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Sharks and Rays: Surviving Through Ages, Facing New Threats

Sharks and rays have been integral to our oceans for approximately 450 million years. However, current estimates reveal that over one-third of these species face severe threats due to unsustainable fishing practices and habitat degradation. A recent study spearheaded by palaeobiologist Manuel A. Staggl from the University of Vienna has explored the impact of global warming on shark diversity, analyzing climate variations from 200 to 66 million years ago. The findings indicate that while warmer temperatures and the expansion of shallow marine environments support biodiversity, elevated CO2 levels pose a significant threat. This research was published in the scientific journal Biology.

Throughout Earth’s history, five mass extinction events have occurred, yet cartilaginous fish, which include sharks and rays, have withstood these catastrophic periods. Today, more than 1,200 species of sharks and rays exist, but their future is jeopardized by excessive exploitation and loss of habitat, which could disrupt entire marine ecosystems.

“The accelerated climate change we are witnessing today could adversely affect these species. In our international study, we aimed to understand the potential impact of recent climate shifts on the evolutionary history of rays and sharks,” commented Staggl. The research team focused on the biodiversity dynamics of these species during the Jurassic and Cretaceous periods — when their evolutionary diversity reached a peak under various environmental conditions. By analyzing fossilized teeth of sharks and rays, they correlated species diversity with ancient climate data. Jürgen Kriwet, a palaeobiologist at the University of Vienna, stated, “Understanding the environmental factors that influence shark and ray biodiversity is crucial for predicting scenarios related to ongoing global warming.”

Key Environmental Factors Impacting Shark Biodiversity

The study identified three main environmental factors affecting shark and ray populations: increased temperatures and expansive shallow marine habitats have a positive influence, while rising carbon dioxide (CO2) levels have detrimental effects. This study marks a significant advancement in recognizing how elevated CO2 concentrations in the ocean harm these species. “Although we don’t yet fully comprehend the mechanisms behind this negative influence, current laboratory studies demonstrate physiological repercussions of high CO2 levels on living sharks and rays, impacting their sensory systems and altering skeletal development,” noted Staggl. Historical data indicate that heightened CO2 levels have historically contributed to the decline of several shark and ray species.

Potential Upsides to Climate Change

Interestingly, the ongoing global warming may present some advantages for sharks and rays. Historical data suggest that rising sea levels and elevated temperatures have previously favored these predators by expanding shallow coastal habitats and promoting the spread of warm marine environments that provide stable conditions year-round.

Staggl highlighted the importance of these shallow seas as biodiversity hotspots. “These environments, which emerge from rising sea levels across extensive continental shelves, allowed sharks and rays to flourish rapidly due to their remarkable adaptability.” Historical climatic conditions during the Jurassic and Cretaceous periods, characterized by significantly warmer temperatures, facilitated the migration of tropical and subtropical ecosystems further north and south, fostering stable and diverse marine communities.

Challenges Ahead

Unfortunately, predicting a positive future for sharks and rays may be overly optimistic, according to Staggl. “The current pace of environmental change is alarming and likely exceeds the adaptive capacity of these species and their ecosystems.” Factors such as overfishing, habitat destruction, and rising CO2 levels threaten to overshadow any potential benefits from climate change.

To alleviate pressure on shark populations, immediate conservation actions are essential. Protecting sharks and rays goes beyond safeguarding individual species; it entails preserving entire marine ecosystems. Kriwet emphasizes this interconnection, stating, “The absence of top predators like sharks can lead to ecosystem collapse. By prioritizing the protection of sharks and rays, we are directly contributing to the health of our oceans, which is vital for various human activities and industries that rely on these ecosystems.”

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