Dive Dry with Dr. Bill

#683: Diamonds and Pearls

Now diamonds are supposed to be a girl's best friend (what about nice guys like me?). However, I've heard pearls can do the trick almost as well. Today I'm going to continue my recent series on the molluscs known as bivalves. You know, the ones with two shells like clams, mussels, scallops and... oysters!

A decade ago our waters were also experienced toasty temperatures like today. Well, maybe even better! Unfortunately back then I wasn't recording my minimum temperatures at depth in my dive log, but if my memory is correct I was seeing temperatures in the low to mid 70s at depths of 150 ft. I even set a record of 100+ consecutive dives without once "soiling" my wetsuit. There are two types of divers: ones who pee in their wetsuits and ones who lie about it.

During 2005-06 I was seeing an unusual bivalve usually attached to our soft corals or gorgonians. They reminded me of the winged oysters I'd seen on gorgonians in the tropics. In fact, I was pretty sure what I was seeing was the winged or rainbow lipped pearl oyster (Pteria sterna).

A few experts told me that wasn't possible since the species was known from more southern waters in the Gulf of California (Sea of Cortez) and the Pacific coast of Baja. Back in the days when I served as marine biologist and underwater videographer for Lindblad Expeditions, I would see them in the waters off our base in La Paz as well as other sites we explored in the Sea of Cortez. But, no... they couldn't be up here I was told. Or could they?

I remain convinced that I was seeing this species during 2005 and 2006. I don't remember seeing them after the waters cooled back down in 2007, or even during a few warm water episodes since then like the one we've experienced the past two years. However, these oysters were observed by yours truly at a number of sites on both our leeward and windward coasts.

So why hasn't it appeared again in our waters? Back in my column #128, written in 2005, I speculated on two ways the species might have entered our waters. During El Niño events a coastal counter-current often develops running north from Baja into our region. Like many other marine critters, this species produces larvae that drift in the plankton with the currents. It is possible that it arrived that way back then.

But why hasn't it appeared more recently I ask... doesn't everyone? We've seen plenty of more southerly species enter our region during this warm water event. Perhaps I need to revisit the second option I considered... arriving via boat (and I don't mean the Catalina Express or Newport ones).

These winged pearl oysters are known to spawn during the colder months in the Sea of Cortez. During our bitter cold southern California winters, yachters often head south to places like La Paz to enjoy the (usually) better weather there. It is not inconceivable that winged pearl oyster spat might attach to the hull of boats or be taken in by cooling systems. In the first case it is quite likely they might survive passage around Cabo San Lucas and arrive back off our shores.

But why not this year or other warm water episodes since 2007? I can only speculate of course so if you're a gambler, I wouldn't place any bets on what I'm about to say. Perhaps our warm winters and past high fuel prices have kept yachters closer to home rather than cruising to beautiful region around La Paz.

An interesting side note to this was presented in my column #265 written back in 2007. I was diving a reef off Salta Verde Point where winged pearl oysters were still present. I happened upon one that was moving up the food chain (so to speak). No, it wasn't consuming something higher up than its normal plankton. It was being consumed by a knobby sea star (Pisaster giganteus). Apparently the starfish didn't care about how it arrived, or even the possibility of a pearl inside the shell (must have been a male).... as long as it was tasty!

© 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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Young winged pearl oyster on gorgonian at Sea Fan Grotto and mature on in the Casino Point Dive Park;
close up of living oyster and the shell of one eaten for dinner (perhaps by an octopus or starfish) at Salta Verde in 2006.

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