Sometimes, red algae grow in coral-like formations. A PhD student is the first to identify 21 of these reefs off the coast of Greenland.
By Martine Lind Krebs
The fishermen in Greenland are all too familiar with them—coral-like growths that become stuck in their nets when they are fishing for cod, lumpfish or salmon. In reality, they are free-growing coralline algae that grow to form coral-like reefs. However, while coral is formed from marine invertebrates, coralline red algae are a plant.
Grows 1 mm per year
Coralline algae are known from the tropics to the Arctic. Special light conditions and the currents cause them to grow in reef-like formations. Like this, they are also known as rhodoliths or maerl.
However, they do not grow overnight. Red algae grow at a rate of just 1 mm per year, so it takes about 1,000 years to form a one-metre-high reef.
Mapping of coralline algae in Greenland
Even though people have known about the presence of the reefs for a long time, no attempts have been made to map and describe them before now.
Helle Jørgensbye, a PhD student at DTU Aqua, has—together with Jochen Halfar from the University of Toronto—conducted the first mapping of coralline algae in Greenland. At the same time, their studies have revealed that the maximum depth at which red algae are found in Greenland is not 50 metres as previously thought, but 77 metres.
Helle Jørgensbye has identified 21 red algae reefs in Greenland at depths of 15–25 metres, and even though red alga in coralline formations are relatively rare, she is convinced that there are more.
The results have just been published in the magazine Polar Biology. DOI: 10.1007/s00300-016-1975-1
Sea urchins dislodge the red algae. Knowledge about where red algae are growing in Greenland may be useful in future for the commercial fishing of sea urchin. Photo Jonas Thormar.
Skyscrapers on the sea floor
From studies in other parts of the world, we know that red algae reefs, like coral reefs, support a high degree of biodiversity.
The significance of the red algae reefs for the fish stocks in Greenland has never been studied, but Helle Jørgensbye believes that they may play a crucial role in the life cycle of cod, which has also been proved in Norway.
“The reefs are like tower blocks. Many fish can live there in a relatively small area. We already know that a lot of creatures live on the reefs, for example blue mussel larva, sea urchins and crustaceans. So I’m very keen to see what young cod use the reefs for,” she says.
Sea urchins also benefit greatly from Greenland’s red algae—they eat from them. Greenland already engages in exploratory fishing activities for sea urchin, which is a big delicacy in Asia.
Mapping the reefs does not take place by sailing around Greenland with lots of biological equipment. Instead, Helle Jørgensbye searched the archives at the Botanical Garden at the Natural History Museum of Denmark in Copenhagen. Here, she discovered coralline red algae which had been collected in Greenland as long ago as the 1870s, among other things by the renowned botanist L. K. Rosenvinge. But no one had previously systemized and mapped the finds.
One of the red algae at the Natural History Museum of Denmark was even collected by the well-known polar researcher Peter Freuchen.
She compared her findings from the museum with new research from the large fjord near Nuuk, Nuup Kangerlua, which was carried out by the co-author of the article, Jochen Halfar from the University of Toronto.
Back catalogue of climate change
Because the red algae grow as slowly as they do, they can be extremely old. At Labrador in northern Canada, red algae have been found which are 1,600 years old, making them some of the oldest living organisms on earth.
Red algae can be dated like trees, as they also have growth rings. The rings are so fine that you can actually see whether the red algae were covered by sea ice in a particular year.
“The red algae can thus be used to measure climate change. If, for example, you study red algae in front of a glacier, they can be used to see how the glacier has behaved over time. In fact, you could call them a kind of back catalogue of climate change,” says Helle Jørgensbye.
Red algae are found as far north as Upernavik on the west coast of Greenland, which shows that they can survive with very little light. On the other hand, the reefs are vulnerable to trawling and fishing nets, or if the place they are found is used as a dumping area and they become covered with mud.