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2 Oceanologia

2 2022

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Factors responsible for the sudden outburst of Noctiluca scintillans in the Chennai coastal waters, southeast coast of India – a case study

Mishra Pravakar, Begum Mehmuna, Gera Anitha, Kumar B. Charan, Garlapati Deviram, Pradhan Uma Kanta, Vashi Athan, Bandyopadhyay Debasmita, Naik Subrat J., Panda Uma Sankar, Ramana Murthy Mallavarapu Venkata

Oceanologia

2022

No. 64 (4)

781--788

The paper discusses the factors associated with the sudden outbreak of the nocturnal heterotrophic bioluminescent dinoflagellate Noctiluca scintillans along the Chennai coast. The bloom occurred along a stretch of 16 km following a spell of heavy rain in August 2019. The density of N. scintillans varied from 1000 to 19000 cells/L, with a distinguished distribution pattern. High N. scintillans abundance was recorded at Panaiyurkuppam and Kovalam, with 19000 cells/L and 18000 cells/L, recorded respectively. Adequate nutrients brought by substantial rainfall and a high abundance of the diatom Thalassiosira sp. triggered the N. scintillans bloom. The low wind speed (5 m/sec), lowering of atmospheric temperature (from 24.00 to 31.00°C, 27.5 ± 1.17°C), high rainfall (6 mm within one day), and low sea surface temperature (SST) (from 25.20 to 31.00°C, 29.37± 1.17°C) are probable environmental cues. Local hydrodynamics and the diverging currents governed the presence and dispersion of the bloom in the region.

Algal bloom, hypoxia, and mass fish kill events in the backwaters of Puducherry, Southeast coast of India

Mishra Pravakar, Naik Subrat, Babu P. Vipin, Pradhan Umakanta, Begum Mehmuna, Kaviarasan Thanamegam, Vashi Athan, Bandyopadhyay Debasmita, Ezhilarasan Pazhaniyappan, Panda Uma Sankar, Ramana Murthy Mallavarapu Venkata

Oceanologia

2022

No. 64 (2)

396--403

The Chunnambar backwater of Puducherry experienced changes in water quality over a period. The most significant impact was the sudden mass fish kill event coincided with the Pseudo-nitzschia bloom. On 25th September 2019, a mass fish kill event was reported, i.e. about a 0.25 metric ton (MT) floating on the water surface. On 29th September 2019, a much larger (∼1 MT) than the earlier incident had occurred. Sampling was carried out to assess the causes thereof. The results indicate that high organic matter and bacterial loads accumulated in the water and sediment due to the closure of the river mouth for an extended period. High ammonia (61.4 µM) and phosphate (6.2 µM) levels attributed to eutrophic conditions in the water column and hypoxemia due to low dissolved oxygen (1.62 mg/L at St.1 and 2.4 mg/L at St.5) and algal bloom were the proximate cause of these sudden fish kills. We recommend periodic dredging to facilitate proper water exchange between the backwater and the sea.