4/5/2021: Florida Trip Rambles- The sea-land-sea story of Porcellio laevis

At the behest of budding bug enthusiast Carlos Michaelsen, we visited a pull out in the Florida Keys that reportedly had a good population of easily accessible isopods. While it was originally thought that they were Porcellio scaber (which piqued my excitement as they’d be the southernmost recorded Porcellio scaber in the US), upon arriving we found a mix of Porcellionides floria and Porcellio laevis. While these species are pretty common in the keys, it wasn’t their presence that shocked me; it was their microhabitat preference!

Terrestrial isopods are descended from aquatic ancestors and are very uniquely adapted for terrestrial living. They do still respire through gills, and thus are restricted to humid climates, moist microhabitats, or wet weather for their activities.

Even more interesting are the brutal forces imposed on ocean and seaside organisms, primarily with respect to staying hydrated. Ocean organisms must keep their internal organs free of the concentrated saltwater surrounding them, while freshwater organisms face the opposite dilemma of losing their salts to the surrounding freshwater. For these reasons salt and freshwater organisms tend to have very different physiologies, and species that can move between the two salinities even more so.

But here we have our little Porcellio laevis. An organism descended from a marine ancestor which moved to colonize the freshwater-influenced land, but has now began a journey back to the sea. It’s not unusual to find seaside isopods; there is a great diversity of shoreline isopod species. However, the family that Porcellio laevis belongs to is strictly terrestrial; they have long abandoned their marine roots. To find these guys hanging out with strictly marine isopods below the tide line in direct contact with seawater was absolutely mind blowing.

Also of note was the lack of Ligia, a genus of freakishly large isopods that usually prowl the shoreline. Perhaps the absence of these isopods has allowed for the gradual colonization of the niche by Porcellio laevis in this one occasion.

Regardless, I was impressed and amazed that these terrestrial isopods had once again taken up residence on the seashore. Maybe in millions of years and with an odd chain of events they may one day return fully to the sea.

These salty Porcellio laevis were quite a sight to sea.

-Kyle