The humpback whale (Megaptera novaeangliae) is a Baleen whale, ranging in length from 12 to 16 meters and weighing approximately 36,000 kilograms. The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the water. Males produce a complex whale song, which lasts for 10 to 20 minutes and is repeated for hours at a time.
There are four global populations, all being studied. North Pacific, Atlantic, and southern ocean humpbacks have distinct populations which make an annual migration. One population in the Indian Ocean does not migrate. Found in oceans and seas around the world, humpback whales typically migrate up to 25,000km each year, feed only in summer, in polar waters, and migrating to tropical or sub-tropical waters to breed and give birth in the winter. During the winter, humpbacks fast and live off their fat reserves. The species' diet consists mostly of krill and small fish.
Identification: Humpback whales can easily be identified by their stocky bodies with obvious humps and black dorsal colouring. The head and lower jaw are covered with knobs called tubercles, which are actually hair follicles and are characteristic of the species. The long black and white tail fin, which can be up to a third of body length, and the pectoral fins have unique patterns, which enable individual whales to be recognised. Several suggestions have been made to explain the evolution of the humpback's pectoral fins, which are proportionally the longest fins of any cetacean. The two most enduring hypotheses are the higher maneuverability afforded by long fins, or that the increased surface area is useful for temperature control when migrating between warm and cold climates. Humpbacks also have 'rete mirable': a heat exchanging system, which works similarly to the same structured system in certain species of sharks and other fish.
Lifecycles: Newborn calves are roughly the length of their mother's head. A 15m mother would have a 6.1m newborn weighing in at 1.8tons. They are nursed by their mothers for approximately six months, then are sustained through a mixture of nursing and independent feeding for possibly six months more. Humpback milk is 50% fat and pink in color. Females reach sexual maturity at the age of five with full adult size being achieved a little later. According to new research, males reach sexual maturity at approximately 7 years of age. Fully grown the males average 15 to16m, with females being slightly larger at 16 to 17m, and a weight of 44 tons.
The humpback social structure is loose-knit. Usually, individuals live alone or in small transient groups that assemble and break up over the course of a few hours. Groups may stay together a little longer in summer in order to forage and feed cooperatively. Longer-term relationships between pairs or small groups, lasting months or even years, have been observed, but are rare. Recent studies extrapolate feeding bonds observed with many females in Alaskan waters over the last 10 years. It is possible some females may have these bonds for a lifetime. Whilst the range of the humpback overlaps considerably with many other whale and dolphin species, it rarely interacts socially with them although humpback calves have been observed in Hawaiian waters playing with bottlenose dolphin calves.
Courtship rituals take place during the winter months, when the whales migrate toward the equator from their summer feeding grounds. Competition for a mate is usually fierce, and female as well as mother-calf dyads are frequently trailed by unrelated male whales; groups of two to twenty males typically gather around a single female and exhibit a variety of behavior in order to establish dominance in what is known as a competitive group.
Whale song is assumed to have an important role in mate selection; however, scientists remain unsure whether the song is used between males in order to establish identity and dominance, between a male and a female as a mating call, or a mixture of the two. All these vocal and physical techniques have also been observed while not in the presence of potential mates. This indicates that they are probably important as a more general communication tool.
The manta ray, Manta birostris, is the largest of the rays, with the largest known specimen having been more than 7.6 m across, with a weight of about 2,300 kg. It ranges throughout tropical waters of the world, typically around coral reefs. Mantas have been given a variety of common names, including Atlantic manta, Pacific manta, devilfish, and just manta. Recent studies have suggested that what is called manta ray are at least two different species, one smaller local and one much larger and migratory.
Evolution and Anatomy: Manta rays may have evolved from bottom-feeders, and then adapted to become filter feeders in the open ocean, allowing them to grow larger than other ray species. Due to being plankton feeders, some of the ancestral characteristics have degenerated. For example, all that is left of their oral teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. Their dermal denticles are also greatly reduced in number and size but are still present. They have a much thicker body mucus coating than other rays. Their spiracles have become small and non-functional, as all water is taken in through their mouth instead.
They are variable in colour, ranging from black, greyish blue, to greenish or reddish brown above (black colour morph sometimes with whitish, triangular shoulder patches), and nearly black, white with various degrees of greyish blotching (the precise pattern of blotching has been used to identify individuals), to almost pure white below; one albino specimen has been reported.
Diet: Mantas feed on plankton, fish larvae and the like, passively filtered from the water passing through their gills as they swim. Small prey organisms are caught on flat horizontal plates of russet-coloured spongy tissue spanning spaces between the manta's gill bars. Mantas often swimming in slow somersaults (vertical loops) that are repeated over and over (this behaviour may keep the rays within a patch of particularly rich feeding, and may also concentrate planktonic prey to facilitate feeding); most often encountered as solitary individuals, but members of this species often aggregate in regions offering predictably rich feeding (such as off the Kona Surf Hotel at night and off Yap, in the western Caroline Islands) -- with up to 50 individuals clustered in the same general area, but not forming true schools.
Distribution: mantas are circum-tropical and generally found between 35 degrees north and south latitude, including: off southeastern South Africa, Madagascar, Mozambique, Tanzania, Kenya, and Somalia; in the Gulf of Aden, Red Sea, Arabian Sea, and the Bay of Bengal, off Burma (Myanmar), Thailand, Malaysia, Indonesia, northern Australia, New Guinea, Solomon Islands, Philippines, Kampuchia, Viet Nam, China, Korea, and southern Japan; off Guam, Palau, Yap, New Caledonia, Fiji, and Hawaii; off southern California to northern Peru, North Carolina to southern Brazil, the Azores, Senegal to Liberia. Mantas most often are found in near-shore waters (mainly over continental and insular shelves, but occasionally over deep water), near coral and rocky reefs and are usually encountered near the surface or mid-waters of lagoons or seaward reefs, particularly near surge channels.
Reproduction: Mantas are ovoviviparous, with each of the pups wrapped in a thin-shell that hatches inside the mother, later to be born alive; one specimen harpooned off North Carolina expelled a pup (with one pectoral fin wrapped above its body, and the other wrapped below) in mid-trajectory when it leaped, a behaviour which may represent spontaneous abortion (ejected prematurely due to capture stress) or be part of normal birthing (If so, what a dramatic way to enter the world!).
Typically litter size is limited to only 1 or 2 (usually 2) pups, with birthing apparently occurring in relatively shallow water, where the young remain for several years before expanding their range farther offshore. Growth of newborns is apparently very rapid, virtually doubling the disc width at birth during the first year of life; males may mature at a disc width of about 4.0-4.5 metres, females at a disc width of about 5.0-5.5 metres.
Mating behaviour in this species has been filmed off the Ogasawara Islands, Japan, and featured one or more males rapidly chasing a female for 20-30 minutes, after which one male nips the tip of either of the female's pectoral fins (which severely impairs her swimming), moves to her ventral surface, and inserts one of his claspers (paired intromittant organs, developed along the inner margins of the pelvic fins) into her cloaca (vent), thereby mating belly-to-belly; the male may hold onto the (much larger) female's pectoral fin for several minutes after removing his clasper, eventually letting her go free.
Behaviour: Mantas frequent reef-side cleaning stations where small fish such as wrasses and angelfish swim in the manta's gills and over its skin to feed, in the process cleaning it of parasites and removing dead skin. Manta rays have a symbiotic relationship with cleaner fish. The rays come to the reef hoping that friendly cleaner fish will come to them. Often times, the rays will frequent the same area over and over and these are referred to as cleaning stations. The predators of the Manta ray are mainly large sharks, however in some circumstances orcas have also been observed preying on them. Mantas are extremely curious around humans, and are fond of swimming with scuba divers. They also often surface to investigate boats without engines running. They have the largest brain-to-body ratio of the sharks and rays.
Conservation Status: Mantas seem to be fairly abundant in some areas of the world, rare or absent in others. Until we understand the extent and dynamics of Manta stocks, there is no way to assess their conservation status. Based on their low birth rate, Mantas are probably highly vulnerable to sustained fishing pressure and habitat degradation. This likelihood would seem to favor a cautionary approach to Manta exploitation and management until such time as we have the sound scientific data to make a more informed assessment of this species' risk of extinction.
So little is known about the basic biology and life history of Mantas, little can be said about their importance from a scientific or ecological standpoint. It can be argued that Mantas are important because they add to the beauty, diversity, and mystery of our world. Without Mantas, our planet would seem a significantly poorer place.
The whale shark, Rhincodon typus, is a slow moving filter feeding shark that is the largest living fish species. It can grow up to 13m in length and can weigh up to 13.6 tonnes. This distinctively-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae. The shark is found in tropical and warm oceans and lives in the open sea and can live for about 70 years. The species is believed to have originated about 60 million years ago. Although whale sharks have very large mouths, they feed mainly, though not exclusively, on plankton, microscopic plants and schools of small fish.
Naming: The species was identified in April 1828 following the harpooning of a 4.6 metre specimen in Table Bay, South Africa. It was described the following year by Andrew Smith, a military doctor associated with British troops stationed in Cape Town. He proceeded to publish a more detailed description of the species in 1849. The name "whale shark" comes from the fish's physiology; that is, a shark as large as a whale that shares a similar filter feeder eating mode.
Anatomy and appearance: This species is closely related to the bottom-dwelling sharks, Orectolobiformes, which include the wobbegong. There is a pattern of lines and spots on the skin of each shark which enables them to 'blend' into their surroundings. This 'camouflage' makes the sharks less conspicuous in their oceanic environment. The unique patterning does not change over time and can be used to identify individual sharks.
As a filter feeder it has a capacious mouth which can be up to 1.5 metres wide and can contain between 300 and 350 rows of tiny teeth. It has five large pairs of gills. Two small eyes are located towards the front of the shark's wide, flat head. The body is mostly grey with a white belly; three prominent ridges run along each side of the animal and the skin is marked with a "checkerboard" of pale yellow spots and stripes. These spots are unique to each whale shark and because of this they can be used to identify each animal and hence make an accurate population count. Its skin can be up to 10 centimetres thick. The shark has a pair each of dorsal fins and pectoral fins. A juvenile whale shark's tail has a larger upper fin than lower fin while the adult tail becomes semi-lunate (or crescent-shaped). The whale shark's spiracles are just behind the eyes.
The whale shark is not an efficient swimmer since the entire body is used for swimming, which is unusual for fish and contributes to an average speed of only around 5 km/h. The largest specimen regarded as accurately recorded was caught on November 11, 1947, near the island of Baba, not far from Karachi, Pakistan. It was 12.65 metres long, weighed more than 21.5 tonnes, and had a girth of 7 metres
Diet: The whale shark is a filter feeder - one of only three known filter feeding shark species (along with the basking shark and the megamouth shark). It feeds on macro-algae, plankton, krill, and small nektonic life such as small squid or vertebrates. The many rows of teeth play no role in feeding; in fact, they are reduced in size in the whale shark. Instead, the shark sucks in a mouthful of water, closes its mouth and expels the water through its gills. During the slight delay between closing the mouth and opening the gill flaps, plankton is trapped against the dermal denticles which line its gill plates and pharynx. This fine sieve-like apparatus, which is a unique modification of the gill rakers, prevents the passage of anything but fluid out through the gills (anything above 2 to 3 mm in diameter is trapped). Any material caught in the filter between the gill bars is swallowed.
Reproduction: The reproductive habits of the whale shark are obscure. Based on the study of a single egg recovered off the coast of Mexico in 1956, it was believed to be oviparous, but the capture of a female in July 1996 which was pregnant with 300 pups indicates that they are ovoviviparous. The eggs remain in the body and the females give birth to live young which are 40 cm to 60 cm long. It is believed that they reach sexual maturity at around 30 years and the life span has been estimated to be 70, possibly up to 100 years.It is, at present, not known where whale sharks breed. Only one pregnant whale shark has ever been recorded. There have been very few juvenile whale sharks seen at any location throughout their range.
Distribution and habitat: The whale shark inhabits the world's tropic and warm-temperate seas. While thought to be primarily pelagic, seasonal feeding aggregations of the sharks occur at several coastal cities such as Gladden Spit in Belize; Ningaloo Reef in Western Australia; Utila in Honduras; Donsol, Pasacao and Batangas in the Philippines; off Isla Mujeres and Isla Holbox in Yucatan Mexico; Ujung Kulon National Park in Indonesia; Nosy Be in Madagascar; Jangamo and Tofo reefs in southern Mozambique, and the Tanzanian islands of Mafia, Pemba and Zanzibar. Although it is often seen offshore, it has also been found closer to shore, entering lagoons or coral atolls, and near the mouths of estuaries and rivers. Its range is generally restricted to about ±30 ° latitude. It is capable of diving to depths of 700 metres (2,300 ft), and is migratory.
Migration: Whale sharks are regarded as highly migratory - although these 'migration patterns' are poorly understood. Previous research at NMP suggests the sharks may undertake a northerly migration when leaving the area. Their seasonal appearance at Christmas Island and sightings near Ashmore Reef provide support for this theory. Sadly, it is when the sharks leave Australian waters that they are potentially at risk of 'unsustainable hunting pressure'. Satellite tracking of whale sharks in US waters and also in the South China Sea reveal that whale sharks can travel great distances (1000's of kilometres). These migrations may take years to complete. A far greater understanding of whale shark movements will be possible with the continuation of tagging and tracking studies throughout the world. To date, short-term movements and behaviour of whale sharks at NMP have been successfully investigated using acoustic tracking.
It will be interesting to determine the preferred habitat of whale sharks visiting the Australian coastline. Further information on the ecology and oceanography from locations where shark sightings are common will provide a better understanding of the reasons for whale shark movements. In addition, satellite technology will enable researchers to map the movements of tagged sharks and broaden our knowledge of this species.
Natural events (e.g. weather patterns) and the particular physical geography of a region can influence productivity. Warm tropical surface-waters are often nutrient-poor, in contrast to areas of cold-water (nutrient-rich) upwellings. Some long-distance migrators travel to and from areas of increased food abundance e.g. another filter-feeder - the humpback whale. Additional information on the biology and ecology of whale sharks is needed to help with conservation and management.
Behaviour toward divers: This species, despite its size, does not pose any significant danger to humans. It is a frequently cited example when educating the public about the popular misconceptions of all sharks as "man-eaters." They are actually quite gentle and can be playful with divers. Divers and snorkelers can swim with this giant fish without any risk apart from unintentionally being struck by the shark's large tail fin.
Conservation status: The whale shark is targeted by commercial fisheries in several areas where they seasonally aggregate. The population is unknown and the species is considered vulnerable by the IUCN. All fishing, selling, importing and exporting of whale sharks for commercial purposes has been banned in the Philippines since 1998, India in May 2001, followed by Taiwan in May 20.
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2m and 40kg (Maui's Dolphin), up to 9.5m and 10tonnes (the Orca). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacean order, and relatively recent: dolphins evolved about ten million years ago, during the Miocene. Dolphins are among the most intelligent animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture.
Several species of dolphin can be observed within the area including the very acrobatic Spinner Dolphin, the Spotted Dolphin, the Common Dolphin (often schooling in mixed groups with the Spinner Dolphin), the large and curious Bottlenose Dolphin, and the shy Humpback Dolphin.
Antonomy: Dolphins have a streamlined fusiform body, adapted for fast swimming. The tail fin, called the fluke, is used for propulsion, while the pectoral fins together with the entire tail section provide directional control. The dorsal fin, in those species that have one, provides stability while swimming. Though it varies per species, basic coloration patterns are shades of grey usually with a lighter underside, often with lines and patches of different hue and contrast.
The head contains the melon, a round organ used for echolocation. In many species, elongated jaws form a distinct beak; species such as the Bottlenose have a curved mouth which looks like a fixed smile. Some species have up to 250 teeth. Dolphins breathe through a blowhole on top of their head. The trachea is anterior to the brain. The dolphin brain is large and highly complex and is different in structure from that of most land mammals. Unlike most mammals, dolphins do not have hair, except for a few hairs around the tip of their rostrum which they lose shortly before or after birth.
Senses: Most dolphins have acute eyesight, both in and out of the water, and they can hear frequencies ten times or more above the upper limit of adult human hearing. Though they have a small ear opening on each side of their head, it is believed that hearing underwater is also if not exclusively done with the lower jaw, which conducts sound to the middle ear via a fat-filled cavity in the lower jaw bone. Hearing is also used for echolocation, which all dolphins have. It is believed that dolphin teeth function as an antenna to receive incoming sound and to pinpoint the exact location of an object. The dolphin's sense of touch is also well-developed, with free nerve endings densely packed in the skin, especially around the snout, pectoral fins and genital area. However, dolphins lack an olfactory nerve and lobes and thus are believed to have no sense of smell. They do have a sense of taste and show preferences for certain kinds of fish.
Behaviour: Dolphins are social, living in pods of up to a dozen individuals. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in pods is not rigid and interchange is common. However, the cetaceans can establish strong bonds between each other. This leads to them staying with injured or ill individuals, even actively helping them to breathe by bringing them to the surface if needed.
Dolphins are known to engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is covered with scars from teeth marks made by other dolphins. It is suggested that male dolphins engage in such acts of aggression for the same reasons as humans: disputes between companions or even competition for other females. Acts of aggression can become so intense that targeted dolphins are known to go into exile, leaving their communities as a result of losing a fight with other dolphins.
Locally: During the civil war periods, Dolphins were seen as food by the local fishermen; in addition they were and still are victims of foreign trawlers illegally fishing in Mozambican waters. Although these mammals are now protected they are shy and need to regain the trust in humans. They are seen throughout the year, and best observed during calm weather and flat seas.
Sea Turtles (superfamily Chelonioidea) are turtles found in all the world's oceans except the Arctic Ocean. There are seven living species of sea turtles: Flatback, Green Turtle, Hawksbill, Kemp's Ridley, Leatherback, Loggerhead and Olive Ridley; five of which are found within southern Mozambiques waters.
Sea turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, sea turtles can quickly replace the air in their lungs. The lungs are adapted to permit a rapid exchange of oxygen and to prevent gasses from being trapped during deep dives. During routine activity green and loggerhead turtles dive for about 4 to 5 minutes and surface to breathe for 1 to 3 seconds. Turtles can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or to escape predators.
All species of sea turtles are listed as threatened or endangered. The leatherback, Kemp's ridley, and hawksbill turtles are listed as critically endangered. The olive ridley and green turtles are considered endangered, and the loggerhead is a threatened species. Historically hunting and egg collection have been the largest concerns, but now bycatch is a significant threat. Moreover, global warming may also cause a threat to sea turtles: since temperatures in the sands define the sex of the turtle while developing in the egg, many feared rising temperatures would only produce one sex, but more research remains to be done.
Green Turtles (Chelonia mydas) are the quintessential sea turtle, possessing a dorsoventrally-flattened body covered by a large, teardrop-shaped carapace and a pair of large, paddle-like flippers. Despite the turtle's common name, it is lightly-colored all around while its carapace's hues range from olive-brown to black in Eastern Pacific green turtles.
The turtle is actually named for the greenish coloration of its fat and flesh. Unlike other members of its family such as the hawksbill and loggerhead turtles, Chelonia mydas is mostly herbivorous. The adults are commonly found in shallow lagoons, feeding mostly on various species of seagrass.
Hawksbill Turtles (Eretmochelys imbricata) are a critically endangered sea turtle appearing similar to that of other marine turtles. It has a generally flattened body shape, a protective carapace, and its flipper-like arms are adapted for swimming in the open ocean. E. imbricata is easily distinguished from other sea turtles by its sharp, curving beak with prominent tomium, and the saw-like appearance of its shell margins.
While the turtle lives a part of its life in the open ocean, it is most often encountered in shallow lagoons and coral reefs where it feeds on its chosen prey, sea sponges. Some of the sponges eaten by E. imbricata are known to be highly toxic and lethal when eaten by other organisms. In addition, the sponges that hawksbills eat are usually those with high silica content, making the turtles one of few animals capable of eating siliceous organisms.
Because of human fishing practices, Eretmochelys imbricata populations around the world are threatened with extinction and the turtle has been classified as critically endangered by the World Conservation Union.
Loggerhead Turtles (Caretta caretta), The loggerhead turtle has a rusty coloured carapace. It is one of the largest cheloniid turtles, and carries more encrusting organisms such as barnacles on its carapace than the other marine turtles species. This species is distinguished mainly by its large head and strong jaws.
As with leatherbacks, loggerheads are highly migratory, making some of the longest journeys known of all marine turtle species. The possibility that juvenile loggerheads cross the Pacific Ocean has been corroborated by studies showing Baja Californian loggerheads have a genetic affinity with those found in Japan, and recently the first trans-Pacific migration of a loggerhead was recorded with a satellite transmitter. It is thought that an ability to detect wave direction and the Earth's magnetic field enables this species to navigate across open oceans.
Loggerhead turtles eat many types of invertebrates, in particular molluscs and crustaceans, and can change the seabed by "mining" the sediments for their favourite prey. Also, loggerhead turtles carry veritable animal and plant cities on their shell. As many as 100 species of animals and plants have been recorded living on one single loggerhead turtle. These animals and plants depend on turtles to have somewhere to live and to prosper. The future for many of these species is intimately linked to marine turtle survival.
Leatherback Turtles (Dermochelys coriacea) are the largest of all living sea turtles and the fourth largest modern reptile behind three crocodilians; adults average at around one to two meters long and weigh from around 250 to 700 kilograms. The largest ever found however was over three meters from head to tail and weighed 916 kilograms.
It can easily be differentiated from other modern sea turtles by its lack of a bony shell; instead, its carapace is covered by skin and oily flesh. Like other sea turtles, the leatherback's flattened forelimbs are specially adapted for swimming in the open ocean. Claws are noticeably absent from both pair of flippers. The leatherback's flippers are the largest in proportion to its body among the extant sea turtles. Leatherback front flippers can grow up to 2.7 meters in large specimens, the largest flippers (even in comparison to its body) of any sea turtle.
Adult Dermochelys coriacea subsist on a diet almost entirely composed of jellyfish. Due to its obligate feeding nature, it has been hypothesized that leatherback turtles play a role in the control of jellyfish populations.
Coral reefs are among the most diverse and productive communities on Earth. Normally found in the warm, clear, shallow waters of tropical oceans worldwide, reefs have functions ranging from providing food and shelter to fish and invertebrates to protecting the shore from erosion.
Formation: The prime reef builders (or hermatypic) corals are the stony or hard corals of the order Scleractinia in the class Anthozoa of the phylum Cnidaria. Approximately 6,000 species of Anthozoans exist, all of them marine. A coral "head", commonly perceived to be a single organism, is formed from thousands of individual but genetically identical polyps; each polyp only a few millimetres in diameter. Over thousands of generations the polyps lay down a skeleton that is characteristic of their species.
Tiny polyps of each coral consist of a fleshy sack with a ring of tentacles which sits in a limestone skeletal case, secreted by the polyp. It is the build up of this calcium carbonate that gives a reef its main structure. While corals are the chief architects of reef structure, they are not the only builders. Coralline algae cement various corals together with compounds of calcium, and other organisms such as tube worms and molluscs donate their hard skeletons. Together these organisms construct many different types of reefs.
Lifecycles: Polyps, usually a few millimeters in diameter, and are formed by a layer of outer epithelium and inner jellylike tissue known as the mesoglea. They are radially symmetrical with tentacles surrounding a central mouth, the only opening to the stomach or coelenteron, through which both food is ingested and waste expelled.
Although corals can catch small fish and animals such as plankton they obtain most of their nutrients from photosynthetic unicellular algae called zooxanthellae (Symbiodinium microadriaticu), with which they have an indispensable symbiotic relationship. Consequently, most corals depend on sunlight and grow in clear and shallow water, typically at depths shallower than 60m; other corals that do not have associated algae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3000m.
Millions of these single-celled algae are living as symbionts within their tissues. Zooxanthellae produce sugars and oxygen through photosynthesis thus helping the coral in the process of producing limestone or calcium carbonate. The algae benefit from a safe environment, and use the carbon dioxide and nitrogenous waste produced by the polyp. Due to the strain the algae can put on the polyp, stress on the coral often triggers ejection of the algae, known on a large scale as coral bleaching, as it is the algae that contribute to the brown coloration of corals; other colours, however, are due to host coral pigments.
Corals reproduce both sexually and asexually while an entire colony, many meters in diameter, can start out as a single polyp. A head of coral grows by asexual reproduction of the individual polyps. Corals also breed sexually by spawning, with corals of the same species releasing gametes simultaneously over a period of one to several nights around a full moon.
Importance: Coral reefs are among the oldest ecosystems on Earth, supporting a phenomenal diversity of species and providing irreplaceable sources of food and shelter. Although they cover less than 1% of the Earth’s surface, they are home to 25% of all marine fish species.
This importance also applies to human needs, being important for subsistence, fisheries, tourism, shoreline protection, and yielding compounds that are important in the development of new medicines (presently cancer, HIV and cardiovascular disease treatments). It is estimated that coral reefs provide $375 billion per year around the world in goods and services with at least 500 million people relying on coral reefs for food, coastal protection, and livelihoods.
Using carbon dioxide to create its limestone base coral reefs have a huge impact in controlling the amount of CO2 in the oceans and atmosphere. Without coral, the amount of carbon dioxide in the water would rise dramatically and that would affect all living things on Earth and dramatically increase global warming. In addition, coral reefs are very important because they protect coasts from strong currents and waves by slowing down the water before it gets to the shore.
Threats: It is estimated that 20% of the world’s coral reefs have been effectively destroyed in the last few decades and an additional 20% or more are severely degraded, particularly in the Caribbean Sea and Southeast Asia. Because many coral reef organisms can tolerate only a narrow range of environmental conditions, reefs are sensitive to damage from environmental changes; corals can die if the water temperature changes by more than a degree or two beyond its normal range or if the salinity of the water drops. The narrow niche that coral occupies and the stony corals' reliance on calcium carbonate deposition means they are also very susceptible to changes in water pH: Ocean acidification, caused by dissolution of carbon dioxide in the water that lowers pH, is currently occurring in the surface waters of the world's oceans due to increasing atmospheric carbon dioxide. Lowered pH reduces the ability of corals to produce calcium carbonate skeletons and, at the extreme, results in the dissolution of those skeletons entirely. Without deep and early cuts in anthropogenic CO2, scientists fear that ocean acidification may inevitably result in the severe degradation or destruction of coral species and ecosystems. Corals are also susceptible to natural diseases and dramatic natural events such as hurricanes can cause severe damage.
Population growth and urban development currently rank among the greatest threats to coral reefs. Development activities cause erosion, resulting in the run-off of sediments which eventually reaching the reefs. Also storm water runoff carries fertilizers and sewage into the ocean, damaging coral reefs. Increase of nutrient concentrations within the reef environment is followed by increase of algae, which may smother corals.
Along with human population growth, the harvest of resources from the sea is ever-increasing. Overfishing has changed the ecological dynamics of marine communities, allowing some organisms to dominate reefs that once were kept in check by large reef fish populations. Fishing practices have also become more destructive as fish populations decrease; in some regions, indiscriminate fish traps are used while in other areas the use of dynamite and cyanide have become common practice.
Cleaning Stations: A cleaning station is a location where fish and other marine life congregate to be cleaned. The cleaning process includes the removal of parasites from the animal's body (both externally and internally), and can be performed by various creatures (including cleaner shrimp and numerous species of cleaner fish, especially wrasses and gobies).
When the fish approaches a cleaning station they will pose in an 'unnatural' way to show the cleaner fish that they want to be cleaned and pose no threat, this can be pointing in a strange direction and/or opening the mouth wide. The cleaner fish will then eat the parasites directly from the skin of the cleaned fish. It will even swim into the mouth and gills of the fish to be cleaned. Cleaning stations are often associated with coral features, located either on top of a coral head or in a slot between two outcroppings.
