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Ocean acidification alters ecosystems
More than 1,200 species of sharks and rays currently live, over a third of which are acutely threatened by overfishing and the destruction of their habitat. The biodiversity of these animals, which belong to the cartilaginous fish, was influenced by a series of events during the Mesozoic era (252 to 66 million years ago).
Sharks and rays have been populating the oceans for 450 million years and have often benefited from higher temperatures in the past. However, today's global warming, with rising CO₂ levels in the oceans, is affecting them. According to a study involving the University of Vienna, the acidification of seawater is changing environmental conditions so rapidly that the already threatened cartilaginous fish can hardly adapt.
An international research team analysed fossil shark and ray teeth from the Jurassic and Cretaceous periods to determine the factors influencing species diversity. In earlier warm periods, higher temperatures, rising sea levels and more shallow coastal areas were crucial for the spread of animals. This led to stable tropical and subtropical ecosystems with great diversity.
However, the latest findings show that a high CO₂ content in the atmosphere also increases the CO₂ content of the oceans, leading to acidification of the water. While this has little effect on bony fish, it could have a negative impact on cartilaginous fish, particularly on their embryonic development. Laboratory tests support this assumption.
Although sharks and rays have survived extreme climate conditions in the Earth's history, they may not be able to benefit from the current warming. The rapid increase in temperatures and CO₂ concentrations, combined with the destruction of habitats, makes adaptation difficult. The exact mechanisms as to why high CO₂ levels were less problematic in the past are still unclear.
Researchers emphasise the urgency of protective measures for sharks, rays and their ecosystems. As top predators, they play a central role in the balance of the seas. Their loss could destabilise entire marine habitats.
More information:
The question of how global warming affects the diversity of cartilaginous fish was investigated by the team led by Manuel A. Staggl and Jürgen Kriwet from the Institute of Palaeontology at the University of Vienna:.
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