Sharks have long fascinated scientists and ocean enthusiasts alike for their remarkable ability to continuously replace their teeth throughout their lives. This evolutionary adaptation is crucial for their survival, as sharks depend heavily on their sharp, durable teeth to capture and process prey. Unlike humans, sharks do not settle for a single set of teeth but instead continuously shed and regrow new teeth in a conveyor-belt-like fashion. However, in the face of a rapidly changing environment driven by human-induced climate change, even such extraordinary biological features might be vulnerable to disruption. Recent research from Germany has now revealed that increasing ocean acidification—a direct consequence of rising atmospheric carbon dioxide—could severely compromise the structural integrity of shark teeth, potentially undermining one of the ocean’s most efficient predators.
Ocean acidification refers to the ongoing decrease in ocean pH levels due to the absorption of excess CO2 emitted by human activities such as fossil fuel combustion and deforestation. Presently, the average pH of the world’s oceans hovers around 8.1, which is slightly alkaline and conducive to the maintenance of various marine life forms. However, projections indicate that if current emission trends continue unchecked, by the year 2300, the ocean pH could drop to approximately 7.3. This seemingly small numerical change reflects an almost tenfold increase in acidity, creating a hostile chemical environment for calcified and mineralized structures in marine organisms.
The team of researchers, led by Maximilian Baum and senior author Professor Sebastian Fraune from Heinrich Heine University Düsseldorf (HHU), sought to investigate how this fundamental shift in ocean chemistry affects shark tooth morphology, focusing on the Blacktip reef shark (Carcharhinus melanopterus). Utilizing over 600 teeth discarded from sharks housed at Sealife Oberhausen aquarium, the investigators selected 16 pristine and undamaged specimens for a controlled acidification experiment. The shark teeth were submerged for eight weeks in seawater tanks with two different pH settings: 8.1 to simulate current ocean conditions and 7.3 to represent future acidified oceans.
Upon completion of the incubation period, the research team employed microscopic and imaging analyses to assess tooth surface morphology and structural integrity. The results were stark and revealing. Teeth subjected to acidified conditions exhibited pronounced surface degradation manifesting as cracks, holes, and erosion predominantly on the roots where mineralization is crucial. Moreover, these teeth displayed significant alterations in their circumference, appearing larger under two-dimensional imaging due to a roughened and irregular surface texture. These morphological changes imply a weakening of the tooth’s mechanical properties, thereby compromising their ability to withstand the physical stress of capturing prey.
While shark teeth are composed of highly mineralized phosphates—components that generally confer hardness and durability—the study demonstrates that even this biochemical robustness offers limited protection against the corrosive effects of increased acidity. Fraune emphasized that shark teeth, though ingeniously designed biological weapons optimized for slicing through flesh, are far less adapted to endure prolonged exposure to harsh chemical environments. The findings suggest that as the oceans become more acidic, shark teeth may degrade faster, potentially leading to higher incidences of tooth breakage or loss.
This alteration in tooth morphology and functional resilience may have profound ecological consequences. Sharks occupy apex predator roles in marine ecosystems, shaping community structures and maintaining the balance of prey species. A reduction in their efficiency at hunting due to compromised teeth could trigger cascade effects throughout the marine food web. Moreover, Blacktip reef sharks frequently swim with their mouths partly open to facilitate respiration, which leads to constant exposure of their dental surfaces to seawater. This behavior potentially increases their susceptibility to acid damage, making the issue even more pressing.
The study notably focused on non-living mineralized tissue since it used discarded shark teeth detached from the animal. Consequently, the natural reparative processes that living sharks might employ, such as rapid tooth regeneration or remineralization, were not accounted for. The researchers acknowledge that living sharks may compensate for increased dental damage by faster tooth replacement cycles; however, this adaptation might incur higher energetic costs in acidified waters, potentially affecting overall health and fitness. Baum commented that slight reductions in seawater pH, even less severe than projected for 2300, could disproportionately affect species with slower tooth replacement rates or impose cumulative damage over longer periods.
Beyond the direct implications for sharks, this research sheds light on the broader vulnerabilities of marine calcifiers facing environmental change. Much of the attention on ocean acidification has traditionally centered on shelled invertebrates and corals, whose calcium carbonate-based structures are known to be sensitive to acidity. This study extends concern to phosphate-based mineralized tissues, revealing a more widespread potential impact. The microscopic surface irregularities and corrosion observed could compromise functional properties vital for survival, such as cutting efficacy and resistance to mechanical stress, turning nature’s most efficient predatory tools into liabilities.
Looking forward, the authors advocate for expanded research to include live specimens and more nuanced biochemical and biomechanical analyses. Understanding how living sharks manage and potentially mitigate dental corrosion in acidified oceans, including changes in tooth chemistry, regeneration rates, and associated energetic costs, remains a critical frontier. Such insights will be crucial to assess whether sharks can adapt to shifting environmental baselines or face population declines driven by deteriorating foraging ability.
In the context of global climate change, this research offers a sobering reminder that the impact extends well beyond rising temperatures, encompassing chemical alterations of the ocean’s fundamental properties with cascading effects on ecosystems. Magnified by the centrality of sharks in marine food chains, any threat to their survival tools—teeth—is tantamount to destabilizing entire oceanic communities. The degradation of shark teeth under simulated future ocean acidification scenarios underscores the necessity for urgent mitigation of CO2 emissions to preserve marine biodiversity and ecosystem function.
Ultimately, maintaining oceanic pH values near current levels is vital to safeguard the physical integrity of predatory tools such as shark teeth, pivotal for feeding and survival. The observed chemical corrosion and structural degradation, even at the microscopic level, could precipitate profound changes in predator-prey dynamics, with unknown but potentially severe consequences. As Baum eloquently concluded, this study exemplifies how climate change permeates through every link in ecological networks, threatening species reliant on biomechanical adaptations finely tuned over millions of years. It is a compelling call to action to address environmental changes before the sharpness of the ocean’s top predators is irreversibly dulled.
Subject of Research: Animals
Article Title: Simulated ocean acidification affects shark tooth morphology
News Publication Date: 27-Aug-2025
Web References: http://dx.doi.org/10.3389/fmars.2025.1597592
Image Credits: Max Baum
Keywords: Ocean acidification, Shark teeth, Blacktip reef shark, Tooth morphology, Ocean pH, Climate change impact, Marine predators, Phosphate mineralization, Structural degradation, Marine ecosystems
