Coral Reef Animals - Introduction

Coral reef animals are overwhelmingly the most conspicuous component of coral reef life, occurring in truly astounding numbers and variety in virtually every part of coral reef ecosystems.

Two major groups of animals inhabit coral reefs: animals with backbones (called vertebrates) and those without these structures (called invertebrates).

Vertebrate Coral Reef Animals

Among vertebrate animals, only a relative few groups contain species that are commonly considered part of coral reef communities. These are introduced below. Several other types of vertebrates (e.g., dolphins, porpoises, sea birds) are occasionally seen hunting or feeding in waters around coral reefs, but these are occasional visitors that spend most of their life cycles in other habitat types.

Reef Fishes

Reef fish. © Fotolia.com

Of the several types of vertebrate animals commonly found on coral reefs, fishes are the only group normally present in great abundance and diversity.

Hundreds or even thousands of different species may be found in some of the larger reef ecosystems. They are abundant in all three major reef zones, from the lagoon shoreline to the deepest reaches of the fore reef.

Because they represent a such a highly conspicuous and ecologically influential component of the coral reef fauna, we have devoted a separate 3-page section of our website to discussing them.

Sea Snakes

A sea snake. © Fotolia.com

Sea snakes are found only in the Indo-Pacific region (excluding the Red Sea). There are more than 60 recognized species, but of these only a relative few are common residents of coral reef areas.

Sea snakes have evolved from terrestrial snakes, and like all reptiles are air breathers. Adaptations for aquatic life include paddle-like tails and laterally compressed bodies, both of which enhance swimming ability.

Many sea snake species are highly venomous, and should never be closely approached or threatened by coral reef divers or snorkelers.

Sea Turtles

Of the seven recognized species of sea turtles, three are regular or occasional visitors to coral reefs in some parts of the world.

Hawksbill turtle. © Fotolia

On both Indo-Pacific and Caribbean reefs, the species most often seen resting on the reef proper is the Hawksbill turtle Eretmochelys imbricata, a species that also feeds in the lagoon or back reef zone of coral reef ecosystems. Hawksbill turtles have been heavily overexploited for their meat and shells, and are listed by the IUCN as "critically endangered".

The green sea turtle (Chelonia mydas) also frequents coral reef ecosystems of both the Greater Caribbean and Indo-Pacific regions. This species feeds primarily on the seagrasses found in protected back reef lagoons. The green sea turtle is considered endangered.

The flatback turtle (Natator depressusis) spends much of its time in the open sea, and is only seen in coral reef areas in a few parts of the Indo-Pacific region; most notably coastal waters of Indonesia, northern Australia, and Papua New Guinea. Flatback turtles are a threatened species.

Sea turtle research and conservation efforts are underway around the world to try to stem the declines of the once large populations of these beautiful animals.

Dugongs and Manatees

Dugong feeding. © Fotolia

Dugongs (Indo-Pacific) and manatees (Caribbean) were once plentiful in coral reef lagoons. These peaceful giants - related to elephants - consume prodigious quantities of seagrasses.

They have been traditionally hunted by native peoples for food for many centuries with minimal apparent effects on their populations. Over the last century however, extensive hunting, habitat loss, entanglement in fish nets, and coastal pollution have contributed to the rapid decimation of these animals. Now threatened with extinction, conservation efforts continue but thus far have seen little success.

Common Invertebrate Reef Animals

Among coral reef animals, invertebrates are by far the most diverse and numerous. They are the primary builders of coral reefs and an integral part of many aspects of the ecology of coral reef ecosystems.

Invertebrate animals occur in all coral reef zones and habitats, and are instrumental in the movement and cycling of nutrients through the ecosystem. Many of these animals live in coral reef sediments, and engage in activities such as burrowing or tunneling that shape the very nature of these environments.

Some invertebrate animals (parasites) infest the bodies of other invertebrates and fishes, while others are vectors for disease. Still others serve a cleaning function, removing parasites and damaged tissue from other types of reef life.

Even a summary treatment of what is currently known about the amazing variety of form, life histories, behavior, and ecology of invertebrate animals living in coral reef habitats would fill many volumes, and a great deal remains to be learned in this area.

There are six ubiquitous and particularly influential invertebrate groups of invertebrate coral reef animals, which are briefly introduced below.

Corals form most of the underlying structural foundation of coral reefs. This group includes many familiar creatures such as reef-building corals, sea fans, sea whips, fire corals, and anemones. These animals (Phylum Cnidaria) are characterized by radial symmetry and the presence of numerous feeding tentacles bearing stinging cells that are used both for prey capture and defense.

Sponges are among the most colorful and abundant of all coral reef animals. They occur at all depths on coral reefs, from shallow lagoons to the deep reef face. Sponges are primitive, sedentary animals that filter feed on tiny food particles carried in the water sweeping over them. Different species may exhibit vase-like, tubular (photo left), or encrusting structural forms.

Echinoderms are diverse in body form, and include such familiar marine animals as sea stars ("starfish") and sea urchins, along with less known creatures such as brittle stars and others. They are widely distributed throughout coral reef ecosystems, and some types occur in high numbers. "Echinoderm" means "spiny-skinned", a distinctive trait of these animals.

Mollusks are a widespread and abundant group of coral reef animals. The the main types of mollusks common on coral reefs are gastropods (snails and relatives - see conch shell pictured left), bivalves (clams and relatives), and cephalopods (octopi and squid). Certain coral reef gastropods (cone shells) are among the deadliest of all venomous marine animals.

Crustaceans include some of the most familiar and commercially valuable coral reef animals, including shrimp, spiny lobster, and crabs. Like their related terrestrial counterparts the insects, crustaceans possess external jointed skeletons, segmented bodies, and numerous appendages. Many members of this group of animals play a vital role in coral ref food webs.

Polychaetes are for the most part far less well-known or conspicuous than the other coral reef invertebrate groups mentioned above. Nonetheless, they are present in great abundance and are heavily preyed upon by many types of reef fishes. This group includes some creatures familiar to scuba divers, such as feather dusters, fire worms, and bristle worms.

We have devoted a separate page of our web site to a more in-depth discussion of each of these groups of invertebrate coral reef inhabitants. These pages may be accessed through the Section Menu provided below.