Extracellular phosphatase enzyme activity in reef waters of the central Great Barrier Reef

A fluorometric procedure was applied to measure changes in phosphatase activity in seawater flowing across reef flats at Bowl and Hopkinson Reefs on the central Great Barrier Reef. Seawater samples were collected at 50 m intervals across the reef flat during low tide, commencing at the reef front using a volume transport method and a time-distance-depth record was maintained allowing measurements to relate to the distance a water mass had flowed across the coral reef flat. Water samples were collected below the surface using a dip-scoop, filtered through 10 µm mesh and stored in the dark before being assayed.Fluorescence was measured on 2 ml filtered (Nucleopore, 0.2 µm) and unfiltered subsamples on addition of 50 µl of a 5.0 mM solution of the enzyme substrate (4-methylumbelliferyl phosphate) and then at hourly intervals. An 8 hour period of incubation was required to determine statistically significant rates of hydrolysis from oligotrophic water samples. This research was initiated to examine the importance of the hydrolysis of organophosphates by alkaline phosphatase enzymes as a source of inorganic phosphate, a nutrient essential for primary production. The assay used was able to determine low levels of enzyme phosphatase activity in marine waters based on the enzymatic hydrolysis of the fluorogenic substrate, 4-methylumbelliferyl phosphate.