Alien-like crustacean plankton get barcodes
Naturalis Biodiversity CenterIn the open ocean, zooplankton play 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 seafloor or attached to surfaces. 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 like aliens."
Hyperiids look so strange and otherworldly that they’ve even inspired Hollywood. One of the species we studied was actually used as a model for the creature in the sci-fi film Alien.This species captures small jellyfish, hollows them out, and lays its eggs inside. The jellyfish then serves as a protective vessel — almost like a spaceship — for brooding the young. The mother goes in and out to hunt for plankton at depths of 500 to 800 meters while her offspring develop inside."
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 hyperiid amphipods, Katja and her colleagues collected zooplankton species along a ~15,000 kilometer transect across the open Atlantic Ocean. These animals are widespread and common throughout the world’s oceans, where they play a key role in marine ecosystems. Amphipods often live in symbiosis with other zooplankton, such as jellyfish, and serve as prey for larger animals — including fish that are important to commercial fisheries.
Yet we still don't know how many species of amphipods there are. So why is it that we don't know much about hyperiids? According to Katja, this is, in part, 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, for example. You need a research vessel with a crane and nets, which is of course very expensive and time-consuming 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 responds 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 barcodes available to other researchers. "Around ten 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 led by PhD student Alice Burridge. However, 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 hyperiid amphipods collected along a north–south transect of the Atlantic Ocean. From these samples, they generated DNA barcodes for 63 different species, which have now been added to the Biodiversity of Life Database (BOLD). According to Katja, this is a significant contribution: “For 17 of these species, no DNA barcodes had previously been recorded from the Atlantic, and for 26 species, no DNA barcodes existed at all.”
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 available: "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. But without a good reference, you still 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 discovered a great deal of variation within individual species — suggesting that some hyperiids currently classified as a single species may actually represent several, as yet undescribed, species. Katja explains with enthusiasm: “When you examine a species found from the North Atlantic all the way to the South Atlantic, it might look the same at first glance. But when you look more closely, you realize it’s not. We’ve been calling it one species, but in reality, it could be five. As an evolutionary biologist, I find that fascinating.”
Accurately distinguishing between species is essential if we want to understand how marine life responds to a rapidly changing ocean. “As humans, we’re not very familiar with life in the ocean”, Katja explains. “If we assume something is a single species when it’s actually several, we risk missing crucial differences. These species might have completely different diets or live at different depths. We’re greatly underestimating the true diversity of plankton — and by grouping distinct species together, we may overlook how differently they respond to climate change.”
So there is still a lot to discover about hyperiid amphipods. Katja therefore wants to emphasize that publishing the DNA barcodes is very important, but only a small step towards 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.”
More information
- The scientific article: 'Genetic diversity of hyperiid amphipods along a meridional transect in the Atlantic Ocean' (pdf: 4,2 MB), published in Contributions to Zoology.
Text: Naturalis Biodiversity Center
Images: Katja Peijnenburg & Erica Goetze
Video: CNRS