We've all seen them. Whether you're looking at cliffs by the ocean or watching a nature documentary on whales, barnacles are some of the most visually distinct animals in the ocean. But what most people probably don't see are the different forms that barnacles take on during their lifetime!
Barnacles belong to the phylum arthropoda, the same phylum that crabs and lobsters are in. Although they may not look very similar to crabs as adults, nearly all arthropods have the same first stage of development after they hatch, the nauplius. This microscopic spaceship-looking creature uses its feathery legs to propel itself through the water column, feeding on zooplankton and plants.
The next stage of larvae for barnacles is the cyprid, which scours the ocean floors and rocks looking for good real estate. It turns out that many species of cyprid, much like the people on HGTV, can be very picky with their housing choices. Barnacle cyprids are very specific in where they settle and some species tend to favor some spots over others based on things like how smooth the area is. But how exactly do they make this decision? One answer lies in intricate protein complexes involved in settling that are found on the barnacle's cuticles (the exoskeleton on arthropods similar to our nails). These protein complexes act as pheromones that stick to the surface that the cyprid walks on and act as a cue to other cyprids that this may be a good place to settle down in. This could help explain why barnacles accumulate in a single space, a phenomenon known as biofouling.
A barnacle Cyprid Larvae
But how exactly do barnacles pick up on these cues? Cyprid larvae have rather sophisticated antennules which contain small bristle-like organs called setae. These setae are capable of chemoreception, (tasting and smelling), which they use to determine if an area is suitable to settle into by picking up on settlement-inducing protein complexes. Analyses of the RNA transcripts of these setae revealed that specific gene homologues (a gene inherited by two species from an ancestor) play a key role. The TRPM gene complex in mammals encodes a variety of ion channels that act as sensors for pain, cold, and other irritants. Barnacles have related genes that are activated by an increase in chemicals that may cause irritation, leading the barnacle larvae to determine that this area may not be a good place to settle down, which they signal to other cyprids.
So you see, investigating larval dispersion and settlement for barnacles can be a complicated task for scientists. Because barnacles provide important filtering services for ecosystems, finding out the exact specifications for how they determine where they want to live for the rest of their adult lives is a significant project for investigators. This info can also be useful for shipyards seeking to develop methods to keep barnacles away from the bottom of their vessels. Whatever the reason for exploring this, scientists still have a lot to learn.
