Alien-like crustacean plankton gets barcodes
Naturalis Biodiversity CenterIn the open ocean, zooplankton plays a very important role in the food web. The diversity of zooplankton is therefore a good indicator of the health of the ocean. Due to the short lifespan of plankton, the species composition reacts quickly to the effects of climate change, for example. To monitor these effects, it is important to distinguish between plankton species at the species level and to map their habitats. But above all, it is very interesting to learn more about plankton.
From twilight zone to horror
Katja Peijnenburg is an evolutionary biologist specializing in zooplankton. Together with her colleagues, she studied a special group of amphipods. She explains why these animals are so interesting: "Many amphipods live on the seabed. But the group we studied, the hyperiids, has colonized the open water column and is planktonic throughout its life, especially in the deeper water layers. This is the twilight zone of the ocean, between 200 and 1,000 meters deep. They have very special adaptations to live there. For example, they have very elaborate and developed eyes. Some species have as many as twelve independent retinas per eye! This makes them look alien-like."
The amphipods look so alien, they have even made it to the big screen. "One of the species we have worked on was used as a model for the horror film Alien. That species catches little jellyfish, hollows them out, and lays eggs in them. It then becomes a kind of spaceship for her brood care. She goes out to hunt plankton at a depth of 500 to 800 meters."
Amphipods of the genus Phronima lay their eggs in jellyfish en make a sort of spaceship out of them for their brood care (source: CNRS)
Important, but not well known
To study the amphipods, Katja and her colleagues collected planktonic amphipods along around 15,000 kilometres of the open Atlantic Ocean. The species in this animal group are widespread and common in the world's oceans. There, amphipods are an important part of various ecosystems. They live in symbiosis with other zooplankton such as jellyfish and are prey for larger animals, including fish that are important for commercial fishing.
Yet we still don't know how many species of amphipods there are. So why is it that we don't know much about amphipods? According to Katja, this is due to where the animals live. “The main reason is that it's not easy to take samples in the South Atlantic Ocean at a depth of 500 meters. You need a research vessel with a crane and nets, which is of course very expensive to organize.”
More research on plankton
According to Katja, research on plankton is getting more attention. “People are very interested in plankton at the moment, because it quickly reacts to climate change. The distribution areas of the different species are shifting towards the poles at a rate of ten to twenty kilometers per year. By measuring the diversity in the ocean, you can see what is happening at the base of the food chains.”
That is why Katja felt the need to make the DNA barcode available to other researchers. "Six or seven years ago, this research was an internship project by Marloes Tump, the lead author of the article. We had previously written a manuscript about which species occur where. But these DNA barcodes were not yet available in a publicly accessible database. I felt an obligation to make the data available so that others could continue working with it."
In total, the team examined 273 amphipods, collected from north to south in the Atlantic Ocean. This yielded DNA barcodes for 63 species, which have been added to the Biodiversity of Life Database (BOLD). According to Katja, this is significant data. “No DNA barcodes were known for 17 species from the Atlantic Ocean, and no DNA barcodes were known for 26 species.”
No more need for a microscope
Amphipod expert Ronald Vonk collaborated on the research and explains why it is so important to make the DNA barcodes public: "Now it is no longer necessary to first identify the individual amphipods under a microscope based on their morphological characters. We already carried out this time-consuming process prior to barcoding, and now those codes are linked to the morphological characters of the amphipod species and can be found in the DNA reference database and our Naturalis collection.“
According to Katja, DNA barcodes are crucial for new methods of researching marine life. ”A lot of work is now being done with environmental DNA. You can filter seawater and find all kinds of DNA from organisms that live in it. You end up finding an enormous amount of DNA. But without a good reference, you don't know what's in it. That's one of the reasons why I think it's so important to describe everything that lives in the ocean and add it to a reference database."
New species to discover
The team also found a lot of variation within the species. This indicates the presence of as yet undescribed species of amphipods. Katja is enthusiastic about this: “If you have one species that occurs all the way from the North Atlantic to the South Atlantic and you look at it closely, you'll see it's not all the same. We humans have given it all one species name, but in fact it may be five different species. As an evolutionary biologist, I find that fascinating.”
Moreover, distinguishing between species is important if we want to know how life in the oceans is changing. "As humans, we are not very familiar with ocean life. If we think that it's all one species, but there are actually several, then they probably have a completely different biology. For example, they may eat different things or live at different depths. We greatly underestimate the diversity that exists in the ocean. We lump everything together that’s actually different species that may also respond differently to climate change."
So there is still a lot to discover about amphipods. Katja therefore wants to emphasize that publishing the DNA barcodes is very important, but only a small step toward learning more. “This is really just mapping biodiversity. We realize very well that with this research we are only scratching the surface. There is still a lot of unknown biodiversity in the ocean, but for amphipods this is a big step forward.”
Text: Naturalis Biodiversity Centre
Images: Katja Peijnenburg & Erica Goetze
Video: CNRS