Effects of clam gardens on the growth, survival, and genetic responses of Pacific littleneck clams (Leukoma staminea)

Photo taken by Monique R. Raap

Clam gardens, established and maintained by coastal Indigenous Peoples of northwest North America, are intertidal habitat modifications that enhance clam productivity and provide opportunities for securing local food. We wanted to assess whether Pacific littleneck clams had differential growth, survival, and genetic responses depending on the type of beach they were in (i.e. untended clam garden versus unmodified control beaches).

Previous studies have suggested that clam growth and survival may be better in clam gardens than on unmodified beaches, partly due to the amount of shell fragments (added by local Indigenous Peoples) in the former. To investigate this, Pacific littleneck clams were transplanted to nearby clam garden or unmodified beaches within Kanish Bay, Quadra Island, BC for 16 weeks.

Read this open access paper on the FACETS website.

After 16 weeks we found that clam growth and survival were not linked to whether the site was a clam garden or an unmodified beach. Beach characteristics (e.g. more or less sand or gravel) did affect clam growth and survival; individuals on beaches with fine to coarse sand sizes did well, whereas those on beaches with small rocks, very fine sand, silt, and organics performed worse.

Some gene responses did change depending on whether the beach was a clam garden beach or an unmodified beach: genes associated with immune and stress-related functions were seen both over- and under-expressed in clam garden beaches (e.g. a heat-shock protein transcript was found to be under-expressed in the clam gardens and a universal-stress-protein annotated transcript was overexpressed in the clam gardens). Beaches with higher clam survival had an increase in expression of genes involved in immune defense.

Localized environmental factors are likely to have a greater effect on Pacific littleneck clams than whether the clams were located on a modified or unmodified beach. It should be noted that the clam garden beaches used had not been actively maintained in some time, so future work should examine the effects that an active clam garden and its sediment characteristics have on clam growth and survival. Future work could also use the genetic resources developed by this project to examine further how clams are responding to differing environments along the coastline of BC.

Read the paper — **Effects of ancient anthropogenic clam gardens on the growth, survival, and transcriptome of Pacific littleneck clams (Leukoma staminea) *by Monique R. Raap, Helen J. Gurney-Smith, Sarah E. Dudas, Christopher M. Pearce, Jong S. Leong, Ben J.G. Sutherland, and Ben F. Koop in FACETS.*