Optical assessment of phytoplankton nutrient depletion

The ratio of light absorption at 480 and 665 nm by 90% acetoneextracts of marine phytoplankton pigments has been examinedas a potential indicator of phytoplankton nutritional statusin both laboratory and field studies. The laboratory studiesdemonstrated a clear relationship between nutritional status(carbon/nitrogen ratio) and the absorption ratio that was independentof light and temperature climate. The absorption ratio for nutrient-repletecells was shown to vary between taxonomic groups. However, theinter-specific variation was less than the differences observedbetween nutrient-replete and nutrient-depleted cells. The fielddata suggest that the absorption ratio may be a useful indicatorof nutritional status of natural phytoplankton populations,and can be used to augment the interpretation of other data.