Coral reefs in the ocean: What are coral reefs?

What are Coral reefs?

Picture of coral reefs
Picture showing coral reefs in the ocean

Coral reefs are large underwater ecosystems formed by reef-building corals. It is composed of the calcareous exoskeletons of corals. The Coral Reef is formed of colonies of coral polyps bind together by limestone (calcium carbonate). Most of the coral reefs are built from stony corals that secrete hard carbonate exoskeletons which support and protect the coral.

These hard coral species that build reefs are known as hermatypic corals because they extract calcium carbonate from seawater to create a hard and durable exoskeleton. Also, there are other species of corals known as soft corals that are not involved in coral reef-building. These soft corals are usually flexible organisms and often resemble plants and trees.

Coral reefs are among the most productive of all ecosystems. They have beautiful and colorful forms of biodiversity. These reefs grow best in warm, shallow, clear, and agitated water. Shallow coral reefs however form some of the most diverse ecosystems on earth. Thus they are sometimes called the rainforests of the sea. It is said that Coral reefs first appeared at the dawn of the Early Ordovician about 485 million years ago, displacing the sponge and microbial reefs of the Cambrian.

Are Coral reefs plants?

Coral reefs are not plants. They however have soft corals that are usually flexible organisms and often resemble plants and trees. Most people think coral reefs are plants or rocks. This is a wrong assumption. Coral reefs consist and are formed by corals that are alive. Hence they are not rocks. Although some of these corals attach to submerged rocks at first excreting their exoskeleton and begin to form colonies that join with others to form the coral reef. Moreso, the corals of the coral reefs do not manufacture their own food as plants usually do. So coral reefs are not plants but a large underwater ecosystem formed by corals.

These reefs formed, occupy less than 0.1% of the global ocean area, still, they provide a home for about 25% of all marine species. Marine species like fish, worms, mollusks, echinoderms, sponges, crustaceans, tunicates, and other cnidarians are common habitants of the reef. Coral reefs can be seen commonly in tropical waters at shallow depths. Even though they exist too on a smaller scale in deep and cold water in other areas. Moreso, coral reefs tend to flourish well in ocean waters with fewer nutrients.

What is a Coral?

corals form coral reefs

A coral is a marine invertebrate that takes root on the ocean floor. Corals are sessile animals of the phylum Cnidaria within the class Anthozoa. Most people think corals are plants or rocks. However, corals are alive, unlike rocks. Moreso, they do not manufacture their own food as plants usually do. Rather they have tiny tentacle-like arms which they use to capture food from the water into their mouths.

Corals form colonies of genetically identical sac-like animals. These identical sac-like animals are polyps. Hence, corals are composed of hundreds to thousands of individual polyps since they are colonial organisms. That is each individual coral is a polyp and most of the structures people call coral are made up of hundreds to thousands of tiny coral polyps. However, the polyp is a sac-like animal that is usually a few centimeters in height and has a diameter of few millimeters.

These corals are the reef builders that secrete limestone (calcium carbonate) to form a hard skeleton and inhabit tropical oceans. The coral polyps live on the limestone exoskeletons of their ancestors as they add their own exoskeleton to the existing coral structure. With one tiny exoskeleton at a time, as the centuries pass, the coral reef gradually grows. The reef grows until it becomes a massive feature of the marine ecosystem.

Coral types

  1. Hard corals
  2. Soft corals

Corals are generally classified under hard corals and soft corals.

Stony corals or hard corals

Stony corals or hard corals are the most familiar and widely distributed corals. They are solitary and colonial in their habit. These stony corals have more than 8 septa and simple tentacles. Hard or stony corals are referred to as hermatypic corals because they are known as reef-building corals.

Brain coral is an example of hard corals which are the reef building corals
Brain coral in the reef

These hard corals are actually a fundamental part of building the coral reef. However, their polyps secrete skeletons of limestone which eventually become rock. Their skeleton is almost pure limestone and is deposited in a cup-shaped form with the polyp inside. Hard corals require the symbiotic algae (zooxanthellae) that live within their tissues for their survival. These zooxanthellae are what give the corals their colors.

However stony or hard coral species can be found in all of the world’s oceans from the tidal zone to depths of nearly 20,000 feet. Common examples of stony corals include blue coral, mushroom coral, boulder star coral, pillar coral, Acropora sp., brain coral, Great star coral, staghorn coral, Tubastraea sp. and elkhorn coral.

Soft corals

Sea fans are soft corals
Sea fan
Photo Credit: Textbook (Integrated Principles of Zoology Fifteenth edition) By Hickman, Roberts, Keen, Eisenhour, Larson, I’Anson

Soft corals don’t have a rock-like skeleton that is composed of calcium carbonate as hard or stony corals. Instead, soft corals are soft and bendable. They often resemble trees and plants. Since they usually resemble brightly colored plants, they are easy to differentiate from stony corals. These corals grow fleshy rinds for protection and wood-like cores for support. Their polyps possess tentacles that give a feathery appearance and occur in numbers of eight.

Generally, soft corals are seen in caves or ledges of oceans. They are referred to as Ahermatypes because they are non-reef building corals. Unlike hard coral, soft corals do not always have a symbiotic association with zooxanthellae. Even though many of them still utilize the presence of the symbiotic algae. Common examples of soft corals include Sea pen, Dendronephthya sp, black corals, seas fans, Alcynonium digitatum, and sea whips.

How are Coral reefs formed?

A coral reef begins to form when the coral polyp attaches itself to a rock on the seafloor or other hard surfaces along the edges of islands. Hermatypic corals and coralline algae are the most important organisms that precipitate calcium carbonate from seawater to form reefs. However hermatypic corals are very essential for the formation of large reefs because reefs do not occur where these corals can not live. Hence, as these coral polyps live, reproduce, and die, they leave their skeletons behind. So the coral reef is formed by layers of these skeletons covered by living polyps. Moreso, these polyps reproduce either by budding or spawning.

Individual colonies of polyps grow by asexual reproduction (budding) whereby a bud remains attached to the original polyp. Then a colony develops eventually by the continual addition and growth of new buds. The old polyps beneath die, leaving their skeleton as these new polyps develop. Eventually, the new coral polyps begin to bud or divides into thousands and thousands of clones of themselves. These polyps and their calcareous skeletons connect to one another forming a colony that acts as one. So, as this colony grows over the years, it then joins with other colonies and forms a reef.

By spawning, coral polyps colonies grow. Usually, around a full moon, polyps of the same species release their eggs and sperms simultaneously overnight. The fertilized eggs then form a ciliated larva called planula. These planulae are mobile early forms of the coral polyp that settles to form a new colony when mature. These free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands. Each coral polyp then excretes an exoskeleton near the base and the coral reef gradually grows as the centuries pass. With one tiny exoskeleton at a time, the reef begins to form and grow.

Furthermore, the corals on a reef are then cemented together by organisms. Physical processes like waves washing sand into spaces in the reef and organisms like coralline algae help cement corals on reefs. Coralline algae contribute to the total mass of calcium carbonate on the reef and their precipitation of the calcium carbonate helps to hold the reef together. Moreso, it can take up to 10,000 years for a group of larvae to form a coral reef.

Also, other kinds of animals and plants also contribute to the coral reef’s structure. Organisms such as seaweed, mollusks, algae, seaweed, giant clams, sponges, oysters, and sediment add to the structure of coral reefs. However, such organisms serve as foundations for new corals when they die. Moreso, as corals grow and expand, reefs take on 1 of 3 major characteristic structures. These major structures are fringing, barrier, or atoll. This eventually takes us to the types of coral reefs.

Types of Coral reefs

  1. Fringing reefs
  2. Barrier reefs
  3. Atolls
  4. Platform reefs
  5. Patch reefs

Originally, it was Charles Darwin who classified coral reefs based on their morphology and structure into 3 as Fringing reefs, Barrier reefs, and Atolls. However, some scientists have identified further types of reefs. For instance, Thomas and Goudie list 4 coral reef types as the fringing reef, barrier reef, atoll, and table reef. Whereas, Spalding et al. list 5 coral types as the fringing reef, barrier reef, atoll, platform or bank reef, and patch reef.

Nevertheless, all the 3 main reef types as fringing, barrier, and atoll in their biogeographic profile share similarities. However, parameters like the bottom topography, light, temperature, suspended sediments, depth, wave, and current strength all act to form characteristic vertical and horizontal zones of corals, algae, and other species. Moreso, these zones vary base on location and reef type. However, the major divisions that are common to most reefs as they move seaward from the shore include the reef flat, algal ridge or reef crest, buttress zone, and seaward slope.

  • Fringing reefs

Fringing reefs are also called shore reefs and grow close to the coast in shallow waters. These reefs are the most common and project seaward, directly from the shore as they form borders along the shoreline and surround islands. They lie near emergent land and are fairly shallow, narrow, and recently formed. However fringing reefs can be separated from the coast by a navigable channel, shallow channel, or lagoon. This reef type can be described as reefs that are close to a landmass with either no lagoon or a narrow lagoon between the reef and the shore.

Coral reef drawing showing the Fringing reef type
Coral reef drawing showing the Fringing reef type

Fringing reefs follow coastlines and can extend for many kilometers usually less than 100 meters wide. However, some are hundreds of meters wide. Initially, fringing reefs are formed at the low water level on the shore and expand seawards as they grow in size. However, the final width of the fringing reef depends on where the sea bed begins to drop steeply. The fringe reef surface generally remains at the same height below the waterline.

In older fringing reefs that their outer regions push far out into the sea, their inner part is deepened by erosion and forms a lagoon. The fringing reef lagoons can become several meters deep and over 100 meters wide. Also, the lagoon, like the fringing reef runs parallel to the coast. Some of the best-developed fringing reefs in the world are the fringing reefs of the Red Sea that occur along all its shores except off sandy bays.

  • Barrier reefs

Barrier reefs are large and continuous reefs that are separated from land by a lagoon. They are similar to fringing reefs in that they border a shoreline also. However, they are separated from land by an expanse of water, instead of the barrier reef growing directly out from the shore creating a lagoon of open, often deep water between the reef and the shore. These reefs are broader and lie far away from the coast as a stretch of water separates the reef from the coast. This reef type can be characterized as reefs that run roughly parallel to shore and has wider and deeper lagoon than fringing reefs.

Barrier reef type
Coral reef drawing showing the Barrier reef type

The barrier reef lagoons can be 30-70 meters deep and several kilometers wide. It is said that these reefs are formed either as the sea level rose or the seabed lowered. Formation of the barrier reef takes longer than a fringing reef and this is why they are much rarer. Moreso the outer reef edge of the offshore is formed in open water instead of next to a shoreline.

Barrier reefs are one of the oldest and most beautiful and biologically diverse habitats in the ocean. Their growth range from 0.3 to 2 centimeters per year for massive corals, and up to 10 centimeters per year for branching corals. However, depending on the size of the corals, barrier reefs, as well as atolls, can take from 100,000 to 30,000,000 years to fully form.

Barrier reefs are found on the coasts of Mayotte, Providencia, the Gambier Islands, and on the southeast coast of Kalimantan. Also, they are seen on parts of the coast of Sulawesi,  the south coast of the Louisiade Archipelago, and southeastern New Guinea. The largest and best-known example of a barrier reef is the Australian Great Barrier Reef. Also, other major examples are the New Caledonian Barrier Reef and the Belize Barrier Reef.

Great Barrier Reef

Globally, the largest coral reef system is the great barrier reef. The Great Barrier reef is located in Australia. It is seen in the Coral Sea, off the coast of Queensland. This reef is composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometers. It was selected in 1981 as a World Heritage Site. Also, CNN labeled it in 1997 as one of the seven natural wonders of the world.

  • Atolls

Atolls are ring-shaped and are located near the sea surface. This kind of reef can be characterized as reefs that encircle a lagoon but not an island. They are rings of coral that create protected lagoons usually located in the middle of the sea. This reef type is usually formed when the sea level arises around islands surrounded by fringing reefs or they sink into the sea. These fringing reefs continue to grow and form circles with lagoons inside eventually. They are mostly formed from fringing reefs around volcanic islands as over time, the island may erode away and sinks below sea level.

Atoll is a coral reefs type
Coral reef drawing showing the ATOLL type of coral reef

Atolls get their shape from growing on top of inactive volcanoes or underwater islands.  However, atolls are usually oval or circular with a central lagoon. Also, parts of the reef platform may emerge as one or more islands and the gaps in the reef give access to the central lagoon. The emergent reef part is usually covered with accumulated sediments and coconut trees are the most characteristic vegetation growing on these reefs. Basically, atolls form near the sea surface on underwater islands or on islands that subside or sink.

Atolls are plenty in the South Pacific. For instance, they occur in mid-ocean in French Polynesia, the Caroline Islands, the Marshall Islands, the Cook Islands, and Micronesia. Also, they are found in the Indian Ocean, like around Cocos Island, in the Maldives, the Chagos Islands, and Seychelles. The entire Maldives for instance consists of 26 atolls.

The Tubbataha Reefs Natural Park which is also known as the Tubbataha Natural Park is located in the middle of the sulu sea. It is however a protected area of the Philippines and as a World Heritage Site is a unique example of an atoll reef. The Tubbataha natural park has a very high density of marine species. The North Islet serves as a nesting site for birds and marine turtles. The site is characterized as an excellent example of a pristine coral reef with extensive lagoons and 2 coral islands. However, the bird and marine sanctuary consist of 3 huge atolls. The two atolls are named the North Atoll and South Atoll. It also consists of the smaller Jessie Beazley Reef.

  • Platform reefs

Platform reefs are usually called table or bank reefs. They can form on the continental shelf and in the open ocean. These reefs can form anywhere that the seabed rises close enough to the surface of the ocean to enable the growth of reef-forming corals. They are variable in size and range from a few 100 meters to many kilometers across. Their normal shape is oval to elongated.

The platform reef grows in all directions unlike barrier and fringing reefs which extend only seawards. However, parts of the platform reefs can reach the surface and form small islands and sandbanks around. This may eventually form fringing reefs. Also, a lagoon may form in a platform reef middle.

Platform or table reefs can be found within atolls. In old platform reefs, the inner part of the reef can be so heavily eroded that it forms a pseudo-atoll. However, these can be distinguished from real atolls by detailed investigation, if possible by core drilling.  For instance, some platform reefs of the Laccadives due to water flow and wind are U-shaped.

Bank or platform reefs are seen in the southern Great Barrier Reef, the Swain, and Capricorn Group on the continental shelf. They are found about 100–200 km from the coast. Some table reefs of the northern Mascarenes are several thousand kilometers from the mainland.

  • Patch reefs

Patch reef is a small isolated reef that grows up from the open bottom of the continental shelf or the island platform. These reefs are common isolated and comparatively small reef outcrop within a lagoon or embayment. Patch reefs normally occur between fringing reefs and barrier reefs. They are often circular and surrounded by seagrass or sand. The ring of reduced seagrass cover surrounding the patches is referred to as grazing halo. A patch reef varies in size and rarely reaches the water surface.

Coral reefs ecosystems

Coral reefs ecosystems protect coastlines from storms and erosion. Also, the health, diversity, and abundance of the organisms that make up a coral reef are directly linked to the surrounding marine and terrestrial ecosystems. Seagrass beds and mangrove forests are very important facets of the coral reef ecosystem in the ocean. However, the ecosystem services of mangroves and seagrass are vital to the coral reefs’ long-term health.

These mangroves are salt-tolerant trees and they grow along tropical and subtropical coasts. However, their complex root systems help stabilize the shoreline as they produce nutrients and filter pollutants. These submerged roots provide nursery, feeding, and breeding grounds for fishes, birds, invertebrates, and other marine life. However, many of the animals raised in mangroves migrate to coral reefs for habitat, food, and spawning.

Seagrasses are plants that usually form meadows between coral reefs and mangrove habitats. Hence forming the foundation of many food webs and providing nutrients for organisms such as sea urchins, snails, sea turtles, and manatees. These plants also provide protection and shelter for commercial species such as stone crabs, snappers, and lobsters. Also, they filter the water column and prevent seabed erosion. Additionally, they also release oxygen essential for most marine life.

Also land is another very important element of the coral reef ecosystem. Even though it is often overlooked. Pollutants, litter, and nutrients can enter nearshore waters through underground seepage, streams, rivers, wastewater, and stormwater runoff. Even land areas that are hundreds of miles from the coast can affect the clarity and quality of water flowing to the coral reef. Hence, no matter how far removed a pollutant may seem, it all flows downstream and can affect the marine habitat and the coral reefs.

Additionally, coral reef ecosystems contain distinct zones that have different sorts of habitats. Basically, three major zones are normally recognized. The zones are the fore reef, reef crest, and the back reef (also known as the reef lagoon). These three zones are physically and ecologically interconnected.

A picture Showing the front reef, reef crest, reef flat and lagoon
Drawing of the front reef, reef crest, reef flat, and lagoon
  • Fore reef or Reef front: This is the side of the reef facing the sea. The reef front is parallel to the shore and perpendicular to the predominant direction of the wave travels. It slopes downwards into deeper water. Sometimes gently at first then precipitously. Characteristics assemblages of corals grow deep on the slope. They grow high near the crest and in intermediate zones.
  • Reef crest: The slightly emergent at the top of the reef front is the reef crest. The upper front and the crest bear the greatest force of waves and must absorb great energy during storms. However, at such times, pieces of coral and other organisms are broken off and thrown shoreward onto the reef flat
  • Reef flat: The reef flat slopes down into the lagoon. Hence, the reef flat accumulates calcareous material eventually into coral sand. The sand is stabilized by the growth of plants like coralline algae and turtle grass. These plants become cemented into the mass of the reef by the precipitation of carbonates.
  • Reef lagoon: This is the entirely enclosed region, which creates an area that is less affected by wave action. The reef lagoons often contain small reef patches.

Reef in the ocean

The Coral reef in the ocean forms complex ecosystems with enormous biodiversity. A Coral reef in the ocean can be made up of many species of corals. A healthy reef is a colorful and highly biodiverse area made up of a mishmash of corals and species that inhabit it. Species like sea turtles, fish, sponges, shrimp, crabs, lobsters, crabs, sea horses, and other species inhabit the coral reef. Soft corals may be found within a coral reef ecosystem even though they do not build the reefs themselves.

The reef life and oceanic processes give opportunities for the exchange of seawater, nutrients, marine life, and sediments. The majority of coral reefs exist in waters that are less than 50 m deep. Some of them inhabit tropical continental shelves with no nutrient-rich upwelling occurring. For instance, the Great Barrier Reef. Other coral reefs are seen in the deep ocean as atolls or surrounding islands. Such as in the Maldives. However, the coral reef ecosystem surrounding islands form when islands subside into the ocean. Moreso, atolls form when an island subsides below the sea surface.

Coral reef animals

Enormous numbers of species, invertebrates, and fishes populate the coral reef ecosystem. For instance, there are about 300 species of fish on the Caribbean reefs and more than 1200 on the Australian great barrier reef. There are more than 1,500 fish species that live on the reef. Fishes like the red bass, clownfish, red-throat emperor, coral trout, and several species of snapper are seen in the reef. There are about 5,000 species of mollusks that live on the reef.

It’s interesting that such diversity of coral reef animals and productivity can be maintained since reefs are washed by nutrient-poor waves of the open ocean. Even though little nutrient enters the ecosystem, little is lost because the interacting organisms are so efficient in recycling. The corals even feed on the feces of fish swimming over them. Species like sea turtles, fish, sponges, shrimp, crabs, lobsters, crabs, sea horses, and other species inhabit the coral reef. Soft corals may be found within a coral reef ecosystem even though they do not build the reefs themselves.

Fish in the coral reef

There are fishes that live in the coral reefs or in close relation to them. Among the myriad inhabitants of the coral reefs, fishes stand out as colorful and interesting to watch. Hundreds of fish species can exist in a small area of a healthy reef. Many of these fishes could be well camouflaged or hidden. However, these reef fishes have developed many ingenious specializations adaptations to survive on the coral reefs.

Coral reefs provide homes for 25% of all marine fish species. However, overfishing, increased pollution, degradation, and loss of coral reef habitat are threatening the survival of the fish in the coral reefs and the reef itself.

Coral Reef Bleaching

Hermatypic (reef-building) corals require warmth, light, and the salinity of undiluted seawater. They require light because of the mutualistic dinoflagellates algae (zooxanthellae) that live in their tissues. These microscopic zooxanthellae are important to the corals as their photosynthesis and fixation of carbon dioxide furnish food molecules for the corals. Also, they recycle phosphorous and nitrogenous waste compounds that otherwise would be lost and enhance the coral’s ability to deposit calcium carbonate.

Coral reef bleaching occurs when the corals expel these zooxanthellae (symbiotic algae) that live in their tissues. The corals usually do this when they are stressed by changes in light conditions, temperature, or nutrients. This eventually causes the corals to turn completely white, resulting in what is known as coral bleaching.

However, coral doesn’t necessarily die when it bleaches. Even though they can survive a bleaching event, they are under more stress and can be subject to death. Nowadays, coral bleaching is of particular concern especially because of climate changes and increased atmospheric temperature.

Coral reef bleaching is associated with global warming and the resultant increase in ocean temperature. This is because as the water warms, heat damages part of the photosynthetic processes in the zooxanthellae. Thus leading to the buildup of harmful oxidants. The oxidants diffuse into the coral tissues, destroying the finely tuned mutualistic relationship between the coral and the zooxanthellae. The zooxanthellae eventually die or are expelled in what seems to be an immune response from the coral. However, if the zooxanthellae expelled do not recolonize the coral within a few months of leaving, their absence can cause the death of individual corals and the coral colony they belong to.

Bleaching levels in 2002 on the great barrier reef in Australia were the worst recorded in history. There were 60% of the entire reef showing bleaching. In some areas, bleaching was visible in 90% of the coral present. Caribbean reefs also showed 90% bleaching which was accompanied by the death of half of the affected corals. However, Coral reef bleaching is associated with the devastation of coral reefs.

Coral bleaching can be caused by a variety of conditions:

  • Increase in seawater temperature (probably due to solar irradiance)
  • Changes in seawater chemistry  due to ocean acidification or pollution
  • Increased levels of sediment in seawater
  • Exposure of the corals to chemicals (e.g sodium cyanide used in the capture of coral reef fish)

Effect of coral reef bleaching

  • The decline of coral reef ecosystems may lead to the loss of habitat for numerous plant and animal species depending on them.
  • Populations of reef-dependent marine life and reef fishes can drop precipitously.
  • Coral bleaching can cause some species to become locally extinct.
  • Also, a degraded coral reef is vulnerable to invasive species like some kind of algae and seaweed that has the potential to bring about significant and long-lasting structural changes to affected reefs.

Dying Coral reefs

Coral reefs provide ecosystem services for fisheries, tourism, and shoreline protection. The Estimated annual global economic value of coral reefs is between US$30–375 billion and US$9.9 trillion. Hence dying coral reefs has a negative effect on our ecosystem. Coral reefs are sensitive to water conditions, hence they are fragile. This puts them under threats from excess nutrients, increased temperatures, overfishing, oceanic acidification, overfishing, sunscreen use, and some harmful land-use practices like seeps and runoff. We have to save coral reefs from dying as they are of great importance in the ecosystem.

Threats to Coral reefs

  • Ocean acidification
  • Waves
  • Weather and climate change
  • Predation
  • Pollution
  • Overfishing


  • Ocean acidification

Since an important part of the coral reefs is their calcium carbonate skeleton, ocean acidification is a major threat to coral reefs. Corals with their calcium carbonate skeletons get under stress from ocean acidification. Acidification of the ocean lowers the pH of the ocean and makes it difficult for corals and other animals that have calcium carbonate skeletons.

The rising of carbon dioxide levels in the atmosphere causes ocean acidification. Rising levels of carbon dioxide in the atmosphere are mostly from burning fossil fuels. However, the carbon dioxide is absorbed by seawater causing chemical reactions that produce carbonate and bicarbonate ions.

The Coral polyps then bring in seawater containing bicarbonate, carbonate, and calcium ions into a calcifying space. This calcifying space is between the surface of the existing skeleton and its cells. The polyps then pump hydrogen ions out of this space to produce more carbonate ions. This eventually makes it easier to make calcium carbonate (limestone) for their skeletons.

However when the oceans absorb excess carbon dioxide, as is happening nowadays. There are more bicarbonate ions and fewer carbonate ions in seawater. Thus, making it harder for corals to form their calcium carbonate skeletons. Once these reef-building corals cannot form their exoskeleton, the coral reef cannot exist. Hence ocean acidification has become a serious threat to these corals and their reefs and can result to dying coral reefs.

  • Waves

Powerful and large waves from cyclones and hurricanes can flatten or break apart large coral heads. Hence scattering their fragments. Although a single storm barely kills off an entire colony, a slow-growing coral may be overgrown by algae before they can recover.

Reefs can also be threatened by tidal emersions. This is because long periods of exceptionally low tides eventually leave shallow-water coral heads exposed. Hence damaging the reefs. However, the extent of damage depends on the time of the day and weather conditions. This is because corals exposed during daylight hours are prone to the most ultraviolet radiation. This sort of exposure can actually overheat and dry out the tissues of the coral. Hence they may become so physiologically stressed and begin to expel their symbiotic zooxanthellae, which definitely leads to bleaching. In many cases, it may lead to the death of the coral. Hence resulting in coral reefs dying.

  • Weather and climate change

Anthropogenic activities like the burning of fossil fuels and deforestation can increase greenhouse gases which causes oceanic temperatures to rise. This also changes storm patterns and contributes to the rise in sea level. These changes eventually lead to more coral bleaching events.

Also, weather-related damage occurs to reefs. Water patterns like El Nino can alter rainfall which results in an increase in sea surface temperature, increased salinity, and decreased sea level.

El Nino is a weather pattern that usually occurs in the Pacific Ocean. During this weather time, unusual winds cause warm surface water from the equator to move east. The warm surface water moves toward Central and South America. This weather can cause more rain than usual in South and Central America and also the United States.

However, Coral reefs may recover from periodic traumas caused by natural occurrences or weather. Although if they are subjected to numerous and sustained stresses including those imposed by humans, they may die as the strain may be too much for them to endure. Hence some weather-related factors are responsible for the dying coral reefs we experience nowadays.

  • Predation

Corals are vulnerable to predation as fishes, barnacles, marine worms, crabs, sea stars, and snails prey on the soft inner tissues of coral polyps. In extreme cases, if predation populations become too high, the entire reef can be ruined.

  • Pollution

Pollution is a significant threat to coral reefs. Human activities like dredging, coastal development, deforestation, agricultural activities, and sewage treatment plant operations can lead to pollutant discharges and land-based runoff. This runoff can contain sediments, insecticides, nutrients, oil, chemicals, insecticides, and debris. Once such pollutants enter the water habitat of the coral reefs, there is a negative impact. The water nutrient levels can increase and promote the rapid growth of organisms and algae that can smother corals. Moreso, debris like plastic bags can quickly become entangled on a coral and smother it.

Coral reefs can also be affected directly or indirectly by anti-fouling paints and coatings, leaking fuels, and other chemicals that enter the water. For instance, petroleum spills do not always seem to affect corals directly. This is because the oil normally stays near the water surface and much of it eventually evaporates within days into the atmosphere. However, there can be a negative impact if corals are spawning and an oil spill occurs. The sperm and eggs can be damaged because they float near the water surface before they eventually fertilize and settle. Hence, in addition to the oil pollution compromising water quality, it can also disrupt the corals’ reproductive success. Thus, making the corals vulnerable to other types of disturbances.

  • Overfishing

Coral reefs are destroyed in many areas when coral heads and brightly colored reef fishes are collected for the jewelry trade and aquarium. Some divers are careless or untrained and can trample fragile corals.

Also, many fishing techniques can be destructive. Such as blast fishing and cyanide fishing. Dynamites or other heavy explosives are used in blast fishing to startle fishes out of their hiding places. This fishing technique can crack and stress corals so much that they expel their zooxanthellae and a large section of the reefs can be destroyed. However, more than 40 countries are affected by blast fishing activities.

In cyanide fishing, cyanide is sprayed or dumped onto reefs to stun and capture live fish. This eventually kills coral polyps and degrades the coral reef. Moreso, more than 15 countries have reported activities of cyanide fishing.

Another damaging fishing technique is deep water trawling. This involves dragging the fishing net along the sea bottom. These trawlers catch fish by dragging nets along the ocean bottom. Hence, reefs in the path of the fishing net eventually get mowed down. Also, a fishing technique known as Muroami involves reefs being pounded with weighted bags to startle fish out of crevices. This definitely causes huge damage to the reef and results in dying coral reefs.

Most times, fishing nets that are left as debris can cause problems in areas of wave disturbance. For instance, live corals in shallow water can become entangled in these nets and torn away from their bases. Moreso, anchors that are dropped from fishing vessels onto reefs can break and destroy coral colonies. Also, ships that become grounded on coral reefs can cause immediate or long-term damage to the coral reefs.

How to save coral reefs?

These coral reefs are some of the Earth’s most economically valuable and biologically rich ecosystems. However, coral reefs and the magnificent creatures that live in them are in danger if actions are not taken to protect them. They are threatened by an increasing range of impacts including pollution, invasive species, diseases, bleaching, and global climate change. The rapid decline and loss of these valuable, ancient, and complex ecosystems have significant social, economic, and environmental consequences in the United States and around the world. Hence we need to save these coral reefs.

This is why the President of the United States established the U.S. Coral Reef Task Force (USCRTF) in 1998 to protect and conserve coral reefs. Therefore the USCRTF is responsible for mapping and monitoring coral reefs in the U.S. coral reefs. The task force also researches the causes of coral reef degradation and finds solutions to them. Hence the task force promotes conservation and the sustainable use of coral reefs.

How you can help save coral reefs
  1. Practice safe and responsible snorkeling and diving when visiting coral reefs.
  2. When visiting coral reefs, always take a reef-friendly approach to sun protection because some ingredients in sunscreen can kill or be harmful to corals.
  3. Try to always dispose of your trash properly and practice recycling because marine debris can cause harm to corals.
  4. Volunteer if possible to help keep the streams and rivers around you clean.
  5. The use of fertilizer should be minimized because overuse of fertilizers when washed into waterways can compromise the quality of water that these coral reefs live in.
  6. Always use modes of transportation that are eco-friendly.
  7. Try to reduce stormwater runoffs in order to prevent water pollution. You can do this by installing rain gardens or water catchments.
  8. Practice saving energy at work and at home.
  9. When buying aquarium fish try to ensure it was collected in a sustainable manner and avoid purchasing corals that are alive.
  10. Most importantly, educate people around you on how to save coral reefs and why they are important.

Why are coral reefs important?

  1. Coral reefs are important because they support more species per unit area than any other marine habitat, thus providing an ecosystem for life in the water.
  2. The biodiversity in the coral reefs is considered important to finding new medicines. Presently, many drugs are being produced from coral reef plants and animals as possible cures for arthritis, viral infections, cancer, arthritis, bacterial infections, and other diseases.
  3. Commercial and subsistence fisheries are supported by healthy coral reefs.
  4. The coral reef is also a source of food.
  5. Business opportunities and jobs are created for the local community from the existence of the coral reef through tourism and recreation.
  6. Local economies gain billions of dollars through recreational fishing trips, diving tours, hotel bookings, and restaurants patronage from visitors or tourists visiting the coral reefs.
  7. Studying coral reefs is essential to provide a clear, scientifically testable record of climatic events such as major storms or human impacts over the past years. Records of such climatic events can be recorded and studied by the changes in the growth pattern of the coral reefs.
  8. The Coral reef structure helps buffer shorelines against 97% of the energy from waves, floods, and storms. This helps to prevent erosion, property damage, and even loss of life.
  9. Coral reefs are sources of nitrogen and other vital nutrients for marine food chains.
  10. These coral reefs also assist in carbon and nitrogen-fixing in the ecosystem as well as nutrient recycling.

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