Qualitative analysis of food webs in the Pacific Ocean Wealth from Oceans J Young, J Dambacher, R Olson, V Allain, F Galvan-Magana, M Lansdell, N Bocanegra- Castillo, V Alatorre-Ramirez, S Cooper, L Duffy
Acknowledgements
Origins of the study
Reports also in PFRP Newsletter, GLOBEC newsletter
Skipjack tuna trophic links Prey Fam Tot Wt g % Wt 'Other Teleostei' 2049 56.3 Scombridae 557 15.3 'Other Cephalopoda' 308 8.5 Ommastrephidae 153 4.2 'Unidentified' 145 4.0 Exocoetidae 76 2.1 Engraulidae 59 1.6 Gempylidae 59 1.6 Carangidae 40 1.1 Thalassocarididae 26 0.7 'Caridea' 17 0.5 'Hyperiidea' 16 0.4 Alepisauridae 15 0.4 Bramidae 13 0.4 Monacanthidae 10 0.3 Acanthuridae 9 0.3 'Decapoda' 8 0.2 'Stomatopoda' 7 0.2 Argonautidae 7 0.2 Serranidae 6 0.2
Multiple predators
Understanding complexity through system structure or if this is all we know then what do we know?
1 1 2-4 Bray-Curtis you are who you eat. 2 5 3 6 4 7 2,4 5-7 1 3 Social network you are who you eat and who eats you! 5-7
Aim Perturb an influential species (yellowfin tuna) that could be directly affected by ocean warming and trace the effects to commercially important species in three different regions of the Pacific Ocean
Stomach collections CSIRO (PESCI) data base Stomachs collected : CSIRO 3102, SPC 1691, IATTC 3882 Sampling area ~ 35 million km2 Prey taxa 651 overall 248 taxa > 1% wet weight
Qualitative analyses: method flow chart Full diet matrix (after removal of weak links and isolates Role equivalence (social network theory) Key player analysis Reduced model/ Aggregation (REGE) Fragmentation the species/group that, when removed, causes the most disruption or fragmentation is the key player Reach the influence of a species/group Qualitative dynamics Perturbations of species/groups to positive or negative inputs e.g. temperature
SW Pacific Food Web: Key Player Analyses Removal/Fragmentation yellowfin tuna
Key players - identified from their reach through, and their ability to fragment, a food web sw cw ce Lancetfish + + Mahi + Opah + Skipjack + Albacore + Yellowfin + + swordfish + tripletail + squid + + Insert presentation title
Southwest Pacific Ocean 5.0 Key players yellowfin tuna Swordfish lancetfish squid small fish 4.5 4.0 3.5 3.0 2.5 2.0 12 210 197 15 swordfish 77 152 74 75 76 124 106 169 121 yft 115 44 66 70 65 122 165 168 149 83 155 163 156 157 114 108 112 126 167 120 161 151 14 2 13 68 212 174 215 116 177 119 117 127 209 38 5 lancetfish 4 147 123 3 193 37 192 219 196 191 195 25 69 squid 35 34 52 238 153 27 63 180 S = 109 179 64 203 199 201 202 200 206 207 205 Small fish TL=3.6 95 142 49 100 93 96 140 92 72 105 102 94 236 90 39 71 9 235 239 145 234 41 182 241 232 185 228 1.5 183 1.0
Central Western Pacific Ocean 5.0 Key players albacore mahi mahi squid, small fish 4.5 4.0 3.5 3.0 2.5 2.0 152 77 75 76 74 11 124 166 106 111 73 121 115 44 130 148 129 165 70 66 168 65 170 133 135 136 110 122 107 158 126 163 162 160 83 157 128 171 68 150 151 208 212 132 214 127 67 86 210 213 3 4 5 30 193 218 197 23 219 29 37 24 21 22 164 26 84 16 18 19 20 17 28 238 220 176 188 186 S = 142 153 189 27 190 187 180 61 64 62 56 203 207 199 204 42 TL=3.5 7 93 236 139 140 98 49 55 138 97 137 131 141 101 104 50 100 99 54 48 80 87 6 40 9 10 8 88 46 230 146 235 239 221 224 225 144 145 143 175 181 248 241 240 227 184 233 1 1.5 183 1.0
Central Eastern Pacific Ocean 5.0 4.5 43 33 165 76 65 109 44 yft 77 169 106 75 124 74 115 121 170 122 110 168 134 108 159 31 45 157 32 160 154 126 125 4.0 172 113 211 85 23 198 127 173 215 219 37 36 24 26 28 20 18 Key players yellowfin tuna Triple tail mahi mahi skipjack small fish 3.5 3.0 2.5 2.0 1.5 153 27 57 60 51 59 58 64 56 194 178 204 118 98 95 89 91 88 79 53 81 80 82 47 78 9 6 229 143 226 223 S = 91 TL=3.5 239 231 245 242 222 247 237 244 246 217 216 103 1.0 243
Aggregated food webs of three regions of the Pacific Ocean. South Western Pacific Ocean Central Western Pacific Ocean Central Eastern Pacific Ocean Predation Trophic Level Tier T 1 mean 4.3 SD 0.02 T 2 4.2 0.31 T 3 3.4 0.66 T 1 4.4 0.13 T 2 4.0 0.47 T 3 3.8 0.55 T 4 3.2 0.63 T 1 4.2 0.27 T 2 4.2 0.29 T 3 3.6 0.65 Nodes represent groups of taxa with similar predator prey relationships and are arranged in predation tiers (Tn) Groups with asterisks contain key players. Shown for each tier are mean and standard deviation of trophic levels of taxa in each group. These network structures were used to create qualitative models of each pelagic ecosystem, which were used for perturbation analyses. T 4 3.0 0.76
SW Pacific Food Web: climate change scenarios -+: mako shark + - +: yellowfin tuna -: bigeye tuna - -: swordfish, albacore, southern bluefin tuna -: squid
Perturbation response of increasing yellowfin tuna on other commercial fish species South western Pacific Central western Pacific Central eastern Pacific Mahi mahi Skipjack Albacore Bigeye tuna - + - - - + - - + + + - - - na swordfish
Conclusions, caveats and future research Identified species that were key players in the three regions Positive perturbation of yellowfin tuna impacted commercially important species in SW Pacific, varying results in other regions Sharks not keystone species (support from quantitative studies) Response of a species to a change in ocean conditions (e.g. ocean warming) depends on food web structure importance of detail in trophic studies Caveats Sampling methodology (Lancetfish longline caught v rainbow runners purse seine) Future research Fisheries exploitation and feedbacks that drive fishing fleet Direct comparisons with quantitative models