Dive Dry with Dr. Bill

#709: Disco Clam

A few years ago I spent three weeks in the Philippines diving first at Anilao with Club Ocellaris, then in Puerto Galera with Action Divers and finally a few days in Manilla to visit with friends. It was a pretty spectacular trip. I shot so much video footage I have yet to edit it into a trip video. The effort was even more difficult since many of the species I filmed had not been described by biologists and therefore had no scientific names!

My time at Club O was a diver's dream. I met up with my roommate Erik Goosens from Switzerland since we both were booked on a connecting flight in Taipei, Taiwan. Once we were there, Evie Go from Manila joined us at Club O. The dive staff was fantastic. We did four dives a day with some lasting well over two hours on a single tank for a total of 42 dives in 11 days. With that much diving all we had time for was eating and sleeping.

Then I was off to Puerto Galera. The three of us shared a car driven by Redjie and I was dropped off in Batangas at the ferry to Sabang while Erik and Evie went on to Manila. Upon arriving in Puerto Galera, I lugged my dive bag and personal bag along the shore for what seemed like miles until I found Action Divers and Banana Moon, my hotel. I had a package deal there for $95 which included three dives a day, my hotel room (with a terrific view of Verde Island across the channel) and breakfast.

One species I really wanted to film in the waters around Puerto Galera was the disco clam (Ctenoides ales), also known as the electric clam, file clam and flame scallop. Technically it is a member of the mollusc family Limidae. We have a representative in our waters which I first came to know as Lima dehiscens, but which has apparently had a name change to Limaria hians. Hard to keep up with those taxonomists!

The disco clam is known from tropical Indo-Pacific waters including Indonesia, Palau and the Philippines. It is a bivalve mollusc, meaning it has two shells like mussels, clams and scallops. The mantle or body coloration is reddish-orange. Like other file clams, including our local species, it has many long, tentacle-like extensions along its margin.

This species exhibits flashes of light that look like the filament of an electric light. You know, the ancient technology prior to CFL and LED bulbs. One might assume that the light is emitted by a bioluminescent process. You've seen such things in fireflies... and here on Catalina when you flush your salt water toilet in the dark, or go skinny dipping late at night!

However, a graduate student named Lindsey Dougherty discovered that the light flashes were created due to the reflection of ambient light by tissues at the edge of their mantle. This highly reflective tissue contains tiny spheres of silica. This tissue is alternately exposed and then covered by the reddish-orange mantle to give the impression of a flashing light. It is the only bivalve species known to do this.

Dougherty was uncertain as to why these molluscs flash. Certainly they are not doing so for Mardi Gras beads or to join a flash mob. One possibility is that the light may scare off a potential predator. Another is to synchronize spawning, although I didn't see any disco clams nearby. However, some reports suggest they do live in clusters. A third hypothesis is that the light might attract the plankton that the species chows down on. Doughtery indicated that the plankton are immobilized by toxic mucus.

Filming the disco clam reminded me of those glorious days (NOT) back in the late 1970s. At that time disco was all the fashion and the likes of flashing disco balls, John Travolta and the Bee Gees singing "Staying Alive" were prevalent symbols. Unfortunately my upstairs neighbors at the time would play this era's music late in the night and early in the morning. Ugh.

© 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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The flash sequence of the disco clam and nightmares of disco past.

This document maintained by Dr. Bill Bushing.
Material and images © 2017 Star Thrower Educational Multimedia