Pneumatocyst

This article is about algae. For lung and other pneumatocysts, see pneumatocele. For the similarly pronounced stinging cells, see nematocyst.

In phycology, a pneumatocyst is a floating structure that contains gas found on brown seaweed. A seaweed's thallus may have more than one. They provide buoyancy to lift the blades toward the surface, allowing them to receive more sunlight for photosynthesis.

Floating kelp (Macrocystis pyrifera) with many pneumatocysts

The proportion of gases in the pneumatocysts varies depending on the physiological status of the alga and the partial pressure of gases in the surrounding air or water.^[1] The pneumatocyst can hold O₂, CO₂, N₂,^[1] and CO.^[2]

Pneumatocyst from Nereocystis luetkeana