On the Greek islet of Formicula, researchers have found rare Mediterranean monk seals will take refuge in an air-filled “bubble cave,” according to a recent study. This type of hidden chamber, accessible via underwater passages, allows the seals to breathe, and possibly hide from tourists, the researchers said.
Mediterranean monk seals (Monachus monachus), the world’s rarest pinniped, are the only seals found in the Mediterranean Sea. Fewer than 1,000 of them remain, according to the IUCN, the global wildlife conservation authority.
Historically, these seals hauled out on open coastal beaches to rest, molt and give birth to pups. But with increasing human disturbance from tourism, fishing and land development, they retreated to marine caves along the Mediterranean coastline to rest and breed.
Study lead author Joan Gonzalvo of the Ionian Dolphin Project at the Tethys Research Institute in Italy described the “ideal cave” to Mongabay as one with a pool, a dry beach for hauling out, an entrance corridor and protection from adverse weather and choppy seas. Typically, these caves are accessible by entrances above or below water level.
During a habitat assessment in the Inner Ionian Sea Archipelago, the team was setting up a camera to monitor one of these “comfortable” marine caves on Formicula when they discovered that an underwater corridor connected to it led to a second smaller chamber. This “bubble cave” had water and a pocket of air on top, but no dry beach or platform to haul out. The team placed an underwater camera in the bubble cave to monitor whether seals used it.
Over 141 days, mostly during the summer and autumn months of 2020-21, researchers captured monk seals using the main cave on 30 days, the bubble cave on 119 days, and both caves on 23 days. Seals visited the bubble cave in groups of one to three and were observed resting and sleeping.
Gonzalvo said they were surprised to see the seals used the “wet, less comfortable” bubble cave more than the main cave. However, despite not being suitable for breeding and molting, the bubble cave appears to provide a space for seals “to rest and to chill and to look for shelter from unwanted human presence,” he said.
Tourism in the Ionian Sea can be intensive in the summer months, when tourists sometimes approach seals, even pursuing them inside the caves, the authors said. No-entry zones have recently been established around Formicula to protect the seals.
Gonzalvo added any future habitat assessments for Mediterranean monk seals should consider bubble caves as an important habitat.
Jason Baker, a marine biologist not involved in the study, told Science that “it makes sense to inventory these kinds of habitats,” but added that it would be ideal if more habitat could be protected so seals did not need to avoid humans.
Banner image: A Mediterranean monk seal off Formicula in Greece. Image supplied by Joan Gonzalvo/Tethys Research Institute.
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This story first appeared on Mongabay
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