Spatial and seasonal variations in coastal water characteristics at Kalpakkam, western Bay of Bengal, Southeast India: a multivariate statistical approach.

A study was carried out in the coastal waters of Kalpakkam with the objectives to evaluate the seasonality in hydrobiological parameters in surface and bottom waters, and assess the anthropogenic stress and monsoonal flux on a spatiotemporal scale. The study covered an area of approximately 100 km2 in the coastal environment. Relatively high values for pH, temperature, and TP were observed during the post-monsoon (POM) season. The monsoon (MON) season was linked with TN, ammonia, and DO concentrations as all these parameters have shown increased values during this season due to freshwater input. The summer (SUM) season was characterized by salinity, turbidity, nitrate, phosphate, and silicate, indicating a true marine environmental condition for plankton production. Principal component analysis (PCA) and cluster analysis (CA) indicated the presence of distinct coastal water masses with respect to seasons and sampling regions. The spatial pattern indicated the distinctness of the coastal nearshore water (CNW) and coastal offshore water (COW) with respect to water quality. The CNW was more dynamic due to direct external influence as compared to the relatively stable COW environment. Similarly, the study region in the northern part, which is continuously exposed to the backwater inputs and tourism activities, was statistically different from the southern part.

First report on the occurrence of Gonyaulax polygramma bloom during the onset of Noctiluca scintillans bloom along the Tuticorin coast, southeast coast of India.

Dense and green-coloured patches were encountered on the sea surface waters of the Tuticorin coast on 22nd October 2022. Microscopic investigation revealed that the discoloration is caused by plankton, green Noctiluca scintillans. In order to find out the causes that trigger the bloom of N. scintillans, plankton samples were collected for 5 days in fourteen days duration from 22nd October to 4th November. During the peak bloom period, the abundance and biovolume of N. scintillans reached 1.56 × 104 cells/L and 21.8 × 1010µm3/L, respectively. The highest concentration (73.65 mg/m3) of chlorophyll-a was recorded during blooming period that was caused by Gonyaulax polygramma and endosymbiont, Pedinomonas noctilucae in N. scintillans. Formation of G. polygramma bloom is being reported for the first time in Tuticorin, southeast coast of India, with a species abundance of 36.9 × 104 cells/L. Present study concluded that besides the optimum hydrological conditions and eutrophic nature of the system, abundant prey (G. polygramma) facilitated the N. scintillans bloom.

Intense bloom of the diatom Hemidiscus hardmanianus (Greville) in relation to water quality and plankton communities in Tuticorin coast, Gulf of Mannar, India.

The present study reports a dense bloom of the marine-diatom Hemidiscus hardmanianus observed off the Tuticorin coast in the Gulf of Mannar (GoM), India. The surface water discoloration (pale green) was observed during a coastal survey conducted in the initial period of the northeast monsoon (October 2018). The bloom extended over an area of approximately 5 km2 around the Tuticorin harbor. Distribution and relative abundance of the phytoplankton and zooplankton species together with the water quality and Chlorophyll-a were studied in the area of bloom. H. hardmanianus density was maximum (10.57 × 104 cells L-1) in the bloom site, which was almost 97% of the total phytoplankton population. The present report is the first record of H. hardmanianus bloom in the Gulf of Mannar. The chain-forming diatom Biddulphia biddulphiana was also observed in strong numbers (802 and 432 cells L-1), which has been rarely reported from the Indian coastal waters.