The distribution of sites (symbols) and macroalgal species (crosses) over environmental gradients (arrows), showing the separation of Antofagasta Bay from Mejillones Peninsula.

<p>A species-conditional triplot based on a canonical correspondence analysis, with <i>P</i>. <i>purpuratus</i> δ¹³C and δ¹⁵N included as environmental gradients. Eigenvalues of dimension 1 (horizontal) = 0.20 and dimension 2 (vertical) = 0.19; eigenvalue of the axis 3 (not displayed) = 0.09. Scale marks along the axes apply to the species and sites scores. Species crosses represent the weighted average of their ‘niche’ (by site), though labels were omitted to avoid cluttering the plot (listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130789#pone.0130789.s003" target="_blank">S2 Table</a>). Rare species which occurred at <2 sites were removed <i>a priori</i> to analysis, as recommended by Bocard et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130789#pone.0130789.ref058" target="_blank">58</a>]. Site symbols show Mejillones Peninsula (locations 2 & 3) and Bay (location 1) in black, and Antofagasta Bay (locations 4 & 5) and Coloso Point (location 6) in grey. 2D triplot displays 26.9% of total inertia (= weighted variance) in the observed occurrences and 65.3% of variance in the weighted averages and class totals of macroalgal species with respect to the environmental variables.</p

The spatial separation of two distinct assemblages of dominant taxa.

<p>Spatial co-occurrence (positive correlations, bold) and separation (negative correlations) of taxa by abundance (n.b. presence/ absence for <i>L</i>. <i>nigrescens</i>), and taxa abundance associations with upwelling influence (^a<i>P</i>. <i>purpuratus</i> δ¹⁵N). All correlations are Spearman’s Rank with non-spatial p-values shown in brackets as</p><p>*** P < 0.001,</p><p>** P < 0.01,</p><p>*P < 0.05.</p><p>For clarity, only one half of the symmetrical correlation matrix has been included.</p><p>The spatial separation of two distinct assemblages of dominant taxa.</p

Geographical variation of standardised δ¹⁵N at sites along the coastline.

<p>The solid line shows size-corrected <i>P</i>. <i>purpuratus</i> δ¹⁵N, whilst the dashed line shows the mean (± SD) across standardised δ¹⁵N of all consumers (<i>P</i>. <i>purpuratus</i>, <i>E</i>. <i>peruviana</i>, <i>S</i>. <i>viridula</i>, <i>T</i>. <i>atra</i>) and putative resources (POM, epilithic biofilm, <i>Ulva</i> sp.). Site labels are presented below the graph in sequence around the coast, with the main geographical features summarised at the base of the graph (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130789#pone.0130789.g001" target="_blank">Fig 1</a> for more detail).</p

The geographical switching in importance of POM and brown macroalgae to the diets of intertidal consumers.

<p>Dietary contributions by resources to (<b>A</b>) the mussel <i>P</i>. <i>purpuratus</i> and (<b>B</b>) grazer species together, estimated by SIAR mixing models run separately for Mejillones Peninsula and Bay (locations 1–3), and Antofagasta Bay with Coloso Point (locations 4–6). Plotted are the 95, 75 and 50% Bayesian credibility intervals, with significance of differences between peninsula and bay estimates. ‘Brown macroalgae’ represents <i>L</i>. <i>nigrescens</i> and <i>D</i>. <i>kunthii</i>, which were combined due to isotopic similarity (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130789#pone.0130789.g002" target="_blank">Fig 2</a>). The food webs of (<b>C</b>) Antofagasta Bay and (<b>D</b>) Mejillones Peninsula plotted figuratively. Arrow weight represents dietary importance by SIAR proportion estimates (mode).</p

The anomalous warmth of Antofagasta Bay and upwelling context of the Mejillones Peninsula (arrow in map B) along the wider coastline of Northern Chile.

<p>(A) Coastal primary productivity (chlorophyll a concentration, logarithmic colour scale) and (B) cool upwelled water (sea surface temperature, SST) parallel to the coastline. (C) A ‘zoomed-in’ view of the Mejillones Peninsula with SST (note different temperature scale to ‘B’) shows ‘locations’ (10 km scale, black lines), ‘sites’ (1 km scale, small black points) and the city of Antofagasta (black diamond). All SST and chlorophyll a concentrations are mean values from estimated daily aqua MODIS satellite data [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130789#pone.0130789.ref036" target="_blank">36</a>] collected between December 2011 and February 2012 at a scale of 4.6 km. Euclidean distance from most northern to most southern sites was approximately 83 km. Where mentioned in the text, sites are numbered from ‘1’ to ‘3’ from north to south, nested within each location.</p