Sharks and rays have inhabited the oceans for roughly 450 million years, yet over a third of existing species face severe threats from overfishing and habitat destruction. An international team of researchers, led by palaeobiologist Manuel A. Staggl from the University of Vienna, has explored the impact of global warming on shark diversity by examining climate changes that occurred between 200 and 66 million years ago. The findings indicate that increased temperatures and more shallow water areas positively affect these species, while elevated CO2 levels have distinctly negative consequences. This research was recently published in the scientific journal Biology.
Throughout Earth’s history, there have been five mass extinctions, yet cartilaginous fish, encompassing sharks and rays, have persisted through them all, with over 1,200 known species today. Despite their resilience, more than a third of these species are currently at serious risk due to their lifestyles, rampant over-exploitation, and habitat loss, which could significantly affect many ecosystems.
“The rapid climate warming we are experiencing may adversely affect this group of animals. Through an international study focusing on previous climate changes, we investigated the potential impacts on rays and sharks,” states Manuel A. Staggl from the University of Vienna. The research team analyzed the factors influencing shark and ray biodiversity during the Jurassic (200-143 million years ago) and Cretaceous (143-66 million years ago) periods, which were instrumental in the evolution of these species across various environmental conditions. By examining fossilized shark and ray teeth, they assessed species diversity for each era and correlated it with climate data from those times. “We aimed to pinpoint which environmental components affect shark and ray diversity to inform future scenarios concerning current global warming,” explains Jürgen Kriwet, a palaeobiology professor at the University of Vienna.
Key Environmental Factors Influencing Diversity
The research identified three crucial environmental factors: higher temperatures and greater shallow water zones positively influence biodiversity, while increased carbon dioxide (CO2) levels have a detrimental impact. This study is the first to clearly highlight the negative relationship between CO2 concentrations in marine environments and shark and ray biodiversity. “We have yet to fully understand the specific mechanisms behind CO2‘s harmful effects on these species,” Staggl notes. However, contemporary laboratory studies on sharks and rays have shown that elevated CO2 levels can cause direct physiological changes, affecting their senses and altering skeletal development during embryogenesis. The fossil record supports the notion that higher CO2 concentrations contributed to the extinction of certain shark and ray species.
Climate Change: A Double-Edged Sword?
Conversely, the ongoing global warming could present new opportunities for sharks and rays. Historical rising sea levels and warmer waters have previously enhanced the biodiversity of these predators, mainly due to the creation of shallow coastal zones and the expansion of consistently warm marine environments.
The increase in sea level has been particularly significant. “Shallow seas that cover extensive continental areas create biodiversity hotspots; sharks and rays can quickly and efficiently adapt to and inhabit these regions,” Staggl explains. The notably higher temperatures during the Jurassic and Cretaceous periods allowed tropical and subtropical ecosystems to expand further poleward and develop stable ecosystems with a greater variety of species.
The Future Looks Grim
Yet, assuming a positive future for sharks and rays would be overly optimistic, Staggl cautions, “The pace of environmental change is currently rapid—likely too rapid for these animals and their ecosystems.” The combined threats of overfishing, habitat loss, and rising CO2 levels will probably prevent these predators from benefiting significantly from global warming.
To alleviate the environmental pressures on sharks, immediate protective measures are essential. This involves not only safeguarding the sharks and rays themselves but also preserving entire ecosystems. “The collapse of ecosystems could occur without top predators,” Kriwet stresses. “By protecting sharks and rays, we directly invest in the well-being of our oceans, which is vital for the communities and industries that rely on these ecosystems,” concludes the palaeobiology professor.
