A Giant (Rock Scallop) Mystery

An ex-boyfriend once complained: “I’ve never met a woman who asked so many questions!” At the time, of course, he was trying to avoid answering one.

What can I say? The mysteries of life intrigue me. One of them involves the giant rock scallop (Crassadoma gigantea). Everything I’ve read says they have orange mantles but that’s not always the case. Some have black mantles; others have dark green, cream or beige. I know this because I have at least 80 photographs of scallops taken in Southern California waters (from oil rigs, seamounts and the Channel Islands) over the past 30 years. The significance of the colors — if there is any — is unknown. I queried Kristine Barsky, Senior Invertebrate Specialist, California Department of Fish and Game, who told me, “Although mantle color has been investigated, no one has come up with an explanation for the variations in color.”
The light sensing “eyes” on the mantle may also vary in color, though that’s difficult to tell from photos. While they are usually yellow (or perhaps on yellow stalks) with blue centers, sometimes only the blue is visible and eyes on dark mantles appear to be yellow or white.
The giant rock scallop, formerly known as the purple hinged rock scallop, is a member of the Phylum Mollusca, Class Bivalvia, Subclass Pteriomorpha, Order Ostreoida, Family Pectinidae. 
Scallop sexes are separate and reproduce by broadcast spawning twice a year. Warm water or some other stimulus triggers one or more scallops to release sperm or eggs and then all of the scallops in the area start spawning. Chance meetings of sperm and eggs in midwater result in fertilized eggs. Larvae hatched from these eggs drift in the water before settling down. As juveniles, rock scallops have symmetrical shells and, unattached to anything, are able to “swim” by clapping their valves. 
When a juvenile reaches a diameter of one to two inches, it will cement its right valve to a hard surface, where it will spend the rest of its life. The shell will grow thick and heavy while conforming to the irregular terrain on which the scallop lives. 
The valves of giant rock scallops have purple hinges, hence the former name. The shell’s prominent ribs provide an ideal habitat for all sorts of colorful marine life, including sponges, club-tipped anemones, hydroids, tunicates, barnacles and algae. These miniature gardens provide camouflage, making rock scallops hard to see unless the valves are open and the mantle is visible. 
Giant rock scallops are found along the West Coast from British Columbia to Baja California and to depths of 150 feet. They are estimated to live 25 years and can be as large as 10 inches in diameter. Six inches is considered good sized. 
Scallops may be collected in many areas of California, just make sure you’re not in a Marine Protected Area that prohibits their take and that you have a current California Fish and Game sport fishing license. There is no season. The bag limit is 10 and while there is no size limit, conservation minded divers do not take small ones. Scallops may only be taken by hand using a dive knife or abalone iron.
Because the shells are miniature ecosystems, home to more than just the scallop, the best way to take this shellfish is to insert a thin, sharp knife and slice close to the shell on one side, severing the muscle. This will prevent the scallop from closing. Slice between the shell and the muscle on the other side and you can scrape the insides out, leaving the shell and all the creatures on it intact.
The scallop’s edible part is the firm, marshmallow shaped adductor muscle, which may be cream colored or pale orange. If you discard the rest of the innards underwater you’ll find yourself very popular with the fish. Put the scallops in a plastic bag and slip them into a BC pocket. Don’t slice the muscle in two or you’ll have two scallops in the eyes of Fish and Game Wardens, not one.
Rock scallops are easy to photograph. Approach them slowly because if they sense your presence, the valves will snap close. They will also close if you touch them, so avoid doing that as well. Even if the valves close, however, it will usually be only moments before they reopen because that’s how the animal feeds. Be patient. Good things come to those who wait!
COPYRIGHT © 2019 CALIFORNIA DIVING NEWS. ALL RIGHTS RESERVED.Website hosted and managed by Make Me Modern.