Ocean Acidification: Shell Dissolution & Food-Web Collapse

Ocean Chemistry

Atmospheric CO₂ 280 ppm

Warming anomaly 0.0 °C

Fishing pressure on predators low

Live Readouts

8.10

Ω (aragonite)

3.40

Avg shell integrity

100%

Years elapsed

Biodiversity index100%

Pteropods

100%

Predatory fish

100%

How it works

Dissolved CO₂ forms carbonic acid, lowering seawater pH and, with it, the concentration of carbonate ions that shelled plankton need to build calcium carbonate shells. This model runs a simplified but structurally real three-step cascade:

pH(CO2)   = 8.1 − 1.3·log10(CO2 / 280)
Ω(pH)     = 3.4 · 10^(1.5·(pH − 8.1))      [aragonite saturation]
dShell/dt = +g·(Ω−1)  if Ω≥1,  −k·(1−Ω)  if Ω<1   [shell grows / dissolves]

Pteropods (free-swimming sea-butterfly snails) are a keystone prey species — their aragonite shells dissolve directly when Ω drops below 1 (undersaturated water). Population follows logistic growth reduced by shell damage and fishing-driven predator release:

dP/dt = r·P·(1−P/K) − m·(1−shell)·P
dF/dt = a·P·F − d·F − h·F        [fish feed on pteropods, h = fishing pressure]
Biodiversity index = weighted geometric mean of shell integrity, P/K, F/K

Turn up CO₂ and Ω falls below 1 (undersaturation) — shells stop forming faster than they dissolve, the pteropod population collapses, and predatory fish that depend on them follow with a lag. This mirrors real observations off the US West Coast and in the Southern Ocean, where pteropod shells have already been found measurably pitted and dissolving in acidified upwelled water.

Healthy pteropod shell Dissolving shell (Ω<1) Predatory fish

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