Goose barnacles of the genus Lepas live exclusively on debris floating in the open ocean. Like other barnacles, their larvae spend the early part of their life swimming freely and then, in a final larval phase called the cyprid stage, search out a floating object on which to settle. Once they find a suitable object, says marine biologist Hank Carson, “cyprids in general do do a fair bit of exploration for that cementation spot” upon it, and with good reason: they’ll spend the rest of their life there. Among the criteria they assess is how crowded a spot is, what the underlying substrate consists of, and how deep it is. Once satisfied, they glue their heads in place.
In general Lepas barnacles like to spread out, and prefer a spot in the shade; they grow best away from the top of the water column. The reason is that close to the waterline, the rising and falling of waves periodically exposes the animals to the air, which interferes with their feeding. It’s unhealthy for them in other ways, too. “The uppermost centimeters of water are normally a quite harsh environment with strongly changing ecological parameters, like water temperature, salinity (heavy rains or intense evaporation in tropical areas). Moreover they are subjected to intensive UV radiation,” says Hans-Georg Herbig of the Institut für Geologie und Mineralogie in Cologne, Germany. “From several organism groups it is known that they avoid the uppermost centimeters of the water column.”
