The Elasmobranchs
Sharks
Characteristics
Sharks have a very streamlined, fast body (called fusiform), which is true of most predatory fish. They hunt using 6 senses; smell, sound, sight, touch (they sense vibrations in the water with their lateral line), electroreception, and lastly taste.
Sharks, like humans, are late to reach sexual maturity and have very few, but well developed, offspring. In most cases, male sharks can be identified by claspers located in the pelvic region (like small ‘arms’ used for holding onto a female during mating).
Importance
Sharks are rightfully called the ‘kings of the sea’, because in most marine food chains they are the top predator, and thus are a top-down control on the entire ecosystem. Sharks maintain the ecosystem balance and they play a big role in nutrient cycling and export from reefs. The most common species of sharks you are likely to see are those associated with a coral reef environment such as Black Tip Reef sharks.
Notes
It is uncommon to see sharks during the EMP due to their fear of divers
Rays
Characteristics
Sting Rays and Ribbon Rays feed primarily on benthic invertebrates such as crabs and shrimps. They are primarily nocturnal hunters, and will usually be found under coral heads or buried partially in the sand during the day.
- Blue Spotted Ribbon Ray – rounded body, easily recognized by its bright blue spots.
- Blue Spotted Sting Ray -Diamond Shaped body, easily recognized by its bright blue spots.
- Jenkins Whip Ray – largest species on Koh Tao, body is rounded diamond shape, brown or tan in color
Importance
Rays are considered to be meso-predators (in the middle of the trophic structure), and so thus an important link between the top and bottom of the food chain. They are important in controlling populations of invertebrates, but are also a food source for higher order predators such as sharks. They are sensitive to changes in the environment, and also allow us to gain information on the abundance of crustaceans and bivalves on the reef.
Notes
Be sure to look well under the rock overhangs and coral heads for the rays during the fish survey of the EMP.
Bony Fishes (Class Actinopterygii)
Butterfly Fishes (Family: Chaetodontidae)
Most of the butterflyfish are very colorful and live in close association with corals. All of the butterflyfish have a similar body shape, which is plate-like (thin, tall, and round) and are of the order of perciform fish (meaning perch-like).
They are the opposite shape of a shark’s mouth, which illustrates how important a role predation has played in their evolution. Butterflyfish are the easiest fish to spot while conducting the EMP, and usually occur in pairs, but sometimes can be found in schools.
Characteristics
Butterflyfishes are thin, tall, and plate-like (laterally compressed) to avoid predation. To further avoid predation, the tail of most butterfly fish looks just like the head, and often they have a line over their eye for disguise. Together these confuse predators, who don’t know which direction to sneak up on the fish, or which way the fish is going to swim to get away.
Importance
Butterflyfish only live in healthy reefs, graphs of coral abundance and butterfly fish abundance tend to be very closely correlated, and you can use one to estimate the other.
Economically speaking, they are important for reef tourism, as they are a favorite of SCUBA divers and snorkelers. Although they are fished in some areas, they do not provide a good source of protein.
In many areas they are a prized fish for the aquarium trade due to their bright colors, and are threatened by overcollection. Often times, cyanide or other poisons are used to stun and collect them, leading to the death of corals and many other reef animals.
Weibels Butterfly Fish
Bright to dull orange with diagonal black stripes, it is one of the larger butterflyfish species. Note the black stripe over the eye and the similarity between the head and tail. This species is a true omnivore, feeding on a diverse diet of algae, zooplankton, coral polyps, small invertebrates, clams (including Tridacna species), and tubeworms.
8 Banded Butterflyfish
Yellowish white with black vertical bands, it is one of the smaller butterfly fish species. The juvenile and adult fish are nearly identical in coloration and shape. Juveniles will most often be found in table corals, and adults roam the reef to feed on coral polyps (this species is an obligate corallivore.)
Lined Butterfly Fish
White body with yellow tail, thin blue-black stripes running vertically down the body (looks like lined paper turned sideways). One of the largest butterflyfish species, they have a diverse diet of coral polyps, algae, and small invertebrates.
Copper Banded Butterfly fish
Another of the larger species included in our surveys, has a white-gold body with copper colored vertical stripes. Extended mouth facilitates a diverse diet of small invertebrates including worms, mollusks, and crustaceans. Note false eye (black spot) on tail for fooling predators. In some areas, referred to as the Beaked Coral Fish.
Long-Fin Banner Fish
White body with two vertical stripes and yellow tail. Easy identified by long white ‘banner’ and large pectoral fins. Feeds primarily on zooplankton, but also small reef invertebrates. In some areas they are called the Pennant Coralfish, and can sometimes be confused with the Moorish idol.
Groupers (Family: Serranidae)
Characteristics
Groupers are ambush predators; comparing them to the butterfly fish, they appear stronger, more streamlined, and faster. Groupers are generally demersal (live along the bottom) and can be found on top or under rocks and corals. They lie and wait for small fish or invertebrates to come close and then use their draw-bridge like mouth to suck the prey in. Their lower jaw is spring loaded and opens and closes in a fraction of a second, but in doing so increases the volume of the mouth up to 500%, creating a current that few prey species can escape.
Importance
Groupers are predators, but are also a prey species for larger fish (mesopredators). They are a prized fish for human consumption, and are thus threatened by overfishing (especially the large species). Because of their behavior, they are one of the primary species caught through spearfishing.
Notes
Although there are generally several species of grouper on any particular reef, you will not need to differentiate them by species. Instead, you will differentiate the groupers by size; larger or smaller than 30 centimeters. Your instructor will show you what 30 cm looks like underwater; also it is the same as the length of a standard EMP slate. The reason this is done, is like in many other fish species, they are protogynous, meaning that they change sex as they mature. All immature groupers are female, and only change to male in their adult life stage.
Parrot fish (family: Scaridae)
Characteristics
Parrot fish have a very fitting name for many reasons; they tend to be brightly colored, have fused teeth which form a parrot like beak, and swim with their pectoral fins in a bird-like fashion. Many species have the ability to secrete a mucus ‘cocoon’ while sleeping, which protects them from predation by electrosensory enabled elasmobranch species.
Importance
Parrot fish are one of the most abundant and effective fish grazers of micro- and macro-algae. They use their beak to scrape algae from rocks and dead coral which prevents it from overtaking the corals, opens up clean areas for settlement of coral larvae, and regulates nutrient levels in the reef. In some areas of the world, parrot fish can grow quite large and will actually use their beak to bite chunks off of the coral. This has given them the reputation as contributing greatly to bioerosion of the reef, however in those species (primarily Humphead Parrotfish) coral is not their primary food source.
Notes
During the EMP you will differentiate the parrot fish in two groups, small (less than 20 cm) and large (greater than 20 cm). This is because, like the groupers, they all start of as females, and become males after developing to a certain age/size. Juvenile parrot fish tend be a duller green color, and are sometimes confused for the moon wrasse by beginning students.
Often, in shallow reef areas, mixed schools of juvenile parrot fish and rabbit fish can be found. These are generally harems of females presided over by a single large male. During the EMP you should try to estimate the number of fishes in the school, but be sure to also differentiate between the parrot fish and rabbit fish.
Rabbit fish (Family: Siganidae)
Characteristics
Rabbit fish are a common reef fish, and resemble the simple fish profile that everyone can recognize. They have a nose (rostrum) which resembles a rabbit’s, and also play a very similar ecological role to rabbits; being prolific herbivorous grazers. Their dorsal fin is composed of 13 spines, which are venomous. Being stung is painful, but not actually life threatening for humans. Some of the more common rabbitfishes include: the Double Barred Rabbit fish, the Java Rabbit Fish (Top), and the Gold Saddle Rabbit fish. Rabbit fish can be found solitarily, but more commonly will be observed in schools.
Importance
Rabbit fish are important reef herbivores feeding on benthic algae and biofilm. On many reefs in the Indo-Pacific they are one of the most abundant and important fish grazers. They are also an important prey species for many predatory fish including sharks, groupers, and barracudas. They are an important food source in many developing countries, and are threatened by over-fishing.
Notes
You do not need to differentiate rabbit fish by species or size for the EMP.
At night rabbit fish can be found sleeping with their dorsal and anal fin spines extended, making them a more difficult meal for nocturnal predators.
Snappers (Family: Lutjanidae)
Characteristics
Snappers are predatory fish with a perciform shape. They appear strong and streamlined when compared to the herbivorous fishes. There are several species of snapper in the Indo-Pacific, the most common in reef areas are of the genera Lutjanus such as the Russel’s Snapper, the Spanish flag Snapper, and the Blackspot Snapper.
Importance
Snappers are secondary or meso-predators which feed on crustaceans and other fish. Some species also eat zooplankton, and are thought to be an important control on larval supply to the reef (Including COTs and Drupella). They are also a favorite of the fishing industry, and can be used to assess fishing related threats.
Notes
Snappers can be solitary or in schools, and are usually quick to flee from divers. They generally average 20-30cm, but occasionally much larger ones can be found on the reef.
Surgeonfish (Family: Acanthuridae)
Characteristics
Surgeonfish (also known as Unicorn fish) are mostly herbivores fishes, and derive their name by the very sharp spines protruding from the tail, which look like a surgeon’s scalpel. They can be easily identified by their unique body shape and colorful spine (usually orange or yellow).
Importance
In some areas they tend to exist in large schools where they play an important role as a reef herbivore, often competing with damsel fishes for food. They are also prized in the aquarium industry and can be a victim of over-collection.
Notes
In many areas of the Indo-Pacific, Surgeonfish can exist in large schools, but in other areas they can be quite rare. In areas where they are rare, please record any Surgeon Fish outside the survey area into the notes section of your slate.
Sweetlips (Family: Haemulidae)
Characteristics
Sweetlips are part of the Emperor fish family, which can grow quite large. Visually, their body shape appears like a mix between the groupers and snappers. Adults are generally white or dull colored with black spots, while juveniles are brightly colored and very ornate.
Importance
Sweetlips are important predatory fishes that feed on crustaceans and other benthic invertebrates. They are a favored fish by the fishing industry, and are indicators of fishing pressure on the reefs.
Notes
Juveniles and adults have very different appearances, and live in different areas of the reef. The juveniles can usually be found living solitarily in the shallow reef areas, and will stay in the same place for about 1 month while developing. Adults are more likely found in pairs or small groups, hiding under rocks or coral heads during the day and feeding at night.
Triggerfish (Family: Family Balistidae)
Characteristics
Triggerfish are large reef fishes with an oval body and a strong mouth. They swim using their dorsal and anal fins in an undulating motion. Many of the larger species are notoriously territorial, and can be quite aggressive (In particular the Titan and Yellow Margin Triggerfishes). They have two ‘Triggers’ which are used to warn intruders and lock themselves into cracks in the reef while sleeping.
Importance
Large Trigger fish are important top predators on the reef. They help to control the populations of coralivorous gastropods, mollusks, bivalves, and echinoderms (feeding on both Drupella and COTs). They are very intelligent fishes and often use tools such as rocks to break open clams or other shelled organisms.
Notes
Some species, such as the Titan Triggerfish, often attack when a diver enters their territory, especially during mating seasons. To avoid problems, do not swim directly towards or over them, but instead remain calm, lay low, and wait for the fish to move away from you.
Red Breasted Wrasse (Family: Labridae)
Characteristics
The Labridae family of fish (Wrasses) is very large and diverse. This species is one of the most widespread in the Indo-Pacific and larger Wrasse, growing up to 40 cm. They are easily identified by their black and white striped body and red head/breast. They can generally be found in areas of mixed coral and rubble.
Importance
Red Breasted Wrasse (also called Red Breasted Maori Wrasse) are large fish which require a high abundance of marine invertebrates to survive. Like the Triggerfish, they have a diverse diet and are able to feed on hard shelled invertebrates and sea urchins.
Notes
The Red Breasted Wrasse is often found in fishing cages, and does not seem to mind divers.
Bluestreak Cleaner Wrasse (Family: Labridae)
Characteristics
The Bluestreak Cleaner Wrasse is a small (less than 10 cm) fish that generally stays in one place on the reef, its cleaning station. When potential ‘clients’ pass by, the fish will perform a sort of dance to indicate that it is open for business. If the client agrees, it will take on a passive body position (usually the head elevated and the mouth open. The cleaner wrasse will then remove ectoparasites from the client fish’s body.
Importance
Cleaner wrasse are important to the health and longevity of many other species of fish on the reef. Since they generally stay in the same area, we can accurately track their populations over time.
Notes
There are several species of fang blennies which have evolved to imitate the cleaner wrasse, please learn the difference between the two so that you only count the wrasse.
Moray Eels (Family: Muraenidae)
Moray eels are actually a type of bony fish, they are not related to snakes as some may infer. There are over 200 species of moray eels worldwide. They have poor eyesight, but that is made up for by a highly acute sense of smell. They have two sets of jaws, oral and pharyngeal, the later of which can be articulated forward and back to rip apart prey.
Characteristics
Moray eels have a serpentine shape, and live in burrows in the sand, or crevices and holes in corals and rocks. They feed on crustaceans, mollusks, and small fish. Most species are mesopredators, and sometimes become prey for barracuda, large groupers or sea snakes. Although species like the Giant Moray can be considered an apex predator.
Importance
As predators, eels are important in regulating the balance of the reef. They are also sensitive to habitat destruction and declines in water quality. Some of the more rare and ornate Morays are also threatened by the aquarium trade, and can be sold for a high market price.
Notes
They generally will not be found during very bright days, but can readily be found on deeper sites, when visibility is poor, or when it is overcast. This is another reason why it is important to record the weather/viz when conducting the EMP.
Superfamily: Chelonioidea
Sea Turtles (Superfamily: Chelonioidea)
Characteristics
Of the 7 species of sea turtles, 2 can commonly be found on Koh Tao, Greens and Hawksbills. Olive Riddley’s are also recorded int eh region, but are rare.
Importance
Turtles are an indicator of biodiversity and anthropogenic pressures. Sea Turtles have lived in the sea since the time of the dinosaurs, but today are faced with extinction due to human activities (primarily by marine debris, fishing, by-catch, and habitat destruction). As turtles migrate over great distances and through both national and international waters making their protection very difficult.
Notes
Report sea turtle photos to ‘Koh Tao Turtles’ and ‘Tao Talay Aow Thai’ on Facebook.
Family: Elapidae
Sea Snakes
Characteristics
There are about 69 species of sea snakes, all within the Indo-Pacific, some of which are the most venomous snakes in the world. The have a paddle-like tail, and their lungs extend most of the length of their bodies so that they can hold air for dives. They are generally found in shallow, warm tropical seas in sheltered areas or around islands. They generally feed on small fish, using chemosensory to detect prey as their vision is limited.
Importance
Sea snakes are subject to overfishing and by-catch, with four species listed by the IUCN, 1 as vulnerable, 1 as endangered, and 2 as critically endangered.
Notes
Although some of the most poisonous species of snakes on earth, Sea Snakes and Sea Kraits are generally not a threat to divers unless they are provoked. They are much more dangerous when on land (Sea Kraits) or when caught in a fishing net.