Exception to the rule

Ask any marine biology student to list some interesting factoids about barnacles, and one of them should be “Barnacles are benthic and sessile” by which they mean that barnacles live their entire lives glued to a single spot. This definitely describes what it means to be benthic. Barnacles are indeed stuck, for better or worse, to the location that their cyprid larva selected. Once the cyprid glues its head to the rock or other hard substrate, that’s it. A bad choice could mean that the barnacle starves, desiccates, or is unable to mate. A good choice means an opportunity to live long and prosper.

How is it, then, that we have things that are called pelagic barnacles? These are barnacles that live permanently attached to objects that move through the water. The objects can be living (e.g., whales or turtles) or non-living (e.g., boats). Pelagic barnacles are not just traveling versions of the species we see in the intertidal or on docks and pilings—they are different species altogether.

Yesterday morning I went to Younger Lagoon to see what had happened during the most recent storm. The lagoon had once again breached through to the ocean, and bits of Monterey Bay were sloshing into the lagoon. None of that was unexpected.

What did catch my eye were the fuzzy blotches on some of the pieces of wood that had washed up onto the beach.

A closer look confirmed my thought that these were pelagic barnacles in the genus Lepas. These are a type of gooseneck barnacle, similar in overall morphology to the very common intertidal Pollicpes polymerus.

These barnacles were small, and having been emersed for at least several hours were definitely not looking their best. They didn’t smell dead just yet, but since they had zero chance of getting back into the water before the next high tide, were doomed. A few of them had their cirri—the modified thoracic appendages that barnacles sweep through the water when feeding—extended, which I’ve seen before with barnacles on their last leg. See what I did there? I did touch some of the cirri, and the barnacles did not respond at all, although they had not yet dried out to the point of crispiness.

Lepas makes a living attached to objects that float in the ocean. I usually see them on logs or smaller pieces of wood, as they are here, but do occasionally find tiny ones on the blades of giant kelp (Macrocystis pyrifera). Living attached to objects that float with the currents means the barnacles are constantly moving through the water, able to feed 24/7 without the constraints of high and low tide. Compared to the robust gooseneck and acorn barnacles of the rocky intertidal, Lepas is translucent and delicate, with plates that are only weakly calcified. Given its lifestyle, Lepas rarely has to withstand bashing surf or waves; by the time it does, its substrate is inevitably headed onto shore, where the barnacles will die anyway.

So there you have it—a barnacle that flouts the rule and manages to be both benthic and pelagic. Or perhaps I should say that it is benthic but has a pelagic lifestyle. Either way, Lepas is making the best of both worlds, isn’t it?