Ecological Archives E091-249-A1

Jada-Simone S. White and James L. O’Donnell. 2010. Indirect effects of a key ecosystem engineer alter survival and growth of foundation coral species. Ecology 91:3538–3548.

Appendix A. Sampling methods and results concerning experimental reef characteristics prior to and after manipulations.

Methods

We identified and marked 32 reefs colonized by Stegastes nigricans (Fig. A1) and 8 interspersed reefs naturally devoid of S. nigricans and associated turf (i.e., healthy Porites reefs, Fig. A2). Prior to any manipulations, we measured the density of S. nigricans and physical characteristics of each reef, including: footprint (maximum length and perpendicular width, cm), average and maximum heights (cm), water depth (cm), distance to the three nearest neighbors (cm), and percent composition (using fixed point contact, at 10 cm intervals, of 3 transects perpendicular to the longest reef axis). For reef composition, corals living upon the reefs belonging to Acropora, Montipora, or Pocillopora were combined into one category (Branching corals) for convenience.

Results

TABLE A1. Design schematic.

Notes: (A) Factorial manipulation of Stegastes nigricans and algal turf presence and removal on 32 colonized reefs. Naturally absent Porites reefs served as a positive control (N = 8 for all treatments). (B) For each of the 40 experimental reefs, we outplanted one of each sub-treatment (cage, cage control, and open) for each species (Acropora striata, Montipora floweri, Pocillopora verrucosa, and Porites australiensis) yielding 480 experimental nubbins total.

TABLE A2. Differences in average physical characteristics among ALL experimental reefs prior to manipulations (PROC GLM, SAS 9.13).

Physical Reef Characteristic Variable F value df Pr > F
Reef size (length × width) Treatment 0.49 4, 39 0.74
Depth to sand Treatment 1.94 4, 39 0.13
Average Height Treatment 1.19 4, 39 0.33
Maximum Height Treatment 1.24 4, 39 0.31
Reef isolation (avg. dist. to 3 nearest reefs) Treatment 2.38 4, 39 0.07

Notes: Mean values (± 95% CI) are reported in the Experimental Reefs section.

TABLE A3. Differences in average benthic composition among Stegastes nigricans reefs prior to manipulations (PROC GLM, SAS 9.13).

Benthic Category Variable F value df Pr > F
Algal Turf Treatment (before) 1.03 3, 28 0.39
Porites spp. Treatment (before) 1.60 3, 28 0.21
Branching Corals Treatment (before) 0.17 3, 28 0.92
DeadCoral/ CrustoseCorallineAlgae Treatment (before) 0.89 3, 28 0.46
Macroalgae Treatment (before) 0.77 3, 28 0.52

Notes: Benthic categories were arcsine squareroot transformed prior to analyses. The positive control reefs (i.e., those naturally devoid of Stegastes and Turf = Porites reefs) were not included as we expected differences due to the higher coral cover and absence of turf (Table A3 and Fig. A1).

TABLE A4. Differences in average (arc sine square root) benthic composition between experimental and control reefs prior to manipulations (PROC TTEST, SAS 9.13).

Benthic Category Variable t df Pr > F
Algal Turf Reef Type 9.76 38 < 0.0001
Porites spp. Reef Type 15.63 38 < 0.0001
Branching Corals Reef Type 3.21 38 < 0.003
DeadCoral/ CrustoseCorallineAlgae Reef Type 1.27 38 0.21
Macroalgae Reef Type 0.51 38 0.61

Notes: Reef type refers to reefs colonized by Stegastes nigricans (prior to any manipulations) versus control reefs (uncolonized by S. nigricans = Porites reefs). Benthic categories were arcsine square-root transformed. Sample sizes are not equal, but assumptions of normality and equal variance were met.

TABLE A5. Differences in average (arc sine square root) benthic composition among Stegastes nigricans reefs after experimental manipulations (PROC GLM, SAS 9.13).

Benthic Category Variable F value df Pr > F
Algal Turf Treatment (after) 10.25 3, 28 0.0001
Porites spp. Treatment (after) 1.61 3, 28 0.21
Branching Corals Treatment (after) 0.47 3, 28 0.71
DeadCoral/ CrustoseCorallineAlgae Treatment (after) 40.25 3, 28 < 0.0001
Macroalgae Treatment (after) 3.17 3, 28 0.04

Notes: Benthic categories were arcsine squareroot transformed prior to analyses. The positive control reefs (i.e., those naturally devoid of Stegastes and Turf = Porites reefs) were not compared in this analysis as we were testing the effects of the removal treatments and initial differences were already established (Table A3 and Fig. A3).

FIG. A1. Photographic example of a (A) ‘Stegastes reef’ (N = 32) and (B) ‘Porites reef’ (N = 8) with nubbins outplanted randomly by species and sub-treatment (orange flags).


FIG. A2. Photographic example of the species x sub-treatments combinations that were outplanted to EACH experimental reef type (N = 12 nubbins / reef).


FIG. A3. Mean percent benthic cover of reefs (± 95% CI) by treatment prior to experimental manipulations (see Tables A2 and A3).


FIG. A4. Mean percent benthic cover of experimental and control reefs (± 95% CI) one month after experimental manipulations began (see Table A4).

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