Rock types, density, pit volume, and bioerosion estimates, ± is standard deviation.

<p>Rock types, density, pit volume, and bioerosion estimates, ± is standard deviation.</p

Unaccounted rock block change.

<p>Percent of the inorganic weight change in the rock block units not accounted for by the inorganic weight of the residue + inorganic gut content. All three groups are significantly different from each other (F_2,12, p < .0001; Tukey HSD test). The rock with the smallest grain size (mudstone) has the highest percentage missing and medium-grain sandstone with the largest grain size the least percentage. Sandstone = circles (tan = medium-grain, orange = fine-grain); mudstone = brown squares (n = 5 each treatment).</p

Sea urchin growth during one-year experiment.

<p>Test volume based on modified oblate spheroid estimate from test height and diameter [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191278#pone.0191278.ref031" target="_blank">31</a>]. Sandstone = circles (tan = medium-grain, orange = fine-grain); mudstone = brown squares; granite = gray diamonds (n = 10 each treatment). The black stars are the means (± sd) of all urchins at each time point. The urchin silhouettes are scaled-sizes of the average diameter and height for each of the three sampling time points (30 mm scale).</p

Inorganic weights from bioerosion.

<p>A. Waste residue from bioerosion. The inorganic weight after the fraction from fecal pellets subtracted. B. Gut Content from bioerosion. The inorganic weight after the fraction from ingested algae subtracted. In both plots sandstone = circles (tan = medium-grain, orange = fine-grain); mudstone = brown squares; granite = gray diamonds (n = 5 each treatment).</p

Three dimensional surface plots.

<p>Rock substrates used in the one-year experiment. Units on all axes are mm and plots are means (n = 10) at the start (top) and after the exposure of each replicate to a single grazing sea urchin for one year (bottom). The medium-grain sandstone showed the most intense levels of bioerosion and pit formation and the relief (color) z-axis scale is 4x the scale for the fine-grain sandstone, mudstone, and granite.</p

Rocky intertidal pool.

<p>Purple sea urchins occur in high densities in the intertidal and shallow subtidal where many are nestled in cavities (“pits”) carved out of the rock substratum. The “hand-in-glove” fit of the urchins to the pits is apparent upon close examination (inset). The sedimentary sandstone at this site (Bean Hollow, California, USA) is typical of many sites along the west coast of North America. The exposed rocks at this site are of the Upper Cretaceous Pigeon Point Formation, which is part of the Franciscan Complex that makes up much of the central coast of California.</p

Dry weight change.

<p>The mass lost from each treatment was significantly greater than zero in all but the glass controls. The different letters above the data points indicate groups that are significantly different. Sandstone = circles (tan = medium-grain, orange = fine-grain); mudstone = brown squares; granite = gray diamonds; glass = open triangles (n = 5 each treatment).</p

Principal component analysis.

<p>The first two principal components accounted for 77.4% of the variation. The four treatments (n = 10) are distinguished by different colored symbols which match the colors of the 68% confidence ellipses for each group: sandstone = circles (tan = medium-grain, orange = fine-grain); mudstone = brown squares; granite = gray diamonds. Vectors of loadings for the five different body components are also plotted (black arrows).</p

Field estimates of sizes of pits and urchin occupants.

<p>Cube-root of pit volume plotted against cube-root of test volume of urchin occupant. Sandstone = tan circles (n = 50); mudstone = brown squares (n = 47); granite = gray diamonds (n = 9). ANCOVA revealed no significant difference in slopes and the same regression described all three data sets (r² = 0.91, F_1,95 = 956.7, p<0.0001). Least squared means of sandstone and mudstone were not significantly different from each other but both were significantly different from granite. The silhouettes of urchins and pits are scaled-sizes of the average diameter and height of urchins, and depth and width of the pits. The urchin silhouettes contain the average height:diameter ratios of the tests, which had the same pattern (no difference between sandstone and mudstone, but both sedimentary rocks were different from granite).</p