Epizoic growth by Acrosiphonia is very common. Epizoic growth simply means that the alga is growing on the surface of an animal. Many trips to locations with Acrosiphonia will reveal, after close inspection, a number of lucky (or poor?) limpets with Acrosiphonia growing on their backs!
Not much research has been done on the costs and benefits for the algae and for the limpet involved.
One personal theory that I have (with absolutely no proof to back it up, yet) is that by growing on the limpet it is much less likely for the algae to be grazed upon.
Research on the benefits and costs of the algae were performed as part of the research apprenticeship of the ZOOBOT course series at Friday Harbor Labs. Presence of Acrosiphonia on limpets increases drag forces, but decreases desiccation stress by reducing limpet body temperature when exposed during low tides.
Acrosiphonia also acts as a limpet parachute. Limpets with Acrosiphonia almost never land on their backs if dropped in water. Limpets without algae on their backs almost always land on their backs. This parachute effect happens very quickly, within the first few centimeters of water.
Website created by:
ZooBot Spring Quarter 2009
Friday Harbor Laboratories
University of Washington
All images created by the author, except where indicated, and cannot be used without permission from the author.