce excess organic nutrients that are then used by the coral polyps. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Indeed, the relationship is responsible for coral reefs in the sense that without their symbionts, coral growth would be too slow for the corals to form impressive reef structures. Some corals get up to 90% of their nutrients from their zooxanthellae symbionts

Although corals are found growing in most areas of a healthy coral reef, the elevation of the reef flat relative to sea level (and considering tidal range) imposes significant constraints on coral growth. In general, only a small number of hardy coral species can thrive on the reef flat, and these cannot grow above a certain height because the polyps can withstand only limited exposure to the air at low tide. Of course some reef flats carry a meter or so of water over the surface, and then coral growth can be prolific. It is the upward growth of coralline algae on the outer part of the reef flat that ultimately results in an overall rise in the surface elevation of a reef, which typically slopes gently downward in towards the shore or lagoon and very steeply downward in the seaward direction. Prolific growth of these algae is a response to water motion bringing in inorganic nutrients and removing waste products. The damaging effects of exposure at low tide on the algae is ameliorated somewhat by constantly breaking waves on the reef edge. Nonetheless, it is the case that mature reefs are in equilibrium with both sea level and wave regime with respect to their elevation, and excess production of limestone moves away from the margin to expand the reef laterally and fill in low areas.

The more prolific growths of corals are to be found in water deeper than where the bottom is exposed at low tides: on the frontal reef slope (fore-reef), in lagoons, and along reef channels that bisect the flat. Under conditions of clear, moving seawater, corals provide the bulk of the skeletal material comprising the reef and the structural complexity that results in a high diversity of reef associated fishes and invertebrates.

Coral reef formations

Diagram of a fringing coral reef.

Coral reefs can take a variety of forms, defined in following:

• Apron reef — short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.

• Fringing reef — reef that is directly attached to a shore or borders it with an intervening shallow channel or lagoon.

• Barrier reef — reef separated from a mainland or island shore by a deep lagoon; see Great Barrier Reef.

• Patch reef — an isolated, often circular reef, usually within a lagoon or embayment.

•  Ribbon reef — long, narrow, somewhat winding reef, usually associated with an atoll lagoon.

• Table reef — isolated reef, approaching an atoll type, but without a lagoon.

• Atoll reef — a more or less circular or continuous barrier reef surrounding a lagoon without a central island; see atoll.

• Bank Reef — Bank reefs are larger than patch reefs and are linear or semi-circular in outline.

World-wide distribution of reefs

Locations of coral reefs.

Coral reefs are estimated to cover 284,300 square kilometers, with the Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) accounting for 91.9 percent of the total. Southeast Asia accounts for 32.3 percent of that figure, while the Pacific including Australia accounts for 40.8 percent. Atlantic and Caribbean coral reefs only account for 7.6 percent of the world total (Spalding et al., 2001).

Coral reefs are either restricted or absent from along the west coast of the Americas, as well as the west coast of Africa. This is due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (Nybakken, 1997). Corals are also restricted from off the coastline of South Asia from Pakistan to Bangladesh (Spalding et al., 2001). They are also restricted along the coast around north-eastern South America and Bangladesh due to the release of vast quantities of freshwater from the Amazon and Ganges Rivers respectively.

Famous coral reefs and reef areas of the world include:

• The Great Barrier Reef - largest coral reef system in the world, Queensland, Australia

•  The Belize Barrier Reef - second largest in the world, Belize, Central America

• The Red Sea Coral Reef - located off the coast of Egypt and Saudi Arabia.

• Many of the numerous reefs found scattered over the Maldives

Ecology and biodiversity

Pennant-fish, Pyramid and Milletseed Butterfly-fish school at Rapture Reef, French Frigate Shoals

Coral reefs support an extraordinary biodiversity; although they are located in nutrient-poor tropical waters. The process of nutrient cycling between corals, zooxanthellae, and other reef organisms provides an explanation for why coral reefs flourish in these waters: recycling ensures that fewer nutrients are needed overall to support the community.

Cyanobacteria also provide soluble nitrates for the coral reef through the process of nitrogen fixation. Corals absorb nutrients, including inorganic nitrogen and phosphorus, directly from the water, and they feed upon zooplankton that are carried past the polyps by water motion (Castro and Huber, 2000). Thus, primary productivity on a coral reef is very high. Producers in coral reef communities include the symbiotic zooxanthellae, coralline algae, and various seaweeds, especially small types called turf algae, although scientists disagree about the importance of these particular organisms (Castro and Huber, 2000).

Coral reefs are home to a variety of tropical or reef fishes, such as the colorful Parrot-fishes, Angelfishes, Damselfishes and Butterfly-fishes. Other fish groups found on coral reefs include Groupers, Snappers, Grunts and Wrasses. Over 4,000 species of fishes inhabit coral reefs (Spalding et al., 2001).

Reefs are also home to a large variety of other organisms, including sponges, Cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including Shrimp, Spiny Lobsters and Crabs), Molluscs (including Cephalopods), Echinoderms (including Starfish, Sea- urchins and Sea- cucumbers), Sea- squirts, Sea- turtles and Sea- snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins being the main group. A few of these varied species feed directly on corals, while others graze on algae on the reef and participate in complex food webs (Castro and Huber, 2000; Spalding et al., 2001).

A number of invertebrates, collectively called cryptofauna, inhabit the coral rock substrate itself, either boring into the limestone surface or living in pre-existing voids and crevices. Those animals boring into the rock include sponges, Bivalve molluscs, and Sipunculans. Those settling on the reef include many other species, particularly crustaceans and Polychaete -worms (Nybakken, 1997).

Due to their vast biodiversity, many governments world-wide take measures to protect their coral reefs. In Australia, the Great Barrier Reef is protected by the Great Barrier Reef Marine Park Authority, and is the subject of many plans and pieces of legislation, including a Biodiversity Action Plan.

 Threats to reefs

Bio-erosion (coral damage) such as this may be caused by coral bleaching.

Human activity continues to represent the single greatest threat to coral reefs living in Earth's oceans. In particular, pollution and over-fishing are the most serious threats to these ecosystems. Physical destruction of reefs due to boat and shipping traffic is also a problem. The live food fish trade has been implicated as a driver of decline due to the use of cyanide and other chemicals in the capture of small fishes. Finally, above normal water temperatures, due to climate phenomena such as El Niño and global warming, can cause coral bleaching. According to The Nature Conservancy, if destruction increases at the current rate, 70% of the world’s coral reefs will have disappeared within 50 years. This loss would be an economic disaster for peoples living in the tropics. Hughes, et al, (2003), writes that "with increased human population and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially. For example, markets for fishes and other natural resources have become global, supplying demand for reef resources far removed from their tropical sources".

Currently researchers are working to determine the degree various factors impact the reef systems. The list of factors is long but includes the oceans acting as a carbon dioxide sink, changes in Earth's atmosphere, ultraviolet light, ocean acidification, biological virus, impacts of dust storms carrying agents to far flung reef systems, various pollutants, impacts of algal blooms and others... Reefs are threatened well beyond coastal areas and so the problem is broader than factors from land development and pollution though those are too causing considerable damage.

 Land development and pollution

Extensive and poorly managed land development can threaten the survival of coral reefs. Within the last 20 years, once prolific mangrove forests, which absorb massive amounts of nutrients and sediment from runoff caused by farming and construction of roads, buildings, ports, channels, and harbors, are being destroyed. Nutrient-rich water causes fleshy algae and phytoplankton to thrive in coastal areas in suffocating amounts known as algal blooms. Coral reefs are biological assemblages adapted to waters with low nutrient content, and the addition of nutrients favors species that disrupt the balance of the reef communities. Both the loss of wetlands and mangrove habitats are considered to be significant factors affecting water quality on inshore reefs.

Poor water quality has also been shown to encourage the spread of infectious diseases among corals.

Copper, a common industrial pollutant, has been shown to interfere with the life history and development of coral polyps. A large area of the Gulf of Mexico is hypoxic during the year, killing countless marine life and threatening the Flower Gardens reef system.

 Live reef fish trade

The hobby of keeping saltwater aquaria has experienced an increase in world popularity since the 1990s. Beyond sales of aquaria, air pumps, food, medications and other supplies, the primary product of the aquarium industry is fish. However, the world market is limited in the diversity of collected species. For example, among 4000 coral reef fish species, only 200–300 are exploited. Selection of species results from a demand for fish being highly colorful and being able to be maintained and fed in aquaria. The last point is very important in the choice of imported species.

Although a few fish species (e.g. Pomacentridae) can be reproduced in aquaria, 95% of exploited fish are directly collected in the coral environment. Intense sampling of coral reef fish, especially in South-East Asia (including Indonesia and the Philippines), has caused great damage to the environment. A major catalyst of cyanide fishing is poverty within fishing communities. In areas like the Philippines where cyanide is regularly used to catch live aquarium fish, the percentage of the population below the poverty line is 40%. In such developing countries, a fisherman might resort to such unethical practices in order to prevent his or her family from starving.

Most 80–90% of aquarium fish exported from the Philippines are captured with sodium cyanide. This toxic chemical is dissolved in sea water and released into fish shelters. It has a rapid narcotic effect on fish, which are then easily captured. However, most fish collected with cyanide die a few months after capture from extensive liver damage. Moreover, other fish species that are not interesting for the aquarium market also die in the field.

Dynamite Fishing

Dynamite fishing is another extremely destructive method that fishermen use to harvest small fish. Sticks of dynamite, grenades or home made explosive are lit or activated and thrown in the water. Once the dynamite goes off the explosion brings about an underwater shockwave causing the internal organs of fish to liquefy killing them almost instantly. A second blast is often set off after the first to kill any larger predators that are attracted to the initial kill of the smaller fish. This method of fishing not only kills the fish within the main blast area but also claims the lives of many reef animals that are not edible or wanted. Also many of the fish do not float to the surface to be collected but sink to the bottom. The blast also kills the corals in the area eliminating the very structure of the reef, destroying the habitat for fish and other animals important for the maintenance of a healthy reef. Areas that used to be full of coral become deserts, full of coral rubble, dead fish and little else, after dynamite fishing.

 Coral bleaching

During the 1998 and 2004 El Niño weather phenomena, in which sea surface temperatures rose well above normal, many tropical coral reefs were bleached or killed. Some recovery has been noted in more remote locations, but global warming could negate some of this recovery in the future. Toxins in the tissue are produced when the water temperatures climb, causing coral bleaching.

However, Ben McNeil of the University of New South Wales hypothesises that reefs are not in decline, and may exceed pre-industrial levels by as much as 35% by 2100, especially because of the positive influence of global warming. However, growth in some reefs due to global warming is expected to be offset by declines in other reefs, due to the comfortable temperature range for a coral being close to the temperature at which they bleach.

Some suggest that while reefs may die in certain areas, other areas will become habitable for corals, and form coral reefs.  Others yet point to data that suggests that the global temperature has never changed by more than a degree for a very long time. (See Global warming controversy).

 Destruction worldwide

Southeast Asian coral reefs are at risk from damaging fishing practices such as cyanide and blast fishing, over-fishing, sedimentation, pollution and bleaching. A variety of activities, including education, regulation, and the establishment of marine protected areas are under way to protect these reefs. Indonesia, for example has nearly 33,000 square miles of coral reefs. Its waters are home to a third of the world’s total corals and a quarter of its fish species. Indonesia's coral reefs are located in the heart of the Coral Triangle and have been victim to destructive fishing, unregulated tourism, and bleaching due to climatic changes. Data from 414 reef monitoring stations throughout Indonesia in 2000 found that only 6 percent of Indonesia’s coral reefs are in excellent condition, while 24 percent are in good condition, and approximately 70 percent are in poor to fair condition (2003 The Johns Hopkins University).

General estimates show approximately 10% of the coral reefs around the world are already dead^]Problems range from environmental effects of fishing techniques, described above, to Ocean acidification. Coral bleaching is another manifestation of the problem and is showing up in reefs across the planet.

Protection and restoration of reefs

Inhabitants of Ahus Island, Manus Province, Papua New Guinea, have followed a generation-old practice of restricting fishing in six areas of their reef lagoon. While line fishing is permitted, net and spear fishing are restricted based on cultural traditions. The result is that both the biomass and individual fish sizes are significantly larger in these areas than in places where fishing is completely unrestricted (Cinner et al. 2005).

It is estimated that about 60% of the world’s reefs are at risk due to destructive, human-related activities. The threat to the health of reefs is particularly strong in Southeast Asia, where an enormous 80% of reefs are considered endangered.

 Marine Protected Areas

One method of coastal reef management that has become increasingly prominent is the implementation of Marine Protected Areas (MPA's). MPA's have been introduced in Southeast Asia and elsewhere around the world to attempt to promote responsible fishery management and habitat protection. Much like the designation of national parks and wild life refuges, potentially damaging extraction activities are prohibited. The objectives of MPA's are both social and biological, including restoration of coral reefs, aesthetic maintenance, increased and protected biodiversity, and economic benefits. Conflicts surrounding MPA's involve lack of participation, clashing views and perceptions of effectiveness, and funding.

Indonesia currently has nine MPA's, claiming a total 41,129 square kilometers of coastal waters are to be under protection. A study done on one of the more recently established MPA's in Indonesia showed the need for co-management when it comes to the success of managing MPA's. This collaborative approach emphasizes the cooperation and partnership between parties at the national, provincial, and local community level.

The coral reefs in the Philippines and Indonesia are disappearing rapidly due to dynamite and cyanide fishing. Between 1966 and 1986 the productivity of coral reefs in the Philippines dropped by one-third as the national population doubled (State of the Reefs).  In Indonesia as well, over eighty percent of the coral reefs are under threat (The Jakarta Post). These two locations are home to the world's most diverse range of corals. If the rate of destruction does not diminish, seventy percent of all the world's coral reefs will be gone in the next twenty-five to forty years (the Philippines).  

 References:

1.   Ryan Holl (17 April 2003). Bioerosion: an essential, and often overlooked, aspect of reef ecology. Iowa State University. Retrieved on 2006-11-02.

2.    Australian Government Productivity Commission (2003). Industries, Land Use and Water Quality in the Great Barrier Reef Catchment - Key Points. Retrieved on 2006-05-29.

3.   Rachel Nowak (2004-01-11). Sewage nutrients fuel coral disease. New Scientist. Retrieved on 2006-08-10.

4.   Emma Young (2003). Copper decimates coral reef spawning. Retrieved on 2006-08-26.

5.     CIA - The World Factbook -- Philippines. CIA. Retrieved on 2006-11-02.

6.   David LECCHINI, Sandrine POLTI, Yohei NAKAMURA, Pascal MOSCONI, Makoto TSUCHIYA, Georges REMOISSENET, Serge PLANES (2006) "New perspectives on aquarium fish trade" Fisheries Science 72 (1), 40–47. Blackwell Synergy. Retrieved on 2007-01-16.

7.    Kate Ravilious. "Coral reefs may grow with global warming", New Scientist, 2004-12-13. Retrieved on 2006-08-10.

8.    Save Our Seas, 1997 Summer Newsletter, Dr. Cindy Hunter and Dr. Alan Friedlander

9.    Tun, K., L.M. Chou, A. Cabanban, V.S. Tuan, Philreefs, T. Yeemin, Suharsono, K.Sour, and D. Lane, 2004, p:235-276 in C. Wilkinson (ed.), Status of Coral Reefs of the world: 2004.

10. Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins, 2006, Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A guide for Future Research, NSF, NOAA, & USGS, 88 pp.

11.  Coral Reef Management, Papua New Guinea. Nasa's Earth Observatory. Retrieved on 2006-11-02.