Ay, Corambe!

A couple of weeks ago, Eric noticed some Giant Kelp blades (Macrocystis pyrifera) washed ashore on the outer beach.  They had large patches of bryozoan colonies (Membranipora sp.), and when he looked closely, he spotted a tiny egg mass on one of the colonies.  We thought it might belong to a nudibranch, so we brought the kelp blade into the lab and did a quick visual inspection, but we couldn't find a nudibranch at the time.

We decided to put the kelp blade in a tank with seawater to look at again later.  I hadn't had a chance to do so until yesterday.  I wasn't really that hopeful, so I was surprised to see new egg masses when I picked up the kelp blade this time (see below)!

 

The egg mass is the crescent-shaped gelatinous object filled with tiny developing embryos.  It's attached to the bryozoan colony.  A few of the bryozoans are out and feeding to the left of the egg mass.

Discovering new egg masses was a good sign, so I started scanning the bryozoan colony with my hand lens and I'm guessing you know what happened next.  I found one!  This nudibranch is incredibly well camouflaged against the bryozoan colony (see next image).

 

Meet Corambe steinbergae (formerly Doridella steinbergae)!  Note that it's mostly transparent except for the fine white lines that mimic the skeletal structure of the bryozoan.  There are also small red-brown splotches — do they blend in with the background of the kelp? 

Here's another picture with a different individual that's a little easier to see.  These nudibranchs are tiny, I'm guessing 5 mm or less in length.

 

Eventually I found one that had crawled part way on to the kelp (next image).  Look for the smooth rhinophores at the anterior (head) end near the bottom of the picture.  (This feature separates them from a similar species, Corambe pacifica).

 

Corambe steinbergae and Membranipora have been the subject of classic research on inducible defenses.  The nudibranchs eat the bryozoans. [I read that they can eat up to 150 zooids per day!  Zooids are the members of the bryozoan colony — they are visible as rectangular units in the photographs above.]  To defend themselves, the uneaten portions of the bryozoan colony respond by growing significant spines which make it harder for the nudibranch to access the remaining zooids.  The bryozoan can grow spines in response to the nudibranch within as little as 2 days!