ocean acidification and new zealand coastal waters catriona hurd, department of botany, university...

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