Ocean acidification and New Zealand coastal waters Catriona

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

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

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)

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

Predictions on how seaweed productivity will be affected • Increase in growth and productivity of fleshy seaweeds – Seaweeds reliant on only CO 2 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

Coralline seaweeds • Global distribution • Invertebrate recruitment and settlement Paua larva – 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

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

Impacts of high CO 2 (low p. H) - Echinoderms • Keystone species controlling kelp distributions • Fished extensively worldwide • Production of outer test affected during larval settlement stage at high p. CO 2

Molluscs – reduced Calcification at low p. H Ecosystem function – Bioturbators, Food source & Habitat modifiers C. gigas Net calcification rate umol Ca. CO 3 g FW-1 h-1 M. edulis Gazeau et al. 2007

Bivalves – reduced Calcification at low p. H Incubations at p. H 7. 3 (max p. H decrease in business-as-usual climate change scenario by year 2300) (Caldeira and Wickett, 2003) control 55 % growth reduction & 65% metabolic depression Diversion of energy to shell maintenance from growth & reproduction Michailidis et al. (2004)

Economic importance Mussel farms How will lower p. H affect Greenlip Mussels, Paua and other NZ commercial species? • 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 Photos and data from www. fish. govt. nz

p. H Ecosystem responses • Volcanic CO 2 -vents • Coralline seaweeds replaced by fleshy species at low p. H • Decline in all calcareous invertebrates at low p. H Hall-Spencer et al. (2008) Nature 454

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

New Zealand coastal waters: What do we need to know? • Species-specific responses to OA – Select ‘model’ seaweed 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