When I was a uni student some people used to think it was terribly witty to hold up signs saying “Save the krill, harpoon a whale”. Some time ago I wrote an article on research showing that fewer whales actually meant less krill. The explanation for this puzzle was that whales fertilise the ocean. Their faeces is rich in iron, which phytoplankton feed on and is in turn eaten by krill.
However, I was left still puzzled. Whales don’t produce iron through some strange alchemy after all. If they absorb the iron through the krill and then release it again how do they add to the system? I can’t remember if I didn’t think to ask this question until after the interval was over, or if I asked it and didn’t get an answer I could understand. I guessed that maybe there was a problem if the krill hoarded all the iron so that the phytoplankton died. Whales were needed to come along and kick the cycle over. IIRC whales were better at this than some other marine species, whose faeces was more likely to sink to the bottom of the ocean, taking the precious iron with it.
Today however, I had this explained. Interviewing the prolific Professor Carlos Duarte about a related but separate matter I learned that whales take in the iron, from what source is not clear, when they are in tropical or northern waters, most of which are not deficient in iron. Then they return to the Southern Ocean, do their business while feeding on the krill that has flourished because of the same thing the previous year. Duarte described them as gardeners, bringing the nutrients to where they are needed.
Environmentalists are often attacked for only being concerned about the “charismatic megafauna” the big cuddly or beautiful animals rather than the less glamorous species that dominate the ecosystem. Examples like these however, remind us how important these big species can be. Antarctic krill are by body weight the only species on Earth that outranks humans and the basis of much of the global foodchain but they need baleen whales to flourish.
It was very much a marine biology day, as it turned out. The interview with Duarte was about a surprising comparison of the Arctic and Antarctic food chain. It turns out that in the Antarctic 41% of common species are predators, but in the Arctic this is 81%. Duarte described the Arctic food web as “top heavy” and therefore more vulnerable to disruption. He says the reason for this is that it is much newer. Changes to glaciation a million years ago disrupted the system and it has yet to fully settle, whereas the Antarctic has not changed drastically in much longer. Human impacts, such as wiping out Stella’s Cow, may also have been a factor.
For the next Cool Scientist I interviewed Dr Lexa Grutter, one of my favourite scientists. Grutter has transformed our knowledge of cleaner fish, with one fascinating discovery after another, even though for the last six years she has been too sick to research full time, let alone scuba dive on the reef.
In other whale-related writing, last week I did an interview, which I only got to write up today, about the first intact specimens of what is considered the world’s rarest whale, the spade-toothed beaked whale. Prior to a mother and calf ending up beached as in New Zealand’s Bay of plenty all we knew about these whales was that they existed and were a different species from Grays beaked whale, which they closely resemble. We knew that much from three fragments of skull and jaws, two washed up in New Zealand and one in Chile. As the scientist who identified the two stranded whales as being spade-toothed, “The fact that such a large species has never been seen alive shows how little we know about the deep southern ocean.”
I also did an interview about some impressive but deeply disturbing research on ocean acidification, of which more later.
Explanation: One person expressed confusion about this line “Antarctic krill are by body weight the only species on Earth that outranks humans” what I mean is that the total mass of all the Antarctic krill (a species, not just a geographical designation) is greater than that of any other species – by some estimates 10% of the mass of all the animals on Earth. Krill are small, but there are a lot of them. I’ve seen it reported that humans are second, although I suspect cows give us a run for our money.