clam experiment background

As previously described, approximately 320 clams of two species were collected for an experiment to understand the impact of ocean acidification (OA) conditions on clams in the Puget Sound. One species, Leukoma staminea, is natively distributed in the intertidal zone of the Eastern Pacific Ocean from Alaska to Northern Mexico. It has traditionally been an important wild harvested seafood source in the Puget Sound, and anecdotal accounts indicate that populations may be declining. The other species, Ruditapes philippinarum, is native to the Western Pacific and is raised globally in aquaculture production. R. philippinarum is naturalized in the Puget Sound, and is also raised in hatcheries and dispersed in order to boost the quantity of clams harvested from beaches.

Clams collected were approximately the same size. A subset of 20 clams from each species were analyzed for gonad maturity using histology, and shells were measured beforehand by length and width, with the distribution as follows

Species Length (mm +/- s.d.) Width (mm +/- s.d.)
L. staminea 37 +/- 4.6 44.4 +/- 5.6
R. philippinarum 37.5 +/- 4.4 51.3 +/- 4.7

20 clams from each species were placed in 20 liter tanks. Treatments included ambient seawater taken from Clam Bay off of Manchester, WA, and seawater with increased carbon dioxide concentration. Seawater was held in four large header tanks, with water pH determined with durafet probes linked to a relay system. OA condition was held at 7.35 pH +/- 0.2, while ambient pH was near 7.8 for the duration of the experiment. Two header tanks were used for each treatment and each supplied water into four tanks split between the two species, so that two tanks for each species received water from the same header. Tanks were continuously supplied with water with an overflow. Clams were fed a combinatin of three live algae species and diatoms at a rate which provided ad libitum feeding.

Temperature was held for three weeks at 10 C, and then gradually ramped up and held at 18 C to induce gonadal development. The experiment intended to induced spawning to collect gametes and produce larvae to understand transgenerational impacts of OA. The success of spawning and subsequent analyses will be discussed in a later post.

Written on June 3, 2022