Indian Journal of Geo Marine Sciences Vol. 47 (08), August 2018, pp. 1648-1651

Incidence of heterotrophic red bloom along Chavakkad, southwest coast of India.

KC Vijayalakshmy*, M Abhijith, MK Megha, AA Mohamed Hatha & A V Saramma Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Lakeside Campus, Fine Arts Avenue, Kochi - 682016, India. *[E. Mail: [email protected]]

Received 19 January 2017; revised 30 March 2017

In the last few decades, south west coast of India has experienced massive inter monsoon blooms because of the unicellular siliceous diatoms due to nutrient enriched water from convective mixing and eutrophication. At latent phase of monsoon, these have been replaced by large red heterotrophic , Noctiluca scintillans which results an oxygen deficient condition in euphotic zone. Here we communicate an extensive bloom of Noctiluca scintillans from Chavakkad, Kerala.

[Key words: Noctiluca scintilans, Chavakkad, Cell size, Eutrophication]

Introduction Materials and Methods. The Southwest coast of India is prone to algal From the bloom area Chavakkad (10° 33' 9.4932'' blooms in monsoon season as a result of upwelling N & 76° 0' 57.0708'' E) (Fig: 1), 50 litres of surface and high riverine discharge. A massive bloom was water was filtered through phytoplankton net made observed along the coast of Chavakkad (10° 33' of bolting silk with a mesh size of 20μm. The cells 9.4932'' N & 76° 0' 57.0708'' E) Kerala, India for a were preserved in 3% neutralized formaldehyde and period of one week beginning from 9th September Lugol’s iodine solution. Species identification 2016. The coastal sea along 15 km stretch had turned was done using Leica DM 2000 Phase contrast red, accompanied by conspicuous bioluminescence at microscope. Microalgae were identified by using 12-17 night. Microscopic observation of samples collected standard keys . Sedgewick-Rafter counting from the bloom area revealed that the bloom was chamber was employed for quantitative analysis. caused by red Noctiluca scintillans, which frequently Pigments were analyzed as per the methods of 18 form blooms over northern, eastern and western Strickland and Parsons . Arabian Sea overlapping with the green Noctiluca in Temperature was measured using a precision o their distribution1-7. Noctiluca is classified as harmful mercury thermometer with an accuracy of ±0.01 C. 19 algal bloom species as they cause large scale Salinity was estimated by the method of Mohr . mortality of caged fish8. Measurements of pH were made using a portable pH meter (Perkin Elmer, accuracy +0.01). For the Noctiluca scintillans Macartney is a large estimation of dissolved oxygen, samples were unarmoured dinoflagellate that is widely reported collected in 50 ml ground stoppered BOD bottles and as a ‘’ organism in temperate, tropical and fixed using Winkler’s A&B solutions20. polar waters9.There have been 39 causative species Nutrients (nitrite, phosphate and silicate) were responsible for bloom along Indian waters, N. estimated using filtered water samples (GF/C filter scintillans is one among them. Red Noctiluca is paper; pore size 1.2 µm) by following the methods of heterotrophic, acts as a microzooplankton grazer in Strickland and Parsons18. Nitrate was estimated by the the food web, and is more restricted to oligotrophic method of Fischer and Zhang21. warmer summer seasons at a temperature range of 25-30 º C7. Noctiluca blooms have already been Results and Discussion reported from Gujarat coast10and off Kochi11 along the Even though Noctiluca scintillans imparted southwest coast of India. 7.5×105 cells/L (Fig: 2), the bloom was not mono- VIJAYALAKSHMY et al.: NOCTILUCA SCINTILLANS BLOOM OFF CHAVAKKAD 1649

Fig. 1 — Location of Noctiluca scintillans Macartney bloom.

Fig. 3 — N. scintillans cell showing heterotrophy

During the present bloom, the cell size of N. scintillans ranged from 560 to 650µm in diameter. An inverse relationship between cell size and nutrient condition has been observed by many workers.22- 23.The smaller the cell size (340–450μm), better the nutritional conditions, whereas the larger cells (400– 1200μm), indicate poor nutritional status24-25. Larger size of N. scintillans cells constituting the blooms in

the present study reflects a poor nutritional level of Fig. 2 — Noctiluca scintillans bloom the environment. The frequency of Noctiluca bloom is higher during specific and was accompanied by other species. In all, monsoon season (August to October) coinciding with 12 species of microalgae were identified from the the end of upwelling season26. bloom area. Except Tripose furca and fusus, Since, N. scintillans is a heterotrophic form its the other species observed along with the bloom- bloom is usually preceded by a diatom bloom27. It has forming species were diatoms. They were Cyclotella also been reported that N. scintillans blooms occur striata (1250 cells/L), Chaetoceros debili commonly and were sustained along with multi series (250 cells/L), Paralia sulcata (250 cells/L), diatom blooms that were generated by upwelling– Fragillariopsis oceanica (125 cells/L), Trieres induced eutrophic conditions during the southwest mobiliensis (128 cells/L) and Nitzschia longissima monsoon period in Kochi waters11&28. There is a (520 cells/L). Many Noctiluca cells were found tendency of zooplankton, fish larvae and fish shoals harbouring diatoms within the cells. Detailed (mackerels, sardines and anchovies) to avoid the investigation revealed the presence of diatom bloom waters of Noctiluca, because of the associated cells and remnants of co-occuring phytoplankton oxygen depletion, gill clogging and high ammonia species in the food vacuoles of Noctiluca cells levels29. Recent studies of Escalera et al., (2007) (Fig: 3). A similar observation has been made by showed that N. scintillans may act as a route to Padmakumar et al.11 from off Kochi. The heterotrophic disseminate phycotoxins to higher trophic levels by red N. scintillans without endosymbionts surviving feeding on toxigenic microalgae30. solely by grazing has been seen confined to the At the time of the bloom, water temperature was southwest coast of India, in summer when the region 27º C, salinity 40 psu and pH 8.4. The concentration experiences upwelling. The comparatively high of dissolved oxygen was very low in the bloom area concentration of chlorophyll a (10.4 µg/L) observed (2.2mg/L); the high cell density of the dinoflgellate in the bloom sample may be due to the presence of might have been a reason for that. Reported bloom of diatoms associated with the bloom. Noctiluca at Gulf of Mannar has been bleached corals 1650 INDIAN J. MAR. SCI., VOL. 47, NO. 08, AUGUST 2018

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