• Resurrection ecology

    Brought back to life

    It is just like Jurassic Park – okay, maybe only a little bit like that. Piet Spaak is not bringing dinosaurs to life, but daphnids. That is pretty cool, too.

    in short

    RUG alumnus and aquatic ecologist Piet Spaak has devoted his life to the daphnid (water flea).

    The daphnid may seem like an insignificant creature, but it is valuable for learning more about ecosystems and evolution.

    Spaak allowed eggs to hatch, some of which had been buried in the sediment of the Swiss lakes for decades. The daphnids which had been brought to life thus had the same characteristics that the creatures had 60 years ago.

    The ‘old’ daphnid turned out to be more resistant to pollution than its present day descendent.

    The original Daphnia longispina also made way for the Daphnia galeata or a hybrid of the two. That species was better equipped to cope with the new environment.

    The loss of biodiversity is worrying. ‘We have to realize that each bit of biodiversity that we lose makes our ecosystem more vulnerable as a whole.’

    full version

    Reading time: 6 minutes (1,125 words)

    It is a seriously underestimated creature, the daphnid. Daphnids are teeny tiny crustaceans, only one to two millimeters long, millions of which are found together in lakes and pools. Their goal in life: to eat algae and reproduce until they are eaten by a fish. This makes them a keystone species in learning more about how ecosystems and evolution work.

    RUG alumnus Spaak is an aquatic ecologist at the Swiss water institute EAWAG, but he has devoted his life to that small creature. ‘There is nothing better than a daphnid,’ he says. On Thursday, he visited the Groningen Institute for Evolutionary Life Sciences (Gelifes) to give a lecture about his research.

    Take the fact that they predominantly reproduce asexually, for instance; girl power, he calls it. Put a daphnid – typically a Daphnia galeata – in a jar with algae and in no time, the algae will be gone, but you will have a jar full of wriggling clones.


    It is only when times get tough, such as during a food shortage or excessive pollution, that they turn to sex. The female then produces two eggs which she protects in a sac inside her body. Once she gets bored, she releases them. ‘The convenient thing is that a daphnid is transparent, so you can see how many eggs they have’, Spaak says gleefully. The eggs are fertilised by a ‘sister’ which is produced for the occasion by the males. This is how the possibility for bringing new characteristics to the species arises occasionally.

    And then there is the fact that the sexually fertilised eggs sometimes do not hatch at all, lying dormant in decades old sediment layers of fresh water lakes instead. You can also date the eggs: each year, a new layer of algae is formed, and these layers can be counted just like the rings of a tree. With the help of caesium 137 tests which recognise particles that were released by nuclear explosions, it can be precisely determined which sedimentary layer is from the years of the Chernobyl disaster, as well as the above ground atomic tests in 1965 in America.

    Lastly, you can hatch the eggs just by putting them in a bowl of water, giving them a little bit of light and ensuring the temperature is mild, ‘about 20 degrees’.


    The end result is a daphnid with the genetic material of the species from 60 years ago, which is infinitely interesting for evolutionary biologists who want to know how the changes in water quality have affected various organisms. Ecosystems were being polluted at a breakneck pace in Europe 50 years ago: heavy metals ended up in the surface water. Washing detergents were full of phosphates, which meant that the lakes and ditches were so nutrient-rich that algae growth went through the roof. ‘And if the algae was not eaten, it would die, sink to the bottom and rot. In the rotting process, the algae would use up so much oxygen that the fish would die.’

    How did aquatic life equip itself to deal with this threat? After all, there are still daphnids and fish in the water of the Greifensee, which is where Spaak is doing most of his research.

    Spaak knows the answer, because when he brought the daphnids from the ‘70s and ‘80s back to life, he found that they were more resistant to lead pollution than their modern-day descendants. In other words, the creatures developed resilience in a relatively short period of time which they subsequently lost. ‘We don’t know why exactly’, he acknowledges. ‘It seems to have cost them something from an evolutionary perspective, which resulted in them losing their ability once more when waste water treatment plants started cleaning up the water.’


    Is that bad? Spaak hesitates. He does not really like the word ‘bad’. The daphnid is not an endangered species and Spaak himself is not willing to take to the streets to defend his beloved arthropod. But when the lakes were polluted, the characteristics of the galeata, which reacted better to the high levels of nutrients, could have saved the ecosystem. The fish do not care about which daphnids they eat. But what if something like that were to happen again? How many hits can an ecosystem take?

    If he knows anything, it is that the ecosystems he studies are extremely complex and you cannot just tinker about with one component. ‘Fishermen in Switzerland complain because they don’t catch many fish’, he says. ‘Due to the water being cleaner, it is less nutrient-rich and there are fewer fish. They argue that the waste water treatment facilities could be switched off every now and then, for example.’


    The extinction of species occurs much quicker in fresh water areas than on land or at sea, says Spaak. ‘Seventeen of the more than one hundred known species of fish in Switzerland are extinct, and 60 per cent of the known water plant species are endangered. At the other end of the chain, fewer and fewer species are coming into existence or being discovered’, says Spaak.

    We should be concerned, he says. ‘We have to realise that each bit of biodiversity that we lose makes our ecosystem more vulnerable as a whole. If something should go wrong, be it a natural disaster or an epidemic, there are not enough species to take the blow.’