Appendices
O’Connor, Emmerson, Crowe & Donohue.
Distinguishing between direct and indirect effects of predators in complex
ecosystems
Appendix A. Description of the experimental site.
The experimental site at North Beach, Rush, Co. Dublin, Ireland (53°31.4’N,
6°04.9’W), is an intertidal rocky reef composed of a mixture of sandstones, shales and
limestones. The substrate is relatively undulating and contains a network of patches
of bare rock, barnacle covered rock, mussels and macroalgae. The mussels, Mytilus
edulis, form mono-layered patches that provide habitat for diverse assemblages of
invertebrates (O'Connor & Crowe 2007), and often include algae and barnacles
attached epibiotically as is common in this region (O'Connor, Crowe & McGrath
2006; O'Connor 2010). The most abundant perennial macroalgae is Fucus serratus,
which grows in patchily distributed stands attached to rock and to a lesser extent
attached to mussels. Algal assemblages are dominated by taxa such Ulva spp., F.
serratus, Ceramium rubrum, Porphyra sp., Fucus vesiculosus, Palmaria palmata,
Chondrus crispus and Corallina officinalis (Table 1; O'Connor & Crowe 2008).
Table 1. Algae found in experimental plots over the duration of the experiment.
Phylum
Taxon
Ochrophyta
Fucus serratus
Leathesia difformis
Chlorophyta Ulva intestinalis
Ulva lactuca
Rhodophyta
Ceramium rubrum
Chondrus crispus
Corallina officinalis
Ecotcarpus spp.
Gelidium pusillum
Gracilaria gracilis
Lithothamnia spp.
Nemalion
helminthoides
Osmundea pinnatifida
Palmaria palmata
Polysiphonia fucoides
Porphyra umbilicalis
REFERENCES
O'Connor, N. E. 2010. Shore exposure affects mussel population structure and
mediates the effect of epibiotic algae on mussel survival in SW Ireland.
Estuarine, Coastal and Shelf Science 87:83-91.
O'Connor, N. E. and T. P. Crowe. 2007. Biodiversity among mussels: separating the
influence of sizes of mussels from the ages of patches. Journal of the Marine
Biological Association of the United Kingdom 87:551-557.
O'Connor, N. E. and T. P. Crowe. 2008. Do mussel patches provide a refuge for algae
from grazing gastropods? Journal of Molluscan Studies 74:75-78.
O'Connor, N. E., T. P. Crowe, and D. McGrath. 2006. Effects of epibiotic algae on
the survival, biomass and recruitment of mussels, Mytilus L. (Bivalvia :
Mollusca). Journal of Experimental Marine Biology and Ecology 328:265276.
Appendix B. ANOVA tests for experimental artefacts of the cages used to simulate
the local extinction of target consumers.
Table 1. Results of ANOVA testing for cage effects on (a) total algal cover, (b)
mussel cover and (c) grazer biomass (n = 4 experimental plots).
Source of
variation
Cage
Residual
(a)
d.f. MS
1
6
F
P
(b)
MS
F
P
(c)
MS
F
P
72.00
0.03 0.86 200.00 0.62 0.46 45.60 0.65 0.45
2227.33
322.91
70.28
Appendix C. Results of SIMPER analyses identifying the taxa contributing most
strongly to differences in algal assemblage structure following the loss of primary
consumers.
Table 1. SIMPER (similarity of percentages; Clarke and Warwick 2001) analyses of
taxa contributing to differences in algal assemblage structure following the loss of (a)
grazing gastropods (average dissimilarity = 76.93%) and (b) mussels (average
dissimilarity = 84.15%), based on log (x + 1) transformed algal cover data (n = 4).
Avg. Diss. = Average dissimilarity contributed by each taxon; Diss/ SD = measure of
the variations in contribution to dissimilarity (Clarke 1993); % Contribution =
percentage contribution of each algal taxa to the overall Bray-Curtis dissimilarity
between assemblages with and without (a) grazers and (b) mussels.
(a)
Taxa
Fucus serratus
Porphyra
umbilicalis
Ulva spp.
Polysiphonia spp.
Osmundea
pinnatifida
Ectocarpus
siliculosus
Lithothamnia
Chondrus crispus
Leathesia difformis
Corallina
officianalis
(b)
Taxa
Lithothamnia
Osmundea
pinnatifida
Corallina
officianlis
Average Cover
Grazers
Grazers
present
absent
1.21
3.96
0.81
2.31
Avg.
Diss
16.00
13.33
Diss/
SD
1.74
1.26
%
Contribution
20.80
17.33
0.96
0.30
0.35
2.21
1.77
1.23
11.99
9.06
7.98
1.60
1.11
1.27
15.59
11.77
10.37
0.35
0.93
4.66
0.76
6.05
0.91
0.47
0.00
0.20
0.23
0.50
0.74
0.48
4.52
4.17
3.19
2.05
0.76
0.82
0.54
0.46
5.87
5.42
4.14
2.66
Average Cover
Mussels
Mussels
present
absent
0.91
4.01
0.35
3.47
Avg.
Diss
15.78
15.34
Diss/
SD
1.75
1.92
%
Contribution
18.75
18.23
0.47
12.80
1.49
15.21
3.08
Chondrus crispus
Ectocarpus
siliculosus
Palmaria palmata
Fucus serratus
Ceramium rubrum
Ulva spp.
Leathesia difformis
Porphyra
umbilicalis
Gelidium latifolium
Nemalion
helminthoides
Polysiphonia spp.
Graciliaria
verrucosa
0.20
0.35
2.13
1.58
7.49
5.74
1.36
1.02
8.90
6.82
0.00
1.21
0.00
0.96
0.00
0.81
1.21
0.83
0.98
0.20
0.70
0.00
5.20
4.50
3.95
3.69
2.44
2.22
0.87
1.00
0.78
0.77
0.68
0.49
6.18
5.35
4.69
4.39
2.90
2.64
0.00
0.00
0.55
0.23
2.21
1.14
0.56
0.30
2.63
1.35
0.30
0.00
0.23
0.23
1.05
0.59
0.45
0.29
1.25
0.70
REFERENCES
Clarke, K. R. 1993. Nonparametric multivariate analyses of changes in community
structure. Australian Journal of Ecology 18:117-143.
Clarke, K. R. and R. M. Warwick. 2001. Change in marine communities: an approach
to statistical analysis and interpretation. 2nd edition. Primer-E Ltd., Plymouth,
U.K.
Appendix D. ANOVA test for effects loss of crabs, grazers and mussels, both
separately and together, on whelk biomass.
Table 1. Results of ANOVA testing for effects loss of crabs, grazers and mussels,
both separately and together, on whelk biomass (n = 4 experimental plots). Whelk
data were square-root-transformed.
Dependent variable
Source of variation
d.f.
MS
F
P
Whelk biomass
Loss of crabs
Loss of primary consumers
Loss of crabs*loss of
primary consumers
Residual
1
2
2
1.56
0.04
0.22
3.31
0.09
0.47
0.086
0.91
0.63
18
0.47