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It’s easy to see why marine mammals like killer whales might get stressed when kept in captivity. But how do smaller creatures fare when held in tanks? According to a new study, at least one type of marine invertebrate—the sea urchin—is affected. But it isn’t the length of time that urchins spend in a tank that has the biggest impact—it’s the simple act of being picked up.

Most of the research on stress in captured-and-released wild animals has been done on vertebrates such as fish, birds, and turtles, rather than on invertebrates. Sea urchins are sometimes collected and translocated to help restore species that are declining due to overharvesting or warming waters. Yet no one had studied how the stress of captivity might affect them when reintroduced to the wild.

The idea for this study came in 2016 when Isabelle Côté, a professor at Simon Fraser University in British Columbia, taught a course at the Bamfield Marine Sciences Centre (BMSC) on Vancouver Island. The group of 10 students decided to look at the effects of handling and captivity on the red sea urchin, which is abundant in the northeast Pacific. The students spent a week collecting nearly 200 urchins from waters around BMSC. All of these urchins were handled—picked up and tagged with a number—but their period of captivity varied. Some were released immediately, and others were held for either one, two, three, or four days.

Surprisingly, the duration of captivity had almost no effect on the urchins’ behavior when they were returned to the wild. But handling did. When turned upside down, the handled urchins took twice as long to right themselves as ones that were never handled. “When an animal is on its back, it’s most vulnerable and has a harder time fleeing or fighting,” explains Miriam Ashley-Ross, a professor at Wake Forest University in North Carolina who was not involved with the study, and whose lab has researched righting behavior in tarantulas. That delay in righting itself is significant enough to give a predator time to attack, says Côté.

The students hope their research can be applied to more endangered species of urchins, says lead study author Aneesh Bose, now a postdoctoral researcher with the Max Planck Institute for Ornithology at the University of Konstanz, Germany. “Our study highlights the importance of respecting nature and admiring wild animals from a distance, or handling them with extreme care,” says Bose. “Rushing up to handle them can have unforeseen consequences even after we let them go again.”