A bio-physicochemical perspective of the Bay of Bengal

Abstract

Knowledge of bio-physicochemical variables is essential to better understand the functioning of tropical marine ecosystems, which are rich in biodiversity and provide nutrition and livelihoods to billions of people in the developing countries. This study analysed the spatial and temporal variability of phytoplankton and zooplankton with chlorophyll, primary productivity, temperature, salinity, oxygen and nutrients in the Bay of Bengal (BoB), collecting data from the World Ocean, and COPEPOD and Aqua MODIS records. The results indicated a strong gradient in bio-physicochemical conditions of the BoB, from the coast to the open sea. Specifically, the spatial variability in chlorophyll was negatively correlated (R2 = 0.59) with temperature and zooplankton, while a positive correlation (R2 = 0.70) was noted between chlorophyll and silicate, nitrate, phosphate, dissolved oxygen and salinity. All the variables exhibited a strong vertical gradient at depths up to 500 m. Temperature, nutrients, zooplankton and to a lesser extent salinity and rainfall had an influence on the annual abundance of phytoplankton. Over the long term, a significant positive trend in temperature and a significant negative trend in primary productivity were observed in the BoB. The findings of this study will be useful to draw insights on the state of fisheries habitats and the overall environmental conditions of the BoB in response to future climate changes.

The Bay of Bengal exposes abundant photosynthetic picoplankton and newfound diversity along salinity‐driven gradients

“…Nutrient limitation is exacerbated by strong salinity gradients (Madhupratap et al, 2003) and the system is substantially independent of thermally‐driven seasonal variations, that occur in some subtropical gyres, given its consistently warm surface waters (~26–29°C). Furthermore, strong stratification also contributes to a quiescent environment, which may further limit the overall nutrient supply to the system, restricting primary productivity (Prasanna Kumar et al, 2002; Sarker et al, 2020). Thus, in many respects, salinity is considered a leading control on the dynamics of the photic zone, and shapes its shallow, spatially and temporally variable mixed layer (ML) of oligotrophic conditions (Mahadevan et al, 2016).…”

Phytoplankton ecology in different coastal habitats along the northern Bay of Bengal

“…Sarker, Panassa, Hossain, Chowdhury, et al. (2020) and Zafar (2007) also reported the dominance of diatom in the coastal and estuarine habitats of Bangladesh. Phytoplankton species composition is largely dependent on the nutrient concentrations (Edmondson, 1970; Howarth, 1988).…”

“…Therefore, in general, temperature and salinity are considered as important drivers of phytoplankton (Wiltshire et al., 2015). In tropical areas, sun light is not a limiting factor and temperature is optimal for growth of phytoplankton throughout the year (Sarker, Panassa, Hossain, Chowdhury, et al., 2020). In addition, salinity remains higher during dry season in the tropical region.…”

“…For example, light availability, temperature and zooplankton are the major drivers in temperate ecosystem (Wiltshire et al., 2015). Conversely, nutrient is the major driver of the phytoplankton community dynamics in tropical ecosystem (Sarker, Panassa, Hossain, Chowdhury, et al., 2020). Of note, three nutrients such as silicate, nitrate and phosphate, and zooplankton were identified as the most important predictors for phytoplankton community in the tropical ecosystem of Bay of Bengal (Sarker, Yadav, Hossain, Chowdhury, Kabir, et al., 2020).…”

“…Fisheries of this area are particularly influenced by the spatial and temporal variability of plankton community structure. However, this tropical ecosystem is less studied from oceanographic point of view (Sarker, Panassa, Hossain, Chowdhury, et al., 2020) and little is known about the plankton community. A few studies carried out on the taxonomy of plankton, and their abundance and occurrence in relation to environmental variables (Sarker et al., 2018).…”