Coral garden
Cook Island Aquatic Reserve supports a relatively high cover of hard and soft coral compared to nearby rocky reefs, including a diverse mix of tropical, subtropical and cosmopolitan species. These corals grow alongside a variety of tropical and temperate algae and invertebrates, including anemones.
Soft and branching hard corals with feather stars in the coral garden (Photo: Gary Shuttleworth)
Cook Island Aquatic Reserve may be the northern range limit for the subtropical endemic coral (Pocillopora aliciae). (Ecological Service Professionals)
Coral assemblages
These coral assemblages are important as they feature some species at their southern range limit, and others at their northern range limit, such as the subtropical endemic coral Pocillopora aliciae. See second image above.
In the northern and southwestern sections of the aquatic reserve, rocky reefs are protected from the predominant south-easterly swell and so support well-established areas of hard and soft corals.
Where are they?
Coral gardens in the northern section of the aquatic reserve are dominated by a variety of hard corals.
In the southwestern section of the aquatic reserve, a mixture of soft and hard corals dominates the boulder field.
Beyond the coral gardens, corals and anemones can be encountered in low densities among the bedrock and boulders, particularly in shallower sections along the western edge of the reserve.
Hard coral forms (morphologies) include plate, table, foliaceous, branching, and encrusting corals.
Table coral above and plate coral below, fish are Eastern pomfreds (Photo: Hamish Malcolm)
Branching Acropora coral (Photo: Brigitte Sommer)
Encrusting coral (Paragoniastrea australensis) with green symbiotic algae (Photo: Hamish Malcolm)
Marine life
Corals, particularly hard corals that produce a hard skeleton, increase habitat area and complexity by providing ledges and crevices in which many animals live or seek shelter.
Coral garden habitat in Cook Island Aquatic Reserve hosts a diverse array of fish and invertebrates, including tropical and temperate species.
Each coral consists of a colony of polyps that are clones. The polyps are food for some animals, including colourful sea slugs (e.g. Phyllodesmium magnum), snails (e.g. common egg cowrie and toenail egg cowrie), and several species of butterflyfish.
Coral polyps have tiny stinging tentacles for self-defence and feeding. They filter plankton from the water, but some reef-building corals also have a mutually beneficial relationship with a single-celled organism called zooxanthellae. The zooxanthellae convert sunlight into food that they share with their coral polyp host.
Green turtle resting amongst boulders in coral garden (Photo: Gary Shuttleworth)
Blacktip rockcod sheltering in a foliaceous hard coral (Photo: Gary Shuttleworth)
Blue sea star (Linckia laevigata) (Photo: Gary Shuttleworth)
Coral gardens provide a place for vulnerable hawksbill turtles to rest (Photo: Brigitte Sommer)
Banjo ray amongst the corals (Photo: Rudi Vir)
Black coral among algae covered boulders and bedrock (Photo: Hamish Malcolm)
Rainbow mantis shrimp sheltering inside a hard coral (Photo: Rudi Vir)
Common egg cowries feeding on leather soft coral (Photo: Ecological Service Professionals)
Toe-nail egg cowrie feeding on leather soft coral (Photo: Professor Stephen Smith)
Nudibranch feeding on soft coral in the coral garden (Photo: Professor Stephen Smith)
Anemones
Anemones are relatives of corals and can be seen among the hard and soft coral gardens. They provide a unique haven for certain species of damselfish, including the Barrier Reef anemonefish and juvenile threespot humbugs.
These fish swim among anemone’s tentacles without being stung, helping them avoid predators. In turn, the scraps of food and waste left by these fish become food for the anemones.
Anemones have stinging tentacles that immobilise their prey of small fish and invertebrates. However, anemones can still be food for other animals, including some species of nudibranchs, fish, and sea stars.
Bubble-tip or Bulb-tentacle sea anemone (Entacmaea quadricolor) (Photo: Hamish Malcolm)
Bubble-tip anemone in a coral garden (Photo: Ecological Service Professionals)
Barrier Reef anemonefish and threespot humbugs in an anemone (Photo: Ecological Service Professionals)
Striped agile shore crab sheltering between boulders and bubble-tip anemones (Photo: Ecological Service Professionals)
Juvenile Barrier Reef anemonefish in a bubble-tip anemone (Photo: Professor Stephen Smith)
