This week we carried out experiments in the lab to investigate the effects of salinity on the barnacle Balanus glandula. These curious crustaceans that range from smaller than a few millimetres, to giants 15cm in diameter, are totally fascinating. Despite the fact that these animals spend their adult lives stuck onto a rock, or sometimes even other animals like whales, barnacles can be found all around the world. The manner in which they do this is through their larval stages. Barnacles have tiny planktonic larva, meaning that their larva drift and wander on the currents of the ocean to wherever they may take them. It is at this stage in their lives that the barnacles are able to travel massive distances, sometimes colonizing different areas far and wide across the ocean. Once they have found a surface they quite like, the larva slap their foreheads onto it and cement themselves (and quite strongly) to it, and undergo a metamorphosis that ultimately results in an adult barnacle.
The salinity of the water in which they live is very important for many barnacle species as their blood concentrations tends to match that of the surrounding water. Thus, large changes in salinity can have very serious consequences for barnacles, like decreases in performance or even death! In order to prevent these problems, barnacles will close their opercular valves to seal themselves inside in an attempt to avoid the environment’s changes in salinity. However, this is not a permanent solution as eventually the barnacle’s blood concentration will change to match that of the environment’s. Climate change is increasing the amount of freshwater going into the oceans (and therefore decreasing the salinity of coastal areas) which can have significant effects on marine ecosystems. This is why research on the effects of salinity stress on marine ecosystems is so important.
Have you ever wondered how barnacles feed if they can’t even move from place to place? Barnacles feed by extending their feeding appendages called cirri into the water, filtering out tiny food particles, then retracting the cirri to eat the food. As you can imagine, a barnacle isn’t likely to catch a whole lot of food in one go, so it beats its cirri repeatedly in order to obtain as much food as it requires.
Watching barnacles feed is quite fascinating. Bioluminescent dinoflagellates (tiny plankton that produce light when stimulated) are also quite fascinating. Watching barnacles feeding on bioluminescent dinoflagellates is even more fascinating! Watch it here: