Effect of physico-chemical regimes and tropical cyclones on seasonal distribution of chlorophyll-a in the Chilika Lagoon, east coast of India

Water column properties associated with massive algal bloom of green Noctiluca scintillans in the Arabian Sea

An algal bloom of Noctiluca scintillans (NS) was monitored for 20 days in the Arabian Sea during February 2017. The stations under the influence of NS had low temperature and high salinity compared to outside indicating influence of convective mixing. The microscopic cell count of NS reached a value of 52,600 cells l-1. The surface variability in oxygen and pCO2 measured alongside showed a strong disconnect. Modest supersaturation of surface waters (ΔpCO2 = 3-75 μatm) was observed around the NS bloom compared to outside. However, as these stations were under the influence of convective mixing, the observed change in pCO2 due to subsurface ventilation cannot be ruled out. From the viewpoint of climate change and its influence on oceanic processes, constant monitoring of this bloom becomes essential due to its survival strategy in nutrient-depleted conditions and light of the present observations.

Status and conservation challenges of the second-largest seagrass bed in India: Chilika lagoon

Studies related to seagrass ecology, conservation, and management are sparse and highly biased in India. Even though the geographical distribution of seagrass is diverse in India, about 74% of the scientific publications have been made from Palk Bay and the Gulf of Mannar from Tamilnadu. Chilika, the largest lagoon in Asia, harbors the second largest seagrass meadow in India 22% of the total. The lagoon acts as a potential blue carbon stock and helps in thriving a rich floral and faunal biodiversity. However, the critical role of seagrass in this unique lagoon ecosystem is still poorly understood. This review is aimed at synthesizing the published literature about seagrass in Chilika. We believe this information would encourage more in-depth and diverse seagrass studies in the region and identify future priority areas for research. A total of seven species have been recorded from 169.2 sq. km of seagrass patch in Chilika. For the last two decades, no significant signs of decline in seagrass beds from this lagoon have been reported. Still, various natural and anthropogenic stressors could put this unique ecosystem under severe stress. Moreover, lax enforcement of existing legislation and a general lack of knowledge among the stakeholders about their ecosystem services can be significant impediments to their conservation. More targeted research on Chilika seagrass in changing climate regimes and their sustainable intensification is the need of the hour.

Effect of Tidal Cycle on Escherichia coli Variability in a Tropical Estuary

A faecal indicator bacteria, Escherichia coli (E. coli), is widely used in monitoring health of estuaries, where tidal amplitude plays a critical role in its variability. Mahanadi estuary, formed at the mouth of a major tropical river Mahanadi, has large socio-economic importance. This anthropogenically stressed estuary remains understudied with respect to E. coli. Hence, this study addressed E. coli variability in Mahanadi estuary with novel sampling strategy that can be implemented at other tropical estuaries. The sampling strategy includes simultaneous measurements, at lesser-saline upper-estuary and higher-saline lower-estuary, over a tidal cycle. Although no significant variability of E. coli was observed between upper and lower-estuary, overall average count was higher during low tide and lower during high tide attributed to salinity fluctuations. Intermittent surpass of E. coli counts above recommended limits in Mahanadi estuary, indicated potential health risk, thus demands for frequent water quality monitoring and management strategies.

Long-term trend and environmental determinants of phytoplankton biomass in coastal waters of northwestern Bay of Bengal

The present study is focused on understanding long-term trend in distribution of chlorophyll-a and its association with water quality parameters in coastal waters of northwestern Bay of Bengal. In situ observations were carried out in monthly frequency during January 2009 to March 2017 at two ecologically important study sites, off Gopalpur and off Visakhapatnam. A bimodal distribution of chlorophyll-a was observed off Gopalpur with primary and secondary peak during pre- and post-monsoon, respectively. In contrast, maximum chlorophyll-a concentration was noticed in monsoon irrespective of sporadic higher magnitudes during pre-monsoon in coastal waters off Visakhapatnam. The pivotal role of river influx and coastal upwelling was discerned in enriching coastal waters off Gopalpur with macronutrients and in turn on chlorophyll-a distribution. Adequate availability of silicate signified favorable condition for diatom growth in coastal waters off Gopalpur leading to preponderance. Influence of coastal upwelling and nutrient-controlled growth of phytoplankton was observed in coastal waters off Visakhapatnam.