Seawater constitutes about 90 per cent of the habitable space on Earth. Yet less than five per cent of the ocean realm have been explored. Many marine plants and animals are still waiting to be discovered. Thanks to its biodiversity, the ocean performs many important functions and safeguards human wellbeing.
Planet ocean: the realm of biodiversity
From tiny single-celled organisms to gigantic marine mammals, the ocean is home to a large variety of species – with vast numbers still waiting to be discovered. However, the diversity of plants and animals on land and at sea was even greater before humankind made its appearance. Since the dawn of the anthropocene, we humans have brought about tremendous change to life on Earth. We do not yet fully understand what kind of repercussions the environmental changes caused by our lifestyles will have. But we do know they will eventually affect us directly. Therefore, it is crucially important to keep our impact on nature within bounds.
Seawater covers two thirds of our planet and constitutes about 90 per cent of the habitable space on Earth. But so far, we have only explored less than five per cent of the ocean realm. The Census of Marine Life, an international, ten year initiative to assess the biodiversity of the ocean, discovered more than 6000 new marine species. And still the participants in this project are not even able to estimate how many species live in coastal areas, the regions we claim to know best. Their approximations vary from around 180,000 to more than 10 million species.
Tropical reefs: treasure-troves of biodiversity
Tropical coral reefs give us an idea of the diversity that marine life is able to unfold in one single location. They cover just one per cent of the ocean, but are home to a quarter of all marine species. One square metre of these treasure-troves of biodiversity hosts around 1000 different species.
Warming increases the risk of coral bleaching from which organisms find it hard to recover. According to model calculations, temperatures cannot be allowed to rise by more than 1.2 degrees Celsius if at least half the reefs are to survive. However, this prognosis does not take into account the additional risks posed by ocean acidification.
Stony corals, which form the basis of each colourful reef, grow their solid skeletons from aragonite, the more soluble form of calcium carbonate. In more acidified water, they grow more slowly – under extreme conditions more slowly than the reef erodes. In addition, their skeletons remain more sensitive and thus more susceptible to storms or to organisms that burrow inside the coral or attack its calcium carbonate structure. Because some coral species are better equipped to cope with environmental changes, climate change may reduce the biodiversity of the reefs.
Diversity ensures important functions
Biodiversity, the diversity in species, genetic material and biological communities, is a basic requirement for ecosystem functioning and ultimately even human wellbeing. Only if the various organisms within the marine ecosystem fulfil their roles, can the ocean maintain its functionality and productivity. The ocean regulates our climate and mitigates the effects of climate change, supplies us with food, provides us with inspiration and recreation and it shapes cultural identities. A loss of species can pose a substantial risk for ecosystems as well as the goods and services they provide.
Goods, services and adaptability at risk
The greater the species diversity in a marine community is, the greater its ability to adapt to changes – simply because internal functions and interactions are shared by several types or organisms.
On the other hand, systems formed by only a few species or those strongly relying on certain key players are especially vulnerable. This is why marine life in the Arctic and Antarctic requires special protection.