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Dive Dry with Dr. Bill

#639: Feeling a Little Sheepish... or Crabby?

Last weekend I finally submerged once more into the briny deep off Casino Point. Over the past six weeks I've used several excuses for not diving here at home after my stay in Palau. Of course all the video I shot there had me cemented to the chair in front of my computer to edit the trip video, and even though the water has been warm here all year it is still 20-22 degrees colder than my bottom temperatures in Palau in March. The dominance of the darned Asian seaweed Sargassum horneri and the lack of our native giant kelp have also been factors in my reluctance to get wet.

My Palau video just needs a few minor adjustments before it is used by Palau Dive Adventures to promote diving in that incredible destination, so gathering a little new video could be justified. I also needed to document the life-and-death cycle of the "devil weed" as it finally disappears from our waters for another season. With its demise, the giant kelp is beginning to return... although I am fearful that the El Niño forecast for this year will decimate it before we get real kelp forest development.

My last two dives in the park, separated by nearly a month, did reveal that a visitor to the shallows has finally appeared... but not "on time." I'm referring to the sheep crab (Loxorhynchus grandis), a species of spider crab found from Point Reyes in northern California to Punta Bartholeme in Baja California. These crusty crustaceans may be seen on rocky shores and sandy bottoms down to a depth of about 500 ft. They are a pretty large crab with carapaces (bodies) reaching over six inches in width and long legs (which I appreciate since I'm a leg... and brain... man).

Many divers find their appearance to be something prehistoric or even alien, but they are natives here. During much of the year they are at depths well beyond those I dive today. However as the water warms up in the shallows, they get that "urge to merge" common to most species and begin gathering up in recreational SCUBA depths. I've often seen them appear in February, but this year I didn't observe any until April. I'm not sure whether the prevailing warm water the past year has affected their sex drive or not.

Even casual observation reveals whether a sheep crab is male or female. The males have longer and more massive chelipeds than the females. What, you say? In common parlance we refer to these body parts as claws. Another way to tell the boys from the girls is to look at their underside. Generally one should avoid touching them as their chelipeds can inflict a nasty pinch on human fingers. The "buoys" have a long pointed telson (aka tail section) and the "gulls" have a broad oval shaped one.

I haven't observed any mating this year but in the past I have had opportunities to film this delicate ritual. In fact one year I played matchmaker for a male sheep crab by bringing a pretty little filly to him. I have observed mating in several positions and am impressed by the fortitude of the males. In some cases they lasted half an hour... and without resorting to Viagra or Cialis. Following their conjugal bliss, the male tenderly embraces the lady. Well, actually he grabs her and holds onto her for some time... occasionally employing a death-grip bear hug and sometimes even holding her aloft in his chelipeds. Why? Most likely so no other male can get to her, thus ensuring his paternity without need for a DNA test.

Apparently the female has no desire to undergo this humiliation more than she has to. They have evolved a way to store sperm for later use, so they don't need the males around for future broods. Don't get any ideas, ladies! Each individual clutch of eggs may number between 125,-500,000. They are carried under the broad telson or tail section for protection.

My readers, being highly intelligent advanced beings, are already aware that crabs, shrimp, lobster and other crustaceans have a "hard shell finish" (without the need for Turtle Wax). Like trying to fit into an older wetsuit that has "shrunk," this can make it quite difficult to grow. Therefore these critters molt their hard exoskeletons and grow a new, larger one to accommodate their increased size. I wish I could do that with my clothes. However, sheep crabs apparently reach a limit. After their terminal or final molt, they can no longer increase in size... or replace lost legs. Hopefully I've reached my final size and will begin to shrink if I can stick to my diet.

© 2015 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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Head region of sheep crab and entire crab; "wanna fight?" and male and female telsons (tails)

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia