Deep Trouble from our Damaged Oceans

How Our Seas are Changing,
by Callum Roberts, Allen Lane, 390pp.

Reviewed: 15 September 2012

The deafening political noise around atmospheric carbon emissions can distract us from the even more critical state of our planet’s oceans. The usual political failures, tendentious denialism and buck-passing seem to frustrate any attempt to moderate human destruction of the environment on which our collective future depends. Complacent land-dwellers see oceans as a limitless, self-renewing resource. We associate alarm about the oceans with the hairiest fringes of environmentalism. Professor Callum Roberts assembles a sobering case for how human abuse of the oceans is hastening us toward extinction, and suggests some things we could do to delay it.

The plight of the seas is not about the extinction of photogenic clown-fish or pretty pink corals – it is about threats to the very engines of life as evolved on this planet. Earth only acquired its oxygen-rich atmosphere in the latest ten percent of its history, and it was ocean-dwelling bacteria that generated the oxygen in quantities that enabled the evolution of land-based plants and animals, ourselves included.

The oceans are still the primary forces that drive earth’s atmosphere and the climate we experience from it. The mass and energy of the oceans is many times that of the atmosphere, and slow-moving oceanic currents transfer solar and geothermal heat between equator and poles, setting up the forces that we experience as climate and weather events like El Nino or the tropical monsoons.

Warming oceans will eventually produce radical changes in local climate, with some winners and many losers. Sea-level rises, from melting ice and from expansion of the ocean water itself, will not be sudden. But even recent rates of 3 millimetres per year will present massive problems for most of the world’s most densely-populated cities and agricultural zones, which happen to be located near sea-level. Roberts attributes most of the current warming to human atmospheric pollution, and he warns that warming could accelerate quite suddenly as permafrost, under shallow Arctic seas, melts to release massive amounts of trapped methane. The process has already begun in the Russian Arctic.

The geological record shows that sea levels once rose three metres within a century, at the dawn of human pre-history about 120,000 years ago. The cause was probably a greenhouse of volcanic ash and gases, but it demonstrates that the balance between ocean, ice and atmosphere can cross a tipping point with dramatic and rapid results. Since human-generated greenhouse emissions are the only factor within our own control, Roberts supports the absolute urgency of exploring every possible strategy to restrain emissions and promote environmental carbon sequestration.

As a professor of Marine Conservation, Callum Roberts is most directly engaged with ecology within the oceans. He sees modern humans as responsible for the gravest threat to the ocean biosphere in 55 million years – which puts us on a threat level equivalent to the asteroid strike blamed for the last Great Extinction Event. We are destroying the ecology of our oceans by what we take out of them, but more importantly what we put into them. The oceans are becoming more acidic due to human carbon, nutrient and other chemical emissions, and this threatens to annihilate organisms that sustain the lowest levels of the oceanic food-chain.

The web of micro-organisms that condition the water, oxygenate the atmosphere, and feed the next level of life, is becoming unbalanced with potentially dire consequences. Pesticides and other residual chemicals, shunned on land, continue to accumulate in the oceanic biomass. Excess nutrients, flooding from our agriculture and aquaculture practices, create semi-desert monocultures where once biodiversity prevailed in the nurseries of oceanic life. Mangroves, coastal sea-grass plains, and coral reefs are the most directly affected and the most critical to maintain life in the seas.

Roberts recognizes and supports the harvesting of marine life for human consumption, but he castigates the stubborn way that humans persist in destroying that upon which our growing population depends. Since the development of steam-powered trawlers, we have a history of unsustainable fish harvesting. We defy an elementary rule of capitalism, by consuming the capital resource rather than the income it generates. More and more mechanical power has been employed to harvest smaller and fewer fish. Globally, the wild fish harvest has been in decline for the past fifteen years. But commercial interests, with government connivance, employ more and more powerful machinery to hoover up the last remnants of wild fish populations from places where they could previously hide and breed. And in employing these powerful trawls and dredges, the industry is progressively destroying the reefs and the biodiverse seabeds that nurture future generations of the fish they are catching. As collateral damage, by-catch fish not wanted for sale are destroyed often at a rate far higher than the target species.

Further damage results from the human preference for fish at the top of the food chain. The mass harvesting of shark, large squid, tuna, salmon, cod, lobsters and other predators unbalances the ecosystem in ways that can result in collapse of complex ecologies. Over-fishing of lobsters has led to local population explosions of sea anemones and extinction of corals. Human transportation of fish and other marine species to new habitats has also been highly destructive in ways that were never predicted. And size limits on individual fish, which encourage taking the biggest specimens, can also backfire, because in many species the older, larger animals produce many times the offspring of their younger, smaller sisters.

Without drastic action, Roberts sees our strip-mined oceans reduced to supporting vast rafts of plastic rubbish and populated by little more than hordes of jellyfish and scavenging prawns. He tries to relieve the gloom with some positive suggestions. Most immediate and achievable is his advocacy of substantial marine reserves, including mid-ocean reserves, where fish species can breed, viable stocks recover, and natural biodiversity can survive. Where reserves have been implemented the evidence of recovery is overwhelming, bringing objection only from the most short-sighted opportunist fishing interests.

For fish-eaters stricken with guilt, he offers a few choices for low-impact predation. The rule of thumb is to favour eating from low down the food chain – so eating molluscs, sardines and small crustaceans is more ocean-friendly than tucking into tuna or salmon. Now that’s a challenge that could really hurt.

Richard Thwaites is a land-dwelling omnivore with a taste for fish and challenging books.