This week, IoM Friends of the Earth’s Tony Brown looks at the impact of rising ocean acidification on our planet, and our diets
In 2010, a report by the US National Research Council found that pH levels – the level of acidity or alkalinity – at the oceans’ surface had fallen from a measure of 8.2 in pre-industrial times, to 8.1 in modern times.
This has taken place as something between a quarter and a third of man-made CO2 emissions have been added to the natural absorption rates of those oceans.
Since pH is measured on a logarithmic scale, this means that there has been a 10-fold decrease in alkalinity – or to put it another way, an increase in acidity.
The rate of change is 100 times faster than anything the world’s oceans have experienced for the last few million years.
By 2100, pH levels could, it’s estimated, drop to between 7.7 and 7.8, if we continue to emit CO2 at present rates. A pH of 7.0 is ‘neutral’, so this is significant – it would be the lowest level for 55 million years, when during the Paleocene-Eocene thermal maximum (PETM), a sudden die-off of shell-based ocean life forms took place in the space of around 1,000 years. If projections are correct, our extra CO2 emissions will cause a similar demise in a few centuries, with no time for species to evolve or adapt.
After the PETM die-off, it took 100,000 years for crustaceans to gradually return.
Already, as acidification (or, more correctly, less alkaline) conditions progress, there are signs that organisms such as corals and oysters are beginning to struggle to secrete enough calcium carbonate to satisfactorily form their shells, as carbonate ions in the ocean decrease.
The shells of some animals have been found to be thinner than they were 300 years ago.
In February of this year, an acidification ‘spike’ around the coast of British Columbia wiped out an estimated 10 million scallops.
It looks as if our Manx scallops will have to face the effects of increased acidity over the years, as well as over-exploitation!
Formanifera, the tiniest shelled plankton, are also having trouble growing; and this matters because as the bottom rung of the food chain, plankton are the food base for almost all sea animals.
It’s easy to see how this could have disastrous effects for a range of life forms, including, of course, ourselves.
Coccolthophores, the shelled plankton that process sunlight in the same way plants do, also suffer from changes in ocean chemistry.
In the laboratory, pteropods, which are tiny swimming snails, dissolve in water with low alkalinity.
In the arctic, where acidification is progressing fastest, they may already be on the verge of extinction – a cause for concern, since they’re commonly consumed by fish such as salmon, haddock, cod and pollack.
Then there are the prawns, shrimp, crabs and lobsters which, although not as affected by less alkaline oceans as their shells are made out of the polymer chitin, changes in the ocean chemistry seems to harm the working of their gills and to alter the behviour of the young crustaceans.
The direct effect on finned creatures such as monkfish, hake, sardines and tuna is so far little understood, but there’s no doubt that a combination of over-fishing and changes in the food chain (such as those we’ve looked at here) are putting them on the ‘at risk’ lists.
What all this means is that deep, and vast, dead zones along the coasts are beginning to appear, where huge blooms of toxic algae, which thrive in less alkaline waters and are fed by human pollution, are causing oxygen depletion and rendering these areas virtually lifeless.
On top of all this, warming waters and strengthening currents have enabled some tropical species of fish to move polewards, devouring kelp forests and seagrass meadows, and leading to profoundly adverse effects on ecosystems and biodiversity.
This has already led to the collapse of Japan’s abalone fisheries where 40 per cent of the local kelp and algae beds have vanished since the 1990s under the accumulation of parrot and rabbit fish.
In the east Mediterranean, hundreds of kilometres of ocean forests have been destroyed by the influx of tropical fish leading to a fall of some 40 per cent in the variety of marine species to be found there.
So there’s even more reason than ever for us to cut our CO2 emissions dramatically, and take steps to remove the excess from the atmosphere by re-planting vast acres of forest, while at the same time halting deforestation.
If we don’t, it seems that your average wild seafood eater may have only jellyfish and a small amount of plankton on their dinner plate by the next century.