Why does the ocean sunfish bask?

Basking at the sea surface is a well known, but peculiar behavior of ocean sunfish (Mola mola). One of hypotheses for this behavior is parasite elimination. However, in oceanic regions, very little direct evidence exists for this form of interspecific communication. In pelagic waters of the North Pacific Ocean, we observed a school of 57 ocean sunfish, that were heavily infested around the base of their dorsal fins with the ecto-parasite Pennella sp. We photographed a Laysan albatross (Phoebastria immutabilis) nearby that picked a Pennella sp. from one of ocean sunfish and ate it. We hypothesize that ocean sunfish did “bask” to look for skin cleaning and that this symbiotic cleaning behavior by the albatrosses may be a common feature of the biology of the ocean sunfish. Here we provide more photographs to show heavy parasite infections and scars after parasite removal by “cleaners,” and discuss how important a symbiotic cleaning relationship could be in the open ocean ecosystem.