Divers, Your Very Presence Affects Reef Fish Behavior

While fish on heavily dived reefs in, say, the Caribbean may be accustomed to seeing divers, does that mean they've adjusted to their presence? That's what researchers from Ohio State University wanted to know, so they studied the interactions between cleaners like wrasses and shrimp with their "client" reef fishes on two reefs with differing levels of diver usage.

In a study published in the online journal PLOS One, they compared the frequently-dived house reef of the Coral View Resort in Utila, Honduras, to an unmarked reef with far fewer divers in a marine preserve in the nearby Cayos Cochinos, observing cleaning activities among 18 fish types for a maximum of five dives a day. They also set up GoPros to film cleanings when no divers were around.

The researchers didn't find significant differences between the two reef systems with respect to coral cover, richness of fish species or cleaning station density. However, when divers were present, cleanings happened less frequently than when divers were absent and only cameras viewed the fish. At the Coral View reef, divers observed a cleaning rate four times higher than they did at Cayos Cochinos, but it was still 50 percent less than the filmed cleaning rate at Cayos Cochinos when no divers were around. Cleaning behavior resumed much faster at Cayos Cochinos when divers left.

Those findings show that divers have a definite impact on the reef ecosystem, at least in the Bay Islands, the researchers believe, stating "Despite the generally positive relationship between historical levels of diver activity and resilience to diver presence, full habituation across all individuals and species of reef fish has not been achieved at Utila: direct diver presence continues to depresses cleaning rates."

So next time you want to watch some cleaners and clients in action, consider how you may affect them when you're front and center. Back off a bit to give them some comfort space.