Tales from the Green Sands (7)

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Science is not magic, nor does it work any. A scientific experiment is only any good if you build in a control group. In any scientific experiment you hope to measure an effect of the experimental treatment you have imposed onto your subjects. This can be the effect of certain chemicals on eating behaviour in rats, the effect of psychological stress on decision making in humans, or even a model simulation of average global temperature changes under different CO2 emission scenarios. However, without the control group, the values you measure can be as good as any. Rather, if you have a similar group of subjects, which pass through the experiment unaware of any treatment you have bestowed onto the others, you have yourself an experimental control group. That control group provides a baseline, that tells you what the background values are of the process you are trying to investigate. And when you know the background values of your control group, you can demonstrate what the effect is of the particular treatment you are investigating.

In our case, we were investigating the effects of the presence of naturally dissolving olivine on the environmental chemistry of an entire bay on an island in the Hawai’ian archipelago. To incorporate a control group, we would need an entire bay, without dissolving olivine, preferably on the same island. The best control group we could have is a typical tropical white sand beach, which consists almost entirely of calcareous sand. “That should not be too hard on a tropical island, right ?”, I hear you exclaim. Well…sort of…yes, or rather: no. It is harder than one might think. White sand beaches are normally formed by…coral reefs. Yes, the tiny sand grains on tropical white sandy beaches once were colourful corals. How ? Well, there is a group of fish that eats the calcareous skeleton of corals, in order to reach microscopic algae that live INSIDE the coral skeleton. That’s right, corals do not only have algae in their soft parts, but also inside their “bones”. These highly specialised fish, called parrotfish, have strong teeth that look like a parrot’s beak to grind the coral skeleton, so they can reach their food. What happens inside the parrotfish’ body stays inside the parrotfish’ body. But what comes out is freshly ground coral, in tiny white, calcareous sand grains. Next time you are snorkelling around a tropical coral reef, keep a look out for parrotfish. You are bound to see one pooping, which looks like it has a fast-sinking, white smoke trail behind it. Tropical white sand beaches are actually parrotfish poop, people…get used to it !

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So, what does this have to do with finding an experimental control group, while investigating an olivine beach on Hawai’i ? Well, most land masses on Earth are hundreds (if not thousands) of millions of years old, which is plenty of time for organisms to settle and evolve. In contrast, the Hawai’ian islands are relatively young. The oldest islands, located in the North-Eastern tail of the archipelago, already exist for several million years, while Hawai’i (Big Island) is only max. 400.000 years old. Now, think of the beautiful, but rather violent manner in which these volcanic islands are born: enormous volumes of red-hot molten rock are pushed from the fluid belly of the planet through fault cracks in the massive crust, only to solidify once it comes into contact with seawater. This is still going on on the south coast of Big Island. Every year, the island grows towards the south-east, by lava flowing into the Pacific Ocean. The newly formed rocks cool down, and -after a while- become colonised by living organisms, like corals. Given enough time, both parrotfish and pounding waves will grind corals into white sand beaches. But when an oceanic island in the center of the largest water body on the planet has only just been born, there has simply not been enough time to form white sand beaches. Luckily, the north-western parts of Hawai’i are old enough to have some stretches of white beach, and we had secured a permit to go sampling on Makalawena Beach. Unluckily, however…the ocean was much (MUCH !) rougher than you see on the regular websites praising this secluded paradise.

Although very nice for surfing, it was impossible to snorkel out and safely collect samples from further into the bay, as we had done at Papakolea/Mahana. Because the sea state did not quiet down during the entire period, we had to modify our plans somewhat. We were able to collect water, sediment, algae and rock-based animals close to the beach…always keeping one eye on the huge waves rolling in.

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