No abstract

Oceanic waters of the Northern Arabian Sea experience massive algal blooms during winter-spring (mid Feb-end Mar), which prevail for at least for 3 months covering the entire northern half of the basin from east to west. Ship cruises were conducted during winter-spring of 2001-2012 covering different stages of the bloom to study the biogeochemistry of the region. Phytoplankton analysis indicated the presence of green tides of dinoflagellate, Noctiluca scintillans (=N. miliaris), in the oceanic waters. Our observations indicated that diatoms are coupled and often co-exist with N. scintillans, making it a mixed-species ecosystem. In this paper, we describe an approach for detection of bloom-forming algae N. scintillans and its discrimination from diatoms using Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua data in a mixed-species environment. In situ remote sensing reflectance spectra were generated using Satlantic™ hyperspectral radiometer for the bloom and non-bloom waters. Spectral shapes of the reflectance spectra for different water types were distinct, and the same were used for species identification. Scatter of points representing different phytoplankton classes on a derivative plot revealed four diverse clusters, viz. N. scintillans, diatoms, non-bloom oceanic, and non-bloom coastal waters. The criteria developed for species discrimination were implemented on MODIS data and validated using inputs from a recent ship cruise conducted in March 2013.

Background:Oral submucous fibrosis is a chronic debilitating disease of oral mucosa and is characterized by generalized fibrosis of the oral soft tissues which tends to present itself clinically as palpable vertical fibrous bands. Hence, this study was conducted to evaluate histopathologically the collagen fiber bundle orientation in relation to epithelium and to find the reason for unidirectional orientation of clinically palpable fibrous bands.Materials and Methods:The study included 33 cases of oral submucous fibrosis and 8 cases of normal tissue.Results:Histologically most of the collagen fibers were parallel to the epithelium, and there was a statistically significant difference in orientation between oral submucous fibrosis and control groups in both buccal mucosa and labial mucosa.Conclusion:The reason for unidirectional alignment of clinical fibrous bands could be due to chronic stimulation of oral mucosa by the irritants leading to change in the orientation of collagen fiber bundles, which might result in scar formation similar to that of wound healing, where the collagen fibers are oriented parallel to the epidermis.

This study presents in situ evidence for the blooms of Trichodesmium erythraeum observed in the shelf waters of the South Eastern Arabian Sea (SEAS) during the onset of the southwest monsoon in June 2009. Evidence showed that water surface discoloration was caused by the accumulation of T. erythraeum, and that the water column contained a colony of T. thiebautii. The surface water color in the bloom region varied from pale brown to pinkish red. Pale brown indicated healthy algae at the peak of its photosynthetic activity, while pinkish red indicated the presence of photosynthetically less active filaments. Zooplankton abundance, especially copepodites, in the bloom area substantiated the theory that Trichodesmium filaments are excellent epiphytes to which the copepodites cling. The bloom area was very fertile with copious quantities of dissolved oxygen (6.85 ml L -1 ), PO 4 -P (0.108 µmol L -1 ) and SiO 4 (1.29 µmol L -1 ). Lower NO 3 -N (0.028 µmol L -1) values in the bloom area did not appear to affect Trichodesmium growth from molecular nitrogen fixation. However, lower NO 3 -N values altered the normal phytoplankton composition of this area.

Arabian Sea (AS) is known to have seasonal phytoplankton blooms during winter and summer driven by dynamically distinct physical forcing mechanisms and associated nutrient dynamics. A 1‐D coupled physical‐biogeochemical model based on North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO) with nitrogen and silicon cycles is adapted for the AS environment. The model is implemented to investigate the role of nitrogen (nitrate + ammonium) versus silicate limitation on plankton biomass. The seasonal cycle of plankton biomass is well simulated by the model along bio‐Argo (during a period from 2013 to 2016) and ship cruise tracks (for the single year 2009). Further, three sensitivity simulations are conducted by suppressing (1) nitrate availability (representing new production), (2) ammonium availability (representing regenerated production), and (3) silicate availability (for diatom production). The new production represents 80% of the total primary production in the AS and implicitly controls 70% of total zooplankton production annually. The regenerated production augments small phytoplankton (by ~50%; e.g., flagellates) and small zooplankton (by ~20%; e.g., ciliates) growth with negligible effects on large phytoplankton (e.g., diatom) and predatory zooplankton (e.g., copepods). The diatom production remains within the observed range due to silicate limitation which is fundamental in the model for realistic simulation of chlorophyll. Silicate is the primary limiting nutrient in diatom bloom in the subsurface chlorophyll maxima with maximum limitation occurring during the winter season, due to the deeper silicicline as compared to shallower nitricline. At the surface, both nitrogen and silicate co‐limit the total production; however, nitrogen is a stronger limiter than silicate from March to June. The study highlights the relative role of silicate versus total nitrogen (nitrate + ammonium) in limiting primary production in the AS.