By now you must know that one of my favorite subjects for photography, and therefore my columns, is the group of shell-less snails known as nudibranchs. Please don't relate them to their relative the common garden slug... they are much more colorful, both in appearance and behavior. Of course in the warmer waters between Long Point and the East End here on Catalina we usually don't see many nudibranchs until we descend into the 80-150 foot depth range. They are much easier to locate in mainland waters or in the cooler northern Channel Islands where they are often found at shallow depths.
Readers also know that the themes that carry through many of my writings are those of "munching" and "mating," two of the most critical activities undertaken by all species. We must "munch" to grow bigger as individuals and become reproductively mature. Then we must "mate" (do we have to?) to ensure that our species continues with another generation. Of course "breathing" is another critical activity as is "defending your life" (although that's related to avoiding another species' "munching").
Today I'll delight you with the story of the noble dorid, currently Peltodoris nobilis although it has had several previous scientific names. To the best of my knowledge this nudibranch does not belong to any royal family, nor has it been declared a Lord, Baron or Marquis. That would be especially difficult since they are hermaphrodites, being both male and female. I guess that's one good way to establish gender equality. And it certainly has no relationship to the Nobel Prize which my Harvard friend Dr. Marty Chalfie recently won for chemistry. Those words both have the same letters but quite different meanings, one based on blood lines and the other on merit!
In earlier years I mainly observed noble dorids on my dives in the northern Channel Islands or the oil rigs off the mainland coast. It was a rare day when I encountered one in our waters. All that changed when I started my deep diving two years ago. For many decades I kept my diving above 100 feet since most of the giant kelp forests that I study are within that depth range. Once I started dropping below that, I started seeing noble dorids as well as a number of other nudibranch species much more frequently. I have speculated (in scientific terms, hypothesized) that these deeper waters, being colder, have more nutrients. More nutrients mean more plankton, and that means more filter and suspension feeders. Nudibranchs often munch on these critters so they are also more abundant "down under."
This nudibranch is one of the dorids unlike the Spanish shawl I wrote about recently which is an aeolid. The difference is that the gills are arranged in a retractable circlet towards the rear of the body in the dorids. The aeolids have a shag carpet of gills, known as cerata, along their upper body surface which cannot be withdrawn into the body. The noble dorid is said to average about two inches but may reach up to eight inches in length. They are known from Alaska to the Coronados Islands in Mexico just "south of the border." This distribution indicates they are a cold water species and helps explain why they are found in deeper, colder water here in the southern part of their range. It is reported they may be found as deep as 750 ft... but "I'm not going there."
Just like their aeolid brother/sisters, the noble dorid mates with other noble dorids (have to keep the royal blood line pure) by lining up with their right sides pressed together. The male organ of one injects gametes into the female organ of the other and vice-versa. The fact that they are hermaphrodites makes Saturday nights much easier. Instead of waiting for a lovely lady (or macho man) to walk by, any individual of their species they encounter could be a suitable mate. Makes the odds much better!
Most of the noble dorids I've seen elsewhere were yellow in color, often with darker spots on the dorsal surface. However, I began seeing bright orange noble dorids as well, and wondered why. The probable answer to that question came when I started discovering noble dorids nibbling on orange sponges! Hmmm... a little Jimmy Buffet immediately comes to mind, "nibbling on sponge.... cake." I'm not sure what is so noble about attacking Sponge Bob Square Pants since they have limited defenses and are quite spineless (as in lacking backbones). Perhaps the typical yellow noble dorid becomes orange when it munches away on these sponges. After all, you are what you eat (minus what you excrete).
NOTE: Of course the print version of these columns does not show the color in my subjects. For those of you with Internet access, all of my columns are archived on my web site with the images in full color. The URL is www.starthrower.org/products/DDDB/column.htm.
© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!
Orange (left) and yellow (right) noble dorids; the gill cluster and
two noble dorids munching on an orange sponge.
This document maintained by
Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia