The Buoyant Properties of Codium

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Abstract
Factors contributing to the buoyant properties of C. fragile ssp. tomentosoides were examined. The intracellular fluid has a low K/Na ratio and low SO42- content and the density of the intact plant is less than a Codium species of comparable structure with a high K/Na ratio and higher SO42- content. However, the thallus is denser than seawater except where gas bubbles form on or within the thallus as a result of photosynthetic production of O2. Active photosynthesis can lead to more or less permanent accumulation of gas in the medullary region, the hollow thallus segments developing a characteristic reflectance. The static lift of these segments may be as much as 40 mg ml-1 but in itself is insufficient to account for the substrate/plant weight ratios of most drift material. Apparently, the ability of the plant to transport molluscs and rocks is primarily due to the form of the plants imparting an additional hydrodynamic drag on the substrate. Calculations of drag forces for a range of plant sizes and velocity regimes support this conclusion.