Reef fish - AbsoluteAstronomy.com

Coral reef fish are fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

which live amongst or in close relation to coral reef

Coral reef

Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...

s. Coral reefs form complex ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

s with tremendous biodiversity

Biodiversity

Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

. Among the myriad inhabitants, the fish stand out as particularly colourful and interesting to watch. Hundreds of species can exist in a small area of a healthy reef, many of them hidden or well camouflaged. Reef fish have developed many ingenious specialisations adapted to survival on the reefs.

Coral reefs occupy less than one percent of the surface area of the world oceans, yet they provide a home for 25 percent of all marine fish species. Reef habitats are a sharp contrast to the open water habitats that make up the other 99% of the world oceans.

However, loss and degradation of coral reef habitat, increasing pollution

Marine pollution

Marine pollution occurs when harmful, or potentially harmful effects, can result from the entry into the ocean of chemicals, particles, industrial, agricultural and residential waste, noise, or the spread of invasive organisms. Most sources of marine pollution are land based...

, and overfishing

Overfishing

Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....

including the use of destructive fishing practices

Destructive fishing practices

The phrase destructive fishing practices has been featured in international fisheries literature for around three decades. No widely accepted definition of the phrase exists, and this will almost certainly remain the situation, given very different national and industry perspectives...

, are threatening the survival of the coral reefs and the associated reef fish.

Overview

Coral reef

s are the result of millions of years of coevolution among algae, invertebrates and fish. They have become crowded and complex environments, and the fish have evolved many ingenious ways of surviving. Most fishes found on coral reefs are ray-finned fishes, known for the characteristic sharp, bony rays and spines in their fins. These spines provide formidable defences, and when erected they can usually be locked in place or are venomous

Venomous fish

Venomous fish are fish that produce venom. There are at least 1200 species of venomous fish, and they include the Stonefish, Lionfish, Scorpion Fish, Stargazer, and Toadfish .-See also:* Hallucinogenic fish...

. Many reef fish have also evolved cryptic coloration to confuse predators.

Reef fish have also evolved complex adaptive behaviours

Adaptive behavior (ecology)

In behavioral ecology an adaptive behavior is a behavior which contributes directly or indirectly to an individual's survival or reproductive success and is thus subject to the forces of natural selection...

. Small reef fish get protection from predators by hiding in reef crevices or by shoaling and schooling

Shoaling and schooling

In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...

. Many reef fish confine themselves to one small neighbourhood where every hiding place is known and can be immediately accessed. Others cruise the reefs for food in shoals, but return to a known area to hide when they are inactive. Resting small fish are still vulnerable to attack by crevice predators, so many fish, such as triggerfish

Triggerfish

Triggerfishes are about 40 species of often brightly colored fishes of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific...

, squeeze into a small hiding place and wedge themselves by erecting their spines.

As an example of the adaptations made by reef fish, the yellow tang

Yellow tang

The yellow tang is a saltwater fish species of the family Acanthuridae. It is one of the most popular aquarium fish.-Appearance:...

is a herbivore

Herbivore

Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

which feeds on benthic turf algae. They also provide cleaner services to marine turtles, by removing algal growth from their shells. They do not tolerate other fish with the same colour or shape. When alarmed, the usually placid yellow tang can erect spines in its tail and slash at its opponent with rapid sideways movements.

Diversity and distribution

Coral reef

s contain the most diverse fish assemblages to be found anywhere on earth, with perhaps as many as 6,000-8,000 species that can be found dwelling within coral reef ecosystems of the world's oceans.

The mechanisms that first led to, and continue to maintain, such concentrations of fish species on coral reefs has been widely debated over the last 50 years. While many reasons have been proposed, there is no general scientific consensus on which of these is the most influential, but it seems likely that a number of factors contribute. These include the rich habitat complexity and diversity inherent in coral reef ecosystems, the wide variety and temporal availability of food resources available to coral reef fishes, a host of pre and post larval settlement processes, and as yet unresolved interactions between all these factors.

There are two major regions of coral reef development recognized; the Indo-Pacific (which includes the Pacific and Indian Oceans as well as the Red Sea), and the tropical western Atlantic (also known as the "wider" or "greater" Caribbean). Each of these two regions contains its own unique coral reef fish fauna with no natural overlap in species. Of the two regions, the richest by far in terms of reef fish diversity is the Indo-Pacific where there are an estimated 4,000-5,000 species of fishes associated with coral reef habitats. Another 500-700 species can be found in the greater Caribbean region.

Body shape

Most reef fishes have body shapes that are different from open water fishes. Open water fishes are usually built for speed in the open sea, streamlined like torpedoes to minimise friction as they move through the water. Reef fish are operating in the relatively confined spaces and complex underwater landscapes of coral reefs. For this manoeuvrability is more important than straight line speed, so coral reef fish have developed bodies which optimize their ability to dart and change direction. They outwit predators by dodging into fissures in the reef or playing hide and seek around coral heads.

Many reef fish, such as butterflyfish

Butterflyfish

The butterflyfish are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Found mostly on the reefs of the Atlantic, Indian and Pacific Oceans, there are approximately 120 species in 10 genera...

and angelfishes, have evolved bodies which are deep and laterally compressed like a pancake. Their pelvic and pectoral fins are designed differently, so they act together with the flattened body to optimise manoeuvrability.

Colouration

Coral reef fishes exhibit a huge variety of dazzling and sometimes bizarre colours and patterns. This is in marked contrasts to open water fishes which are usually countershaded

Countershading

Countershading, or Thayer's Law, is a form of camouflage. Countershading, in which an animal’s pigmentation is darker dorsally, is often thought to have an adaptive effect of reducing conspicuous shadows cast on the ventral region of an animal’s body...

with silvery colours.

The patterns have different functions. Sometimes they camouflage the fish when the fish rests in places with the right background. Colouration can also be used to help species recognition during mating. Some unmistakable contrasting patterns are used to warn predators that the fish has venomous spines or poisonous flesh.

The foureye butterflyfish

Foureye butterflyfish

The Four-eyed Butterflyfish is a butterflyfish . It is alternatively called the Foureye Butterflyfish. This species is found in the Western Atlantic from Massachusetts, USA and Bermuda to the West Indies and northern South America.Chaetodon capistratus is the type species of Chaetodon...

gets its name from a large dark spot on the rear portion of each side of the body. This spot is surrounded by a brilliant white ring, resembling an eyespot

Eyespot (mimicry)

An eyespot is an eye-like marking. They are found on butterflies, reptiles, birds and fish. In members of the Felidae family , the white circular markings on the backs of the ears are termed ocelli, and they are functionally similar to eyespots in other animals.Eyespots may be a form of...

. A black vertical bar on the head runs through the true eye, making it hard to see. This can result in a predator thinking the fish is bigger than it is, and confusing the back end with the front end. The butterflyfish's first instinct when threatened is to flee, putting the false eyespot closer to the predator than the head. Most predators aim for the eyes, and this false eyespot tricks the predator into believing that the fish will flee tail first. When escape is not possible, the butterflyfish will sometimes turn to face its aggressor, head lowered and spines fully erect, like a bull about to charge. This may serve to intimidate the other animal or may remind the predator that the butterflyfish is too spiny to make a comfortable meal.

Just as some prey species evolved cryptic colouration and patterns to help avoid predators, some ambush predator

Ambush predator

Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...

s evolved camouflage that lets them ambush their prey. The tassled scorpionfish

Tassled scorpionfish

The tassled scorpionfish, Scorpaenopsis oxycephala, is a carnivorous ray-finned fish with venomous spines that lives in the Indian and Pacific oceans....

is an ambush predator that looks like part of a sea floor encrusted with coral and algae. It lies in wait on the sea floor for crustaceans and small fish, such as gobies, to pass by.

Gobies avoid predators by tucking themselves into coral crevices or partly burying themselves in sand. They continually scan for predators with eyes that swivel independently. The camouflage of the tassled scorpionfish can prevent gobies from seeing them until it's too late.

The clown triggerfish

Clown Triggerfish

The clown triggerfish, Balistoides conspicillum, is a triggerfish from the order Tetraodontiformes. This reef-associated fish is commonly found in the tropical Indo-Pacific-Distribution and habitat:...

has strong jaws for crushing and eating sea urchins, crustaceans and hard-shell molluscs. Its ventral (lower) surface has large, white spots on a dark background, and its dorsal (upper) surface has black spots on yellow. This is a form of countershading

Countershading

: from below, the white spots look like the lighted surface of the water above; and from above, the fish blends more with the coral reef below. The brightly painted yellow mouth may deter potential predators.

Feeding strategies

Many reef fish species have evolved different feeding strategies accompanied by specialized mouths, jaws and teeth particularly suited to deal with their primary food sources found in coral reef ecosystems. This is not surprising, given the huge variety in the types of prey on offer around coral reefs.

For example, the primary food source of butterflyfish

Butterflyfish

es are the coral pol

POL

-Given name:*Pol Amat , field hockey player from Spain*Pol Antràs , Spanish economist*Pol Cruchten , Luxembourgian film director and producer*Pol Espargaró , Grand Prix motorcycle racer...

yps themselves or the appendages of polychaete

Polychaete

The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...

s and other small invertebrate animals. Their mouths protrude like forceps, and are equipped with fine teeth that allow them to nip off such exposed body parts of their prey. Parrotfish

Parrotfish

Parrotfishes are a group of fishes that traditionally had been considered a family , but now often are considered a subfamily of the wrasses. They are found in relatively shallow tropical and subtropical oceans throughout the world, but with the largest species richness in the Indo-Pacific...

es eat algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

growing on reef surfaces, utilizing mouths like beaks well adapted to scrape off their food. Other fish, like snapper

Lutjanidae

Snappers are a family of perciform fish, mainly marine but with some members inhabiting estuaries, feeding in freshwater. Some are important food fish. One of the best known is the red snapper....

, are generalized feeders with more standard jaw and mouth structures that allow them to forage on a wide range of animal prey types, including small fishes and invertebrates.

Generalized carnivores

Carnivore

A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

s are the most diverse of feeding types among coral reef fishes. There are many more carnivore species on the reefs than herbivore

Herbivore

s. Competition among carnivores is intense, resulting in a treacherous environment for their prey. Hungry predators lurk in ambush or patrol every part of the reef, night and day.

Some fishes associated with reefs are generalized carnivores that feed on a variety of animal prey. These typically have large mouths that can be rapidly expanded, thereby drawing in nearby water and any unfortunate animals contained within the inhaled water mass. The water is then expelled through the gills with the mouth closed, thereby trapping the helpless prey For example, the bluestripe snapper

Bluestripe snapper

The bluestripe snapper, Lutjanus kasmira, is a common species of marine fish of the snapper family Lutjanidae...

has a varied diet

Diet (nutrition)

In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...

, feeding on fish

Fish

es, shrimp

Shrimp

Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

s, crab

Crab

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s, stomatopods, cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s and planktonic crustaceans, as well as plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

and algae

Algae

material. Diet varies with age, location and the prevalent prey items locally.

Goatfish

Goatfish

Goatfishes are tropical marine perciform fish of the family Mullidae. Seldom found in brackish waters, goatfish are most associated with the reefs of the Atlantic, Indian, and Pacific Oceans...

are tireless benthic feeders, using a pair of long chemosensory barbel

Barbel (anatomy)

A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...

s (whiskers) protruding from their chins to rifle through the sediments in search of a meal. Like goats, they seek anything edible: worm

Worm

The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...

s, crustaceans, molluscs and other small invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s are staples. The yellowfin goatfish (Mulloidichthys vanicolensis) often schools with the blue-striped snapper. The yellowfins change their colouration to match that of the snapper. Presumably this is for predator protection, since goatfish are a more preferred prey than bluestripe snapper. By night the schools disperse and individual goatfish head their separate ways to loot the sands. Other nocturnal feeders shadow the active goatfish, waiting patiently for overlooked morsels.

Moray eel

Moray eel

Moray eels are cosmopolitan eels of the family Muraenidae. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water and a few, for example the freshwater moray can sometimes be found in freshwater...

s and coral groupers (Plectropomus pessuliferus) are known to cooperate with each other when hunting. Grouper

Grouper

Groupers are fish of any of a number of genera in the subfamily Epinephelinae of the family Serranidae, in the order Perciformes.Not all serranids are called groupers; the family also includes the sea basses. The common name grouper is usually given to fish in one of two large genera: Epinephelus...

are protogynous hermaphrodite

Hermaphrodite

In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...

s, who school in harems
Harem (zoology)
The term harem is used in zoology to describe the social organization of certain herbivore species, such as those in the Hominidae and Equidae families, into groups of females and young surrounding a single dominant male...

of three to fifteen females. When no male is available, the most aggressive and largest females shift sex to male, probably as a result of behavioural triggers.

Specialised carnivores

Large schools

Shoaling and schooling

of forage fish

Forage fish

Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...

, such as surgeonfish and cardinalfish, move around the reef feeding on tiny zooplankton

Zooplankton

Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...

. The forage fish are, in turn, eaten by larger fish, such as the bigeye trevally. Fish receive many benefits from schooling behaviour

Shoaling and schooling

, including defence against predators through better predator detection, since each fish is on the lookout. Schooling fish have developed remarkable displays of precise choreography which confuse and evade predators. For this they have evolved special pressure sensors along their sides, called lateral line

Lateral line

The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...

s, that let them feel each other's movements and stay synchronized.

Bigeye trevally

Bigeye trevally

The bigeye trevally, Caranx sexfasciatus , is a species of widespread large marine fish classified in the jack family Carangidae...

also form schools. They are swift predators who patrol the reef in hunting packs. When they find a school of forage fish, such as cardinalfish, they surround them and herd them close to the reef. This panics the prey fish, and their schooling becomes chaotic, leaving them open to attack by the trevally.
The titan triggerfish

Titan triggerfish

The titan triggerfish, giant triggerfish or moustache triggerfish is a large species of triggerfish found in lagoons and at reefs in most of the Indo-Pacific, though it is absent from Hawaii...

can move relatively large rocks when feeding and is often followed by smaller fishes that feed on leftovers. They also use a jet of water to uncover sand dollar

Sand dollar

The term Sand dollar refers to species of extremely flattened, burrowing echinoids belonging to the order Clypeasteroida. Some species within the order, not quite as flat, are known as sea biscuits...

s buried in sand.

Barracuda

Barracuda

The barracuda is a ray-finned fish known for its large size and fearsome appearance. Its body is long, fairly compressed, and covered with small, smooth scales. Some species could reach up to 1.8m in length and 30 cm in width...

are ferocious predators on other fishes, with razor-sharp conical teeth which make it easy for them to rip their prey to shreds. Barracuda patrol the outer reef in large schools, and are extremely fast swimmers with streamlined, torpedo-shaped bodies.

Porcupinefish

Porcupinefish

Porcupinefish are fish of the family Diodontidae, , also commonly called blowfish ....

are medium to large sized, and are usually found swimming among or near coral reefs. They inflate their body by swallowing water, reducing potential predators to those with much bigger mouths.
Fish can not groom themselves. Some fish specialise as cleaner fish

Cleaner fish

Cleaner fish are fish that provide a service to other fish species by removing dead skin and ectoparasites. This is an example of mutualism, an ecological interaction that benefits both parties involved. A wide variety of fishes have been observed to display cleaning behaviors including wrasses,...

, and establish cleaning station

Cleaning station

A cleaning station is a location where fish, sea turtles, hippo and other aquatic life, freshwater and marine, congregate to be cleaned.The cleaning process includes the removal of parasites from the animal's body , and can be performed by various creatures A cleaning station is a location where...

s where other fish can come to have their parasites nibbled away. The "resident fish doctor and dentist on the reef is the bluestreak cleaner wrasse

Bluestreak cleaner wrasse

The bluestreak cleaner wrasse is one of several species of cleaner wrasse found on coral reefs in the Indian Ocean and much of the Pacific Ocean, as well as many seas, including the Red Sea and those around Southeast Asia...

". The bluestreak is marked with a conspicuous bright blue stripe and behaves in a stereotypical way which attracts larger fish to its cleaning station. As the bluestreak snacks on the parasites it gently tickles its client. This seems to bring the larger fish back again for regular servicing.

The reef lizardfish secretes a mucus coating which reduces drag when they swim and also protects it from some parasites. But other parasites find the mucus itself good to eat. So lizardfish visit the cleaner wrasse, which clean the parasites from the skin, gills and mouth.

Herbivores

Herbivore

s feed on plants. The four largest groups of coral reef fishes that feed on plants are the parrotfish

Parrotfish

es, damselfish

Damselfish

Damselfish comprise the family Pomacentridae except those of the genera Amphiprion and Premnas. They can grow up to long. While most are marine, a few species inhabit the lower stretches of rivers in freshwater. Damselfish usually have bright colors. in tropical coral reefs, and many of those are...

es, rabbitfish

Rabbitfish

Rabbitfishes or spinefoots are perciform fishes in the family Siganidae. The 28 species are in a single genus, Siganus. In some now obsolete classifications, the species having prominent face stripes—colloquially called foxfaces–are in the genus Lo. Other species like the Masked...

es, and surgeonfishes. All feed primarily on microscopic

Microscopic

The microscopic scale is the scale of size or length used to describe objects smaller than those that can easily be seen by the naked eye and which require a lens or microscope to see them clearly.-History:...

and macroscopic

Macroscopic

The macroscopic scale is the length scale on which objects or processes are of a size which is measurable and observable by the naked eye.When applied to phenomena and abstract objects, the macroscopic scale describes existence in the world as we perceive it, often in contrast to experiences or...

algae

Algae

growing on or near coral reefs.

Algae

Algae

can drape reefs in kaleidoscopes of colours and shapes. Algae are primary producers

Primary producers

Primary producers are those organisms in an ecosystem that produce biomass from inorganic compounds . In almost all cases these are photosynthetically active organisms...

, which means they are plants synthesising food directly from solar energy and carbon dioxide and other simple nutrient molecules. Without algae, everything on the reef would die. One important algal group, the bottom dwelling (benthic) algae, grows over dead coral and other inert surfaces, and provides grazing fields for herbivore

Herbivore

s such as parrotfish.

Parrotfish

Parrotfish

are named for their parrot-like beaks and bright colours. They are large herbivores that graze on the algae that grows on hard dead corals. Equipped with two pairs of crushing jaws and their beaks, they pulverize chunks of algae-coated coral, digesting the algae and excreting the coral as fine sand.

Smaller parrotfish are relatively defenceless herbivores, poorly defended against predators like barracuda. They have evolved to find protection by schooling

Shoaling and schooling

, sometimes with other species like shoaling rabbitfish

Rabbitfish

. Spinefoot rabbitfish are named for their defensive venomous spines, and they are seldom attacked by predators. Spines are a last ditch defence. It is better to avoid predator detection in the first place, and avoid being thrust into risky spine-to-fang battles. So rabbitfish have also evolved skilful colour changing abilities.

Damselfish

Damselfish

are a group of species that feed on zooplankton

Zooplankton

and algae, and are an important reef forage fish

Forage fish

for larger predators. They are small, typically five centimetres (two inches) long. Many species are aggressive towards other fishes which also graze on algae, such as surgeonfish. Surgeonfish sometimes use schooling as a countermeasure to defensive attacks by solitary damselfish.

Symbiosis

Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

refers to two species that have a close relationship with each other. The relationship can be mutualistic, when both species benefit from the relationship, commensalistic

Commensalism

In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...

, when one species benefits and the other is unaffected, and parasitistic

Parasitism

Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

, when one species benefits, and the other is harmed.

An example of commensalism occurs between the hawkfish

Hawkfish

Hawkfish are strictly tropical, perciform marine fish of the family Cirrhitidae. Associated with the coral reefs of the western and eastern Atlantic and Indo-Pacific, the hawkfish family contains 12 genera and 32 species. They share many morphological features with the scorpionfish of the family...

and fire coral

Fire coral

Fire corals are colonial marine organisms that look rather like real coral. However they are technically not corals; they are actually more closely related to jellyfish and other stinging anemones...

. Thanks to their large, skinless pectoral fins, hawkfish can perch on fire corals without harm. Fire corals are not true coral

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

s, but are hydrozoa

Hydrozoa

Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...

ns possessing stinging cells called nematocysts which would normally prevent close contact. The protection fire corals offer hawkfish means the hawkfish has the high ground of the reef, and can safely survey its surroundings like a hawk

Hawk

The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...

. Hawkfish usually stay motionless, but dart out and grab crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s and other small invertebrate

Invertebrate

s as they pass by. They are mostly solitary, although some species form pairs and share a head of coral.

A more bizarre example of commensalism occurs between the slim, eel-shaped pinhead pearlfish

Pearlfish

Pearlfish is a general name for a variety of marine fish species in the Carapidae family. Pearlfish have been found in tropical waters of the Atlantic, Indian, and Pacific Oceans at depths up to along oceanic shelves and slopes....

and a particular species of sea cucumber

Sea cucumber

Sea cucumbers are echinoderms from the class Holothuroidea.They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. There are a number of holothurian species and genera, many of which are targeted...

. The pearlfish enters the sea cucumber through its anus, and spends the day safely protected inside the seacucumbers alimentary tract. At night it emerges the same way and feeds on small crustaceans.

Sea anemone

Sea anemone

Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...

s are common on reefs. The tentacle

Tentacle

A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...

s of sea anemones bristle with tiny harpoons (nematocysts) primed with toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

s, and are an effective deterrent against most predators. However, saddle butterflyfish

Saddle butterflyfish

The Saddle Butterflyfish, Chaetodon ephippium, is a species of butterflyfish . It is found in the Indian and Pacific Oceans from Sri Lanka and the Cocos-Keeling Islands to the Hawaiian, Marquesan and Tuamoto islands, north to southern Japan, south to Rowley Shoals and New South Wales in...

, which are up to 30 cm (12 in) long, have developed a resistance to these toxins. Saddle butterflyfish usually flutter gently rather than swim. But in the presence of their preferred food, sea anemones, this gentleness disappears, and the butterflyfish dash in and out, ripping off the anemone tentacles.

However, there is a mutualistic relationship between sea anemones and clownfish

Clownfish

Clownfish or anemonefish are fishes from the subfamily Amphiprioninae in the family Pomacentridae. Twenty-eight species are recognized, one in the genus Premnas, while the remaining are in the genus Amphiprion. In the wild they all form symbiotic mutualisms with sea anemones...

. This gives the sea anemones a second line of defence. They are guarded by fiercely territorial clownfish

Clownfish

, who are also immune to the anemone toxins. To get their meal, butterflyfish must get past these protective clownfish who, although smaller, are not intimidated. An anemone without its clownfish will quickly be eaten by butterflyfish. In return, the anemones provide the clownfish protection from their predators, who are not immune to anemone stings. As a further benefit to the anemone, waste ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

from the clownfish feed symbiotic algae

Algae

found in the anemone's tentacles.

Toxicity

Many reef fish are toxic. Toxic fish are fish which contain strong toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

s in their bodies. There is a distinction between poisonous fish and venomous fish

Venomous fish

. Both types of fish contain strong toxins, but the difference is in the way the toxin is delivered. Venomous fish deliver their toxins (called venom

Venom

Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

) by biting, stinging, or stabbing, causing an envenomation

Envenomation

Envenomation is the process by which venom is injected into some animal by the bite of a venomous animal. Many kinds of animals, including mammals , reptiles , spiders , insects , employ venom for hunting and for self defense...

. Venomous fish don't necessarily cause poisoning if they are eaten, since the venom is often destroyed in the digestive system. By contrast, poisonous fish contain strong toxins which are not destroyed by the digestive system. This makes them poisonous to eat.

Venomous fish carry their venom in venom glands and use various delivery systems, such as spines or sharp fins, barbs or spikes, and fangs. Venomous fish tend to be either very visible, using flamboyant colours to warn enemies, or skilfully camouflaged and maybe buried in the sand. Apart from the defence or hunting value, venom might have value for bottom dwelling fish by killing the bacteria that try to invade their skin. Few of these venoms have been studied. They are a yet to be tapped resource for bioprospecting to find drugs with medical uses.

The most venomous known fish is the reef stonefish. It has a remarkable ability to camouflage itself amongst rocks. It is an ambush predator

Ambush predator

that sits on the bottom waiting for prey to come close. It does not swim away if disturbed, but erects 13 venomous spines along its back. For defence, it can shoot venom from each or all of these spines. Each spine is like a hypodermic needle, delivering the venom from two sacs attached to the spine. The stonefish has control over whether to shoot its venom, and does so when provoked or frightened. The venom results in severe pain, paralysis and tissue death, and can be fatal if not treated. Despite its formidable defence, the stonefish does have predators. Some bottom feeding rays and sharks with crushing teeth feed on them, as does the Stokes' seasnake

Astrotia stokesii

Commonly known as Stokes' seasnake, Astrotia stokesii is a large species of sea snake found in tropical Indo-Pacific oceanic waters.-Description:...

Unlike the stonefish which can shoot venom, the lionfish

Pterois

Pterois is a genus of venomous marine fish found mostly in the Indo-Pacific, known collectively as the lionfish. Pterois is characterized by red, white and black stripes, showy pectoral fins and venomous spiky tentacles. Pterois are classified into fifteen different species, but Pterois radiata,...

can only release venom when something strikes its spines. Although not native to the US coast, lionfish have appeared around Florida and have spread up the coast to New York. They are attractive aquarium fish, sometimes used to stock ponds, and may have been washed into the sea during a hurricane. Lionfish can aggressively dart at scuba divers and attempt to puncture the facemask with their venomous spines.

The spotted trunkfish

Spotted trunkfish

The Spotted Trunkfish is a member of the family Ostraciidae. It can be found in reefs throughout the Pacific Ocean and Indian Ocean as well as the south eastern Atlantic Ocean...

is a reef fish which secretes a colourless ciguatera

Ciguatera

Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...

toxin from glands on its skin when touched. The toxin is only dangerous when ingested, so there's no immediate harm to divers. However, predators as large as nurse sharks

Nurse sharks

Ginglymostomatidae is a cosmopolitan family of carpet sharks, containing the three monotypic genera of nurse sharks. Common in shallow, tropical and subtropical waters, these sharks are sluggish and docile bottom-dwellers...

can die as a result of eating a trunkfish. Ciguatera toxins appear to accumulate in top predators of coral reefs. Many of the Caribbean groupers and the barracuda for example may contain enough of this toxin to cause severe symptoms in humans who eat them. What makes the situation particularly dangerous is that such species may be toxic only at certain sizes or locations, making it difficult to know whether or when they are or are not safe to eat. In some locations this leads to many cases of ciguatera poisoning among tropical islanders.

The stargazer

Stargazer

The stargazers are a family Uranoscopidae of perciform fish that have eyes on top of their heads . The family includes about 50 species in 8 genera, all marine and found worldwide in shallow waters....

buries itself in sand and can deliver electric shocks as well as venom. It is a delicacy in some cultures (the venom is destroyed when it is cooked), and can be found for sale in some fish market

Fish market

A fish market is a marketplace used for marketing fish products. It can be dedicated to wholesale trade between fishermen and fish merchants, or to the sale of seafood to individual consumers, or to both...

s with the electric organ removed. They have been called "the meanest things in creation".

The giant moray

Giant moray

The giant moray is the largest of the Moray eels, in terms of body mass .-Range:The giant moray is widespread in the Indo-Pacific region, being found in the Red Sea and East Africa, the Pitcairn group, north to the Ryukyu and Hawaiian islands, south to New Caledonia, Fiji and the Austral...

is a reef fish at the top of the food chain

Food chain

A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

. Like many other apex reef fish, it is likely to cause ciguatera

Ciguatera

poisoning if eaten. Outbreaks of ciguatera poisoning in the 11th to 15th centuries from large, carnivorous reef fish, caused by harmful algal blooms, could be a reason why Polynesians migrated to Easter Island, New Zealand, and possibly Hawaii.

Reef sharks and rays

Coral reefs in the Indo-Pacific are dominated by whitetip

Whitetip reef shark

The whitetip reef shark is a species of requiem shark, family Carcharhinidae, and the only member of its genus. A small shark usually not exceeding in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval...

, blacktip

Blacktip reef shark

The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins...

and grey reef shark. Coral reefs in the western Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

are dominated by the Caribbean reef shark

Caribbean reef shark

The Caribbean reef shark is a species of requiem shark, family Carcharhinidae. It is found in the tropical waters of the western Atlantic Ocean from Florida to Brazil, and is the most commonly encountered reef shark in the Caribbean Sea...

. These sharks are all species of requiem shark

Requiem shark

Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...

, and all have the robust, streamlined bodies that are typical of the requiem shark

Requiem shark

. They are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopods. Other species of reef sharks include the Galapagos shark

Galapagos shark

The Galapagos shark is a species of requiem shark, family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species...

, the tawny nurse shark

Tawny nurse shark

The tawny nurse shark is a species of carpet shark in the family Ginglymostomatidae, and the only extant member of the genus Nebrius. It is found widely along coastlines in the Indian and Pacific Oceans, preferring reefs, sandy flats, and seagrass beds from very shallow water to a depth of 70 m...

and hammerheads

Hammerhead shark

The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the...

.

The whitetip reef shark

Whitetip reef shark

is a small shark usually less than 1.6 m (5.2 ft) in length. It is associated almost exclusively with coral reefs where it can be encountered around coral heads and ledges with high vertical relief, or over sandy flats, in lagoon

Lagoon

A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...

s, or near drop-offs to deeper water. They prefer very clear water and rarely swim far from the bottom. Whitetip reef sharks spend most of the daytime time resting inside caves. Unlike other requiem sharks, which usually rely on ram ventilation and must constantly swim to breathe, this shark can pump water over its gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s and lie still on the bottom. They have slender, lithe body, which allows them to wriggle into crevices and holes and extract prey inaccessible to other reef sharks. On the other hand, they are rather clumsy when attempting to take food suspended in open water.
The whitetip reef shark does not frequent very shallow water like the blacktip reef shark, nor the outer reef like the grey reef shark. They generally remain within a highly localized area. An individual shark may use the same cave for months to years. The daytime home range

Home range

Home range is the area where an animal lives and travels in. It is closely related to, but not identical with, the concept of "territory".The concept that can be traced back to a publication in 1943 by W. H. Burt, who constructed maps delineating the spatial extent or outside boundary of an...

of a whitetip reef shark is limited to about 0.05 square kilometre, and at night this range increases to 1 square kilometre.

The whitetip reef shark is highly responsive to olfactory

Olfaction

Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

, acoustic

Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

, and electrical cues given off by potential prey. Its visual system is attuned more to movement and/or contrast than to object details. It is especially sensitive to natural and artificial low-frequency sounds in the 25–100 Hz range, which evoke struggling fish. They hunt primarily at night, when many fishes are asleep and easily taken. After dusk, a group of sharks may target the same prey item, covering every exit route from a particular coral head. Each shark hunts for itself and in competition with the others in its group. They feed mainly on bony fishes, including eel

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

s, squirrelfishes, snapper

Lutjanidae

Snappers are a family of perciform fish, mainly marine but with some members inhabiting estuaries, feeding in freshwater. Some are important food fish. One of the best known is the red snapper....

s, damselfish

Damselfish

es, parrotfish

Parrotfish

es, surgeonfishes, triggerfish

Triggerfish

es, and goatfish

Goatfish

Goatfishes are tropical marine perciform fish of the family Mullidae. Seldom found in brackish waters, goatfish are most associated with the reefs of the Atlantic, Indian, and Pacific Oceans...

es, as well as octopus

Octopus

The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...

, spiny lobster

Spiny lobster

Spiny lobsters, also known as langouste or rock lobsters, are a family of about 45 species of achelate crustaceans, in the Decapoda Reptantia...

s, and crab

Crab

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s. Important predators of the whitetip reef shark include tiger shark

Tiger shark

The tiger sharks, Galeocerdo cuvier, is a species of requiem shark and the only member of the genus Galeocerdo. Commonly known as sea tigers, tiger sharks are relatively large macropredators, capable of attaining a length of over . It is found in many tropical and temperate waters, and is...

s and Galapagos shark

Galapagos shark

s.
The blacktip reef shark

Blacktip reef shark

The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins...

is typically about 1.6 m (5.2 ft) long. It is usually found over reef ledges and sandy flats, though it can also enter brackish and freshwater

Freshwater

Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

environments. This species likes shallow water, while the whitetip

Whitetip reef shark

and the grey reef shark are prefer deeper water. Younger sharks favour shallow sandy flats, and older sharks spend more time around reef ledges and near reef drop-offs. Blacktip reef sharks are strongly attached to their own area, where they may remain for up to several years. A tracking study off Palmyra Atoll

Palmyra Atoll

Palmyra Atoll is an essentially unoccupied equatorial Northern Pacific atoll administered as an unorganized incorporated territory by the United States federal government...

in the central Pacific has found that the blacktip reef shark had a home range of about 0.55 square kilometre, among the smallest of any shark species. The size and location of the range does not change with time of day. The blacktip reef shark may be encountered alone or in small groups. Large social aggregations have also been observed. They are active predators of small bony fishes, cephalopod

Cephalopod

s, and crustacean

Crustacean

s, and also feed on sea snakes and seabird

Seabird

Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...

s. Blacktip reef sharks are preyed on by grouper

Grouper

s, grey reef sharks, tiger shark

Tiger shark

s, and members of their own species. At Palmyra Atoll, adult blacktip reef sharks avoid patrolling tiger sharks by staying out of the central, deeper lagoon.

Grey reef sharks are usually less than 1.9 metres (6.2 ft) long. Despite their moderate size, grey reef sharks actively expel most other shark species from favored habitats. In areas where this species co-exists with the blacktip reef shark, the latter species occupy the shallow flats while the grey reef sharks stay in deeper water. Many grey reef sharks have a home range on a specific area of the reef, to which they continually return. However, they are social rather than territorial. During the day, these sharks often form groups of 5–20 individuals near coral reef drop-offs, splitting up in the evening as the sharks begin to hunt. They are found over continental and insular shelves, preferring the leeward (away from the direction of the current) sides of coral reefs with clear water and rugged topography. They are frequently found near the drop-offs at the outer edges of the reef, and less commonly within lagoon

Lagoon

s. On occasion, this shark may venture several kilometers out into the open ocean

Pelagic zone

Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

.
Shark researcher Leonard Compagno

Leonard Compagno

Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...

comments on the relationship between the three species.

"[The grey reef shark] ...shows microhabitat separation from the blacktip reef sharks; around islands where both species occur, the blacktip occupies shallow flats, while the grey reef shark is usually found in deeper areas, but where the blacktip is absent, the grey reef shark is commonly found on the flats... [The grey reef shark] complements the whitetip shark as it is far more adapt at catching off-bottom fish than the whitetip, but the later is far more competent in extracting prey from crevices and holes in reefs."

The Caribbean reef shark

Caribbean reef shark

is up to 3 metres (10 ft) long, one of the largest apex predator

Apex predator

Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...

s in the reef ecosystem

Ecosystem

. Like the whitetip reef shark, they have been documented resting motionless on the sea bottom or inside caves, unusual behaviour for requiem sharks. Caribbean reef shark play a major role in shaping Caribbean reef communities. They are more active at night, with no evidence of seasonal changes in activity or migration

Fish migration

Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...

. Juveniles tend to remain in a localized area throughout the year, while adults range over a wider area. The Caribbean reef shark feeds on a wide variety of reef-dwelling bony fishes and cephalopods, as well as some elasmobranchs such as eagle ray

Eagle ray

The eagle rays are a group of cartilaginous fishes in the family Myliobatidae, consisting mostly of large species living in the open ocean rather than on the sea bottom....

s and yellow stingray

Yellow stingray

The yellow stingray is a species of stingray in the family Urotrygonidae, found in the tropical western Atlantic Ocean from North Carolina to Trinidad. This bottom-dwelling species inhabits sandy, muddy, or seagrass bottoms in shallow inshore waters, commonly near coral reefs...

s . Young sharks feed on small fishes, shrimps, and crabs. In turn, young sharks are preyed on by larger sharks such as the tiger shark

Tiger shark

and the bull shark

Bull shark

The bull shark, Carcharhinus leucas, also known as Zambezi shark or unofficially known as Zambi in Africa and Nicaragua shark in Nicaragua, is a shark common worldwide in warm, shallow waters along coasts and in rivers...

External links

Featured Creatures in Coral Reefs at the Smithsonian Ocean Portal
Coral Reef Fishes: Adaptations, Diversity, and Economic Value
ARC
Australian Research Council
The Australian Research Council is the Australian Government’s main agency for allocating research funding to academics and researchers in Australian universities. Its mission is to advance Australia’s capacity to undertake research that brings economic, social and cultural benefit to the...

: Centre of Excellence Coral Reef Studies
Scientist Pushes For Coral Triangle Action Australia.to., 7 July 2009.

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