Exploring Our Underwater Mountains

Forest and Bird, Issue 296, 1 May 2000, Page 32

Exploring Our Underwater Mountains

JO MACKAY

discovers a diverse mountain landscape under the sea.

One kilometre below the ocean’s surface — in cold, dense, eternally dark waters — there exist isolated and astonishing communities of sealife. Here marine creatures live on submerged mountains. Fluorescent, deepwa-ter-coral thickets grow on the rocky mountainsides, which host a diverse community of creatures. Fish, squid and sharks are in turn attracted to these fertile hot spots. Tragically, we are discovering most of these incredible bottom-living animals as they are being destroyed — ripped from the ocean floor by deep-sea trawlers. Some of these ‘seamounts’ are extinct underwater volcanoes, rising from the deep-ocean floor. Some are in ranges, others are isolated mountains. A few are live volcanoes, like "The Rumbles, north of White Island off the Bay of Plenty.

In the New Zealand region there are 500 seamounts standing taller than 250 metres above the ocean floor, and possibly another 500 ‘sea hills, similar in size to Auckland’s volcanic cones. Together, New Zealand’s known seamounts (shown on the map on page 35) make up one fortieth of the region’s area. The summits of seamounts, around New

Zealand, on average peak almost one kilometre below the sea’s surface. Some summits are 2.5 kilometres deep. Only 13 are known to peak within 250 metres of the surface. Some seamounts are giants the southern Bollons seamount is 200 kilometres across and 3000 metres high — as tall as Aoraki/Mount Cook. Some peaks on the biggest range in the region, the Louisville Ridge, rise 4000 metres from the sea bed, covering an area the size of Banks Peninsula. Seamounts, hills and knolls are unusual in the deep ocean. They block the rhythmic movement of deep, slow-moving oceanic currents, and cause fast, upwardmoving currents, swirls, and eddies around their sides. These currents mix the deepest waters with the layers above, encouraging nutrient flows.

Most importantly, seamounts provide a rare opportunity for deepsea creatures: to find a hard, bare, rocky surface to cling to. They are home to a distinctive community of benthic (bottom-living) sea creatures. These hard-ground invertebrate communities are almost entirely different from the species that live on the surrounding soft ooze. Seamounts vary greatly in size, depth and topography. There appear to be many creatures unique to certain seamounts. It may be that the isolation of the seamounts, and strong, circular currents, keep some creatures within each seamount area. Corals form the basis of seamount communities. Six species of true corals characterise New Zealand seamounts. The most common reef-building coral Goniocorella dumosa, can grow colonies up to 20 metres tall, at a rate of up to three millimetres per year. They form a bushy, interlocking network of branches and numerous species of attached creatures find a niche in the hollow spaces. Forty-two species of black coral have been growing slowly for centuries in cold, dark New Zealand waters, particularly around the northwest Chatham Rise and southwards towards the Auckland and Bounty islands. They have diverse forms. Some are like a large Japanese fan, with foot-long combs. Others are stick-thin with feather-like ‘branches’ attached to a long ‘stem’. Further north — off the Bay of Plenty and Lord Howe Island — sea fans or gorgonians, including the striking bamboo corals, often dominate. Very little is known about the 37 species so far found. Some look like small branching and tangled shrubs, others like fans, or whips. A BBC photographer in a submersible found that bamboo corals produce bioluminescence

when touched, with light spiralling from the colony base to the most distant branch tips. They appear to grow about 50 centimetres in 70 years. When first brought up from the seabed, corals are often brilliant oranges, reds, or golds. One fragment, about 1.5 metres long, is a large spiral one centimetre in diameter, with a metallic-golden sheen. It has small holes along its side, where tiny fluorescent fans were attached. At least 200 invertebrate species live amongst the coral, as well as many uncounted sponges, hydroids, bryozoans and stylasterids. They include sea cucumbers, brittle starfish, sea lilies, sea-stars and sea-eggs. The stalked barnacle Smilium zancleanum, as long as a human hand, is one of nine seamount-dwelling barnacle species, most of which have been found in only one location. There are 13 species of hermit, stone and true crab recorded from seamounts — more than half not yet named. Seven squid and seven octopus species have been collected. About 140 fish species and 29 shark species spend parts of their life cycles around seamounts. Orange roughy is the most common fish, with black and smooth oreo more numerous in some areas. Baxter’s dogfish is the most common shark. Alfonsino, black cardinal fish, rattails and black javelin fish are also often found.

What's happening to protect seamounts? The Ministry of Fisheries has a responsibility to ensure that fishing is ecologically sustainable. Forest and Bird’s Barry Weeber says there should be a moratorium on deep-sea fisheries and a stocktake of what creatures live there. ‘Otherwise we re paying lip service to biodiversity — we don’t even know what we’ve got and it’s being destroyed’ Forest and Bird has lobbied the Ministry of Fisheries to stop the industry moving onto unfished seamounts, and has called for at least half of the most intensively fished area — the Chatham Rise — to be set aside, to enable some of the "bottomdwelling’ communities to survive. The Ministry is now considering setting aside a small number of seamounts ‘to manage the impacts of fishing on a representative sample. ‘The Ministry’s approach is too little, too late, says Barry Weeber. "By the time it gets round to enacting any policy, the fishing industry will have substantially wrecked many more seamount habitats. There should be an immediate ban on trawling in all unfished areas.

The deep-sea fishing industry has targeted the fertile seamounts since the mid 1980s. About 80 percent of the orangeroughy catch is now taken from seamounts. Scientific knowledge of seamount fauna almost entirely comes from specimens brought in as trawling by-catch. The National Institute of Water and Atmospheric Research Ltd (NIWA) frequently receives, from fishing trawlers, specimens of creatures which have never been seen before. NIWA taxonomist, Dr Steve O’Shea, has witnessed a new species come up with almost every trawl. "We are guessing that there are many localised ecosystems, just because so many species have been found only in certain areas. What is more, the species hauled up in nets is only the ‘big stuff’ — larger than an average net hole of 10 centimetres square. ‘On the seabed, creatures less than one centimetre in size often count for 99 percent of diversity, yet we don’t know what small things are down there, says Dr O’Shea. Dr Malcolm Clark, leader of NIWA’s seamount research, says seamount science is still in the ‘presence-absence’ stage. "We know that some species are present in some areas. We don’t have information on their numbers or densities. We don’t know the relationships that these creatures have with each other, or their geographic and depth distribution. Little funding goes to seamount fieldwork. It is expensive. Fishing by-catch has provided almost all of what we know about these seamount communities.

The threat

There is widespread and growing concern about the impacts of bottom trawling on deep-sea habitat. The fisheries’ impact is intense. Australian studies, using underwater photography, recorded trawled slopes scraped almost bare of life, and found piles of fragmented coral rubble around the base of trawled mounts. They concluded that the

invertebrate sea life was highly vulnerable to trawling. In May 1999, the Australian government declared about 20 percent of the Tasmanian seamounts, some 370 square kilometres, to be marine reserves, protecting the fauna of 70 seamounts. New Zealand figures indicate that most of the by-catch is taken in the first few trawls. The nets have heavy rollers that run along the seamount surface, crushing everything in their path. In a recent survey, six trawls over previously unfished seamounts hauled up three tonnes of coral, while 13 trawls over fished seamounts hauled up only five kilograms of coral. Bottom trawling of seamounts can create the kind of damage that bulldozing blindly through a native forest would do on land. But unlike our forests, where the public knows and cares about how many rare kaka and kiwi are left, we can’t see what’s happening on seamounts, and scientists know very little about the ecosystems. Scientists do know that these deep-water creatures are slow-growing, very long-lived, slow to reproduce and — like creatures in other environments where it is cold or dark and there is little natural disturbance — slow to rebound after disruptions.

A 1999 NIWA report on seamounts, compiled for the Department of Conservation, says ‘in the short-term, the impacts of bottom trawling on resident seamount populations appears to be considerable.... There are sound arguments for providing protection to a number of seamounts. Protection of biodiversity, given a potentially high level of endemism, and the differences between seamount and slope fauna, is important. The report also notes that the fishing industry is actively seeking out new seamounts to target. And it states that there is not yet enough information about seamount fauna to determine which seamounts have representative fauna. A lot more research needs to be done. Meanwhile, unique areas of valuable natural diversity remain unprotected, and vulnerable to damage.

JO MACKAY is a Wellington-based freelance writer about the outdoors and its issues.