Robustness of the quality index (EBQI) with regard to the weighting of compartments (boxes).

<p>The 17 sites are arranged from left to right according to their growing EBQI (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098994#pone-0098994-t004" target="_blank">Table 4</a>) and ecological status (bad through high). Deep red = bad, orange = poor, green = moderate, light blue = good, deep blue = high. In order to test the effect of the weighting of the compartments (boxes) on the EBQI (robustness), weighting values have been randomly perturbed (above, ±1; below, ±2). 1000 iterations were performed. The change of the ecological status (bad through high) of a site, for a given iteration, is shown by the color of the new class within which it falls.</p

Robustness (index of similarity) of the quality index (EBQI) to the weighting of compartments (boxes).

<p>Percentage of times the ecological status of each site was unaltered by random perturbation of the weighting of the boxes (1,000 iterations) by ±1 through ±4. The similarity is equal to 100% when the class of the site is never changed after perturbation and 0% if it is always changed.</p

Conceptual model of the functioning of <i>Posidonia oceanica</i> seagrass ecosystem.

<p>For functional compartments and box numbers, see text. Primary producers are in green; filter-feeders, suspension-feeders, litter, detritus feeders, Dissolved Organic Carbon (DOC) and microbial loops are in orange; predators (including herbivores) are in yellow. The width of the arrows roughly represents the importance of the carbon flow. The proper <i>P. oceanica</i> ecosystem is included within the red rectangle. MPO: Multicellular Photosynthetic Organisms. POM: Particulate Organic Matter. From C.F. Boudouresque, unpublished.</p

Comparison of EBQI with Ecological Quality Ratios (EQRs) based mainly upon <i>P. oceanica</i> (the organism itself) and aimed at establishing the ecological status of the seawater body.

a<p>The metrics of PREI are: shoot density, shoot leaf surface area, ratio between epibiota biomass and leaf biomass, depth of the lower limit and type of this limit <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098994#pone.0098994-Gobert1" target="_blank">[14]</a>.</p>b<p>The metrics of POMI are: shoot density, meadow cover, percentage of plagiotropic rhizomes, shoot leaf surface area, percentage of foliar necrosis, P, N and sucrose content in rhizomes, δ¹⁵N and δ³⁴S isotopic ratio in rhizomes, N content in epiphytes, Cu, Pb and Zn content in rhizomes <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098994#pone.0098994-Romero1" target="_blank">[12]</a>.</p>c<p>The metrics of BiPo are: shoot density, shoot leaf surface area, lower depth limit and lower limit type <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098994#pone.0098994-LopezyRoyo1" target="_blank">[15]</a>.</p><p>PREI, POMI and BiPo indices are based upon distinct but similar metrics and range from 0 (lowest ecological status) to 1 (highest ecological status).</p

Spearman's rank correlations between the status of each compartment (boxes 1 through 13 and SRDI), the other compartments (boxes) and the EBQI (see Table 5).

<p>Bold italic characters: significant (p<0.01).</p

Estimation of time and diving effort needed for data acquisition within each box used in the EBQI.

<p>Estimation of time and diving effort needed for data acquisition within each box used in the EBQI.</p

Sites used to test the proposed ecosystem-based approach to assess the status of the <i>P. oceanica</i> ecosystem. MPA: Marine Protected Area. NTZ: No Take Zone.

a<p>This area is close to the Natural Marine Reserve of Cerbère-Banyuls. Since October 2011, this area has been included within a natural marine park (‘Parc naturel marin du golfe du Lion’).</p>b<p>Since 2010, anchoring is banned.</p>c<p>Since May, 2012, this area has been included within a National Park (‘Parc national des Calanques’). However, it is unlikely that this new status would have already resulted in a perceptible effect.</p

Criteria to assess the Confidence Index (CI) of the status of a compartment (box).

<p>Criteria to assess the Confidence Index (CI) of the status of a compartment (box).</p

Ecosystem status (EBQI) and Confidence Index (CI) for each sampling site, and scale value and CI of each parameter used to obtain them.

<p>Boxes 1 through 13 and SRDI. The status and the Confidence Index (in brackets; CI) is indicated for each box. EBQI ranges from 0 to 10, while the CI is graded from 0 to 4).</p

Relative weighting of each functional compartment (boxes; see Fig. 1 for box number) and ranges of each parameter defined for each grade of ecosystem status.

<p>Between inverted commas: abbreviated name of the functional compartment in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098994#pone-0098994-t004" target="_blank">tables 4</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098994#pone-0098994-t007" target="_blank">7</a>. DM: dry mass, including calcium carbonate. HOM: indicators of high level of organic matter. LOM: indicators of low level of organic matter. MPO: Multicellular Photosynthetic Organisms. POM: Particulate Organic Matter. WM: wet mass. Status: 4 (very good) through 0 (very low).</p