Between the mudflats of the Wadden Sea and the rushing grey waves of the German open sea, the North Sea appears bleak and lifeless. But this is far from the case.
While the mostly sandy seabeds offer less rich habitats than tropical reefs, the North Sea nevertheless hosts more than 10,000 species of animals and plants! These include at least 150 species of fish, ranging from small sand eels and herring to rarities such as the short-snouted seahorse and the angelshark.
In this series, ElasmOcean takes us into the underestimated waters of our home sea, which deserves our appreciation and protection just as much as its larger siblings.
More protection through knowledge, indeed.
Source: CWSS (2012): Wadden Sea Quality Status Report
Humans and "their" sea - tracing the impact
Long before the North Sea reached our coasts, it was a heavily utilised habitat for hunter-gatherers. The young sea only reached its current extent through sea level rise about 20,000 years ago. Consequently, the North Sea is comparatively shallow – in the German Bight, water depths range between 20 and 50 metres.
Human influence has left its mark everywhere: dumped ammunition and wrecks from the Second World War lie in untold numbers on the seabed, whose sandy soils are constantly shifting and impeding salvage operations. The Rhine, Elbe, Weser, and Ems rivers overload the North Sea with fertilisers from German fields. The Terschelling and German Bight Western Approach shipping lanes are among the busiest shipping routes in the world. Offshore wind farms are increasingly occupying space. Furthermore, fishing is so intense that, statistically, every square metre of the German North Sea is swept by a bottom trawl 1.25 times per year.
How anyone can keep track of all this will be explained shortly.
Sources:
Emeis (2015): The North Sea – A Shelf in the Anthropocene. https://doi.org/10.1016/j.jmarsys.2014.03.012
Eigaard (2017): The footprint of bottom trawling in European waters: distribution, intensity, and seabed integrity. https://doi.org/10.1093/icesjms/fsw194
Order or chaos? The spatial plan
Who owns a sea?
Normally, a country is entitled to claim the sea up to 200 nautical miles from its coast – which becomes more complex when these zones overlap. We therefore share the North Sea area with other nations, including Denmark, the Netherlands, and Great Britain. We have reached agreements with these countries, and Germany's Exclusive Economic Zone (EEZ) encompasses approximately 23,417 km² of the North Sea. This "German North Sea" is claimed by many stakeholders: shipping, fisheries, offshore wind farms, submarine cables, resource extraction, the military, recreational sectors, and marine protected areas. To coordinate all of these legally and organisationally, the Federal Maritime and Hydrographic Agency (BSH) continuously works on the spatial plan.
In this context, the BSH conducts its own measurements and research, and uses these findings to coordinate shipping, military operations, and the expansion of wind farms.
Wind farms are fixed-location projects, which requires longer-term planning with fewer modifications. The scope of utilisation is prepared in a spatial offshore development plan, in which environmental impacts are thoroughly assessed. Annual tenders for new sites are intended to provide planning security and ensure efficient expansion with low electricity prices.
And what about the inhabitants of the North Sea? You will find out shortly!
Source: BSH (2025): Flächenentwicklungsplan 2025
Flying penguins
Who inhabits the North Sea? Let us start "at the top".
Some tourists on Heligoland might mistake the residents of the "Lange Anna" for penguins, but the common guillemot and the razorbill are alcids, closely related to waders and gulls. Both species wear dark breeding plumage with a black head in summer, transitioning to lighter plumage in winter. Only the pointed bill visibly distinguishes the common guillemot from the razorbill.
The European population of common guillemots is estimated at 2.4 – 3.1 million individuals, but these animals face increasing threats: marine litter like discarded fishing nets and dolly ropes, rising water temperatures due to climate change, and avian influenza epidemics reduce the survival rates of the common guillemot. It is also now known that the animals react negatively to offshore wind farms, meaning they lose habitat in the North Sea as wind farm areas are constructed.
Sources:
BirdLife International (2018): Species factsheet: Common Murre Uria aalge
Peschko (2024): Cumulative effects of offshore wind farms on common guillemots (Uria aalge) in the southern North Sea - climate versus biodiversity? https://doi.org/10.1007/s10531-023-02759-9
The Arctic master of flight: Northern fulmar
The northern fulmar is a lesser-known inhabitant of the North Sea. It was once so abundant that settler communities relied on it as a primary food source. With only 38 breeding pairs remaining on Heligoland (2019), it is rarely found in coastal waters and is classified as a strictly protected species in Germany. The bird, with its stiff wings and prominent tube-like nostrils that allow for the excretion of salt, is most at home out on the windswept open sea. Here, it feeds on krill, jellyfish, and fish, cackling as it fights with conspecifics over fishery discards. Consequently, it is a frequent ship-follower.
This very habit proves fatal: an estimated 95% of all northern fulmars have plastic in their stomachs, leading to internal injuries or even starvation with a full stomach.
Sources:
Heinrich-Böll-Stiftung: Plastikatlas 2019. ISBN 978-3-86928-200-8
Verein Jordsand: Der Eissturmvogel. https://www.jordsand.de/helgoland/eissturmvogel/
A miniature giant
While it may be fairly small for a baleen whale, the name "common minke whale" hardly does justice to this marine mammal, which can reach up to 8 metres in length. It is a rarely sighted inhabitant of the North Sea – partly because it only occasionally shows its dorsal fin, and partly because the species was severely decimated by whaling and is recovering slowly. In our waters, they are most frequently spotted far out on the "Dogger Bank", a sandy shoal about 20 metres deep.
Today, fishing nets in which the whales become entangled and climate change pose the greatest threats to common minke whales.
They occur in all oceans, but populations from the Northern and Southern Hemispheres rarely meet because of the different seasons in which they migrate towards the equator – perhaps, over time, two new species will emerge from the two current subspecies...
Source: Sun et al. (2022): Estimating the impacts of climate change on the habitat suitability of common minke whales integrating local adaptation. https://doi.org/10.3389/fmars.2022.923205
Sonar – Chinese whispers
Famous, notorious, and shy: the harbour porpoise is native to both the German North Sea and the Baltic Sea.
At 1.4 m, it is a pygmy among marine mammals – with natural predators.
Grey seals occasionally hunt these animals to obtain chunks of their fatty skin. Attacks by bottlenose dolphins are also documented.
In addition, the great white shark and the killer whale are among the natural predators of the harbour porpoise. Intrepidly, killer whales hear up to a frequency of approximately 125 kHz, whereas the echolocation clicks of harbour porpoises are at 130-140 kHz, allowing their vocalisations to just escape the hearing range of the killer whale – an important survival strategy. For comparison: human hearing ranges from about 20 Hz to 20 kHz.
At the top of the list of threats, however, is another: humans. More on this in the next part of the North Sea series.
Source: Miller and Wahlberg (2013): Echolocation by the harbour porpoise: life in coastal waters. https://doi.org/10.3389/fphys.2013.00052
Small whale, short life
The charismatic harbour porpoise is classified as vulnerable overall, and as critically endangered in parts of the Baltic Sea. Recent counts estimate approximately 345,000 individuals in the North Sea and North-East Atlantic. Although they can live up to 24 years and only reach sexual maturity at 5 or 6 years of age, harbour porpoises in the North Sea only live to about 5 years old – an immense threat to the population. Many animals die before they can carry or nurse offspring, as gestation lasts about 10 months and lactation just as long.
The most common threats to these marine mammals are diseases and chemical pollutants, followed by fisheries – either through being caught as bycatch in nets, or due to a lack of prey.
To date, several conservation agreements exist: the Bonn Convention (CMS) lists the harbour porpoise as a migratory species requiring conservation, while the European Habitats Directive provides for Special Areas of Conservation to ensure the maintenance of the species. How this works will be detailed in the next part of the North Sea series.
Sources:
Kesselring et al. (2019): Coming of age: - Do female harbour porpoises (Phocoena phocoena) from the North Sea and Baltic Sea have sufficient time to reproduce in a human influenced environment? https://doi.org/10.1371/journal.pone.0186951
Carlén et al. (2021): Out of sight, out of mind: How conservation is failing European Porpoises. https://doi.org/10.3389/fmars.2021.617478
This series is to be continued.
