Di Tracey talks cold-water corals

Di Tracey talks cold-water corals

“Coral” is a general term used to describe several different groups of animals in the Phylum Cnidaria, so-called because of their microscopic nettle cells (cnidae) that sting or otherwise immobilize their prey for capture. They eat plankton and small fish, depending on the species.

Coral reefs are among the most spectacular ecosystems on the planet, supporting such rich biodiversity and high density of marine life that they have been referred to as the “rainforests of the sea.” These ecosystems are typically associated with warm shallow tropical seas. However, as well as being found in the photic zone of the ocean, where sunlight penetrates (with symbiotic photosynthetic zooxanthellae, a type of alga), corals can also be found in the deep sea – the so-called azooxanthellate (no symbiotic algae) ‘cold-water corals’.

Coral communities can thrive on continental shelves and slopes, sometimes thousands of metres below the ocean’s surface. Yet it has only been over the last two decades that knowledge of the remarkable deepsea corals in the world’s oceans has been revealed.

Here in New Zealand, we have an abundant and diverse deep-sea coral fauna. Scientists have sampled a lot of these corals on previous research surveys and on this particular trip we have collected live footage of deep-sea corals on our underwater camera system DTIS (Deep-Towed Imaging System).

DTIS has recorded beautiful gardens of deep-sea corals on the various Graveyard Seamounts where the water flow and currents around them provide ideal habitat for these suspension feeding animals. From small and delicate lace-like forms (Stylasterids) (see Image 1) to the large and important 3-D reef-like structures of the branching stony corals, (Images 2&3), and gorgonians (Image 4), the coral life is impressive.

Our sled collected a beautiful yellow gorgonian (primnoid) specimen (Images 5). The enlarged polyps represent the brooding polyps that hold the oocytes (Image 6). Only three species of Gorgonians do this, and Primnoids are the first of this group to have been recorded in the literature to hold the larvae until they are released into the deep-sea waters. Other Gorgonians are oviparous.

 So far, the voyage has seen high levels of biological diversity associated with the branching stony coral structures – invertebrates such as sponges, brisingids (Image 7), seastars, crinoids (Image 8), and other forms of corals -  bamboo, primnoids, and stony cup corals.

We have been mapping the extent of these corals in our region, and studying aspects of their biology, such as their growth, to understand their role in deepsea ecosystems which support valuable commercial fisheries like orange roughy (Image 3).

Return to Stories from the Graveyard
Return to Voyage Overview