Monitoring of ocean surface algal blooms in coastal and oceanic waters around India

Abstract

The National Aeronautics and Space Administration's (NASA) sensor MODIS-Aqua provides an important tool for reliable observations of the changing ocean surface algal bloom paradigms in coastal and oceanic waters around India. A time series of the MODIS-Aqua-derived OSABI (ocean surface algal bloom index) and its seasonal composite images report new information and comprehensive pictures of these blooms and their evolution stages in a wide variety of events occurred at different times of the years from 2003 to 2011, providing the first large area survey of such phenomena around India. For most of the years, the results show a strong seasonal pattern of surface algal blooms elucidated by certain physical and meteorological conditions. The extent of these blooms reaches a maximum in winter (November-February) and a minimum in summer (June-September), especially in the northern Arabian Sea. Their spatial distribution and retention period are also significantly increased in the recent years. The increased spatial distribution and intensity of these blooms in the northern Arabian Sea in winter are likely caused by enhanced cooling, increased convective mixing, favorable winds, and atmospheric deposition of the mineral aerosols (from surrounding deserts) of the post-southwest monsoon period. The southward Oman coastal current and southwestward winds become apparently responsible for their extension up to the central Arabian Sea. Strong upwelling along this coast further triggers their initiation and growth. Though there is a warming condition associated with increased sea surface height anomalies along the coasts of India and Sri Lanka in winter, surface algal bloom patches are still persistent along these coasts due to northeast monsoonal winds, enhanced precipitation, and subsequent nutrient enrichment in these areas. The occurrence of the surface algal blooms in the northern Bay of Bengal coincides with a region of the well-known Ganges-Brahmaputra Estuarine Frontal (GBEF) system, which increases supply of nutrients in addition to the land-derived inputs triggering surface algal blooms in this region. Low density (initiation stage) of such blooms observed in clear oceanic waters southeast and northeast of Sri Lanka may be caused by the vertical mixing processes (strong monsoonal winds) and the occurrence of Indian Ocean Dipole events. Findings based on the analyses of time series satellite data indicate that the new information on surface algal blooms will have important bearing on regional fisheries, ecosystem and environmental studies, and implications of climate change scenarios.

An optical system for detecting and describing major algal blooms in coastal and oceanic waters around India

“…The reflectance spectra of N. scintillans and C. polykrikoides blooms observed off northern Arabian Sea and off Gulf of Oman and Arabian Gulf, respectively, as reported in the present work are confirmed by the previous studies ( Tholkapiyan et al . [] and Shanmugam et al . [], respectively).…”

“…It is noteworthy that spatial patterns of N. scintillans bloom observed in chlorophyll and SVD‐images were closely consistent with each other that support the previous finding with the statistically significant relationship between chlorophyll and N. scintillans density during bloom episodes [ Gomes et al ., ]. These images further indicate that the winter blooms of N. scintillans were likely developed in the western Arabian Sea (especially within upwelling and cyclonic eddies in the coastal areas of Oman [ Gomes et al ., ; Tholkapiyan et al ., ]) and flowed northward and then southward into the northern Arabian Sea. The in situ observations made on the three cruises in coastal and open‐sea areas confirmed the movement patterns of these blooms.…”

“…High abundance of Trichodesmium filaments were recorded around 17.169°N and 73.09°E on 25 April 2009 and 17.17°N and 73.16°E on 27 April 2009 off Mangalore coast. The favorable inter‐monsoon conditions—calm weather, bright light, and moderate temperature—were observed to support the occurrence, aggregations, and patchiness of these blooms in the Arabian Sea [ Tholkapiyan et al ., ]. At all the stations within and outside the blooms, necessary optical measurements were performed along with water sampling and physical oceanographic measurements.…”

“…Detection and description are generally based on the bio‐optical algorithms that involve the specific optical properties of Trichodesmium [ Dupouy et al ., 2008; Subramaniam and Carpenter , ; Subramaniam et al ., ; Westberry et al ., ; McKinna et al ., ], spectral analyses of the Rayleigh‐corrected reflectances [ Hu et al ., ], or remote sensing reflectances [ Simon and Shanmugam , ]. On the contrary, the central and coastal regions of the Arabian Sea often experience massive blooms of the dinoflagellate green N. scintillans with a peak from December to March [ Mol et al ., ; Gomes et al ., ; Anantharaman et al ., ; Dwivedi et al ., ; Tholkapiyan et al ., ]. This species contains a gas vacuole that helps their diel vertical movements in the water column.…”

Algal growth simulation post water regulation in a river-connected lake

“…There is worldwide concern about algal bloom currently (Tholkapiyan et al 2014, Lehman 2014, Smida et al 2014). River-connected lakes with frequent algal bloom is always faced with series of environmental problems such as water quality deterioration, water transparency decrease, ecosystem imbalance, drinking water crisis, human health hazards and so on (McLean & Sinclair 2012, Lu et al 2012, Huang 2014).…”