Spatiotemporal variation of alkaline phosphatase activity in coastal waters off Trivandrum

Summary: Phosphatase is an extracellular enzyme which releases inorganic phosphate (Pi) from dissolved organic phosphate and indirectly organic carbon as nutrients for aquatic communities. Here, we have examined spatiotemporal variation in total alkaline phosphatase activity (APA) over a short period off Trivandrum, SW India. Sampling was at 50 m water depth at 5, 15, 25 and 45 m for 5 consecutive days at 6 h intervals during post-monsoon season. Total APA and phosphatase producing bacteria (PPB) were estimated along with pertinent environmental parameters. APA increased with depth up to 3.98 µM P h−1 at 45 m. Increase in pigment concentration with depth is responsible for an increase in APA and Pi uptake. There is a marginal increase in APA towards 18–24 h suggesting feeding activities of secondary producers. On the whole, chlorophyll and phaeophytin were responsible for nearly 45 and 55% variation in APA (p < 0.01, p < 0.001, n = 16), respectively. Total bacterial count (TBC) was responsible for 32% (p < 0.05, n = 16) and total viable direct counts-aerobic (TVCa) for 24% (p < 0.05, n = 16) APA variation. About 38% (p < 0.01, n = 20) variation of APA was linked to chlorophyll at noon and 22% (p < 0.001, n = 20) to PPB at dawn. Thus, it is possible that bacteria and chlorophyll/phytoplankton could be responsible for variation in APA, with the latter contribution greater than the former at noon. Such studies would help to profile the fertility of coastal waters in terms of bioavailable Pi. Laboratory experiments are underway to help us discern the extent of light-dependent contribution of chlorophyll/phytoplankton to APA and light independent participation of bacteria to the process. Keywords: Phosphorus, Alkaline phosphatase activity, Chlorophyll, Phytoplankton, Bacteri