5.2 Structure and distribution of coral reefs in the tropical Pacific

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Vulnerability of coral reefs in the tropical Pacific to climate change

Ove Hoegh-Guldberg, Serge Andréfouët, Katharina E Fabricius, Guillermo Diaz-Pulido, Janice M Lough, Paul A Marshall and Morgan S Pratchett

‘Temperature-related effects of global warming on coral reefs are highly visible, well-defined and extensively documented. The more recently recognised effects of atmospheric carbon dioxide on ocean acidification will have even more profoundly detrimental long-term effects on reefs.’ (Veron et al. 2009)ⁱ

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Contents Page

5.1 Introduction 253

5.2 Structure and distribution of coral reefs in the tropical Pacific 254 5.3 Role of coral reefs in supporting fisheries in the tropical Pacific 258 5.4 Critical requirements for coral reefs 260

5.5 Coral reefs in a changing world 262

5.5.1 Effects of global warming on coral reefs in the tropical Pacific 262

5.5.2 Additional effects of ocean acidification 264

5.5.3 Interactions and synergies 266

5.5.4 Changes to coral reefs over time 266

5.6 Projected vulnerability of coral reefs to climate change 267

5.6.1 Sea surface temperature 267

5.6.2 Solar radiation 269

5.6.3 Ocean acidification 270

5.6.4 Tropical cyclones and floods 271

5.6.5 Sea-level rise 273

5.6.6 Ocean circulation and upwelling 275

5.7 Projected changes: coral reefs under low versus high CO₂ emissions 276 5.7.1 The next two to three decades: coral reefs in 2035 (B1 and A2) 277

5.7.2 Coral reefs in 2100 (B1) 281

5.7.3 Coral reefs in 2100 (A2) 282

5.7.4 Beyond 2100: reef recovery versus complete collapse 283 5.8 Uncertainty, gaps in knowledge and future research 284 5.9 Management implications and recommendations 286 References 289

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5.1 Introduction

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reef Atoll^a Bank^b

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No. reef classes Barrier

reef

Patch reef

Fringing reef

Inter- reefal^c Melanesia

Fiji 18,272 10,000* n/a n/a n/a n/a n/a n/a > 150 New Caledonia 19,100 35,925 15,466 413 3476 733 790 15,047 163 PNG 462,243 22,200* n/a n/a n/a n/a n/a n/a > 150 Solomon Islands 27,556 8535 2191 599 1471 645 1328 2301 134

Vanuatu 11,880 1244 22 40 59 28 629 466 58

Micronesia

FSM 700 15,074 11,859 420 523 21 212 2039 72

Guam 541 238 0 113 19 1 75 30 27

Kiribati 690 4320 3986 114 0 0 0 0 23

Marshall Islands 112 13,930 13,910 20 0 0 0 0 20

Nauru 21 7 7 0 0 0 0 0 3

CNMI 478 250 0 33 25 0 67 125 23

Palau 494 2496 555 17 615 86 163 1060 58

Polynesia

American Samoa 197 368 11 9 5 0 47 296 16

Cook Islands 240 667 548 5 58 1 17 38 37

French Polynesia 3521 15,126 13,524 35 802 27 178 560 66

Niue 259 56 56 0 0 0 0 0 9

Pitcairn Islands 5 48 17 17 0 0 4 10 17

Samoa 2935 466 0 0 203 7 139 117 28

Tokelau 10 204 204 0 0 0 0 0 8

Tonga 699 5811 47 96 564 377 171 4556 70

Tuvalu 26 3175 3040 135 0 0 0 0 18

Wallis and Futuna 255 932 588 75 95 14 56 104 25

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5.3 Role of coral reefs in supporting fisheries in the tropical Pacific

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5.7.1 The next two to three decades: coral reefs in 2035 (B1 and A2)

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2000 2100 2200 2300 460

440 420 400 380 360 340 320

2000 2100 2200 2300 800

700

600

500

400

300

Year

Atmospheric CO2 (ppm) Coral cover relative to today (%)B1 scenario (500–600 ppm) A2 scenario (750–800 ppm)

100

75

50

25

0

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Year Scenario Management

Coral cover Macroalgal cover

% % decrease % % increase

2035 B1/A2

Strong 15–30 25–65 40 130

Poor 15 65 40–60 130–200

2100

B1

Strong 10–20 50–75 50 > 150

Poor < 5 > 85 80 > 250

A2

Strong < 2 > 90 > 95 > 300 Poor < 2 > 90 > 95 > 300

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0% 29% 66% 90% 100% 0% 5% 33% 66% 95% 100%