High molecular weight algal substances in the sea

Phytoplankton exudates into culture media and extracts from littoral algae are shown to contain significant quantities of extracellular materials having molecular weights in excess of 50,000. A recent development in experimental fluid mechanics (the reduction of turbulent friction coefficients of flowing solutions by dissolved macromolecules) has been utilized as a specific test for high molecular weight compounds. Phytoplankton species in all major algal groups could be found which exude high molecular weight compounds into their culture media; the red alga Porphyridium cruentum typically produced friction reductions as high as 60%. Seaweed samples in the Chlorophyta, Phaeophyta, and Rhodophyta showed major changes in turbulent friction coefficient; in some cases the friction was less than 1/2 that of pure seawater. All samples of the genus Porphyra and Gigartina produced substantial friction changes. From these experiments it is concluded that algal exudates can be a prominent source of high molecular weight compounds in the sea.