Underwater Battles: How Benthic Organisms Fight for Space

I happened to see part of an Octonauts cartoon last week (Ok, we were trying to get three 2-year olds to let us eat dinner in peace). In the cartoon, small colonial anemones were zapping one another with stinging tentacles, as they fought over a particular rock to call home. I wondered if that was a real defense tactic, and indeed it is-colonies of anemones even have special polyps that are designated to fight with opposing colonies along the front lines of interaction.

Benthic organisms - those that live on the ocean bottom - often have to fight to defend a prime piece of real estate they have acquired. For example, limpets protect a patch of rock on which they cultivate an algal-film garden, upon which they feed. Like miniature bumper cars, larger limpets physically shove smaller animals out of their garden boundaries.

Corals fight by attacking adjacent colonies with digestive filaments. These are slow-motion battles, unfolding over months and years, and it is not often clear which colony will eventually be the winner.

Some benthic organisms compete by putting energy resources into growing faster than others - for example kelp plants can grow up to 60 cm a day to reach the sunlight filtering down from above. There are even examples of allellopathy, where organisms produce toxic chemicals to kill competitors. A recent study in Fiji found an alga that poisons corals on contact.

Can you think of other examples of benthic battles?

References

Ayre, D. J. and Grosberg, R. K. Behind anemone lines: factors affecting division of labour in the social cnidarian Anthopleura elegantissima. Animal Behaviour 70: 97-110 (2005).

Chornesky, E. Repeated reversals during spatial competition between corals. Ecology 70: 843-855 (1989).

Stimson, J. Territorial behavior of the Owl Limpet, Lottia Gigantea. Ecology 51: 113-118 (1970).