Study Warns Ocean Acidification Could Damage Shark Teeth, Affecting Their Role as Apex Predators
The impact of ocean acidification on one of the ocean’s most formidable predators, sharks, has been explored in a new study published in Frontiers in Marine Science. This research focuses on the potential damage to shark teeth, a critical component of their ecological success and marine ecosystem health.
As carbon emissions continue to rise, the ocean absorbs more carbon dioxide from the atmosphere, causing seawater to become more acidic. This process, known as ocean acidification, can affect numerous ocean species and ecosystems, including sharks.
Maximilian Baum, a biologist at Heinrich Heine University in Düsseldorf, Germany, and lead author of the study, explains, “Since ocean acidification is known to harm calcified structures like corals and shells, we wanted to investigate whether shark teeth might also be vulnerable, especially for species that swim with their mouths open and have constant seawater exposure.”
The research team collected 600 naturally shed teeth from blacktip reef sharks (Carcharhinus melanopterus) at the Sea Life Oberhausen aquarium in Germany. These shark species replace their teeth at varying rates, depending on the species.
For the study, 16 undamaged teeth and 36 teeth with limited damage were placed in two separate 20-liter water tanks for eight weeks. The control tank had a pH level of 8.2, close to the current ocean average, while the other tank contained more acidic water, with a pH level of 7.3, projected to be the seawater pH in the year 2300 according to a 2003 study published in Nature.
According to the National Oceanic and Atmospheric Administration (NOAA), the surface ocean waters’ pH has fallen by 0.1 pH units since the industrial revolution began over two centuries ago, representing an approximately 30% increase in acidity.
The teeth exposed to more acidic water showed “visible surface damage such as cracks and holes, increased root corrosion, and structural degradation,” said Sebastian Fraune, a professor at Heinrich Heine University and leader of its Institute of Zoology and Organismic Interactions.
This damage could potentially impact how sharks find and digest food, as many shark species use multiple rows of teeth simultaneously, and individual teeth can remain in use for weeks or even months. Cumulative damage may reduce feeding efficiency and increase energy demands, particularly in species with slower replacement cycles and numerous simultaneous rows of teeth.
However, the study had limitations, as it focused on teeth shed from sharks in an aquarium environment. The experiment’s representativeness of living shark mouth conditions and the use of an extreme ocean acidification scenario were questioned by some experts.
Nonetheless, Baum and his colleagues maintain that their findings offer a baseline for understanding the vulnerability of shark teeth to ocean acidification. By isolating the chemical effects of acidified seawater on the mineralized structure itself, they hope to provide insights into potential damage to exposed hard tissues like teeth.
The study’s implications highlight the potential risks posed by ocean acidification to these crucial apex predators and their role in maintaining marine ecosystem health. If sharks were to be affected by ocean acidification in combination with other stressors such as overfishing and plastic pollution, this could trigger cascading effects across various marine ecosystems.