The German North Sea is actually one of the best-studied sea areas ever. Nevertheless, scientists there continue to make new discoveries – including now. A team of biologists has discovered five new species of copepods in sediment samples from the German Bight. The crustaceans, which are just a few millimeters in size, can hardly be distinguished from the outside. Only genetic analyzes and high-resolution electron microscopy revealed species-specific differences between the crabs. The researchers suspect that there could be other such “cryptic species” hidden in the fauna of the North Sea.
Marine researchers have been researching the flora and fauna of the German Bight for centuries. Nevertheless, there are still surprises to this day: new species immigrate, others disappear or change under the influence of climate change. The typical inhabitants of the North Sea also include numerous copepods. Despite their small size, these crustaceans play an important role in the marine ecosystem. They are also considered indicators of the effects of human influences and climate change.
Five new species of copepods
To learn more about the copepods of the North Sea, Seher Kuru from the Turkish University of Mersin and his colleagues took a closer look at a genus of tiny sediment dwellers: copepods of the genus Leptastacus. These crustaceans, which are less than a millimeter in size, are among the most common animal inhabitants of the North Sea. Kuru and his team examined crabs from sediment samples from various North Sea areas and used a combination of high-resolution electron microscopy and genetic analyzes to identify the species. They discovered that the copepods, which were previously thought to be one species, belong to five different species. “Our results show that we are not dealing with a single, highly variable species, but with several clearly separated species that remained undiscovered for a long time,” reports senior author Sven Rossel from Senckenberg am Meer in Wilhelmshaven.
Only the combination of genetic and morphological analyzes revealed the hidden biodiversity of the tiny crustaceans. “Such so-called ‘cryptic species’ can hardly be distinguished from the outside, but they differ significantly in their genetic makeup,” explains Rossel. “Our research shows that even very familiar and well-studied habitats such as the North Sea still harbor unknown biological diversity.” The newly identified copepod species have now been named Leptastacus linae, Leptastacus germanica, Leptastacus klaasi, Leptastacus marleenae and Leptastacus konradi.
“Ecologically significant”
The discovery of these five cryptic crustaceans is not only taxonomically interesting: “The discovery of the five new crustacean species is ecologically very significant,” emphasizes Rossel. “Although the animals look the same at first glance, they can occupy different ecological niches and therefore each contribute in their own way to the functioning of the North Sea ecosystem.” Marine benthic animals play an important role in marine ecosystems, such as breaking down organic matter, and are also often used to assess the condition of seabeds. “If we overlook species or group them together incorrectly, it can lead to us misjudging environmental changes,” explains Rossel. “A precise knowledge of biodiversity is therefore a fundamental prerequisite for reliable environmental assessments.”
In order to track down other animal and plant species that may have previously been overlooked, eight German research institutions have started a joint research project. The aim is to systematically record and describe previously undiscovered species, to better understand their ecological significance and to develop protective measures from them. “Only if we really know the species that live here can we specifically protect and preserve them,” says Rossel.
Source: Seher Kuru (University of Mersin, Türkiye) et al., Marine Biodiversity, doi: 10.1007/s12526-025-01583-4