Marine biologists have shown for the first time that corals can cooperate to catch and eat stinging jellyfish which are swept against the walls by sea currents.
The mauve stinger (Pelagia noctiluca) trapped among colonies of the orange coral (Astroides calycularis). Image credit: Musco et al, doi: 10.1002/ecy.2413.
A team of researchers led by Dr. Tomas Vega Fernandez of the Italian National Research Council and the Stazione Zoologica Anton Dohrn, Italy, made the discovery when they spotted venomous jellyfish, called the mauve stinger (Pelagia noctiluca), stuck to undersea cliffs and caves near islands off the coast of Sicily.
“The mauve stinger is a holoplanktonic jellyfish with a phosphorescent bell 3-12 cm wide. It is typical of warm water but currents may transport smacks of jellyfish into temperate and cold seas. Thus, it can be found from the tropics to the north Pacific and Atlantic, including the Mediterranean Sea,” the biologists said.
“This jellyfish species is responsible for most of the painful stings people suffer while swimming in the Mediterranean.”
“The predatory orange coral (Astroides calycularis) is endemic to the Mediterranean Sea, where it can be reef forming. In shallow water, it may cover up to 90% of rocky substrate from the surface down to 15 m depth where it is found in caves and on vertical walls.”
“The species is ‘polystomatous,’ forming small colonies composed of polyps connected to each other as a single organism bearing several mouths. Polyps are typically 4-5 mm in length but larger polyps can grow up to 8 mm long.”
Dr. Vega Fernandez and colleagues made the observations in 2010, 2014, and 2017 in different localities of the Mediterranean Sea.
“The feeding behavior begins when a mauve stinger becomes trapped under an overhang with abundant Astroides calycularis,” the scientists said.
“The pulsating swimming of the jellyfish moves the bell repeatedly against the overhang ceiling. Astroides calycularis polyps first adhere to the bell after which several polyps rapidly engulf the oral arms of the jellyfish, a process lasting between one and five minutes.”
“Single polyps are able to ingest the oral arm tips preventing the jellyfish from escaping, while other polyps collaborate in ingesting pieces of jellyfish arms and umbrella.”
“Some jellyfish escape these attacks or become released as many were observed lying dead on the seafloor, with a hole on the top of the bell possibly caused by the predators.”
“Although both species have been known for years, we had no idea that the coral could catch and eat these jellyfish,” said co-author Dr. Fabio Badalementi, research director at the Italian National Research Council and Honorary Professor at the University of Edinburgh.
“This is a really fascinating observation,” said co-author Professor Murray Roberts, from the University of Edinburgh.
“The conventional wisdom is that corals don’t eat jellyfish, but these results show that we need to keep both our eyes and minds open to new discoveries.”
The findings appear in the journal Ecology.
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Luigi Musco et al. Protocooperation among small polyps allows the coral Astroides calycularis to prey on large jellyfish. Ecology, published online July 30, 2018; doi: 10.1002/ecy.2413
