Ocean Acidification Effects on New Zealand Coastal Ecosystems

1. Ocean acidification and New Zealand coastal waters Catriona Hurd, Department of Botany, University of Otago

2. NZ’s coastal ecosystems • Temperate reefs • Primary producers: • seaweeds and phytoplankton • Secondary producers • Filter feeders: mussels, oysters, barnacles • Grazers: kina, paua, limpets • Predators • Starfish • Fish

3. Which species will OA affect directly? • All algae – fleshy and calcifying • Calcifying invertebrates: • Mollusks: paua (abalone), oysters, mussels • Crustaceans: barnacles, crabs, crayfish • Echinoderms: kina, (urchins), starfish • Sponges • Corals • Bryozoans • Serpulid worms Stanley (2008) Chem. Rev. 108; Hurd et al. J. Phycol. (2009 in press)

4. Seaweed-based ecosystems • Ecosystem engineers • Provide habitat complexity and shelter for animals • Supply 50% of energy to coastal food webs • Some seaweeds are grazed • Most provide food particles - ‘kelp flakes’ • Globally unique ~800 seaweed species ~30% found only in NZ • Hurd et al. (2004) Phycol. Res. 52

5. Predictions on how seaweed productivity will be affected • Increase in growth and productivity of fleshy seaweeds • Seaweeds reliant on only CO2 will have greatest increase • Decline in growth of calcifying (coralline) seaweeds • 80% cover of subtidal habitats around Otago Hurd et al. (2009) J. Phycol. In press

6. Coralline seaweeds Paua larva • Global distribution • Invertebrate recruitment and settlement • Release chemicals that induce attachment and metamorphosis in e.g. paua • Vulnerable • Canaries in the coal mine? Paua larva newly settled on coralline seaweed Nelson (2009) Mar. Fresh. Res. 60

7. Calcifying invertebrates • A substantial proportion of marine invertebrates calcify • Keystone species • kina (sea urchins) • Commercial species • Mussels, oysters, paua (abalone) • Predators • starfish

8. Impacts of high CO2 (low pH) - Echinoderms • Keystone species controlling kelp distributions • Fished extensively worldwide • Production of outer test • affected during larval settlement stage at high pCO2

9. Molluscs – reduced Calcification at low pH Ecosystem function – Bioturbators, Food source & Habitat modifiers C. gigas Net calcification rate umol CaCO3 g FW-1 h-1 M. edulis Gazeau et al. 2007

10. Bivalves – reduced Calcification at low pH Incubations at pH 7.3 (max pH decrease in business-as-usual climate change scenario by year 2300) (Caldeira and Wickett, 2003) control 55 % growth reduction & 65% metabolic depressionDiversion of energy to shell maintenance from growth & reproduction Michailidis et al. (2004)

11. Economic importance How will lower pH affect Greenlip Mussels, Paua and other NZ commercial species? Mussel farms • green lipped mussels • 898 farms, approx. 6535 ha • total revenue $181,400,000 Oyster farms • pacific oysters, North Island • 236 farms, approx. 928 ha • total revenue $26,000,000 Photos and data from www.fish.govt.nz

12. Ecosystemresponses pH • Volcanic CO2-vents • Coralline seaweeds replaced by fleshy species at low pH • Decline in all calcareous invertebrates at low pH Hall-Spencer et al. (2008) Nature 454

13. Seaweeds engineer their own environment • Photosynthesis raises the pH of seawater • Calcification rates of coralline seaweeds enhanced in this seagrass meadow Semesi et al. (2009) Mar. Ecol. Prog. Ser. 382

14. New Zealand coastal waters:What do we need to know? • Species-specific responses to OA • Select ‘model’ seaweed and animal species • Controlled laboratory experiments • Acclimation and adaptation • Ecosystem responses • What knowledge do we have of NZ coastal ecosystems? • Near-shore observatories • Food-web studies