Are cold-water coral reefs canaries in the coal mine of climate change, and what can we do about ?
J Murray Roberts
iAtlantic / OneOcean Webinar
19 Feb 2021
@jmurrayroberts @changing_oceans Plan today
• What are cold-water corals? • Why might they be vulnerable to human activities & climatic changes? • How do we study coral responses to changing ocean conditions? • Can cold-water corals deal with these changes? • What can we do about it?
Image: Rohan Holt Warming
Acidification Deoxygenation
Destructive human use • • • • https://www.frontiersin.org/articles/10.3389/fmars.2018.00460/full Significant Marine Areas by UN CBD (https://www.cbd.int/ebsa/about UN FAO use to define Vulnerable Marine Ecosystems (VMEs) functionality, fragility, life-history and structural complexity See ATLAS project’s VME indicator database ( CWCs also meet the criteria used to define Ecologically or Biologically CWCs meet many (most) of the indicator criteria related to their rarity, For further details http://www.eu-atlas.org/resources/atlas-library.html used by the ) )
Roberts et al. (2009) Cambridge University Press • Abyssal temp ↑ 1◦C within 84 years • O2 declines in areas deep-water formation • Up to 40-55% ↓ in POC flux in some regions • Rapid pH ↓ at bathyal depths What is a coral?
• Not a taxonomic term, equivalent to ‘bug’, ‘worm’ etc.
• Defined by Cairns (2007) ‘Animals in the cnidarian classes Anthozoa and Hydrozoa that produce either calcium carbonate (aragonitic or calcitic) secretions resulting in a continuous skeleton or as numerous microscopic, individualised sclerites, or that have a black, horn-like, proteinaceous axis.’
• The 5 cold-water coral taxa... Taxon Common names No. species No. spp >50 m
Phylum Cnidaria (= Coelenterata)
Class Anthozoa hard corals, stony corals, true corals, cup corals, star corals, solitary Subclass Hexacorallia (= Zoantharia) corals, zooxanthellate corals, azooxanthellate corals Order Scleractinia (= Madreporaria) 1488 622
Order Zoanthidea (in part) zoanthids, gold coral (Gerardia spp.) 3 3
Order Antipatharia black corals, whip corals, wire corals, thorny corals *241 *182
Subclass Octocorallia (= Alcyonaria) soft corals, gorgonians, sea fans, sea whips, sea feathers, precious *3159 *2325
corals, pink coral, red coral, golden corals, bamboo corals, leather
corals, horny corals, sea pens
Class Hydrozoa
Subclass Hydroidolina athecate hydroids • As of early 2007 there were
Order Anthoathecata (= Athecata) 5,160 species of coral
Suborder Filifera • 65% of these occur in water Family Stylasteridae ‘hydrocorals’, lace corals, stylasterids 249 223 >50 m deep Family Hydractiniidae (in part) longhorn hydrozoans (Janaria, Hydrocorella) 3 1 • There are more coral species in Suborder Capitata deep waters than on shallow
Family Milleporidae ‘hydrocorals’, fire corals, millepores 17 0 tropical reefs
Total *5160 *3356 Lophelia pertusa (Desmophyllum pertusum – see advisory on WORMS)
Guinotte et al. (2006) Frontiers in Ecology & the Environment 4: 141-146 after Orr et al. (2005) Nature 437: 681-686 Known distribution of Lophelia, Madrepora, Solenosmilia
Roberts et al. (2006) Science 312: 543
Freiwald (JAGO submersible) Known distribution of Lophelia, Madrepora, Solenosmilia
Roberts et al. (2006) Science 312: 543 Alberto Lindner (NOAA Fisheries) Victoria O’Connel (Alaska Department of Fish & Game) Guinotte et al. (2006) Frontiers in Ecology & the Environment 4: 141-146 after Orr et al. (2005) Nature 437: 681-686 How do corals grow?
• To calcify a coral must bring calcium ions (Ca2+) and Dissolved Inorganic C (DIC) together • At typical surface pH of seawater (8.2), 89% of DIC is bicarbonate - 2- (HCO3 ), 10.5% is carbonate (CO3 ) and 0.5% is carbon dioxide (CO2)
2+ - Ca + 2HCO3 ⇔ CaCO3 + CO2 + H2O 2+ 2- Ca + CO3 ⇔ CaCO3
‘Bjerrum plot’
At pH 8.2 - 89% HCO3 2- 10.5% CO3 0.5% CO2 Seawater carbonate chemistry
• DIC = CO2, carbonic acid, bicarbonate, carbonate • Equilibria between these depends upon temp, salinity, pressure and + pH = -log10[H ]
- + 2- + CO2 + H2O ↔ H2CO3 ↔ HCO3 + H ↔ CO3 + 2H
• Total alkalinity (AT) seawater is concentration of all bases that can accept protons. An index of seawater’s buffering capacity
Seawater carbonate chemistry • Calcium carbonate saturation state (Ω)
2+ 2- * Ω = [Ca ] [CO3 ] / K sp
Ω =1 system at equilibrium; Ω <1 system undersaturated; Ω >1 system saturated
* • K sp is the stoichiometric solubility product • Solubility CaCO3 increases with depth • Aragonite more soluble (lower Ω) than calcite so saturation horizon is shallower.
Nice overview with more detail: https://www.nap.edu/read/12904/chapter/4 Coral calcification remains a ‘black box’
• Two famous schools of thought:
- ‘Physicochemical school’, calcification in extracellular calcifying fluid beneath calicoblastic cells of endoderm
- ‘Organic matrix school’, calcification mediated via an organic matrix secreted by the coral
• See Cohen & McConnaughey (2003) & Tambutté et al (2007b) for more information Schematic representation of coral calcification and dissolution, showing how the saturation state of the calcifying fluid (shaded dark blue; vertically exaggerated) is affected by external pH and the strength of the H+ pump. The latter might be weak, moderate or strong; for strong H+ -pumping corals, the rate of gross calcification may initially increase under increased CO2 levels, as shown in the inset graph, while net calcification rates may decline owing to dissolution of exposed skeleton. From[16]. Nature Climate Change 1: 294-295, © 2011 Coral calcification
• Some corals incorporate significant amounts of C from respired CO2 into skeletal CaCO3 • Carbonic anhydrase (CA) catalyses:
- + CO2 + H2O ⇔ HCO3 + H
• CA located histochemically in calicoblastic epithelium and evidence that it is present in organic matrix proteins
Take home message – corals are really good at controlling the pH at the site of calcification. But….. CO2 If water corrosive
Energy to CaCO3, needed! exposed skeletons will dissolve
Schematic representation of coral calcification and dissolution, showing how the saturation state of the calcifying fluid (shaded dark blue; vertically exaggerated) is affected by external pH and the strength of the H+ pump. The latter might be weak, moderate or strong; for strong H+ -pumping corals, the rate of gross calcification may initially increase under increased CO2 levels, as shown in the inset graph, while net calcification rates may decline owing to dissolution of exposed skeleton. From[16]. Nature Climate Change 1: 294-295, © 2011 Let’s recap ocean ‘acidification’ protons
- + 2- + CO2 + H2O ↔ H2CO3 ↔ HCO3 + H ↔ CO3 + 2H
bicarbonate carbonic ions acid carbonate ions
Pre-industrial atmospheric CO2 280 ppm
Forecasts to >1000 ppm by 2100
https://www.co2.earth/ CO2 dissolution...
• Increased acidity (although not acid conditions) • Lower pH 2- - • Reduce concentration carbonate (CO3 ) relative to bicarbonate (HCO3 )
• Orr et al (2005) modelled effects of CO2 release on carbonate saturation state • Under IPCC ‘business-as-usual’ scenario IS92a projections show S Ocean undersaturated w.r.t aragonite by 2050 & rapid shoaling of ASH by 2100 Modelled depth of the aragonite saturation horizon (a) for year 1765, pCO2 278 ppm; (b) for year 2040, pCO2 513 ppm; (c) for year 2099, pCO2 788 ppm. Green triangles show locations of reef framework-forming scleractinian cold- water corals. Lines are diversity contours for 706 species of azooxanthellate scleractinian corals (see Fig. 2.20, p. 00). Black areas appearing in previously coloured portions of the Southern Ocean and North Pacific in image (c) indicate areas where the ASH depth has reached the surface. Figures reproduced from Guinotte et al. (2006) OA rate today is faster than at any point in last 55 million years
• Rate of CO2 release is unprecedented in geological history
• Buffering by rock weathering (~8 kyr) & deep-sea carbonate sediment dissolution (~2 kyr) cannot keep pace
• Therefore pH and CaCO3 saturation state both decline
Gattuso et al. (2011); Ridgwell & Hargreaves (2007) Tropical coral reefs
Cold-water coral reefs • Aragonite saturation horizon could shoal by 1000–1700 m in the subpolar North Atlantic within the next three decades.
• Present-day transport of carbonate ions towards the deep ocean is about 44% lower than in preindustrial times.
• Doubling CO2 levels within next three decades could reduce the transport of excess of carbonate over aragonite saturation by 64–79 % of preindustrial times Summer 2012...
Roberts et al. (2005) Coral Reefs 24:654-669 Roberts et al. (2009) MEPS 397: 139-151 Hydrography & food supply
• Intensive study of Mingulay Reef Complex
• Landers, moorings, CTD transects and yo-yo sampling
• Rapid downwelling interpreted as a ‘hydraulic jump’
• Second potential food supply from advected bottom waters
Davies et al. 2009 Limnology & Oceanography 54: 620-629 Davies et al. 2009 Limnology & Oceanography 54: 620-629 Scanfish data 2009 Dmitry Aleynik & Mark Inall (SAMS) Murray Roberts (SAMS/UoE)
1. Temperature
2. Salinity
3. Fluorescence
Long-term experiment
• “Future oceans” mesocosms • 80 tanks
• ↑ Temperature
• ↑ CO2 • Combinations of both (9°C 380ppm; 12°C 380ppm; 9°C 750ppm; 12°C 750; 9°C 1000ppm)
• One year incubation period • Growth • Physiology • Biomineralisation • Strength analysis of skeletons
Short term: Variable responses No change or a decrease in calcification and respiration
Mid – Long term: appear to acclimate and continue growing and respiring at ‘normal’ rates
Typical acclimation responses as organisms reallocate energy, pathways to cope Growth rates: • Significant negative correlation with increasing CO2 : Driven by dissolution in high CO2 treatment
Growth forms: • Growth form of new polyps significantly changes
• New polyps are longer and thinner under high CO2 Electron backscatter diffraction of newly-grown polyps
EBSD shows orientation and organization of aragonite crystal bundles • Control is most organized structure
• Under elevated CO2 has poorly organized crystals
Facies
35
R² = 0.947 Weakened skeletons 30
25 breaking force 20
15 Normalised
10 400 500 600 700 800 900 1000 1100 pCO2
• Decreased structural strength after 1 year exposure 123 • Skeletons 20-30% weaker • Impact likely underestimated; Bioeroding sponges will also weaken skeletons more efficiently under 1,2 high CO2 conditions
1Wisshak et al. 2012; 2014, 2Beuck et al. 2007 Skeleton protected by tissue
Skeleton exposed to ocean acidification
SEM images: S. Hennige Coral image: Solvin Zankl, BIOACID OK. But does this translate to the real world?
Is there a place where Lophelia grows under carbonate chemistry conditions analogous to those we’ll see in the future? Guinotte et al. (2006) Frontiers in Ecology & the Environment 4: 141-146 after Orr et al. (2005) Nature 437: 681-686 Corals above Aragonite Saturation Horizon Corals below Aragonite Saturation Horizon
20 cm 20 cm
Synchrotron Reconstructed Coral Images
Animation from Hennige, Wolfram, & Wickes et al., 2020. Crumbling Reefs and cold-water coral habitat loss in a future ocean: evidence of ‘coralporosis’ as an indicator of habitat integrity. Frontiers in Marine Science 7:668 Skeleton protected by tissue Skeleton exposed to dissolution Animation from Hennige et al., 2020. Crumbling Reefs and cold-water coral habitat loss in a future ocean: evidence of ‘coralporosis’ as an indicator of habitat integrity. Frontiers in Marine Science 7:668 Crumbling Reefs Mechanism
Figure from Hennige, Wolfram, & Wickes et al., 2020. Crumbling Reefs and cold-water coral habitat loss in a future ocean: evidence of ‘coralporosis’ as an indicator of habitat integrity. Frontiers in Marine Science 7:668 Multiscale and Current Knowledge Gap
Image from Hennige, Wolfram, & Wickes et al., 2020. Crumbling Reefs and cold-water coral habitat loss in a future ocean: evidence of ‘coralporosis’ as an indicator of habitat integrity. Frontiers in Marine Science 7:668 PhD Research Questions Kelsey Archer-Barnhill
• Do multiple driver interactions have a synergistic or antagonistic effect on live and dead CWC? • How do live CWC react to long-term low oxygen levels? • What is the dead CWC skeletal porosity extent at different Intergovernmental
Panel on Climate Change CO2 projections? • What will CWC reef conditions be in the future?
Image from https://www.dw.com/en/cold-water-corals-tough-times-ahead-in-a-warming-climate/a-39328756 Tjärnö Marine Laboratorium Microcosm Experimental Design
Treatment Parameters Samples Ambient Live and Control Conditions Dead
Triple Stressor: -20 μmol/Kg O2, ↓O2 ↓pH Live and +2°C, 750 ppm CO2 ↑temp Dead Live and Single Stressor: -20 μmol/Kg O ↓O2 2 Dead
Single Stressor: 750 ppm CO2 ↓pH Dead
Single Stressor: 1000 ppm CO2 ↓↓pH Dead
Single Stressor: Extreme CO2 ↓↓↓pH Dead
One Year
Multidisciplinary A new understanding Approach of deep Atlantic ecosystems
Valuing ecosystems
Better spatial planning
Science/Policy interface +56 co-authors (in press)
Morato et al. Ecologically or Biologically Significant Marine Areas (EBSAs)
1. Case Study 7 - Gulf of Cádiz: Coral gardens and sponges at Gazul mud volcano 2. Case Study 9 - Reykjanes Ridge: Hydrothermal vents, Lophelia reefs, sponges 3. Case Study 10 - Davis Strait: Highly diverse sponge communities 4. Tropic Seamount: discovery diverse seamount communities including stalked Poliopogon sponge fields iAtlantic Expeditions (dashed red lines) Partner cruises (dashed white lines) Ocean monitoring arrays (black lines) ARGO floats (grey circles)
• 35 partners, 2 subcontractors, 12 associate partners • €10.6M budget with €30M expedition programme • 12 focal Study Regions 2019 1. Ocean Observation 2. Ocean Mapping 5 Objectives to enhance 3. Ecosystem Assessment 4. Capacity Building 5. Sustainable Management
2020
@iAtlanticEU @iAtlanticEU www.iatlantic.eu [email protected] So, are CWCs canaries in the coal mine of climate change? Unfortunately, yes they are.
• Bottom line – reducing emissions is the priority • Understand implications multiple stressors • Smart spatial management informed by connectivity & climate refugia • Engage all sectors – government, industry, public young & old alike • Don’t be afraid of interdisciplinarity or the science/policy interface • Keep optimistic!
https://www.dosi-project.org/ @iAtlanticEU @iAtlanticEU www.iatlantic.eu [email protected]
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 818123 (iAtlantic). This output reflects only the author’s view and the European Union cannot be held responsible for any use that may be made of the information contained therein. Over the last 20 years we’ve seen an exponential increase in our understanding of cold-water coral habitats and just how important they are to a whole range of ecosystem functions from habitat provision through to nutrient recycling. Over the same period it’s become clear that ocean conditions are changing at rates faster than at any point in geological history. The few species of cold-water coral that form deep-water reef frameworks build their skeletons from aragonite, a mineral form of calcium carbonate particularly vulnerable to ocean acidification. Since cold-water coral reefs grow in seawater already close to the point aragonite dissolves these coral skeletons are very vulnerable to the rapid changes in carbonate chemistry we see spreading across the oceans of the world. Quite a few studies have now explored the effects of ocean acidification on cold-water corals but fewer have looked at the combined effects of other global changes – notably temperature increase or deoxygenation, and very few have looked at the implications of these changes on the dead coral frameworks that are the foundations of cold-water coral reefs. Our research has shown that the dead coral foundations of cold-water corals fundamentally altered by ocean acidification. The skeletons become porous, brittle with symptoms much like osteoporosis in humans. Given the very long time periods any CO2 emission reduction targets will take to reach, it’s vital we do all we can to manage other pressures and look to ensure cold-water corals in climate refugia are fully protected.