Survey & Experiment: <i>L. staminea</i> Biomass, Density and Growth by Intertidal Height vs. Model Predictions.

<p>Actual and predicted A&B) density (count/0.018 m3 +/− SE) C&D) biomass (kg/0.018 m3 +/− SE) and E) growth (mean +/−SE) of surveyed (A-D) and transplanted (E) <i>L. staminea</i> as a function of intertidal height (m above LLWLT) in clam gardens (green triangles) and non-walled beaches (blue circles) in Kanish and Waiatt bays, British Columbia, Canada.</p

Map of Study Area.

<p>This research was conducted on A) the west coast of British Columbia, Canada, in the Inside Passage between B) Vancouver Island and the mainland on the northern end of C) Quadra Island, in Kanish Bay (West, starred) and Waiatt Bay (East, starred).</p

Experimental effects of clam garden treatment and tidal station.

<p>The effects of clam gardens (Beach Type) and tidal station on the growth and survivorship of transplanted <i>L. staminea</i>. * designates significant p-values (p≤0.05).</p

Clam garden effect on density and biomass.

<p>The effect of clam gardens (Beach Type) on density and biomass (per survey transect, 0.027 m³) of <i>L. staminea</i> (littleneck clam), <i>S. giganteus</i> (butter clam), <i>V. philippinarum</i> (Japanese littleneck clam), <i>Macoma</i> spp (macoma clams) and total clams. * designates significant p-values (p≤0.05).</p

Survey<i>: L. staminea</i> Biomass and Density by Tidal Station.

<p>Surveyed A&B) density (count/0.018m3 +/– SE) and C&D) biomass (kg/0.018m3 +/– SE) and of <i>L. staminea</i> as a function of bay (Kanish or Waiatt), site type (Clam Garden or Non-Walled Beach), and tidal station (1 = top of clam habitat, 15 =  top of clam garden wall or ∼0.75 m intertidal height in non-walled beaches).</p

Site Descriptions: Intertidal Height by Tidal Station.

<p>Intertidal height (mean +/–SE) and relative slope (▵y/▵x) from top of clam habitat (tidal station  =  1) to top of rock wall feature in clam gardens and ∼1.0 m above LLWLT in non-walled beaches (tidal station  =  15).</p

Effects of clam garden treatment and oceanographic context.

<p>The effects of clam gardens (Beach Type), oceanographic context (Waiatt Bay vs. Kanish Bay), and Tidal Station on the biomass and density of surveyed <i>L. staminea</i>, <i>S. giganteus</i>, <i>V. philippinarum</i>, <i>Macoma spp</i>, and total clams (per survey transect, 0.027 m³). * designates significant p-values (p≤0.05).</p

Study Design and Predictions.

<p>A) We surveyed clams across a vertical transect (black line) from the top of clam habitat (H) to ∼1.0 m in non-walled beaches (left) and to the edge of the rock wall (W) in clam gardens (right). We then transplanted clams in mesh bags at 5 evenly stratified tidal stations (blue and green colored squares) across a vertical transect (purple line) from the top of clam habitat (H) to ∼0 m in 5 Non-Walled Beaches (left) and to the edge of the rock wall (W) in 6 clam gardens (right). B) Hypothesis 1: predicted clam productivity as a function of tidal station. Tidal station 1  =  top of clam habitat, tidal station 15  =  top of clam garden wall in clam gardens or ∼1.0 m tidal height in non-walled beaches. C) Hypothesis 2: predicted clam productivity as a function of intertidal height.</p

Clam Garden Images.

<p>A) Ancient clam gardens on Quadra Island, BC, Canada, are intertidal beach terraces built by humans by constructing B) a rock wall at low tide typically between 0.7–1.3 m above chart datum. C, D) Quadra Island clam gardens range in size and shape but generally create shallow sloping intertidal terraces encompassing tidal heights of 0.9–1.5 m above chart datum.</p

Gaussian models: effects of clam garden treatment and intertidal height.

<p>Parameters for the modeled responses of biomass (kg/0.018 m³ +/− SE), density (count/0.018 m³ +/− SE), and growth (mean +/−SE) of surveyed and transplanted <i>L. staminea</i> (<i>L.s.</i>) as a function of intertidal height. Each response was predicted by modeling a Gaussian curve to the data, <i>y</i>  =  <i>a</i>*exp(−0.5*((<i>x</i>−µ)/<i>σ</i>)²) (Eq. 1), where <i>y</i> = response, <i>x</i> = intertidal height, <i>a</i> = height, µ = mean, and <i>σ</i> = standard deviation.</p