These Unique Reef Sharks Can Walk on Dry Land
The epaulette shark (Hemiscyllium ocellatum) is a small species of reef shark with a set of unique abilities. It can use its fins to walk both in and out of the water, and it can go without oxygen for up to two hours.
These traits have helped the species succeed in rapidly-changing coral reef environments, in which parts of the reef can become stranded above the waves during low tide. But they could also aid the species in adapting to the climate crisis.
“Studying epaulette shark locomotion allows us to understand this species’ — and perhaps related species’ — ability to move within and away from challenging conditions in their habitats,” Marianne E. Porter, Ph.D., an associate professor at the Department of Biological Sciences at Florida Atlantic University’s (FAU) Charles E. Schmidt College of Science and a senior author on a new study of the unique sharks, said in an FAU press release. “In general, these locomotor traits are key to survival for a small, benthic mesopredator that maneuvers into small reef crevices to avoid aerial and aquatic predators. These traits also may be related to their sustained physiological performance under challenging environmental conditions, including those associated with climate change — an important topic for future studies.”
Epaulette sharks grow to be about 3.3 feet and have adapted to their habitat of the shallow reefs of Australia’s southern Great Barrier Reef as well as New Guinea, according to Live Science. Because of their ability to walk on their fins and survive in low-oxygen environments, they can walk for more than 100 feet on dry land, which helps them as they seek out food.
“You might not think of beautiful, tropical beaches as harsh but in reality tidepools and coral reef environments are pretty harsh, subjected to warm temperatures when the tide is out and a lot of changes, a lot of things happening when the tide comes in and goes out,” Porter told The Guardian. “These little sharks can move from tidepool to tidepool, allowing them to access new pools to forage for food, or tidepools with better oxygenated water.”
And these adaptations could help them in the future as well as the present.
“Past studies have shown that this species is robust (i.e., respiratory and metabolic performance, behaviour) to climate change relevant elevated CO2 levels,” the study authors wrote in Integrative & Comparative Biology.
The current study focused specifically on the movements of epaulette sharks during their earlier life stages: as neonates — or recently-hatched baby sharks — and juveniles, the FAU press release explained. Neonate and juvenile epaulette sharks have different body shapes and feeding patterns. Neonates gain their nutrition from a yolk sac that puffs out their tummies while juveniles are already foraging for crustaceans, worms and small fish. Because of this, the scientists from FAU, Australia’s James Cook University and Macquarie University predicted that the neonates and juveniles would move at different levels of ability.
To test this, they looked at different movement characteristics like velocity, tail beat amplitude and frequency, body curvature, fin rotation and tail motion. They compared these characteristics for the two ages of shark for three types of movement: slow-to-medium walking, fast walking and swimming and used 13 landmarks on the sharks’ bodies to help with their assessments.
In the end, the results surprised them.
“We found that differences in body shape did not alter kinematics between neonates and juveniles,” the study authors wrote.
Porter explained that understanding the young sharks’ movements was especially important.
“Investigating how locomotor performance changes over the course of early ontogeny — perhaps the most vulnerable life stages, in terms of predator-prey interactions and environmental stressors — can offer insights into the kinematic mechanisms that allow animals to compensate for constraints to meet locomotor and ecological demands,” she explained.