Scallop

A scallop relaxing on a rock. Scallops will hang out on the surface of the ocean floor rather than burrowing like their clam cousins. Image taken at the Aquarium of the Bay.

This unassuming little bivalve is one of over 300 species of scallop. These creatures are not only interesting and unique among the shellfish, but they also play an important part in the human world as well.

Scallops are the only shellfish that can move around using jet propulsion. They don’t hide buried in the sand or attach themselves onto hard surfaces (although the juveniles will attach until they are big enough to not be dragged away by strong currents), but rather they lie loosely on the ocean floor.  If danger is near, they will swim away by clapping their shells together (video of scallop swimming here). In order to clap their shells together, they use a very strong circular muscle called the abductor. This muscle is the part that humans will eat when they’re having scallops. It’s a really good food source that’s high in protein, vitamin B and selenium and low in fat.

And we do eat a lot of scallops. In 2008, in the United States alone, 53.5 million pounds of Atlantic Sea scallops worth $370 million was harvested (That’s just 1 type of scallop!). And the good news is that scallops are a good choice for sustainable seafood. Despite the large amount of scallops we’re pulling from the ocean, because of serious declines in the scallop population off the east coast in the early ’80s, the fisheries are now regulated. For example, only scallops above a certain size can be taken, so it’s likely each scallop has had a chance to reproduce before it’s harvested. This combined with the fact that these animals reproduce very quickly (1 scallop can produce up to 270 million eggs in its lifetime) has led to a wonderful come back, as these animals are now abundant again and even spreading their range. This is a good example of how harvesting sustainably has prevented the crash of an entire fishery and led to the protection of a valuable animal, that will continue to be valuable (in a number of ways, as this post will show) for years to come if we continue with our healthy practices. Consider this- if we had continued to overfish these animals 20-30 years ago, would we still have this lucrative industry today, when our economy needs it the most? Just a note, it is still considered better to eat farmed scallops if you have the option. They do use dredges to gather scallops and those can result in by-catch. However, the regulations in place prohibit using dredges in certain areas and in certain seasons to minimize by-catch, so if farmed scallops are not available, wild-caught scallops are a good alternative.

Aside from their economic and nourishment value, these animals are also important in research. As filter feeders, they are useful in evaluating the environmental impact of petroleum spills. But in addition to that, there is some other research going on involving an unusual feature of scallops.

Scallops

An open scallop. Look closely at the little dots along the edges of its mantle, or right near the edges of its shell. These dots are the scallop's eyes. Image taken at the Aquarium of the Bay.

Scallops have primitive eyes all long the edges of their mantle, right near the rim of their shells. In the picture above, you can only see the eyes on the bottom rim, but they do have them on both the top and the bottom. These eyes can detect light and dark, like the shadow of a predator, as well as movement. If it senses danger, it can close up into its tough shell or swim away. Their eyes have a retina and two types of photoreceptors, which are the cells that change light information to chemical information that your nervous system can interpret. So why am I going on about scallop eye biology? These eyes have some similarities to ours, but if something happens to a scallop eye, it can regenerate its photoreceptors. As we work to understand this better, maybe we can find the key to creating or saving photoreceptors in humans who are losing their vision from degenerative diseases. And there you go. Scallops, perhaps one day helping people not go blind.

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