Climate change poses a significant threat to marine ecosystems, and new research suggests that even some shark species may not be immune to its effects. A study conducted by scientists from the Biology of Aquatic Organisms and Ecosystems Lab in France has revealed that the eggs of small-spotted catsharks, Scyliorhinus canicular, could face severe challenges in hatching under worst-case climate scenarios by the end of this century.
The small-spotted catshark, also known as the sandy or lesser spotted dogfish, is currently abundant in the northeast Atlantic Ocean surrounding Europe. However, researchers have observed signs that the species may be becoming more vulnerable to the impacts of a warming planet. Lead researcher Noémie Coulon, a PhD student at BOREA, noted that these sharks are already experiencing habitat loss in coastal areas, particularly during peak egg-laying seasons in summer months.
To investigate the potential future impacts of climate change on these sharks, Coulon and her team designed an experiment to simulate different climate scenarios. They raised and monitored batches of catshark eggs under three distinct conditions, varying the temperature and pH of the water to reflect different climate projections. The researchers used data from the United Nations' shared socioeconomic pathways to create these scenarios, focusing on SSP2, a moderate scenario, and SSP5, the most extreme scenario.
The results of the study were striking. Under the control conditions, which simulated current environmental parameters, 81% of the catshark eggs successfully hatched. Similarly, under the SSP2 scenario, which projected a global temperature rise of about 2.7 degrees Celsius and a water pH drop of 0.2 by 2100, 83% of the eggs hatched. However, the SSP5 scenario painted a much bleaker picture. With a projected temperature increase of 4.4 degrees Celsius and a water pH drop of 0.4, only 11% of the eggs managed to hatch.
The researchers observed that under the extreme SSP5 conditions, the embryos inside the eggs consumed less yolk, grew at a slower rate, and struggled to form their internal gills properly. These factors contributed to the dramatically reduced hatching success rate. Interestingly, the study found no difference in survivability between the groups once the sharks had hatched, which the authors attribute to falling water temperatures as the year progressed.
While the findings of this study are concerning, the researchers emphasize that the SSP5 scenario is considered unlikely by many experts, though some still believe it remains a possibility. The results under the more moderate SSP2 scenario offer a glimmer of hope, suggesting that if humans can prevent the worst-case climate future, these sharks may still have a chance to thrive.
Coulon stressed the importance of these findings, stating that hatching success is crucial for population dynamics, especially for species like skates and sharks that have a slow pace of life. Low hatching rates could critically impact population renewal for these animals. She also pointed out that the study serves as a warning about the potential responses of other marine species that may be even more sensitive to environmental changes.
The research team's work highlights the urgent need for continued efforts to reduce greenhouse gas emissions and mitigate the impacts of climate change. While the study focused on small-spotted catsharks, its implications extend to other marine species and underscore the interconnectedness of ocean ecosystems. As we face the challenges of a changing climate, understanding and protecting vulnerable species will be crucial in maintaining the delicate balance of our oceans.
