Biological impact of elevated ocean CO2 concentrations: lessons from animal physiology and earth history Hans O. Pörtner

Observations: Atmospheric O2 and CO2 levels in earth history Present Level 600 400 300 200 100 500 35 0.5 0.4 0.3 0.2 0.1 30 25 20 15 10 5 Concentration (%) CO2 C O Tr P S D T J K O2 Perm Trias Jurassic Cretaceous Tertiary Cambrian Ordovician Silurian Devonian Carboni- ferous MY before present Late evolution of high species nos. high performance, high activity lifeforms dependent on low CO2 levels? important mass extinction periods Levels are long term means, did short term oscillations occur? after Ruben 1995, 1996, Dudley, 1998

Parallel oscillations of temperature and oxygen levels CO2 „experiments“ in earth history: Water CO2 oscillations in Perm / Trias mass extinctions A warm CO 2 Preconditions in Perm/Trias: No surface to deep ocean currents Pangaea as a super-continent d 13 C ­ Photosynthesis CO 2 Sulfate reduction d 13 C ¯ HCO - H H 2 2 S S cold 3 CO B 2 Glacier H 2 S - up to 1 % (10 000 ppm) CO 2 HCO 3 Did such a situation exist before in earth history? redrawn after Knoll et al. , 1996 Parallel oscillations of temperature and oxygen levels CO2 critical in mass extinctions?

CO2 as a natural factor nowadays, in areas with marine life: - constantly low in most of the pelagic zones of the sea (<500 ppm). - fluctuates when - volcanic emissions occur in the sea (~ 80 000 ppm). - excessive respiration occurs in confined areas hypoxic: rock­pools, sandy sediments, oxygen minimum layers anoxic: marine sediments, stratified bottom waters (up to 16 000 ppm)

Anthropogenic CO2 in the world‘s ocean over time 5000 GtC released, no intentional storage surface waters: up to – 0.77 ΔpH, 1900 ppm CO2 variable bodies of water with - 0.2 to 0.4 pH units 550 ppm CO2 Depth (km) 5000 GtC 550 ppm stabilized <90 % in geol. stor., 10 % leakage 5000 GtC 550 ppm stabilized <100% stored no leakage Biological impact? modified after Caldeira and Wickett, 2003, 2004

A role for ecological and evolutionary physiology What makes organisms susceptible to CO2? Sensitivities differ between organisms, why? Which levels are critical? A role for ecological and evolutionary physiology

Competition with vertebrates led to maximized performance levels and metabolic rates (10 x fish!). Acute effects of high CO2 levels: Squid, elite athletes of the ocean: Illex illecebrosus Lolliguncula brevis Loligo pealei

Squid haemocyanin function during exercise, pH / saturation analysis: extreme pH sensitivity Illex illecebrosus 50 % 100 % 0 % 14.7 PO2 (mm Hg) 146 97 59 28 100 80 60 40 20 7.0 7.4 7.8 8.2 % Saturation 24.8 pHe Ca Ev Ea 2000 ppm 6500 ppm Haemocyanin molecule not relevant for leakage - ∆blood pH > 0.15 (∆Pco2 > 2 000 ppm) reduced scope for activity (sublethal). - ∆blood pH > 0.25 (∆Pco2 > 6 500 ppm) asphyxiation (acutely lethal). Pörtner et al., 2004

CO2 Long term effects at moderate CO2 levels: 15 to 85 % reduction in calcification rates… …due to reduced carbonate levels with a doubling of CO2 (Sabine et al., 2004) CO2 Hoegh-Guldberg, 2004, Source: J. Kleypas

Long term effects in non-calcifying animal species tolerant to CO2 oscillations? Sipunculus nudus eurybathic: found between 0 and 2300 m depths

S. nudus: Extra- and intracellular acid-base status CO2 induced metabolic depression: physiological background S. nudus: Extra- and intracellular acid-base status partial compensation Blood Only partial compensation of extracellular acidosis causing metabolic depression: A typical finding in invertebrates! full compensation Muscle after Pörtner et al. 1998

Reduced exercise capacity Not just pH! Metabolic and behavioral depression caused by adenosine accumulation in nervous tissue of S. nudus Reduced exercise capacity and activity Reipschläger et al., 1997

Metabolic depression and 55 % ( Metabolic depression and 55 % (!) growth reduction in mussels (Mytilus galloprovincialis) under CO2 (permanent extracellular acidosis!!) © M.S. Calle control Water pH 7.3: Maximum pH drop as expected from business as usual scenarios by 2300 (Caldeira and Wickett, 2003) hypercapnia Michailidis et al. (2004)

Control animals repeatedly reburying into sediment 1 % CO2 early 1% CO2 late 3 % CO2 However, tolerance is time limited: Delayed onset of enhanced mortality during long term „disturbed“ maintenance under 1 % CO2 in S. nudus Control animals repeatedly reburying into sediment % Survivors no decrease in body energy stores behavioral incapacitation involved Days of incubation Langenbuch et al. (2004)

Uncompensated acidosis and metabolic depression in several invertebrates Mytilus galloprovincialis Sipunculus nudus …contributing to lower resistance and enhanced mortality? Sepia officinalis ©CephBase Compensated acidosis and, therefore, no metabolic depression in most fish …a reason for enhanced resistance to high CO2? Pachycara brachycephalum Atlantic cod Gadus morhua Antarctic eelpout Heisler, 1986, Larsen et al. 1997, Ishimatsu et al., 2004

Further findings Shirayama and colleagues: - long term reduction of growth, survival, and reproduction in Pacific shallow water sea urchins and snails at 550 ppm CO2, - reduced fertilization of copepod eggs at CO2 levels beyond 1000 ppm. Rates of higher functions are reduced under moderate CO2 elevations. Effects set in early in invertebrates.

Mortality independent on CO2 level and exposure time Principle considerations: Role of time scales and levels for CO2 exposure to become lethal Incipient lethal CO2 level (long term critical threshold) arbitrary units Mortality independent of exposure time Zone of resistance Mortality dependent on CO2 level and exposure time Zone of tolerance Upper median lethal CO2 level (LD50) log exposure time (days, weeks, months, years) → †Acute asphyxiation: squid, fish …..do we know the key physiological mechanisms affected by CO2? No such complete data set exists Critical level and mechanism unknown Tolerable organism and ecosystem (?) responses Pörtner et al., 2004

…..mechanisms also affected by hypoxia and temperature extremes!! CO2 effects: complex physiological background shifting whole animal functioning still incomplete!! …..mechanisms also affected by hypoxia and temperature extremes!! complex physiological background behind higher functions Pörtner et al. 2004

a unifying principle in ectotherms (!) and endotherms (!?). Temperature, hypoxia, CO2 interactions? A recent hypothesis: The first level of thermal intolerance at low and high temperature extremes in METAZOA is a loss in whole organism metabolic flexibility (aerobic scope), a unifying principle in ectotherms (!) and endotherms (!?). Am. J. Physiol 279, R1531-R1538, 2000. Naturw. 88, 137-146, 2001 Am. J. Physiol. 283, R1254- R1262, 2002 Comp. Biochem. Physiol. 132A, 739-761, 2002

affecting growth, exercise, behaviours, reproduction, ….fitness Tp Tp : Pejus T‘s: onset of limitation in aerobic scope Hypoxia, CO2 and thermal extremes act synergistically via the same physiological mechanisms!! Hypoxia, CO2 affecting growth, exercise, behaviours, reproduction, ….fitness 100 Tc % oxygen limited aerobic scope Tc : Critical T‘s: onset of anaerobic metabolism Temperature Cardiac + ventila- tory output functional capacity of oxygen supply Qrest • Qmax after Farrell max Aerobic scope and performance are maximal at the upper pejus temperature. rate of aerobic perfor- mance temperature after Frederich and Pörtner 2000, Mark et al. 2002 Pörtner et al. 2000, 2004, Pörtner 2001, 2002,

…..interaction with CO2 effects? Temperate crustacean, Maja squinado EXAMPLES Temperate cephalopod, Sepia officinalis Antarctic bivalve, Laternula elliptica O2 dependent temperature limits verified across phyla: annelids, sipunculids, molluscs (bivalves, cephalopods), crustaceans, fish and some air breathers, limited evidence in endotherms incl. man. …..interaction with CO2 effects? Atlantic cod, Gadus morhua Antarctic and temperate zoarcids, Pachycara brachycephalum, Zoarces viviparus

Combined effects of CO2 accumulation and global warming: Marginalization of coral reef cover as a special case Pre-industrial pCO2 : 280 ppm carbonate saturation state (Warag) 2060-69; pCO2 : 517 ppm warmer temperatures Hoegh-Guldberg (2004)

Animal limitations in high CO2 oceans Progressive (not beyond critical thresholds?) effects already expected in 450 to 750 ppm surface ecosystems shifted ecosystem equilibra caused by: reduced calcification rates higher ratios of non-calcifiers over calcifiers reduced tolerance to thermal extremes enhanced geographical distribution shifts reduced distribution ranges reduced behavioral capacity, growth, productivity and life span food chain length and composition reduced population densities, ……biodiversity (critical!)? Research needs to further identify mechanisms, titrate/quantify (lab and field) scenarios, address micro-evolutionary potential

CLIMATE CHANGE, CO2 effects, ENERGY BUDGETS Dr. Christian Bock Carsten Burkhard Dr. Martina Langenbuch Dr. Vasilis Michailidis Dr. Anke Reipschläger Susann Schmidt Rolf-M. Wittig

CO2 limitations relevant in evolution? Number of genera severest losses Permian-Triassic mass extinctions Loss of marine invertebrate genera due to CO2? Articulates = Crinoids belonging to echinoderms Obs: highest activity forms were not yet existent!! Physiological characters of eliminated forms? moderately active, moderate calcification sessile, hypometabolic, calcified: larger effect? Pörtner et al., 2004 after Knoll et al., 1996

Processes and Limits: Effects of integrated CO2, O2 and temperature fluctuations CO2 impacts on: Hypoxia tolerance ↑ → Improved extension of passive survival (limited!) BUT Metabolic flexibility (Aerobic scope) ↓ → Long term performance and growth functions ↓ → Thermal tolerance ↓ (tolerance to thermal fluctuations ↓) These interactions and not CO2 alone have likely shaped evolutionary scenarios! Pörtner et al., 2004

Long term effects at moderate CO2 levels: decreased calcification CO2 + H2O + CaCO3 <=> 2 HCO3 + Ca2+ Warag = [Ca2+][CO32-] / K’sp K’sp: solubility product for aragonite. Warag > 1: super-saturation, required for calcification

Close correlation between dry / wet weight and shell length Reduced growth affects shell and soft body alike not just calcification!! dry weight Michailidis et al. (2004)

© M.S. Calle Oxygen consumption control hypercapnia hypercapnia Mytilus galloprovincialis under hypercapnia (water pH 7.3): 65% (!) metabolic depression associated with enhanced N excretion, i.e. protein degradation during permanent (extracellular) acidosis (as seen in S. nudus) control Ammonia excretion Pörtner et al. (1998) Michailidis et al. (2004)

Reduced cellular protein synthesis during acidosis favouring amino acid catabolism in S. nudus ….likely causing reduced growth rates Langenbuch et al. 2004.

Animals died despite return to normocapnia!!! Recent data: Uncompensated intracellular acidosis in cuttlefish (S. officinalis) brain under 24 h of hypercapnia (1%) Sepia officinalis intracellular pH Animals died despite return to normocapnia!!! S. Schmidt, C. Bock, H.O. Pörtner, unpubl.