Deep trouble: Sea to dying sea

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There is a growing scientific consensus across the world that the oceans are in deep trouble and that humanity is responsible.

The symptoms include collapses in fish populations, deaths of coral reefs, the contamination of sea life with toxic chemicals, the pollution of shallow seas with sediment and nutrients causing algal blooms, changes in the currents that distribute energy around the planet and signs that the oceans are becoming more acidic.

In The Silent Deep, due out soon, Australian marine scientist Tony Koslow – formerly of CSIRO, now at the Scripps Institute in California – traces the discovery, exploration and plunder of the deep oceans in the past few decades. In it he states:

“We may think of the deep sea as pristine, but in fact no portion of (it) is today unaffected by human activities.” Koslow likens the unsustainable deep-sea harvest to the destruction by Stone Age hunters of the megafauna of Europe, Asia, the Americas and Australia.

He explains that orange roughy stocks collapsed because they were fished down too fast, before we understood their size and turnover rates and could manage the fishing pressure.

Similar tragedies are occurring worldwide, wherever fish and corals gather on the peaks of deep-sea mounts: “Fishers in 25m boats can level a pristine coral reef at 1000m depth as readily as loggers with chainsaws and bulldozers can clear an old-growth forest.”

John Schubert, the Commonwealth Bank chairman who has taken up the cause of the Great Barrier Reef, has warned of the effect of climate change on the reef, giving as an example the death of half the corals off Great Keppel Island due to bleaching.

Scientists at the Australian Research Council Centre of Excellence for Coral Reef Studies are finding evidence that intact fish populations are essential for corals to recover from such blows.

Australia has been shrewd enough to introduce green zones (no-take areas) on one-third of the Great Barrier Reef, but this doesn’t apply to most of the world’s coral reefs, whose 200 million human dependents will be destitute if their corals die.

One interesting development is the Australian Marine Conservation Society’s increasingly popular Sustainable Seafood Guide, which advises consumers which fish to choose or avoid on the basis of their sustainability.

While the experts may argue about what is and isn’t a sustainable fish stock, the idea of transferring the onus for protecting marine species to consumers, rather than fishers, is a good one. Fishers can hardly be blamed for trying to make a living, but consumers can always purchase and consume more wisely, sending fishers the correct market signals.

The destruction of shallow seas and their aquaculture industries by the discharge of sediment, nutrients and pesticides from the land is a global problem that as yet has few answers, though efforts are being made to solve this in the catchments of the Great Barrier Reef and elsewhere.

An as yet undefined danger from the deep ocean is the so-called clathrate gun, a theory that warming could cause the violent release of trillions of tonnes of frozen CO2 from the seabed, precipitating a runaway greenhouse effect that would leave the planet more like super-hot Venus than Earth.

Another peril is acidification, which could devastate ocean life with planet-wide consequences.

The build-up of CO2 in the atmosphere produces acid rain which, as we have long known, affects the pH of lakes. As the 750 gigatonnes of carbon in the atmosphere increases, it could reduce ocean pH from 8 to 7.4 or lower. There are signs this is happening.

Acid seas would have a devastating effect not only on corals and shellfish, which would be unable to build their calcareous skeletons, but also on plankton, Earth’s most numerous and important life forms.