Nutrient environment of red tide- infested waters off south-west coast of India

Identifying Algal Bloom ‘Hotspots’ in Marginal Productive Seas: A Review and Geospatial Analysis

Algal blooms in the marginal productive seas of the Indian Ocean are projected to become more prevalent over the coming decades. They reach from lower latitudes up to the coast of the northern Indian Ocean and the populated areas along the Arabian Gulf, Sea of Oman, Arabian Sea, and the Red Sea. Studies that document algal blooms in the Indian Ocean have either focused on individual or regional waters or have been limited by a lack of long-term observations. Herein, we attempt to review the impact of major monsoons on algal blooms in the region and identify the most important oceanic and atmospheric processes that trigger them. The analysis is carried out using a comprehensive dataset collected from many studies focusing on the Indian Ocean. For the first time, we identify ten algal bloom hotspots and identify the primary drivers supporting algal blooms in them. Growth is found to depend on nutrients brought by dust, river runoff, upwelling, mixing, and advection, together with the availability of light, all being modulated by the phase of the monsoon. We also find that sunlight and dust deposition are strong predictors of algal bloom species and are essential for understanding marine biodiversity.

Environmental dynamics of red Noctiluca scintillans bloom in tropical coastal waters

An intense bloom of red Noctiluca scintillans (NS) occurred off the Rushikulya estuarine region along the east coast of India, an important site for mass nesting events of the vulnerable Olive Ridley sea turtle. At its peak, densities of NS were 3.3×10(5) cells-l(-1), with low relative abundance of other phytoplankton. The peak bloom coincided with high abundance of gelatinous planktivores which may have facilitated bloom development by their grazing on other zooplankton, particularly copepods. Ammonium concentrations increased by approximately 4-fold in the later stages of bloom, coincident with stable NS abundance and chlorophyll concentrations in the nano- and microplankton. This increase likely was attributable to release of intracellular ammonium accumulated through NS grazing. Dissolved oxygen concentrations decreased in sub-surface waters to near hypoxia. Micro-phytoplankton increasingly dominated chlorophyll-a biomass as the bloom declined, with diminishing picoplankton abundance likely the result of high predation by the ciliate Mesodinium rubrum. Together, these data illustrate factors that can disrupt ecosystem balance in this critically important Indian coastal region.

Phytoplankton community structure in local water types at a coastal site in north-western Bay of Bengal

A comprehensive analysis on seasonal distribution of phytoplankton community structure and their interaction with environmental variables was carried out in two local water types (type 1 < 30 m isobath and Type 2 > 30 m isobath) at a coastal site in north-western Bay of Bengal. Phytoplankton community was represented by 211 taxa (146 marine, 37 fresh, 2 brackish, 20 marine-fresh, and 6 marine-brackish-fresh) belonging to seven major groups including 45 potential bloom forming and 22 potential toxin producing species. The seasonal variability depicted enrichment of phytoplankton during pre-monsoon in both water types. Total phytoplankton abundance pattern observed with inter-annual shift during monsoon and post-monsoon period at both water types. In both water types, diatom predominance was observed in terms of species richness and abundance comprising of centric (82 sp.) and pennate (58 sp.) forms. Pennate diatoms, Thalassiothrix longissima and Skeletonema costatum preponderated in both the water types. The diatom abundance was higher in type 1 in comparison to type 2. In general, SiO4 found to fuel growth of the dominant phytoplankton group, diatom in both the water types despite comparative lower concentration of other macronutrients in type 2.

An overview of historical harmful algae blooms outbreaks in the Arabian Seas

Harmful algae blooms (HABs), often composed of oceanic plants called phytoplankton, are potentially harmful to the marine life, water quality, human health, and desalination plants, a chief source of potable water in the Arabian Gulf. The last decade has seen a noticeable increase in the frequency of HAB outbreaks in the Arabian Seas. This increase is mainly caused by the unprecedented economic growth in the region. The increased human activities in the region have added more stress to the marine environment and contributed to the changes observed in the properties of the marine ecosystem: high temperature and salinity, high evaporation rates, limited freshwater inflow, shallow nature, pollution. However, very few studies that cover the HAB outbreaks, causes, impacts and biological characteristics over the region have been published. This work presents a comprehensive overview of historical HAB outbreaks recorded in the region, and investigate their causes and impact, and seasonal variability.