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 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

Coralline seaweeds

• Global distribution• Invertebrate

recruitment and settlement– Release chemicals

that induce attachment and metamorphosis in e.g. paua

• Vulnerable• Canaries in the coal

mine?

Nelson (2009) Mar. Fresh. Res. 60

Paua larva

Paua larva newly settledon coralline seaweed

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 CO2 (low pH)- Echinoderms

•Keystone species controlling kelp distributions

•Fished extensively worldwide

•Production of outer test affected during larval settlement stage at high pCO2

Net calcification rateumol CaCO3 g FW-1 h-1

Molluscs – reduced Calcification at low pH

M. edulis

C. gigas

Ecosystem function – Bioturbators, Food source & Habitat modifiers

Gazeau et al. 2007

55 % growth reduction & 65% metabolic depression

Diversion of energy to shell maintenance from growth & reproduction

0 20 40 60 80 10012

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Time (days)

Mea

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Incubations at pH 7.3 (max pH decrease in business-as-usual climate change scenario by year 2300) (Caldeira and Wickett, 2003)

controlcontrol

Bivalves – reduced Calcification at low pH

Michailidis et al. (2004)

Economic importance

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

How will lower pH affect Greenlip Mussels, Paua and other NZ commercial species?

Ecosystemresponses

Hall-Spencer et al. (2008) Nature 454

pH

•Volcanic CO2-vents

•Coralline seaweeds replaced by fleshy species at low pH

•Decline in all calcareous invertebrates at low pH

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

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