It’s not quite intergalactic, more barotraumic (I don’t think barotrauma is an adjective, but work with me people). The hitchhikers in this story are not aliens to Earth, although they are still aliens to most of us. They are marine organisms that have hitched a ride on Alvin, the most famous of submersibles, and ended up in the wrong neighbourhood of the deep dark ocean. As much as I jest this is really not amusing in a scientific sense. It’s like a scene from a bad share house, someone’s not doing their dishes, or washing their pistons in this instance, and as a result foreign species are being able to colonize new habitats.
In an article posted on the Nature blog recently, researchers describe their distress to find a population of limpets that had inadvertently hitched a ride to the surface on Alvin, before being brought back down to depth some 635 km north of their native habitat. It appears that the sampling system was not properly scrubbed prior to the dive enabling the rather robust gastropods to survive. Their survival is in itself worth reporting as most specimens die when exposed to such dramatic pressure changes (known as barotrauma, the noun). However in the first instance, the possibility that routine dives could contaminate pristine sites with invasive species needs to be addressed.
It is more often that we hear of ballast water discharge being the preferred carrier of the marine invasive hitchhiker. The worst instance in my memory would be the catastrophic introduction of zebra mussels to the Great Lakes of North America. Authorities believe the mussels were introduced by an ocean-going vessel in 1988. They have subsequently spread and multiplied to plague proportions. They colonize any hard or rocky substrates, even being known to colonize lobsters (?!). Their monopoly over the real estate smothers indigenous species, they filter the water of phytoplankton devastating the base of the food web, and they also bio-accumulate contaminants that are then passed on to higher predators. The damage is not just environmental but also economic, with high costs involved in removing the mussels from the intake pipes of boat engine cooling systems, waste treatment and power plants.
In the case of the deep-sea, we know so little about how these ecosystems function that if we are to ever characterize them correctly we should probably remember our laboratory etiquette: do your dishes and don’t contaminate anyone’s experiment. In such a marginal existence slight disturbances can prove fatal. As an example, in certain deep-sea environments giant tube worms, Riftia pachyptila, need to grow precise distances from chimneys (black smokers) and hydrothermal vents to ensure they can sit on the interface between oxic (oxygen rich) seawater and sulphidic (sulfur rich) vent fluids. Riftia rely on bacteria that inhabit their trophosome (almost like a rudimentary stomach) to oxidize the hydrogen sulfide from vent fluid, using dissolved oxygen in seawater for respiration. Their position around the vent is paramount to their survival. Quite astonishing to think chemosynthetic bacteria provide all the energy and nutrients that the tube worm needs to survive in the darkest ocean. Technically speaking you can not say that they survive independent of sunlight, as it is photosynthesis in surface waters that liberates the oxygen in the first place.
What has this got to do with hitch-hiking limpets? Nothing really, my tenuous link is the importance of real estate in these extreme environments and it’s the first decent segue I could find to tell you about Riftia because I think they are amazingly cool.