frogblog

Coral, A Pessimist in Paradise is the new book (2007) from science writer Steve Jones. It’s a bit of a ramble in parts but interesting enough. His focus is unsurprisingly coral - a quarter of all sea fish live on reefs, polyps lay down calcium carbonate that locks up carbon - but he wanders over any range of ecologically linked topics, especially marine ones.

It’s a sobering read.

He covers the dispute between Darwin and the American zoologist Alexander Agassiz as to the origin of coral atolls. Darwin argued that the coral formed on top of basalt mountains that subsequently subsided. In the process he implicitly put forward a theory of a not-totally-solid Earth, which was pretty challenging in the era before the emergence of plate tectonic theory. The dispute was only resolved when the US decided they wanted to examine the fractured Bikini atolls after nuclear tests and drilled down to find basalt under 1411 m of coral rock. Like an ancient civilisation built upon layer of layer of coral rock, the polyps stayed close to the surface by growing as fast as the basalt rock subsided, but also adjusting to the variations in sea level over the millenia.

Deep sea bottom trawling is one of the issues he touches on at less length than I would have preferred. New Zealand has played a key role in the bottom trawling industry, in the process destroying vast areas of deep sea corals. Deep sea corals are polyps like the near surface tropical coral but their ecology is a bit different (no light so no dinoflagellates). They can be 300 metres high and several kms across. They are oases of fertility inhabited by fish and other creatures in otherwise sterile oceans. And hence why the fishing fleets target them - he estimates that each ton of orange roughy lifts two tons of destroyed ancient deep sea coral.

He also covered the impact of sediment. This is something that is not given a lot of consideration in NZ where tonnes of sediment run off into waterways and ultimately onto the benthus, smothering the sponges and filter feeders living on the sea floor. The impact of land clearance and farming on the Great Barrier Reef is well documented but is continuing anyway.

He covers the near fatal impact of European colonisers on the people of the Pacific at some length. I have spoken about the way the civilisation of Rapa Nui (Easter Island) collapsed from destruction of its natural resource base, and Jones covers this as well as the detrimental impact of Polynesian colonisation on the fauna of many Pacific Islands. However, he also covers the catastropic impact of Western diseases on the people living on the islands and the, at times, barbarous behaviour of the Europeans in destroying the Polynesian civilisations they come across.

And he has an interesting take on symbiosis, seeing it as a relationship with considerable tension and conflict. Often people look to examples of cooperation and altuism in nature to make a case for a genetic basis for human cooperation, but Jones isn’t too sure. He looks at the role of the dinoflagellates, independent photosynthesising organisms that live within the coral polyps and provide them with carbohydrates, protein building blocks and sugars. In return the polyps provide the dinoflagellates with shelter and a supply of carbon dioxide, ammonia and hydrogen ions. Polyps with dinoflagellates on board lay down carbon on average at three times the speed of coral without the extra help. Amazingly tropical polyps with dinoflagellates lay down carbon at twice the rate of a rainforest, and generally in more secure long term storage, though humans are interfering with that.

But it’s not all win-win. Each side of the symbiotic relationship keeps a close eye on the cost/benefit analysis. In the dark the dinoflagellates actually consume more of the resources of the polyp than they contribute. And when food is abundant the polyps do better without the dinoflagellates anyway. And from the dinoflagellates point of view, they divide at a much slower rate when they are inside the polyp rather than swimming free. Thus, if the polyp isn’t getting enough out of the relationship, then the cells housing the dinoflagellates die and the dinoflagellates are expelled. And if the dinoflagellates aren’t getting enough then they produce nitric oxide and flee the host.

Bleaching is an instance in which the dinoflagellates are no longer able to be productive, usually because of raised temperatures, and are expelled from their hosts. The symbiotic relationship takes a break and the dinoflagellates swim free. Not a perfect marriage after all - for richer and poorer is not in the contract. It’s not necessarily the end of the coral, as when things cool down the dinoflagellates, or even new species of dinoflagellates, recolonise the polyps. But not all polyps survive well without their assistants as their metabolism, reef building and sexual activity drop, and a series of bleaching events can kill coral reefs and we are seeing this with increasing frequency. 

Combine global warming with all the other assaults on reefs such as fishing, introduced pests, sediment run-off, mining and tourism and you get a global decline in coral reefs. And like all ecological systems, destroying one part impacts on the rest. The extermination of the turtles and seagrass eating fish in the Caribbean was instrumental in the destruction of nine tenths of the coral in that Sea as the grass grew and its decayed remains shaded out the coral polyps.

The coral will be a witness and a record of our folly or our wisdom.

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