Clam Garden Ecology

The building of a clam garden wall results in the accumulation of shell hash (coarse sand and broken barnacle shells) on the landward side of the wall. The resulting terrace then becomes ideal substrate for clam growth. Recent ecological experiments and field surveys have shown that clam gardens were built at specific tidal heights to maximize optimal clam habitat. Clam gardens on Quadra Island, for example, contain four times as many butter clams and over twice as many littleneck clams compared to non-walled beaches. Moreover, transplant experiments showed that juvenile little neck clams grow 1.7 times faster and are more likely to survive in clam gardens than non-walled beaches.

Sea cucumbers and whelks in clam garden wall. Photo: Nicole F. Smith.
Sea cucumbers and whelks in clam garden wall. Photo: Nicole F. Smith.

While much of the Network’s focus so far has been on clams in the clam garden terraces (mainly butter clam, littleneck, horse clam, and cockles), our observations and that of our First Nations collaborators suggest that the boulder walls themselves create productive rocky reef habitat for octopus, sea cucumber, whelks, chiton, red turban snails and other critters. Many of these are valued foods for coastal First Nations. How these walls compare to natural rocky reef habitat is one of many questions remaining about the use and design of clam garden features. Perhaps as we learn more we’ll find that there’s much more to a “clam garden” than just clams, and that a more appropriate term for these places may simply be “sea garden”.

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