Coral reefs are not only about aquarium-like colourful fish, but also about larger dwellers: predators and good-natured guys.
If the most of the coral reef fish are either well camouflaged or aggressively coloured, the big animals are usually not because they have much less natural enemies. Here are most of the large animals that inhabit reef area.
Nurse sharks are nocturnal animals, spending the day hidden under submerged ledges or in crevices within the reef. By night, the sharks are largely solitary; they spend most of their time rifling through the bottom sediments in search of food. Their diet consists primarily of crustaceans, molluscs, sea snakes and other fish, particularly stingrays. Nurse sharks have been observed resting on the bottom with their bodies supported on their fins, possibly providing a false shelter for crustaceans which they then ambush and eat.
Sadly, the nurse shark is an easy target for local fisheries. Its skin is exceptionally tough and is prized for leather; its flesh is consumed fresh and salted and its liver is utilised for oil.
Nurse shark ©Marina Kudrya
Sometimes nurse sharks share their day shelter with other fish. Here is a nurse shark that have been living together with a green moray eel for many years!
The buddies ©Marina Kudrya
Green moray eel is one of the largest among the morays. Although these nocturnal animals are actually brownish-grey, the mucus they have around their bodies make them look green.
Just like the nurse sharks, green morays are of interest to divers, private aquarists with the facilities to maintain them, and with visitors to large commercial aquaria. The aesthetic appeal of the green moray has therefore generated a great deal of economic interest. And although their meat can be very poisonous due to biomagnification, they are eaten by some indigenous peoples.
Green moray eel ©Marina Kudrya
Cornetfishes are voracious predators of small fish and crustaceans. They can rapidly change color to blend in with their surroundings. Cornetfishes often congregate in large schools of herbivorous fish, blending in with them and striking at other prey. They have been observed to orient vertically in the water to fool prey into thinking they are seagrass or coral. They feed on small forage fish and crustaceans.
Cornetfish can grow up to 2 meters, and actually this one was very long.
Cornetfish ©Marina Kudrya
The barracudas are known for their large size and fearsome appearance. Some species can reach up to 2m in length and 30cm in width! Also they are ferocious, opportunistic predators, relying on surprise and short bursts of speed, up to 43 km/h, to overtake their prey.
Adults of most species are more or less solitary, while young and half-grown fish frequently congregate. Barracudas prey primarily on fish (which may include some as large as themselves). They kill and consume larger prey by tearing chunks of flesh. Barracuda are competitive species and often are seen competing against mackerel, needle fish and sometimes even dolphins for prey.
Barracudas ©Marina Kudrya
Spotted eagle rays are most commonly seen alone, but occasionally swim in groups (especially in mating season). Rays are ovoviviparous: the female retains the eggs then releases the young as miniature versions of the parent.
These rays are commonly observed leaping out of the water. It is not known for sure why they do that; one version is to shake off the parasites. Their daily movement is believed to be influenced by the tides; one tracking study showed that they are more active during high tides.
Mature spotted eagle rays can be up to 5m in length; the largest have a wingspan of up to 3m and a mass of 230 kilos. Their tails are longer than those of other rays and may have 2–6 venomous spines. However eagle rays are not a threat to humans, at least because it’s unlikely we can catch up with them.
The main threat for spotted eagle rays are sharks: lemon shark, bull shark, tiger shark and other; and of course humans catching them for the aquariums.
Spotted eagle ray ©Marina Kudrya
Now turtles! These peaceful animals have hardly ever hurt any human, but now they are critically endangered because of people’s activities.
Marine turtles mostly can be found in coral reefs, but some species travel between oceans. During the first three to five years of life, sea turtles spend most time in the pelagic zone floating in seaweed mats. Once the sea turtle has reached adulthood it moves closer to the shore. Females will come ashore to lay their eggs on sandy beaches during the nesting season. Sea turtles have temperature-dependent sex determination, meaning the developing turtle’s gender depends on the temperature it is exposed to. Warmer temperatures produce female hatchlings, while cooler temperatures produce male hatchlings
Sea turtles are able to grow so large because of the immense size of their habitat: the ocean. Having more room to live enables more room for growth.
Sea turtles are air breathing reptiles that have lungs, so they regularly surface to breathe. Sea turtles spend a majority of their time underwater, so they must be able to hold their breath for long periods. Dive duration largely depends on activity. A foraging turtle may typically spend 5 – 40 min under water, while a sleeping sea turtle can remain under water for 4–7 hours.
Sea turtles: hawksbill and loggerhead ©Marina Kudrya
Although spiny lobsters can grow very big, they are an easy catch for humans. They can offer almost nothing in self-defence, except for their long antennae.
Spiny lobsters tend to live in crevices of rocks and coral reefs, only occasionally venturing out at night to seek snails, crabs or sea urchins to eat. Sometimes, they migrate in very large groups in long files of lobsters across the sea floor. These lines may be more than 50 lobsters long. Spiny lobsters navigate using the smell and taste of natural substances in the water that change in different parts of the ocean. It was recently discovered that spiny lobsters can also navigate by detecting the Earth’s magnetic field. They keep together by contact, using their long antennae.
Spiny lobsters keep predators away with the sounds they make by rubbing their antennae against the smooth part of the exoskeleton.
Spiny lobster ©Marina Kudrya
Groupers are known for having a stout body and a large mouth. They are not built for long-distance, fast swimming. They can be quite large, and lengths over a meter and weights up to 100 kg are not uncommon.
Groupers are mostly monandric protogynous hermaphrodites, meaning they mature only as females and have the ability to change sex after sexual maturity. Some species of groupers grow about a kilogram per year and are generally adolescent until they reach three kilograms, when they become female. The largest males often control harems containing three to 15 females.
Groupers are important food fish, and some of them are now farmed. Unlike most other fish species which are chilled or frozen, groupers are usually sold live in markets. Many species are popular fish for sea-angling.