Impacts of ocean acidification and warming on cold water corals: current and future work

Sebastian Hennige, Wicks L.C., Kamenos N.A., Roberts J.M.

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Cold water corals

Lophelia pertusa (the most common UK coral)

• Scleractinia – framework forming•Complex habitats

• No Symbiodinium (no photosynthesis)

•Global distribution from 40 – 3000m•Reefs can be larger than some tropical(Norway reefs ~2000km2)

•Historically known but relatively unstudied•Joubin 1915

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Ocean Acidification and warming:....The other CO2 problem

• Directly related to atmospheric CO2

• Current atm. pCO2 is 380ppm

• By 2100: 750 – 1000ppm

• pH ↓ from ca. 8.1 to ca. 7.8

•Negative impact on calcifiers:↓ availability of carbonate ionsChange in the ASH depth

Harder to calcifyPotential dissolution

Combined with a potential increase in water temperature by 3°C over a relatively rapid time, these key habitats are under threat

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• By 2100, ASH predicted to be much shallower than present day (Guinotte et al. 2006)

• Deep water calcifiers particularly vulnerable

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Aragonite Saturation Horizon depth:

1995

2100

• What are the long-term effects of increased CO2 and

temperature upon cold water corals- Single and synergistic effects

• Will acclimation occur?- To what extent?

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Aims:

Lophelia pertusa fromMingulay Reef ComplexCa. 180m

• Metabolism• Feeding• Carbon production• Respiration

•Calcification (growth)• Alkalinity anomaly• 45Ca or 14C uptake• Buoyant weight

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Methods – impacts of OA and warming

• Short term experiments on RSS Discovery (21 days)• 380 and 750ppm CO2

(pre-mixed gas bubbling)

• Long term at Heriot-Watt University (18 months)• Gas mixing system

(380, 750 and 1000ppm CO2)

• Two temperatures9°C, 12°C

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Methods – impacts of OA and warming

Results & Discussion: Short term

• Ocean Acidification – respiration

- L. pertusa respiration decreased in acidified conditions (750ppm) over 21 days compared to present day conditions

- Only different after 2 weeks

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Results & Discussion: Short term

• Ocean Acidification – growth (alkalinity anomaly technique)

- L. pertusa calcification rate (alkalinity anomaly) did not change in acidified conditions (750ppm) over 21 days

- Growth rate maintained despite decreased respiration (Large variability) – energetic reserves?

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Results & Discussion: Long Term•At T + 3 months:

•Control has highest respiration rate•Corals at elevated CO2 OR temperature had reduced respiration rates•Corals at elevated CO2 AND temperature had reduced respiration rates

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Control

1 stressor

2 stressors

Results & Discussion: Long Term

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• No significant difference between 750ppm and control. Differs from short term experiment• Acclimation• No difference in respiration between 750

and 1000ppm treatments• No difference in respiration between a

temperature increase, or increase in CO2

• Combined increase in CO2 and temperature• Significant reduction in respiration• Does this tie in with net growth (buoyant

weight?

• Buoyant weight:•Percentage mass change•0-3 months: 750,12C significantly lower growth than control•3-6 months: non significant growth across treatments

•Potentially higher growth in 12C? •Dead skeletons still to be cross compared

Results & Discussion

Conclusions:• Ocean Acidification

- Significant effects in short term, but acclimation occurs by T + 3 months (in terms of respiration).

- Net growth similar

• Temperature- Impact on respiration not significant at T+ 3 months. Enhanced growth?

• Combined effect (most likely scenario)- Significant reduction in respiration rate compared to controls at T+3

months

- Net growth reduced during this time but is this just short term?- Acclimation at what cost, and what are the limits? - To be continued (6 months data to finish processing, 12 and 18

month data to be collected)

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Future work:

• Using cold water corals to look at past climate history

• Funded NERC proposal

• Assessing internal pH regulation in tropical and cold water corals in present and predicted future conditions

• Submitted NERC fellowship

Future work: Where did all the CO2 go?Using cold water corals to reconstruct deglacial CO2 information (NERC)

Why?CO2 responsible for warming the earth during interglacial periods is most likely stored in the deep sea during the intervening cold glacial periods. However, there is much uncertainty over:

• How this happens• Where the CO2 is stored• How it rapidly reaches the surface and atmosphere during deglacials

How?Quantifying the boron fractionation within:1. Laboratory kept skeletons of cold water coral (calibration and validation)2. Historic samples of cold water coral (application)

Boron isotope fractionation in seawater strongly pH dependent, and by quantifying the amount in coral skeletons, we can calculate the ocean pH.

Dr. Laura Wicks, Prof Murray Roberts, Dr. Sebastian Hennige and Dr. Gavin Foster (NOC)

Future work:Coral pH regulation and ocean acidification: ‘winners and losers’

• Reef building corals (tropical and cold) can regulate their internal pH to offset external ocean acidification

• Is this the same across all coral species ?• What is the extent of this regulation under different conditions?• What is the energetic cost of such regulation?

Nearly impossible to determine in intact corals with conventional methods -therefore novel approaches needed

• Tissue cultures• pH dyes with confocal microscopy• Microelectrodes• Boron isotopes

Thanks to:• NERC• DEFRA• DECC• HW technical staff• RRS Discovery participants and crew

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For more information seewww.lophelia.org