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Silica is a vital nutrient for diatoms , a form of phytoplankton , which form delicate microscopic shells of silica . The macroalgae that dominated the first pond of the Kliphoek salina were replaced by phytoplankton that comprised at least 75 % of the living biomass throughout the remainder of the system . Although the growth of phytoplankton in the plume depended on the availability of nutrients and light , the offshore decrease in phytoplankton biomass still satisfied the Sverdrup 's relationship . One study done in the waters off Antarctica where increased UV-B radiation has been measured due to the ozone hole found a 6-12 % decrease in phytoplankton , the organism that forms the base of the food chain in the oceans ( Smith et . Similar diurnal kinetics in natural fluorescence yield were observed in phytoplankton assemblages in a coastal transition region in the Gulf of Alaska . Grazing by Daphnia resulted in changes in the stoichiometry of phytoplankton and bacterioplankton . Since phytoplankton are especially concentrated in the North , the study found an overall annual decrease in phytoplankton globally . The decreased growth rate with depth was not associated with the mass of total seston or its organic content but were proportional to the decrease in phytoplankton biomass with depth ( chlorophyll a decreased from 4.8 to 0.7 micrograms l ‐ 1 between 8 and 34 m ) .