Dive Dry with Dr. Bill

#680: Vicious Beasts

It is certainly human nature to feel a bit of fear when confronted with a vicious predator, sometimes even the thought of one. No one in their right mind (or even their left brain) wants to be swallowed up by a great white, eaten alive by a hungry lion or captured by a crocodile. Of course these "threats" are rarely realities for most unless somehow one of them leaps off the screen of your 3-D TV.

Why back in first grade I used to walk to my elementary school in northern Florida on a rope bridge that crossed a swamp with alligators. I've confronted hungry lions... from outside their enclosures at the San Diego Zoo. And I've had great whites and hundreds of other sharks swim right past me barely batting an eye.

We humans in developed countries generally have little to fear from hungry predators, although our minds often exaggerate the threat beyond reality. Yet many other critters that occupy Planet Ocean have real reason to be afraid... if their tiny brains actually process such an emotion.

I've thrilled you with images of morays and kelp bass attacking poor blacksmith on my night dives. If you used to watch my TV show, you saw plenty of munching in the Macrocystis or giant kelp Unfortunately my video cameras don't have the ability to capture some of the real dangers of the deep.

I'm referring to the vicious beasts known as nudibranchs. Yes, many divers find them warm and fuzzy... or, more appropriately, exotic and beautiful to film. However, many of these shell-less snails are worse than the great whites. After all the landlord may eat but once a month, assuming it gets a well fattened sea lion for dinner. Nudibranchs seem constantly on the prowl looking for tasty sponges, hydroids, bryozoa and other generally defenseless prey. Most species use a rasp-like "tongue" to scrape tissue from their still living meal.

I've written about the incredibly beautiful California blue dorid. Although formerly known as Hypselodoris californiensis it now goes by the moniker Felimare californiensis. Kind of like the Artist Formerly Known as Prince. Considered rare on the California mainland, it is seen with some frequency in Catalina waters. Sponges cower when they see this slug approaching as it tears them apart for munchies. One possible explanation for their rarity is that mainland pollution has caused their poriferan prey to decline in numbers.

Another beautiful but vicious slug (at least if you are a sponge) is the Noble dorid (Anisodoris nobilis). More than once I have filmed two individuals munching on different species of sponge. Often there is a larger individual and a much smaller individual present.

A beautiful and common nudibranch in our dive park is the Spanish shawl (Flabellina iodinea). I've seen it many times on the rocky reef (when it isn't covered with the invasive Asian seaweed), but more frequently on the hull of the Suejac wreck at the harbor end of the park. It prefers to munch on tiny hydroids, relatives of the jellyfish and sea anemones in the phylum Cnidaria.

Another beautiful nudibranch that I've only seen a few times in our waters is the colorful rainbow dorid (Dendronotus iris). They are more frequently encountered in mainland waters. When it comes to something munchable, these nudis prefer a super sized coelenterate (er, cnidarian). They climb up the tube of a cerianthid anemone, grasp the tentacles are begin munching away.

To the poor sponges, hydroids, anemones and bryozoa of Davy Jones' Locker, these slugs are the equivalent of a Tyrannosaurus rex or velociraptor. One species' beautiful photographic subject may be another species' most feared critter.

© 2016 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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!

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California blue dorid and Noble dorids feeding on orange sponge; Spanish shawl feeding on hydroids
and rainbow dorid feeding on anemone tube.

This document maintained by Dr. Bill Bushing.
Material and images © 2015 Star Thrower Educational Multimedia