Summary of Abstract Submission

Abstract Submission No. IO50-06-0011PresentationOral

DE-OXYGENATION AND NOCTILUCA BLOOM

Satya Prakash*1, Rajdeep Roy2, Aneesh Lotliker1

1 INCOIS, Hyderabad, India
2 NRSC, Hyderabad, India

ABSTRACT :

It has been reported recently that massive outbreaks of N. scintillans bloom during winter in the northern Arabian Sea are being facilitated by unprecedented influx of oxygen deficient waters into the euphotic zone. The proposed hypothesis is quite striking and necessitates further investigation. A comprehensive analysis of recent in-situ dissolved Oxygen data from the northern Arabian Sea shows well oxygenated euphotic zone (oxygen saturation >90%), which does not substantiate the proposed hypothesis. Moreover, the occurrence of intense bloom over this basin can be traced back to 1980┐s as evident from NASA's Coastal Zone Color Scanner (CZCS) data. Noctiluca scintillans blooms are even reported from the Bay of Bengal and Andaman Sea (as early as 1958). It is worth noting here that Andaman Sea and Palk strait waters are not characterised by the oxygen deficiency. In fact surface water in the Bay of Bengal is always near the saturation level as shown by the Argo Oxygen data. This clearly shows that, Noctiluca scintillans is not a new phenomenon in this region and undoubtedly their proliferation is not related to the oxygen deficiency in the surface waters. To understand the typical photic depth during the Noctiluca scintillans bloom we undertook a cruise between January┐February 2015. We found the photic depth to be restricted to 30 m which is completely saturated. Since dissolved oxygen concentration in sub-surface waters is a sensitive indicator of physical and biogeochemical changes in pelagic oceans therefore we believe any trend should be interpreted with caution as oxygen depletion within photic zone can lead to complete destruction of pelagic fishes.