Storage of Oxygen in the Bladders of the Seaweed Ascophyllum nodosum and their Adaptation to Hydrostatic Pressure

Abstract

1. Ascophyllum nodosum secretes oxygen into its bladders so freely that the total gas pressure within them is usually above atmospheric pressure. The plant draws on this store of oxygen during the night and when shaded; the advantage of storing the gas under pressure is that withdrawals do not diminish the volume or buoyancy of the bladder whose efficiency as a float is of importance to the plant when competing for sunlight. 2. As the bladder walls are somewhat permeable, the contained gas tends to diffuse out into the sea. Disastrous loss of gas may take place if, during an abnormally high tide, hydrostatic pressure overcoming the resistance of the bladder causes it to collapse with formation of a "dimple". In this event the gas inside takes up the pressure of the water outside and diffuses away more rapidly than before the collapse took place. The bladders lose buoyancy and can no longer support the plant properly; as a result it is starved of sunlight, fails to replace the lost gas and becomes permanently crippled. 3. Plants growing in situations where they are exposed to severe hydrostatic pressure show an adaptive thickening of the bladder walls which enables them to resist deformation and the sequence of events detailed in (2). 4. This adaptation is so closely fitted to the environment that in a zone of A. nodosum fifteen feet wide the plants of the upper level are unable to withstand the hydrostatic pressure obtaining at the lower and, if transplanted there, lose all their gas and perish.