Biodiversity

A race against time in the ocean’s depths

Since life first appeared in the seas around three billion years ago, it has continued to diversify in order to survive the most extreme habitats. But now, overfishing, the destruction of habitat, pollution, the introduction of invasive species and climate change are damaging marine ecosystems and biodiversity. Researchers from the European network MarBEF (Marine Biodiversity and Ecosystem Functioning) have taken on the ultimate marine research challenge: to discover the numerous life-forms present in the oceans, before they disappear forever.

Cnidaria anthomedusae. The cnidarians, which include thousands of different species, exist in two forms, fixed (corals, sea anemones…) and free, like the medusas shown here. © CNRS/Photothèque/Claude Carre Cnidaria anthomedusae. The cnidarians, which include thousands of different species, exist in two forms, fixed (corals, sea anemones…) and free, like the medusas shown here. © CNRS/Photothèque/Claude Carre
Caranx sexfasciatus (or Bigeye), moving around in the Pacific Ocean. The threats to biodiversity concern all species living in and around the oceans, since they are all inextricably linked. © WWF-Canon/Jürgen Freund. Caranx sexfasciatus (or Bigeye), moving around in the Pacific Ocean. The threats to biodiversity concern all species living in and around the oceans, since they are all inextricably linked. © WWF-Canon/Jürgen Freund.

Often referred to as the “cradle of life” on the blue planet, the oceans are teaming with an amazing diversity of species and ecosystems. This richness is relatively unexplored: while 240 000 marine species have been recorded, an estimated 10 million more continue to lurk anonymously. To learn more about these species and their habitats, the European research network MarBEF(1) is trying to discover more about the relationship between biodiversity and the functioning of ecosystems. Uniting over 700 scientists from 92 institutes spread across 24 European countries, the platform enables the integration of multidisciplinary research on marine biodiversity and makes this more widely available.

“By combining a large number of projects, the network enables us to see what the trends are right across Europe,” explains Herman Hummel, Deputy Executive Director at MarBEF. “Our 18 lines of research focus on global trends of marine biodiversity in ecosystems, on the functioning of ecosystems and on the socioeconomic importance of biodiversity.”

Fragile biodiversity

Not all the seas house the same richness of species. “Certain ecosystems are made up of barely 100 species, whereas elsewhere we count thousands,” underlines Herman Hummel. “There are several reasons for these differences: biodiversity is notably lower in the Baltic Sea - which was freed from the glaciers around 10 000 years ago - than in the tropical zones. These were spared the glaciations and so more species have been able to evolve over a longer period of time. Within the same system, the presence of a particular habitat can also result in explosions in diversity, illustrated by the hydrothermal vents found in the deep abysses.”

Similarly, the destruction of marine habitats, like that of the rainforest, is causing the loss of the species that reside there. And in Europe? “Ourmarine ecosystems suffer from overfishing, destruction of habitat, pollution, the introduction of invasive species and global climate change,” explains Herman Hummel. “The consequences for biodiversity are largely unknown. The different species have various roles to play and a minimum number of these participants is necessary to ensure the correct functioning of the ecosystem.”

Ripple effect

From 2-micrometre phytoplankton to giant squid measuring 13 metres, every species living in the oceans is inextricably linked. Each plays a crucial role in the balance of its environment and supports other life forms. Every change affecting one species is therefore likely to have repercussions for a large number of interrelated organisms. Overfishing, for example, does not only affect the hunted species: it throws a whole ecosystem into chaos.

According to different studies, notably those published in Science and Nature, the biodiversity of top predators has radically declined in all oceans over the last 50 years - during which time the population of predators (in particular whales) has fallen by 90 % in the oceans. These disappearances have led to a food-related chain reaction. The small fish proliferate and eat more zooplankton. And the reduction in zooplankton allows the phytoplankton that they feed on to flourish, affecting numerous species. The phytoplanktonic algae encourage the growth of bacteria which deprives the water of oxygen. Certain algae also produce powerful neurotoxins which, once introduced into the food chain, threaten crustaceans, fish, birds, mammals - and humans that feed directly or indirectly on these organisms.

Ecosystems are also disrupted by the arrival of “invasive species”. Transported on the hulls or in the ballast of ships, or via exchanges between shellfisheries, these invaders rapidly spread far from their original habitat, competing with native species. One historic example is that of the slipper limpet (Crepidula fornicata): this mollusc, from the eastern coast of the United States, was introduced into Europe in the 18th century through oyster transfers and has subsequently taken the oysters’ food and space.

Restoring the balance?

The growing development of coastal areas leads to the destruction of coastal habitats, but an even more pressing problem exists in the deep waters. As they absorb atmospheric CO2, the oceans are becoming more acidic, which threatens the primary links in the food chain: coral, shellfish and crustaceans. Moreover, the more acidic water captures less CO2, so its presence in the atmosphere increases, exacerbating climate change. This problem is particularly marked in the Arctic region, where temperatures have risen two or three times more rapidly than elsewhere: by 3°C in the past 50 years. Arctic pack ice has already shrunk by 15-20% over the last 30 years - and unless this trend is reversed, the local flora and fauna could be irreversibly affected.

“There is a fear that some species may be lost, due to pressures on the environment, before they have even been discovered,” stresses Herman Hummel. “That is why we must map marine biodiversity as soon as possible. Our network has already established dozens of databases which have recorded around 70 000 species present in Europe.” Measuring the impact of human activity on marine ecosystems is essential in defining political measures for a sustainable blue planet. Will that be enough? ”We need to construct a network of protected zones large enough to preserve biodiversity effectively,” says Herman Hummel. “These zones need to stretch over several hundred square kilometres to ensure the sustainability of populations.”

Charlotte Brookes

  1. The network of excellence MarBEF is receiving € 8.7 million over five years from the European Union.

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