South Tasman SeA / Lord Howe Rise

Salas y Gómez and Nazca ridges

Imagine a mountain range the length of the southern Andes –110 volcanic peaks, stretching nearly 3,000 km end to end. Imagine these mountains are filled with rare, spectacular wildlife, that nearly half the species they shelter live nowhere else on Earth, and that scientists are discovering new life forms with every expedition. 

Now stop imagining, because these mountains are real: they’re called the Salas y Gómez and Nazca ridges, and are deep in the waters of the South East Pacific.

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These two unique chains of submarine slopes and summits areseparated from South America by the rich, cold waters of the Humboldt Currentand the yawning abyss of the Atacama Trench. Numerous studies have concluded they’reamong the most ecologically significant areas in the high seas – those areas ofthe ocean that lie beyond the jurisdiction of any country. Far below the waves intricategardens of slow-growing corals and gorgonians adorn the rocky slopes in some ofthe clearest waters on the planet, and in the plankton-abundant upwellings overthe ridges sharks, turtles, whales and seabirds gather to forage. This uniqueregion is a vital habitat for commercial species too, from swordfish to jackmackerel, underpinning sustainable food security for millions – but only if welook after it.

Threats and the future

The Salas y Gómez and Nazca ridges are still largely ecologically intact, but biodiversity and ecosystem resilience are never the less under threat. Deep-water trawling has destroyed coral and seabed habitats down to depths of 2,000 m, and has taken a heavy toll in bycatch of animals and plant life alike. Floating plastic debris drives the risk of ingestion and entanglement for nearly 100 species. Meanwhile climate change is making the seas warmer, less oxygenated and more acidic, all of which pose an existential threat to marine biodiversity .

Ominously, there’s cobalt in the crusts of the Salas y Gómezand Nazca ridges, which the deep-sea mining lobby may one day step up effortsto exploit – but doing so would be an ecological disaster.  

We’ve got a time-sensitive window of opportunity. By permanently closing the area to fishing and mining and establishing a high seas MPA, we can save the Salas y Gómez and Nazca ridges for ourselves and for future generations. And with 80% of the mountains still unexplored, there’s surely so much more for them to discover…

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Back to the surface

Emperor Seamounts

No mechanism yet exists to establish marine protected areas (MPAs) in the high seas. It’s critical that the new United Nations High Seas Treaty sets up a global process for the establishment and effective management of a wide-ranging network of MPAs, including highly protected areas where no harmful industrial activities are allowed.

Researchers have called it ‘a volcanic lost world’. In the waters of the South Tasman Sea, a complex of mountains tower above abyssal plains; and a vast plateau – the Lord Howe Rise – looms up in the north to create its own unique landscape a mile below the surface.

The topographical features in these waters between Australia and New Zealand come in many forms. There are seamount summits at depths as shallow as 200 m, while the Lord Howe Rise reaches the surface at the Middleton and Elizabeth Reefs and Lord Howe Island – the three most southerly coral reefs on Earth. Elsewhere are guyots, canyons, ridges and rocky outcrops, with soft sediments making up most of the seabed. In the deeper waters of the South Tasman Sea one seamount towers up to within 25 m of the surface from a base 4,500 m down.

This is a diverse and dynamic ocean area, with high primary productivity supporting a wealth of marine life. The South Tasman Sea ranks highly on four out of the seven Ecologically or Biologically Significant Marine Area (EBSA) criteria, including characterization as an important breeding ground and migration corridor for a large number of species. It also contains five Important Bird and Biodiversity Areas (IBAs), and is frequented by vulnerable species including Antipodean and wandering albatrosses, and providence and Gould’s petrels – 50-65% of the world population of the latter come here in the breeding season. Marine megafauna including humpback and southern right whales gather to rest in the waters below as they journey between their feeding and breeding grounds.

The Lord Howe Rise in the north is home to hundreds of species, many of which are likely to be endemic. Acorn worms, sea pens, whip corals, shrimps and other animals live in its soft sediments, while cold-water corals and sponges populate the rocky seamounts. At least 348 demersal fish species have so far been identified, and 25% of these may be new to science. In fact, surveys have shown that between 31-78% of all species recorded here are new discoveries – and the many areas of the Rise which remain unexplored are sure to reveal more undiscovered marine life.

Threats and the future

The South Pacific Regional Fisheries Management Organization (SPRFMO), which oversees fisheries activity in the region, has identified numerous vulnerable marine ecosystems (VMEs) at fishable depths on Lord Howe Rise and in the South Tasman Sea. But these fragile deep-sea hotspots of biodiversity have to date received almost no official protection from bottom fishing, the biggest threat to their ecological integrity: trawl gear can devastate slow-growing corals and sponges, which may take decades to recover – if they recover at all. Fisheries have targeted orange roughy here since 1988, and activity is still on the rise: Australia fishes on the seamounts in the north-western portion, although so far central and northern sections have remained largely untouched. On the surface, seabirds risk ending up as bycatch when they come into contact with longlining vessels.

Australia and New Zealand have both safeguarded adjacent domestic waters by respectively designating protected areas around Lord Howe Island and the Norfolk Deep, but the lack of protection for the wider area reflects how much harder it is to manage such processes on the high seas. Widespread protection is nevertheless essential: species distribution modelling shows that only closing limited areas on the Lord Howe Rise won’t be enough to protect the rich regional diversity of marine life.

Ecosystem resilience is all the more important in the face of climate change. The South Tasman Sea recorded its longest and most intense heatwave in 2015-16, and projections show such events will almost certainly increase as the planet continues to heat up. The impacts of climate change – particularly warming and ocean acidification – pose a huge threat to the cold-water corals and associated species living on the seamounts. Climate change is also likely to disrupt the East Australian Current  and the Tasman Front, affecting the quality of water and the distribution of nutrients – and hence of the species that depend on them.

Several important bodies have called for this unique area to receive priority protection – and because this truly special place is a global common, we can only effectively protect it through an international treaty. By permanently closing the South Tasman Sea and Lord Howe Rise to fishing and establishing a high seas MPA through a new UN High Seas Treaty, we can save them for ourselves and for future generations.