Myctophid and pelagic shrimp assemblages in the oxygen minimum zone of the Andaman Sea during the winter monsoon

535-541Stratified samples were collected with a Multiple Plankton Net for assessing the myctophid and pelagic shrimps composition from the Andaman Sea during the winter monsoon. Andaman Sea has a fair representation of mesopelagic micronektonic fauna such as the myctophids and pelagic shrimps in the upper 1000 m depth. Among the myctophids, Benthosema fibulatum had the maximum biomass followed by Diaphus lucidus and Benthosema pterotum. Among the pelagic shrimps Sergestus seminudus and Oplophorus types were the dominant species. Sergestes seminudus was present at all depths [up to 1000 m] and its distribution pattern suggested the cocurence of a strong diurnal vertical migration. Temperature decreased from the mixed layer depth downwards. Salinity did not show any significant variation. Dissolved oxygen ranged between 2.8 and 4.8 mL.L-1 in the upper 75 m and from 0.05 to 0.2 mL.L-1 in the 150-650 m column, with a gradual increase in the bottom layers [>0.8 mL.L-1]. Majority of myctophids and shripms occurred in abundance in the oxygen minimum zone [150-650 m]

What Controls the Flushing Efficiency and Particle Transport Pathways in a Tropical Estuary? Cochin Estuary, Southwest Coast of India

Estuaries with poor flushing and longer residence time retain effluents and pollutants, ultimately resulting in eutrophication, a decline in biodiversity and, finally, deterioration of water quality. Cochin Estuary (CE), southwest coast of India, is under the threat of nutrient enrichment by the anthropogenic interventions and terrestrial inputs through land runoff. The present study used the FVCOM hydrodynamic model coupled with the Lagrangian particle module (passive) to estimate the residence time and to delineate site-specific transport pathways in the CE. The back and forth movements and residence time of particles was elucidated by using metrics such as path length, net displacement and tortuosity. Spatio-temporal patterns of the particle distribution in the CE showed a similar trend during monsoon and post-monsoon with an average residence time of 25 and 30 days, respectively. During the low river discharge period (pre-monsoon), flood-ebb velocities resulted in a minimum net transport of the water and longer residence time of 90 days compared to that of the high discharge period (monsoon). During the pre-monsoon, particle released at the southern upstream (station 15) traversed a path length of 350 km in 90 days before being flushed out through the Fortkochi inlet, where the axial distance was only 35 km. This indicates that the retention capacity of pollutants within the system is very high and can adversely affect the water quality of the ecosystem. However, path length (120 km) and residence time (7.5 days) of CE were considerably reduced during the high discharge period. Thus the reduced path length and the lower residence time can effectively transport the pollutants reaching the system, which will ultimately restore the healthy ecosystem. This is a pioneer attempt to estimate the flushing characteristics and residence time of the CE by integrating the hydrodynamics and Lagrangian particle tracking module of FVCOM. This information is vital for the sustainable management of sensitive ecosystems

Response of coastal phytoplankton to upwelling induced hydrological changes in the Alappuzha mud bank region, Southwest coast of India

The response of phytoplankton community to the co-existing events of coastal upwelling and mud banks in the nearshore waters of Alappuzha (15 m depth), located in the southwest coast of India from April to November 2016, is described based on size-fractionated phytoplankton biomass (chlorophyll a), primary production and community composition. The study region exhibited well-distinct spatio-temporal hydrological changes because of the influence of wind-driven coastal upwelling, prevalent during the southwest monsoon (SWM) period. However, the formation of mud banks, in addition to coastal upwelling, was observed at station M2, which facilitated the substantial increase of water column turbidity and inorganic nutrients (ammonium, phosphate, and silicate) during and after the peak SWM period compared to the non-mud bank reference stations (M1 and M3). The prevailing hydrological changes were complemented the corresponding phytoplankton productivity patterns, in which profound domination of nanophytoplankton (2—20 μm) chlorophyll a and primary production was observed throughout the study region, irrespective of seasons. The SIMPER analysis, based on phytoplankton (mostly >20 μm) species composition data (microscopy), revealed the formation of certain characterizing species, mainly comprised of diatoms and dinoflagellates. The consistent predominance of the nanophytoplankton, established under variable hydrological scenarios, showed that the inorganic nutrient (specifically ammonium) availability was instrumental in defining the widespread growth of nanophytoplankton community compared to the prevailing light levels. The present study thus revealed that even the small-sized phytoplankton community could survive in the nutrient-enriched coastal waters, characterised by the co-existing upwelling and mud banks

Field hyperspectral data analysis for discriminating spectral behavior of tea plantations under various management practices

The quality and yield of tea depends upon management of tea plantations, which takes into account the factors like type, age of plantation, growth stage, pruning status, light conditions, and disease incidence. Recognizing the importance of hyperspectral data in detecting minute spectral variations in vegetation, the present study was conducted to explore applicability of such data in evaluating these factors. Also stepwise discriminant analysis and principal component analysis were conducted to identify the appropriate bands for accessing the above mentioned factors. The Green region followed by NIR region was found as most appropriate best band for discriminating different types of tea plants, and the tea in sunlit and shade condition. For discriminating age of plantation, growth stage of tea, and diseased and healthy bush, Blue region was most appropriate. The Red and NIR regions were best bands to discriminate pruned and unpruned tea. The study concluded that field hyperspectral data can be efficiently used to know the plantation that need special care and may be an indicator of tea productivity. The spectral signature of these characteristics of tea plantations may also be used to classify the hyperspectral satellite data to derive these parameters at regional scale