The larvacean Oikpleura sp.

Until yesterday I was unaware of these tiny organisms that I found in a trawl with my plankton net in the Georgia Strait between Vancouver Island and the mainland. Looking at them under the microscope, at first I thought that they were very young fish but experts in microscopic life made a positive identification as being Oikopleura sp.

They are urochardates known as larvaceans, related to the tunicates (sea squirts). Although they are technically invertebrates they have a body plan that resembles a fish with a backbone. These animals have one of the smallest DNA genome sequences of any animal. They live a very short lifespan of only a few days. They release eggs and sperm into the ocean to reproduce. Living only a few days they can appear in large numbers becoming an important component of the food chain.

This example was squeezed out of the water drop when I lowered the cover slip onto the glass microscope slide. It is laying alongside the edge of the glass cover slip and I just happened to notice it when I was scanning the slide for interesting targets.

They carry captured debris in tiny nets which, when they get clogged, are abandoned and eventually sink to the bottom. Carrying remnants of their food (bacteria and phytoplankton) this moves the Carbon from the atmosphere sequestered by phytoplankton as biomass back into the chemical form. In the process they become an important food source for larger organisms. These ‘nets’ are a significant portion of the ‘white snow’ that is observed in the water column slowly sinking to the ocean bottom.