<span style="mso-bidi-font-family:"Times New Roman"" lang="HI">O<span style="mso-bidi-font-family:"Times New Roman"">ccurrence of cyanobacteria (<i style="mso-bidi-font-style:normal">Richelia intracellularis</i>)-diatom (<i style="mso-bidi-font-style:normal">Rhizosolenia hebetata)</i> consortium in the Palk Bay, southeast coast of India </span></span>

453-457<span style="mso-bidi-font-family: " times="" new="" roman";mso-ansi-font-weight:bold"="" lang="HI">Symbiotic association of heterocystous cyanobacterium, Richelia intracellularis Schmidt with oceanic centric diatom, <i style="mso-bidi-font-style: normal">Rhizosolenia hebetata is reported from the Palk Bay, southeast coast of India. One to six trichomes of R. intracellularis were occluded inside the periplasmic space of R.hebetata, with their prominent heterocyst pointing towards the valve of the host. Each of these trichomes had 14 to 23 vegetative cells <span style="mso-bidi-font-family: " times="" new="" roman";mso-ansi-font-weight:bold"="" lang="HI">caped by a terminal heterocyst enriched with the<span style="mso-bidi-font-family: " times="" new="" roman""="" lang="HI"> nitrogenase enzyme. Density of Rhizosolenia containing <i style="mso-bidi-font-style: normal">R. intracellularis ranged between 120 and 260 cells L-1, and present uniformly in the water column. R. intracellularis is<span style="font-size:10.5pt;mso-ansi-font-size:9.0pt; mso-bidi-font-family:" times="" new="" roman""="" lang="HI"> a diazotroph, can contribute substantially to the N2 budgets thereby<span style="mso-bidi-font-family: " times="" new="" roman";mso-ansi-font-weight:bold"="" lang="HI">, promoting a different food web in the Palk Bay. </span

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

Impact of a catastrophic flood on the heavy metal pollution status and the concurrent responses of the bentho-pelagic community in a tropical monsoonal estuary

Consequences of a catastrophic flood on the habitat quality and the concurrent responses of the bentho-pelagic community were studied in Cochin estuary, a eutrophic estuary along the southwest coast of India. The episodic flood in 2018 led to a marked decline in the dissolved nutrients and heavy metal concentrations in water and sediments of the estuary. The pre-flood phytoplankton abundance dominated by a bloom-forming species Cerataulina bicornis experienced a significant drop after the flood. Contrarily, zooplankton and macrobenthos responded favorably towards the flood-imposed habitat alterations. Higher susceptibility to heavy metal pollution and increased grazing pressure from gelatinous carnivores restricted the abundance of Copepoda, the dominant zooplankton taxon during pre-flood. The lower heavy metal concentration in the sediment after the flood favored higher macrobenthic abundance and diversity with a conspicuous change in the community structure from opportunistic polychaetes, indicators of pollution to molluscans and crustaceans, indicators of the healthy benthic zones