Sharks and rays, which have roamed the world’s oceans for around 450 million years, are a group of cartilaginous fish that have survived five mass extinction events. Today, however, more than a third of the known species are critically threatened due to overfishing and habitat destruction. In light of this, an international team of scientists, led by paleobiologist Manuel A. Staggl from the University of Vienna, has investigated how global warming could affect the diversity of sharks and rays, focusing on climate fluctuations between 200 and 66 million years ago. The findings, published in the journal Biology, shed light on the environmental factors that shaped the evolution of these creatures in the past and provide insights into how present-day climate change might influence their future.
A Glimpse into the Past: Sharks and Rays Through Time
The history of sharks and rays dates back over 450 million years. They have persisted through the planet’s most extreme environmental changes, including five mass extinction events. Today, there are more than 1,200 species of sharks and rays, with their habitats spanning the oceans of the world. However, despite their resilience, the current status of sharks and rays is concerning. More than one-third of their species are now critically endangered, facing severe threats from overfishing, habitat destruction, and the growing impacts of climate change. These threats not only jeopardize the survival of these species but also have the potential to disrupt marine ecosystems, as sharks and rays are apex predators crucial to maintaining the balance of the food chain.
In a recent study, Staggl and his team sought to understand how past climate fluctuations influenced the diversity of sharks and rays, specifically during the Jurassic (200–143 million years ago) and Cretaceous (143–66 million years ago) periods. These eras are known as a golden age for sharks and rays, marked by significant evolutionary advances and a diversity of species. The research team examined fossilized shark and ray teeth, comparing species diversity across various periods with climate data from those times.
The Environmental Factors Shaping Shark and Ray Biodiversity
The researchers identified three primary environmental factors that influenced the biodiversity of sharks and rays: temperature, sea level, and CO2 concentration.
- Higher Temperatures: Increased global temperatures were found to have a positive effect on shark and ray diversity. Warmer oceans promoted the expansion of tropical and subtropical regions, which in turn led to the creation of new habitats for these species. The stability of warm waters allowed for more complex ecosystems to thrive, supporting a variety of marine species, including sharks and rays.
- Shallow Water Areas: Shallow seas were another critical factor for the evolution of sharks and rays. As sea levels rose during certain periods, vast shallow seas covered large areas of the continental shelf, creating biodiversity hotspots. These shallow waters were perfect for the rapid colonization of sharks and rays due to their adaptability. The expansion of shallow seas also contributed to the stability and richness of marine ecosystems.
- Higher CO2 Levels: In contrast to the beneficial effects of higher temperatures and shallow waters, increased CO2 levels were found to have a negative effect on shark and ray biodiversity. The study provides clear evidence that elevated CO2 concentrations led to the extinction of some shark and ray species. Although the precise mechanisms remain unclear, laboratory studies of modern sharks and rays have shown that higher CO2 levels can have harmful physiological effects on these animals, including changes in their sensory systems and developmental issues during embryogenesis.
This negative effect of CO2 on marine life is becoming more evident today as increasing CO2 emissions are acidifying the oceans, making them less habitable for marine species. The fossil record indicates that similar increases in CO2 during past periods of climate change contributed to the decline of some cartilaginous fish species.
A Double-Edged Sword: Opportunities and Threats in a Warming World
While the study reveals that rising temperatures and the expansion of shallow water habitats could be beneficial to sharks and rays, the ongoing global warming presents a double-edged sword. Past climate shifts show that the current pace of warming may be too rapid for sharks and rays to adapt to the changing conditions.
The researchers acknowledge that the rise in sea levels and temperatures has previously allowed sharks and rays to diversify and expand into new habitats, but the current rate of change is far more intense than what occurred in the past. With rapid overfishing, loss of critical habitats, and rising CO2 levels, the current challenges facing these species are compounded. In particular, the rapid rate of environmental change may outpace the ability of these species to evolve and adapt, leading to further declines in their populations.
According to Staggl, the quickening pace of climate change is likely to be too fast for many species of sharks and rays to handle. As ocean temperatures rise and ocean acidification progresses, the delicate balance of marine ecosystems is being disrupted, leaving species such as sharks and rays vulnerable. Moreover, overfishing and the destruction of important breeding grounds, such as coral reefs and coastal estuaries, are reducing the available habitats for these apex predators.
The Urgent Need for Conservation
The findings of this study underscore the need for urgent conservation efforts to protect sharks and rays, not just for their survival but for the well-being of the entire marine ecosystem. Sharks and rays are integral to the health of oceans, maintaining the stability of marine food webs by regulating the populations of other species. Without these apex predators, entire ecosystems could collapse.
To safeguard the future of sharks and rays, conservation efforts must address multiple fronts. This includes protecting vital habitats, enforcing sustainable fishing practices, and reducing CO2 emissions to mitigate the effects of climate change. Marine protected areas, stricter fishing regulations, and international agreements on ocean conservation can all play key roles in preserving the habitats and populations of these ancient creatures.
As Jürgen Kriwet, a professor of paleobiology at the University of Vienna, points out, sharks and rays are a critical part of marine biodiversity, and their decline would have far-reaching consequences for the ecosystems they inhabit. “By protecting sharks and rays,” Kriwet says, “we are investing directly in the health of our oceans and the people and industries that depend on these ecosystems.”
Looking to the Future
While the study provides valuable insights into how environmental factors influenced the evolution of sharks and rays in the past, the future of these creatures remains uncertain. The challenges posed by climate change, overfishing, and habitat destruction are unprecedented, and it is unlikely that these species will thrive under current conditions without significant intervention.
The research team hopes that their findings will help inform conservation strategies and guide future studies on the impact of climate change on marine life. The lessons learned from past climate fluctuations can provide a roadmap for understanding how sharks and rays may respond to future environmental changes, offering a glimpse into what may lie ahead for these iconic ocean dwellers.
In conclusion, while sharks and rays have proven to be resilient survivors of past extinctions, their future is far from guaranteed. Climate change, overfishing, and habitat loss continue to threaten these essential species. To ensure the survival of sharks and rays—and the health of the oceans—they must be protected through concerted conservation efforts that address both their immediate needs and the long-term challenges posed by a warming world. The time to act is now, before it’s too late to preserve these ancient and vital creatures of the sea.
Reference: Manuel Andreas Staggl et al, The Drivers of Mesozoic Neoselachian Success and Resilience, Biology (2025). DOI: 10.3390/biology14020142