Study of ecological consequence of the bloom (Noctiluca miliaris) in off-shore waters of the northern Arabian sea

Abstract

Ship based observations during early March 2007 in oceanic waters of the Northeastern Arabian Sea followed by phytoplankton analysis indicated that the bloom Noctiluca miliaris , species of dinoflagellate, dominated oceanic waters of the basin during winter. Dark green discoloration was observe d during February - early March. During the cruise FORV SS-212 Sagar Sampada in February-March 2003, surface water samples measured 64 – 4128 cells. l - 1 and deeper layers (10 - 15 m) supported 1080-2542 cells.l -1 of Noctiluca . Chlorophyll concentrations were in a range 0.4 - 2.0 mg. m - 3 , which reflect unusually high primary production in the deep waters ( > 2000 m). A patter n of zooplankton showed unusually high growth in the bloom waters. Fish catch data ( % hooking rates of tuna) were obtained from Fishery Survey of India and were used to study response of fish to prevailing high productivity in the bloom waters. Fishing in oceanic waters within Indian EEZ indicated no adverse effect of bloom; rather remarkably higher catches resulted from long line operations in the bloom waters. Space-time variability in dissolved oxygen was studied to explain the observed preference of fish in the bloom waters.