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Saturday, November 24, 2012

Jellies in the WGC

Yesterday we sailed over to White Gulch on Tomales Point (northern tip of Point Reyes) for a picnic lunch.  When leaving White Gulch, we encountered fairly high densities of two jellies: a hydromedusa called Polyorchis penicillatus and Moon Jellies (Aurelia sp., probably A. labiata).

Polyorchis is a relatively large hydromedusa — most of the individuals we saw yesterday had bell lengths of ~2-3 cm.  There is red pigment at the base of each tentacle (see below).  (The red coloration is part of the ocelli, or eye spots that are sensitive to light.)



The tentacles are highly contractile, short when pulled in (as above) but extending to 2-3 times the length of the bell when "fishing" (next photo).  Polyorchis trolls for zooplankton such as copepods, and may also feed on the bottom while elevated on its tentacles.


I had a tough time photographing the Moon Jellies while under sail, but here are a couple of shots for the record.  Most of them were ~10-15 cm across.  Note the hundreds of very fine, thread-like tentacles along the margin.


Below you can see the slightly scalloped edge, as well as the four pinkish horseshoe-shaped gonads in the center.


These two species may also be seen in Bodega Harbor, so keep an eye out for them if you're on the marina docks or walking the Spud Point breakwater.


P.S.  For fans of Finding Nemo, do you remember when Marlin (Nemo's dad) and Dory are navigating a dense swarm of jellies in the EAC, or East Australian Current?  The concentration of jellies in White Gulch reminded us of this scene, so we started joking that we were sailing through the jellies in the WGC, or White Gulch Current. 

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