If you asked Valentina Di Santo what was the most surprising finding from her latest research project, she would quickly answer, “Well, first, [the fact that] there is not much known about the effect of climate change on elasmobranchs! Sharks and ray are an important group of meso- and top predators but studies to understand the effect of climate-related stressors have been scarce, especially when compared to the vast literature on the effect of climate change on physiological responses of bony fishes.” As one of the oldest and most diverse group of marine vertebrates, elasmobranchs (sharks, skates, rays and sawfishes) have survived multiple extinctions our planet has previously faced. Wipe-outs that killed off their mighty ancestors and even dinosaurs were no match for sharks… but could they finally be facing a foe even they can’t win against?
Enter climate change.
Due to climate change, our oceans are currently experiencing severe changes, including a rise in temperature, a rise in sea level, and an increase in acidity. Ocean acidification was of particular interest to the Assistant Professor of Functional Morphology at Stockholm University because, as she puts it, “understanding intraspecific variation in responses to stressors is key to identify which traits make individuals and group of elasmobranchs more or less vulnerable to the effects of environmental change.”
Because climate change has already begun, scientists have little time to test how severely it impacts different species. It’s important therefore, that researchers focus on the different characteristics (known as ‘physiotypes’) that make individuals more or less vulnerable to rapid warming and acidification. Some of these traits include body size, local adaptation to fluctuating chemical and physical conditions, age-at-maturity. “One of these [important] traits is, for example, locomotor performance,” adds Di Santo. In many animals, locomotor performance plays a fundamental role in determining their fitness. Locomotor performance is closely related to the morphology of the structures responsible for it, such as limbs and fins. In elasmobranchs, it influences vital functions such as reproduction, migration, predator avoidance, small-scale movements, and more. By delving into the literature, the Di Santon’s team was able to integrate findings from previous work on locomotion of marine sharks and rays to identify characteristics that outline potential vulnerabilities and strength of sharks and rays under climate change.
Diversity has been found to be the key for sharks living as long as they have… and perhaps it is … [+]
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“One of the most intriguing findings is that ocean acidification can affect the skeletal density of elasmobranchs,” says Di Santo. Characterized by a reduction in the pH of oceans over an extended period of time as a result of the uptake of carbon dioxide (CO2) from the atmosphere, ocean acidification has increased due to our burning of fossil fuels and how we use our land (for example, agriculture). Ocean acidity is already affecting oysters, clams, sea urchins, shallow water corals, and deep sea corals, as well as the calcareous plankton in the ocean. “Increase in CO2 produces an increase in skeletal mineralization in the modified pelvic fins of skates (they use these to walk) and the jaws. This is the opposite effect that is commonly observed in shell-forming aquatic invertebrates which show a decrease in mineralization in their exoskeleton.” Skeletal mineralization was also found to directly affects buoyancy and locomotor performance of these animals. However, interestingly, ocean warming decreases the mineralization of pectoral fins. As skates use their pectoral fins to swim, this may means that large scale movements might be impaired by an overall heavier skeleton (ocean acidification) and less stiff pectoral fins (warming) under future ocean conditions.
“From the few studies conducted on them I learned that intraindividual variation (read: diversity) might be one of the important factors to decrease vulnerability to climate change as different populations of the same species may be ‘pre-adapted’ to poor conditions of ocean acidification and warming, show different body sizes and have higher locomotor capacity and endurance,” concludes Di Santo. “This may allow some individuals to be better at escaping predators, explore the environment and relocate to more favorable geographic areas.”
And so it goes: Diversity has been found to be the key for sharks living as long as they have… and perhaps it is the key to their continued survival as well.
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