pneumatocysten

Pneumatocysts, known in Dutch as pneumatocysten, are gas-filled buoyant structures found in certain brown algae (Phaeophyceae), notably the large kelps of the order Laminariales such as Macrocystis and Nereocystis, and in some Sargassum species. These structures provide buoyancy, keeping fronds near the water surface to maximize light for photosynthesis.

They are hollow sacs connected to the thallus by a stalk. They form as gas-filled chambers within the blade tissues; in some species they develop from specialized cells that secrete or accumulate gases. The gas inside is a mixture of gases produced by photosynthesis and exchanged with seawater, often including carbon dioxide, oxygen, and nitrogen. The walls are relatively thin and permeable, allowing gas exchange with the surrounding seawater.

Functionally, pneumatocysts enable vertical positioning of kelp blades toward the surface where light is strongest, thereby supporting growth and photosynthesis. Ecologically, drifting pneumatocysts and detached kelp can form surface mats that provide habitat for plankton and small invertebrates, influence nutrient cycling, and contribute to carbon transport. Sizes vary from a few centimeters to several tens of centimeters in diameter, depending on species and environmental conditions.

In marine ecology and aquaculture, understanding buoyancy provided by pneumatocysts helps explain the distribution of kelp forests and informs practices related to cultivation and harvest. They are a characteristic feature of many large brown algae and play a key role in their life strategy.