Marine Biodiversity

Terms such as species diversity, species richness and biological diversity are often used synonymously with biodiversity. However, as the IPBES definition shows, the concept of biodiversity is more comprehensive. Species diversity and species richness are merely measures of the number of species in a particular ecosystem, habitat or scientific sample. Strictly speaking, they therefore represent only one aspect of biodiversity.

When experts talk about marine biodiversity, they mean the diversity of life in all components of marine ecosystems and at all levels of biological organisation – from genes and populations to individual species, species communities and ecosystems.

• Genetic diversity and individual differences within populations allow marine species to adapt their behaviour and life cycles to the specific environmental conditions of their local habitat.
• Differences between individual species are evident in the fact that organisms look different, have different evolutionary histories, inhabit different habitats and play different roles and functions within them.
• The diversity of communities and ecosystems, in turn, is based on the fact that species live together or side by side in different combinations and also influence or depend on each other in different ways.

The species in a biotic community do not all occur with equal frequency. Often, a few species dominate, while there are many rarer species that were unable to prevail in the selection process but have not disappeared either. They can play an important role in disturbances: if environmental conditions change, they suddenly have an advantage and can take over the role of the dominant species.

However, there are also some habitats in the sea that have extreme environmental conditions. For example, hot springs in the deep sea. The communities in such dark, hot places consist of comparatively few species, but these are perfectly adapted to the extreme conditions.

The communities of marine ecosystems are constantly changing. These processes of change are normal and ensure the resilience of the ecosystem. It is therefore entirely natural for species to migrate in and out or, in some cases, even become extinct.

The migration of foreign species can have a significant impact on established communities and even upset their balance. But not every newcomer is harmful: Japanese wireweed (Sargassum muticum), for example, which was introduced into the North Sea, has integrated itself into the Wadden Sea ecosystem without causing any damage. The bristle worm Polydora websteri, on the other hand, which originates from Asia, bores into the shells of oysters and is therefore considered a shellfish pest.

Particularly dangerous are so-called invasive species. These are new species in a habitat that find no natural predators and can reproduce uncontrollably. In some cases, they reproduce so extensively that they claim all resources for themselves and displace native species. An example of this is the Pacific oyster (Crassostrea gigas) in the North Sea.

The changing processes of ecosystems also include the extinction of animal and plant species. It is a natural part of the evolution of life on Earth. When a species disappears, new or other species usually take over its roles and functions. However, this adaptation takes time. The mechanism works well as long as the extinction rate remains within a normal range—meaning that no more than one in 10,000 species goes extinct within 100 years.

If the number of disappearing species rises far beyond this threshold, the world heads toward a mass extinction. This term refers to periods in which around 75% of all living species vanish within a short geological timeframe (usually less than two million years) without other species filling the functional gaps they leave behind. The last mass extinction occurred 66 million years ago at the end of the Cretaceous period when the dinosaurs disappeared.

The sixth mass extinction in Earth's recent history is currently looming. Due to human interventions in nature and the Earth's climate, the extinction rate has increased 100 to 1,000 times compared to pre-human times. Around one million species are currently at risk of extinction, and many species can no longer be found in parts of their original habitats.

The ocean is also on red alert. New research confirms that if temperatures in the atmosphere and the ocean continue to rise, species losses due to heat stress and oxygen depletion in the ocean over the next 75 years will be as severe as those caused by overfishing, pollution, and habitat destruction. In total, if global temperatures rise by up to 4.9 degrees Celsius by the end of this century, so many marine species would disappear that the conditions for a mass extinction would be met.

To preserve marine and ocean ecosystems and maintain biodiversity, effective ocean management is essential. Marine protected areas must not exist only on paper—the enforcement of regulations must be monitored, and violations must be sanctioned. Only then do we have a chance to prevent a mass extinction.