Moon Jellies, Aurelia aurita

I have received a few questions about the Moon Jelly in recent months, which inspired me to reinvestigate what I knew about this marine invertebrate.  All jellies are a member of the phylum Cnidaria, or stinging animals, but luckily for those of us in the Pacific Northwest the stinging cells of our jellies are quite mild compared with other parts of the world. Moon Jellies use their stinging cells, or nematocysts, mainly to capture their prey- microscopic zooplankton.

For as simple as the moon jelly appear while floating in the tidal currents, their life cycle is incredibly unique and complex.  This jelly goes through six different stages prior to reaching the adult (medusa) which we recognize.  The first stage begin with the broadcast spawning of male sperm into the water which find their way inside mature females to fertilize their eggs.  The fertilized eggs are then released by the female and larvae develops.  As the larvae mature they settle to the seafloor and become polyps, which feed on plankton and continue to mature into strobila. The strobila are basically a stack on one immature jelly on top of another.  Strobila may remain vital for up to two years, according to The Seattle Aquarium!  During this stage the jellies bud sequentially as they develop into ephyra.  Within 42 days these mature into the adult medusa form of the jelly.  The medusa stage will then last for 3-6 months and can grow as large as 18" across.

During the fall many of the jellies will wash up onto the beaches after reaching the end of their adult life cycle.  This can be a result of extreme tides stranding them, or large wave action essentially breaking them apart as they weaken towards the end of their life.  Sometimes, weather conditions can be so mild I would guess the conditions for reproduction are prolonged enough where jellies are able to be observed later into the winter months.