Sunscreen use may be at an all-time high during peak tourism season in Delaware, but excess pollution could have a detrimental impact on the horseshoe crab population.
Part of a 10-week summer scholars program, University of Delaware junior Megan Cain is observing what kind of impact different concentrations of (Hawaiian tropic SPF 30) sunscreen have on horseshoe crab larvae and juveniles.
"Sunscreen pollution has been known to bleach coral, so it’s a big factor in coral bleaching which either sterilizes the coral or can kill the coral, and that’s a big deal with coral reefs," Cain said. "But there’s nothing really being studied on sunscreen pollution in temperate conditions."
After sunscreen pollution was found to be harming coral reefs, some reefs imposed sunscreen regulations. No regulations have been imposed on more temperate environments, because data is lacking.
Cain divided three clutches, or families of eggs, into three different concentrations of water, and is using one concentration of seawater as a control group. She is focusing on the impact of oxybenzone, an active ingredient in sunscreen, by tracking survivorship, rate of development and behavior.
Once a week, she videotapes the juvenile crabs for a five-minute period to see the speed and distance they move and how the concentrations of sunscreen impact the data.
Horseshoe crabs are a keystone species for Sussex County's ecosystem. They ecologically have a greater impact than their numbers would infer, said Danielle Dixson, an assistant professor with the University of Delaware's College of Earth, Ocean and Environment.
“They’re also a prehistoric species, so they’re considered a living fossil," Dixson said. "They haven’t changed much in hundreds of thousands of years, so because of that, they’ve had to deal with a lot of things and now we’re rapidly changing our ecosystems. I think it’s really important that we understand what’s going on with them before their numbers get to a critical level that they’re too low."
Population numbers, however, are better than they were years ago. The species is classified as "nearly threatened."