STEM Logo

Dive Dry with Dr. Bill

#685: Crabby, Crabby Night

OK, so the title is a take-off on Don McLean's "Vincent." What are you going to do? Sue me? Good luck with that... I was a divebum much of my life.

I've written that I rarely do night dives during the winter and early spring. It's not that the water is too cold... especially the past two years! Nice and toasty even when I forget to zip up my wetsuit (which I have the last five dives)! It's because all that lousy Asian seaweed prevents me from seeing much of anything.

However, Aquarium of the Pacific diver Grace Chee wanted to take advantage of her free birthday trip on the Catalina Express to do a night dive and twisted my arm. Well, it didn't really take much twisting. I picked her up at the boat, we suited up and drove down to the dive park to descend on a decent tide.

Yep, the Sargassum horneri was everywhere even though as an annual it is starting to die out early this year because of the warm temperatures. Grace thought it was beautiful. I could only think of the ecological damage it and the unusually warm waters have caused to our native giant kelp forests.

We hadn't kicked very far when a hint of red-orange appeared within the Sargassum, highlighted by my video lights. I was shocked to find a small southern kelp crab (Taliepus nuttallii) up in the thick devil weed. I couldn't tell if it was actually feeding on the Sargassum, but given the absence of its usual tasty giant kelp blade buffet that was my thought.

During previous years when the water was cooler and the Sargassum less dense, southern kelp crabs were a pretty common sight on my night dives. I'd find them munching on kelp blades and stipes... or mating with the males "gently" suspending their mates by one claw. Occasionally I'd even see them climbing the tall giant kelp... almost like Jack and the bean stalk (although I guess I'd play the giant). I was quite pleased to finally see one, my first in nearly a year.

A little further along in our dive Grace spotted two sheep crabs (Loxorhynchus grandis) through a clearing in the devil weed. I dropped down to film them and decided I would once again try to play matchmaker. I checked their undersides but quickly realized that wouldn't work. Both had long, narrow telsons ("tails") indicating they were males. Oh, well.

Several years ago I had done the matchmaker thing when I spotted a male and female in the park. I picked up the little lady and gently carried her over to the young lad. He immediately pounced on her... no introduction or sweet talk. They entwined in non-marital bliss for over 20 minutes as I filmed.

Crab mating is often quite amusing (well, to me... perhaps not to them). Males often "tenderly" hold their ladies tight and walk around with them for much longer than it takes to procreate. I've written in the past about how this helps ensure the lucky lad will be the father for her brood. He keeps her away from the other guys while fertilization of the eggs takes place. I used to see human males doing something similar when I danced at the Chi Chi Club.

Seeing these two species of crabs was a small signal that perhaps life will go on in the kelp forest once the Sargassum dies out and (hopefully) the water cools down next fall. I really want "my" giant kelp forests and their critters back so I don't have to renew my studies and become a coral reef biologist to adapt to our changing waters!

© 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!

To return to the list of ALL of Dr. Bill's "Dive Dry" newspaper columns, click here.


Southern kelp crab in Sargassum (with my finger for comparison) and sheep crab seen on night dive at Casino Point.

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