Interactions of Divers with Reef Biota are More Frequent Among Snorkelers Than Scuba Divers And Increase During Sea Turtle Watching

Abstract

Snorkeling is a popular recreational activity in shallow water of coastal ecosystems. Because snorkeling is commonly assumed to cause comparatively fewer potential impacts to the marine biota than scuba diving, management is generally focused on the latter. We investigated the behavior of snorkelers aiming to quantify their interactions with benthic reef sessile organisms and sea turtles. We also compared the behavior of snorkelers with scuba divers to assess which group of divers is more damaging to the reef biota. Finally, we compared the use of conventional and nonconventional sampling approaches through analysis of social media images to evaluate the reliability of different approaches to investigate the behavior of underwater recreationists. Snorkelers were observed during 5 min; their interactions with benthic organisms were recorded and compared with scuba diver's behavior. Snorkelers'observations were carried out with and without the presence of sea turtles and compared with videos from social media. Videos were extracted from YouTube through a search using keywords and analyzed to quantify the number of interactions of divers with the benthic organisms. Snorkelers caused 33% more contacts and 70% more damage to benthic reef organisms than scuba divers. Most interactions were over the zoanthid Palythoa caribaeorum, which received ~80% of contacts and ~30% of damage. The contact rate of snorkelers with benthic organisms increased 5.5fold when they interacted with sea turtles. Snorkelers sampled through direct observation accounted for more contacts with benthic reef organisms than those observed in social media videos, whereas higher rates of behavioral disturbance to sea turtles were observed in snorkelers sampled in social media videos. As the videos from social media focused on sea turtle watching, they overestimated the amount of snorkelers–sea turtles' interactions but underestimated the amount of contacts with benthic organisms. Our results revealed that snorkeling in shallow waters <2 m deep may represent a considerable amount of impacts to reef benthic sessile organisms and such impacts significantly increase during sea turtle watching.