Supporting InformationO’Gorman and Emmerson 10.1073/pnas.0903682106

Fig. S1. Core web of species interactions over all of the experimental mesocosms. We calculated trophic height (TH) as the average trophic position of a speciesin all food chains of which it is a part. The 9 basal resources at the foot of the web have TH � 1. The 5 long parallel rows have TH � 2. All other taxa are arrangedin the vertical plane according to their TH. A list of the taxa that correspond to each number in the web (along with their linkage density and TH) can be foundin Table S1. Note that species 150 at the top of the web is a parasitic gastropod (feeding on brittle stars). Taxa 48 and 79 at the foot of the web are nonfeedinglarvae.

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Table S1. Key to the taxa in the mesocosm food web shown in Fig. S1

Code Taxa Common name LD TH

1 Carcinus maenas Common shore crab 55 3.092 Ctenolabrus rupestris Goldsinny wrasse 85 3.163 Gaidropsarus mediterraneus Shore rockling 65 3.244 Gobius niger Black goby 96 3.145 Gobius paganellus Rock goby 105 3.146 Marthasterias glacialis Spiny starfish 52 3.267 Necora puber Velvet swimming crab 31 3.138 Palaemon serratus Common prawn 33 3.099 Paracentrotus lividus Purple sea urchin 46 2

10 Taurulus bubalis Sea scorpion 5 3.1611 Gobiusculus flavescens Two-spot goby 80 3.0512 Pomatoschistus pictus Painted goby 67 3.0813 Abra alba White furrow shell 10 214 Acanthocardia echinata Prickly cockle 12 215 Acanthochitona crinitus (chiton) 5 216 Aequipecten opercularis Queen scallop 9 217 Alvania beani (gastropod) 14 218 Alvania semistriata (gastropod) 14 219 Amphilochus manudens (amphipod) 8 2.4620 Anomia ephippium Saddle oyster 15 221 Aora gracilis (amphipod) 10 222 Apherusa bispinosa (amphipod) 5 223 Apseudes latreillei (tanaid) 6 224 Apseudes talpa (tanaid) 6 225 Ascidiella aspersa Dirty sea squirt 6 226 Asterina phylactica (starfish) 13 2.7127 Bittium reticulatum Needle whelk 22 2.6928 Buccinum undatum Common whelk 14 3.0829 Calanoida (copepod) 24 230 Callopora lineata (bryozoan) 5 231 Caprella acanthifera (caprellid) 12 2.4032 Caprella equilibra (caprellid) 12 2.4033 Caprella linearis (caprellid) 12 2.4034 Ceradocus semiserratus (amphipod) 6 235 Cerastoderma edule Common cockle 7 236 Cerithiopsis tubercularis (gastropod) 13 2.4037 Chironomidae spp. (chironomid) 7 238 Chlamys varia Variegated scallop 9 239 Circulus striatus (gastropod) 10 240 Clathrina coriacea (sponge) 15 241 Coriandria fulgida (gastropod) 15 242 Crassicorophium bonnellii (gastropod) 12 243 Crassicorophium crassicorne (gastropod) 12 244 Crisia denticulata (bryozoan) 11 245 Cumacea A (cumacean) 11 246 Cuthona sp. (gastropod) 5 247 Cyclopoida (copepod) 22 2.2048 Cyprid larvae (cyprid) 5 149 Cythere lutea (ostracod) 11 250 Dexamine spinosa (amphipod) 9 251 Dexamine thea (amphipod) 9 252 Disporella hispida (bryozoan) 5 253 Dysidea fragilis (sponge) 15 254 Elasmopus rapax (amphipod) 8 255 Electra pilosa Hairy sea mat 7 256 Elysia viridis Green elysia 6 257 Emarginula fissura (gastropod) 8 2.3358 Epilepton clarkiae (bivalve) 10 259 Epitonium clathrus Common wentletrap 6 260 Ericthonius brasiliensis (amphipod) 12 261 Ericthonius punctatus (amphipod) 12 262 Eubranchus farrani (gastropod) 5 263 Exogone gemmifera (polychaete) 6 264 Foraminifera A (foraminiferan) 10 2

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Code Taxa Common name LD TH

65 Foraminifera B (foraminiferan) 10 266 Foraminifera C (foraminiferan) 10 267 Foraminifera D (foraminiferan) 10 268 Foraminifera E (foraminiferan) 10 269 Foraminifera F (foraminiferan) 10 270 Foraminifera G (foraminiferan) 10 271 Galathea squamifera Black squat lobster 26 3.0272 Gammaropsis maculata (amphipod) 8 2.2073 Gammarus locusta (amphipod) 8 274 Gammarus zaddachi (amphipod) 8 275 Gibbula umbilicalis Flat top shell 9 2.3376 Halacarellus basteri (sea mite) 3 277 Harpacticoida (copepod) 24 278 Hiatella arctica Wrinkled rock borer 15 279 Hymenopteran larvae (hymenopteran) 1 180 Iothia fulva (gastropod) 11 2.5781 Idotea A (isopod) 11 2.5782 Idotea B (isopod) 4 283 Janua pagenstecheri (spirorbid) 10 284 Lasaea rubra (bivalve) 11 285 Lembos websteri (amphipod) 11 286 Leptocheirus tricristatus (amphipod) 11 287 Leptochelia savignyi (tanaid) 7 288 Leptocythere pellucida (ostracod) 11 289 Leptomysis lingvura (mysid) 6 290 Loxoconcha rhomboidea (ostracod) 11 291 Lysianassa ceratina (amphipod) 5 292 Melita palmata (amphipod) 8 293 Microdeutopus anomalus (amphipod) 9 294 Microprotopus maculatus (amphipod) 6 2.3395 Modiolula phaseolina Bean horse mussel 22 2.3696 Monia patelliformis Ribbed saddle oyster 14 297 Munna kroyeri (isopod) 10 2.3398 Musculus discors Green crenella 22 2.3699 Mytilus edulis Common mussel 22 2.36

100 Nannastacus unguiculatus (cumacean) 7 2.33101 Nematoda spp. (nematode) 11 2102 Nereis sp. (polychaete) 10 2103 Odostomia plicata (gastropod) 6 2104 Omalogyra atomus (gastropod) 10 2105 Onoba semicosta (gastropod) 11 2.25106 Ophiothrix fragilis Common brittle star 13 2107 Ophiura ophiura Serpent star 32 2.88108 Ostracod A (ostracod) 11 2109 Ostracod B (ostracod) 11 2110 Ostracod C (ostracod) 11 2111 Paradoxostoma variabile (ostracod) 11 2112 Parvicardium exiguum (bivalve) 14 2113 Parvicardium ovale (bivalve) 14 2114 Parvicardium scabrum (bivalve) 14 2115 Perinereis cultrifera (polychaete) 9 2116 Phyllodocidae sp. (polychaete) 6 2117 Pilumnus hirtellus Hairy crab 36 3.08118 Platynereis dumerilii (polychaete) 10 2119 Podocoryne borealis (hydrozoa) 9 2.50120 Pomatoceros lamarcki (serpulid polychaete) 12 2121 Pomatoceros triqueter (serpulid polychaete) 12 2122 Pontocypris mytiloides (ostracod) 11 2123 Pseudoparatanais batei (tanaid) 6 2124 Retusa truncatula (gastropod) 7 2125 Rissoa parva (gastropod) 15 2.40126 Rissoa sarsi (gastropod) 15 2.40127 Rissoella diaphana (gastropod) 15 2128 Rissoella opalina (gastropod) 15 2129 Sabella pavonina (sabellid) 11 2

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Code Taxa Common name LD TH

130 Sagitta elegans Arrow worm 8 2.64131 Scrupocellaria spp. (bryozoan) 12 2132 Semibalanus balanoides Northern rock barnacle 8 2.53133 Semicytherura nigrescens (ostracod) 11 2134 Serpulid A (serpulid) 11 2135 Siriella armata (mysid) 8 2.64136 Skenea serpuloides (gastropod) 10 2.33137 Spirorbis A (spirorbid) 10 2138 Spirorbis B (spirorbid) 10 2139 Stenothoe marina (amphipod) 6 2140 Syllidae A (polychaete) 4 2141 Syllidae B (polychaete) 4 2142 Tapes aureus (bivalve) 12 2143 Tectura virginea (gastropod) 10 2.25144 Tomopteris helgolandica (polychaete) 8 2145 Tritaeta gibbosa (amphipod) 6 2146 Tryphosella sarsi (amphipod) 3 2147 Tubulipora liliacea (bryozoan) 5 2148 Turbellaria A (flat worm) 5 2149 Typosyllis prolifera (polychaete) 4 2150 Vitreolina philippi (gastropod) 4 3.44151 Xestoleberis aurantia (ostracod) 11 2152 Algae Algae 89 1153 Bacteria Bacteria 53 1154 Cladocerans Cladocerans 8 1155 CPOM CPOM 98 1156 Diatoms Diatoms 74 1157 FPOM FPOM 112 1158 Microphytobenthos Microphytobenthos 80 1

The linkage density (LD) and trophic height (TH) of each taxon are provided.

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Table S2. Length–weight (L–W) relationships used to estimate body size of all taxa identified in the experiment

Taxa L–W Relationship r2

Carcinus maenas y�0.2668x2.9545 0.9693Ctenolabrus rupestris y�0.0057x3.181 0.9734Gaidropsarus mediterraneus y�0.0008x3.3972 0.9847Gobius niger y�0.0074x3.0788 0.9320Gobius paganellus y�0.0014x3.4672 0.9356Marthasterias glacialis y�0.3088x2.7417 0.9187Necora puber y�0.2989x2.9639 0.9204Palaemon serratus y�0.0014x3.3838 0.9201Paracentrotus lividus y�1.2774x2.737 0.9398Taurulus bubalis y�0.0032x3.3258 0.9604Gobiusculus flavescens y�0.0004x3.7234 0.9612Pomatoschistus pictus y�0.0039x3.1954 0.9733Alvania spp. y�0.1391x2.71 0.9877Anomia ephippium y�0.0304x2.9244 0.9428Aora gracilis y�0.0018x3.2994 0.9202Aoridae y�0.0031x2.8427 0.9596Ascidiella aspersa y�0.1159x2.3628 0.8922Bittium reticulatum y�0.1224x2.3117 0.9831Buccinum undatum y�0.0958x3.0601 0.9804Cardiidae y�0.1084x3.0951 0.9870Chlamys varia y�0.0508x3.036 0.9893Clathrina coriacea y�0.2909x1.9999 0.9541Crassicorophium spp. y�0.0046x3.1972 0.9491Cumacea y�0.0101x1.9552 0.8806Dysidea fragilis y�0.1435x1.9328 0.8442Epilepton clarkiae y�0.0959x2.8774 0.9805Foraminifera y�0.1598x3.2349 0.9801Galathea squamifera y�0.0284x4.3903 0.9353Hiatella arctica y�0.053x2.9161 0.9540Janua pagenstecheri y�0.1117x3.0229 0.9314Lembos websteri y�0.0037x2.6724 0.9806Lysianassa ceratina y�0.0096x3.0979 0.9877Melitidae y�0.004x3.095 0.9598Microdeutopus anomalus y�0.0016x3.3615 0.9685Musculus discors y�0.0986x2.7968 0.9766Mysidae y�0.0006x3.2529 0.9236Nudibranchia y�0.0096x2.8116 0.9726Ophiothrix fragilis y�0.4875x2.9185 0.9435Ophiura ophiura y�0.2936x2.5329 0.9603Ostracoda y�0.1738x4.2678 0.7896Parvicardium exiguum y�0.1104x3.0932 0.9786Parvicardium ovale y�0.1018x3.1784 0.9900Parvicardium scabrum y�0.1103x3.0607 0.9870Pectinidae y�0.0698x2.8284 0.9871Perinereis cultrifera y�0.0015x3.0023 0.9733Pilumnus hirtellus y�0.1324x2.963 0.9438Platynereis dumerilii y�0.0113x2.2781 0.8051Polychaeta y�0.0021x2.395 0.8612Pomatoceros spp. y�0.0029x2.781 0.9688Rissoa spp. y�0.1532x2.3992 0.9691Scrupocellaria spp. y�0.00004x2.6928 0.9691Tubulipora liliacea y�0.0504x2.5072 0.9272

For taxa with no L–W relationship, we identified the closest taxa in terms of body shape and used that L–W relationship as a substitute. Weight (y) is measuredin mg. Length (x) is measured in mm.

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