Biologically mediated and abiotic mechanisms
for light enhanced calcification and the cost of
carbonates deposition in corals.
Giovanni Galli
Cosimo Solidoro
National Institute of Oceanography and Experimental Geophysics
(OGS), Trieste, Italy.
Some ways DEB theory can be useful also in
non-DEB models.
Giovanni Galli
Cosimo Solidoro
National Institute of Oceanography and Experimental Geophysics
(OGS), Trieste, Italy.
Coral calcification ecophysiology
• Coral Calcification is a key
process (reefs).
• Corals are colonies of polyps.
• Scale: polyp.
Coral calcification ecophysiology
TA
Ca2+
Ca2+
DIC
Coelenteron
(Gastro-vascular-etc. cavity)
Extracellular Calcifying Medium
(ECM)
TA
P
Skeleton:
CaCO3 + Organic Matter
DIC
R
DIC
TA
Ca2+
Coelenteron:
• Gastric cavity,
• most mass exchange processes (e.g.
P, R) are performed here.
ECM:
• sub-μm interface between living
tissue and skelton.
• The site of Calcification. .
• Active + passive transport.
Coral calcification ecophysiology
• Calcification is influenced by environmental variables (T,
DIC, TA, or pCO2) and by metabolic rates (P, R).
• abiotic and biologically mediated mechanisms:
• e.g. Temperature affects metabolic rates (hence also
calcification), but also high T fosters CaCO3 deposition (in an
abiotic framework).
Coral calcification ecophysiology
• The influence of sw chemistry
(acidification) is obvious:
•Ω=
𝐶𝑎2+ 𝐶𝑂32−
𝐾𝑠
• …but corals are not rocks…
• …skeleton not in direct contact
with sw.
• Active regulation of chem. at the
site of calcification (Al Horani ‘03).
• Requires an energetic investment.
Coral calcification ecophysiology
Metabolic Cost
Theoretical estimates:
• ΔGCoel-ECM, 3-6 kJ/mol (McCulloch ‘12).
• ΔGATP 30 kJ/mol (Anthony ‘03).
• ΔGATP + other transport, 20 kJ/mol
(Hohn ‘15).
Experimental estimates:
• 100/200 kJ/mol (Palmer ‘92, on mollusk).
• Poor prediction of
are fixed.
𝑑𝐽𝐶𝑎𝐶𝑂3
𝑑𝑝𝐻
if costs
• With low costs, little trouble in
allocating extra energy to
calcification (e.g. McCulloch ‘12).
Coral calcification ecophysiology
Light Enhanced Calcification
(LEC)
• On average 3x calcification rates
in the light (Gattuso ‘99).
• Mediated by symbiont
photosynthesis (Allemand ‘13).
• Controversial!
Coral calcification ecophysiology
[some] Hypotheses for LEC,
Biologically mediated:
• Precursors for OM synthesis.
• Oxygen hypothesis (Rinkevich and
Loya ‘84, Al-Horani et al. ‘07).
• ATP hypothesis (Crossland and Barnes
‘74, Chalker and Taylor ‘75).
Abiotic:
• P modifies C budget (Cohen ‘16).
• P modifies H+ budget (Furla ‘00).
Other:
• Dark-repressed calcification
(Marshall ‘96).
• Calcification-enhanced
photosynthesis (McConnaughey and
Whelan 1997).
The coral calcification model
• Each variable/process
has a two-fold effect:
• ‘abiotic’ & ‘biologically
mediated’.
• Comparing ‘bio’ and
‘abio’ effects on
calcification rates and
costs.
The coral calcification model
• After Hohn & Merico (‘12, ‘15), Nakamura
(‘13), McConnaughey and Whelan (‘97), …
• 2 compartments: Coel., ECM.
• CO2 system (@eq.ium).
• Metabolic rates: Pg, R (forced).
• 2 active + 2 passive pathways.
The coral calcification model
DEB-inspired feature I.
• Syntrophic symbiosis,
Zooxanthellae translocate
photosyntate to the host
(Dubinsky and Jokiel ’94; Muller et al. ’09).
The coral calcification model
DEB-inspired feature II.
• Energy expense for calcification
(active transport) is a weighted sum
of energy fluxes
(Fablet et al. ’11; Pecquerie et al. ’12).
𝛼 𝑃𝑔 + 𝛽 𝑅
𝐴𝑇𝑃 =
Δ𝐺𝐴𝑇𝑃
• i.e. CaCO3 is a metabolic product
(sensu Kooijman ‘10).
The coral calcification model
DEB-inspired feature III.
Modelling active transport:
• Membrane transport proteins.
• Ion transport against
concentration gradient.
• Fuelled by metabolic energy.
• Lumping scheme for fast reactions:
from 15 to 4 states,
(Smith & Crampin ’04).
• DEB’s Synthesizing Unit.
Kooijman ‘10
• Cyclic enzimatic reaction, fw & bw
cycle.
Smith & Crampin ‘04
• Model of active ion transport (NaK antiporter, Läuger & Apell ’86).
Läuger & Apell ‘86
The coral calcification model
The coral calcification model
• Ca-ATPase + BAT.
Assumptions:
• 𝐶𝑎2+ = 𝜅 𝐶𝑎2+
• Coel. & ECM in direct
connection (not true but realistic
at steady state).
• Fast binding of Ca2+ and sth.+
due to high sw concentration
(e.g. Na+) → 3-stage reaction.
The coral calcification model
+
𝐸1𝑐 + 2𝐻𝑒𝑐𝑚
⇌ 𝐸2𝑐
𝐸2𝑐 + 𝐴𝑇𝑃 ⇌ 𝐸3𝑐
+
𝐸3𝑐 ⇌ 𝐸1𝑐 + 2𝐻𝑐𝑜𝑒𝑙
𝑑𝐸1
+
= −𝑘1𝑓 𝐸1 𝐻𝑒𝑐𝑚
𝑑𝑡
𝑑𝐸2
+
= 𝑘1𝑓 𝐸1 𝐻𝑒𝑐𝑚
𝑑𝑡
2
2
+
+ 𝑘1𝑏 𝐸2 + 𝑘3𝑓 𝐸3 − 𝑘3𝑏 𝐸1 𝐻𝑐𝑜𝑒𝑙
− 𝑘1𝑏 𝐸2 − 𝑘2𝑓 𝐸2 𝐴𝑇𝑃 + 𝑘2𝑏 𝐸3
𝑑𝐸3
+
= 𝑘2𝑓 𝐸2 𝐴𝑇𝑃 − 𝑘2𝑏 𝐸3 − 𝑘3𝑓 𝐸3 + 𝑘3𝑏 𝐸1 𝐻𝑐𝑜𝑒𝑙
𝑑𝑡
𝐸0 = 𝐸1 + 𝐸2 + 𝐸3
2
2
The coral calcification model
𝐽𝐶𝑎𝐴𝑇𝑃𝑎𝑠𝑒 =
+
𝐸0 𝑘1𝑓 𝑘2𝑓 𝑘3𝑓 𝐴𝑇𝑃 𝐻𝑒𝑐𝑚
+
− 𝑘1𝑏 𝑘2𝑏 𝑘3𝑏 𝐻𝑐𝑜𝑒𝑙
𝑑𝑒𝑛
𝑑𝑒𝑛=
+
𝑘2𝑓 𝑘3𝑓 𝐴𝑇𝑃 + 𝑘2𝑓 𝑘3𝑏 𝐻𝑐𝑜𝑒𝑙
2
+
+ 𝑘1𝑓 𝑘3𝑓 𝐻𝑒𝑐𝑚
+
+ 𝑘1𝑓 𝑘2𝑏 𝐻𝑒𝑐𝑚
2
2
2
+
𝐴𝑇𝑃 + 𝑘1𝑓 𝑘2𝑓 2𝐻𝑒𝑐𝑚
𝐴𝑇𝑃
+
+ 𝑘2𝑏 𝑘3𝑏 𝐻𝑐𝑜𝑒𝑙
2
+ 𝑘1𝑏 𝑘2𝑏 + 𝑘1𝑏 𝑘3𝑓
+
+ 𝑘1𝑏 𝑘3𝑏 𝐻𝑐𝑜𝑒𝑙
2
2
The coral calcification model
• Calibration data from RodolfoMetalpa et al. ‘10.
• Mediterranean Cladocora
caespitosa (acidificationresistent, no reef builder).
• 2x pCO2 (400, 700ppm), 4x T°C
(win/sum, T, T+3°C), 2x
light/dark. n=16.
• CO2 sys., Pg, R, JCaCO3.
The coral calcification model
Comparing bio & abio effects on
calcification for T, DIC, TA, P, R:
• Multiple model runs at each of the
experimental conditions (n=16) in
Rodolfo-Metalpa et al. ’10.
• Each variable/process tuned ±5%
its baseline value while keeping the
rest unchanged (1° order approx.
but workin’ on it).
Results
• Good fit to data.
• Cost ~100-200 kJ/mol (higher
than theoretical estimates, lower
than ‘structure’ costs)…
• Light cost > dark cost…
• ‘acid’ cost > baseline cost
Results
Temperature:
• ‘bio’ effects >> ‘abio’ effects.
• Costs rise with T, despite abio
effects (see McCulloch ‘12).
Results
Photosynthesis (LEC)
• ‘bio’ effects >> ‘abio’ effects.
• LEC is less efficient than nonLEC (costs rise)…
• …but still has higher rates thanks
to energy surplus.
Results
Respiration:
• ‘bio’ effects >> ‘abio’ effects.
• Same ‘bio’, opposite ‘abio’
effects of Pg and R.
Results
DIC & TA
• DIC’s ‘bio’ effects ~= ‘abio’
effects…
• Sharp increase in costs at high
DIC…
• …problematic to allocate extra
energy to calcification in OA
scenario.
Conclusions
• In coral science problems are often
addressed form a carbonates
chemistry perspective…
• According to results, the
calcification machinery is mostly
under biological control.
• …Because acidification effects are
very obvious…
• The ‘energy hypothesis’, although
overlooked provides a plasible
mechanism for LEC.
• …and the sw carbonates system is
well understood.
• A bioenergetic approach can shed
new light on coral ecophysiology.