If you had to put together a list of your top 10 knock-out heavy-weights, I suspect that sea anemones wouldn't be high up. But when Sarah Lane from the University of Plymouth describes sea anemones slugging it out, it is clear that the outcomes are no less cataclysmic. Elongating their bodies and inflating blue stinging blobs – known as acrorhagi – at the base of their tentacles, the combatants slam their bodies down on top of each other. In the process, they rip off the acrorhagi as they drag them along their opponent's flank, depositing toxin-laden stinging cells in their opponent's skin until the vanquished adversary closes up or makes off. According to Lane, the outcome of confrontations is often assumed to depend on the size and strength of the opponents, but she and Mark Briffa – also from the University of Plymouth – wondered whether the local prevailing conditions could also influence the result. ‘The environment is rarely stable’, says Lane, pointing out that sea anemones are often prey to exposure and rising temperatures, both of which could impact their performance when duelling over real estate. ‘We wanted to understand how such environmental variation might affect how fights play out in the wild’, says Lane.
After settling sea anemones (Actinia equina) that had been collected from rock pools on a Cornish beach into their Plymouth laboratory home, Lane transferred half of the animals into water with low oxygen levels. ‘This [oxygen] is a factor that is known to vary considerably within rock pools when the tide is out’, says Lane, adding that the availability can affect the anemones’ strength and stamina. Then, she riled pairs of sea anemones by nestling them together and gave them something to fight over: flowing water. ‘Anemones are scavengers and use their feeding tentacles to catch food passing by in the water column; thus, anemones value flowing water over still water’, she says. Pitting ‘breathless’ anemones from the deoxygenated water against well-aerated animals, as well as coupling pairs of aerated anemones and pairs of oxygen-deprived (hypoxic) anemones, Lane staged some prize fights when the water was flowing and others when it was still – and there was less at stake – before recording which fighter had been overcome at the end of a round.
Comparing the anemones’ prowess, it was clear to Lane and Briffa that the environment affected the animals’ performance dramatically, with the well-aerated anemones out-performing their oxygen-deprived sparring partners, especially when they had a healthy current to duel over. However, Lane admits that she was surprised that despite the lack of oxygen, the hypoxic anemones fought more doggedly than their well-aerated opponents; they were particularly brutal, inflicting more wounds on their adversary, when matched against an equally hypoxic competitor.
So, the environmental conditions that a contestant experiences can affect their performance in combat, ‘by altering an individual's ability to fight and its motivation’, says Lane. And she is eager to stage more anemone fisticuffs, only this time between anemones from different locations on the beach, to find out how much of an impact the real world has in practice on sea anemone boxing bouts.
