Seasonally varying biogeochemical regime around the coral habitats off central west coast of India.

The Western Indian Continental Shelf (WICS) experiences upwelling during the Southwest Monsoon (SWM), leading to deoxygenation and acidification of subsurface waters. The region has patchy growth of corals, e.g. in the Grande Island and Angria Bank. Measurements made during the late SWM of 2022 reveal that the shelf waters around the Grande Island were subject to varying environmental conditions, viz. lower temperature (21.3-26.1°C), oxygen (0-4.9 mL L-1) and pHT (7.506-7.927). Complete anoxia was associated with sulphide build-up to a maximum of 5.9 µmol L-1 at 17 m depth. An additional episodic condition (high temperature, low oxygen and pH) also occurred associated presumably with a plankton bloom in April 2017. Hence, unlike the offshore coral site Angria Bank, waters around the Grande Island experiences extreme changes in physico-chemical conditions (e.g. Ωarg ∼1.2-1.8 during October 2022) seasonally as reported here. The biogeochemical conditions are however not as intense (Ωarg = 0.6) as observed along the eastern boundary upwelling system of the Pacific Ocean.

High total organic carbon in surface waters of the northern Arabian Gulf: Implications for the oxygen minimum zone of the Arabian Sea.

Measurements of total organic carbon (TOC) for two years in Kuwaiti waters showed high TOC levels (101.0-318.4, mean 161.2 µM) with maximal concentrations occurring within the polluted Kuwait Bay and decreasing offshore, indicating substantial anthropogenic component. Analysis of winter-time data revealed a large increase in density over the past four decades due to decrease in Shatt Al-Arab runoff, implying that the dissolved/suspended organic matter in surface waters of the northern Gulf could be quickly injected into the Gulf Deep Water (GDW). Our measurements together with an analysis of previously collected/published data suggest that the recent summer-time declining trend in oxygen in the GDW might be related to eutrophication. Higher preformed TOC and lower preformed dissolved oxygen contents of the high-salinity water mass that flows out of the Gulf and ventilates the mesopelagic oxygen minimum zone (OMZ) of the Northwestern Indian Ocean may cause expansion/intensification of the regional OMZ.

Mud Banks along the southwest coast of India are not too muddy for plankton.

Considering Alappuzha Mud Bank in the southern Kerala coast as a typical case of biologically productive Mud Banks that form along the southwest coast of India during the Southwest Monsoon (June - September), the present study addresses several pertinent missing links between the physical environment in Mud Banks and their influence on plankton stock. This study showed that very strong coastal upwelling prevails in the entire study domain during the Southwest Monsoon, which manifests itself in the form of significantly cool, hypoxic and nitrate-rich waters surfacing near the coast. The upwelled water persisting throughout the Southwest Monsoon period was found to have fuelled the exceptionally high phytoplankton stock in the entire study area, including the Mud Bank region. Having accepted that Mud Banks are special because of the calm sea surface conditions and relatively high turbidity level in the water column around them, the present study showed that except at points close to the sea bottom, turbidity level in the Alappuzha Mud Bank was below the critical level to inhibit the plankton stock. The suspended sediments that form in the Mud Bank occasionally could be attributed to the disturbance of the bottom fluid muddy layer and their vertical spurts.

Declining oxygen in the global ocean and coastal waters.

Oxygen is fundamental to life. Not only is it essential for the survival of individual animals, but it regulates global cycles of major nutrients and carbon. The oxygen content of the open ocean and coastal waters has been declining for at least the past half-century, largely because of human activities that have increased global temperatures and nutrients discharged to coastal waters. These changes have accelerated consumption of oxygen by microbial respiration, reduced solubility of oxygen in water, and reduced the rate of oxygen resupply from the atmosphere to the ocean interior, with a wide range of biological and ecological consequences. Further research is needed to understand and predict long-term, global- and regional-scale oxygen changes and their effects on marine and estuarine fisheries and ecosystems.

Noctiluca and copepods grazing on the phytoplankton community in a nutrient-enriched coastal environment along the southwest coast of India.

The relative grazing impact of Noctiluca scintillans (hereafter referred only Noctiluca) and copepods (Acrocalanus gracilis, Paracalanus parvus, Acartia danae and Oithona similis) on the phytoplankton community in an upwelling-mudbank environment along the southwest coast India is presented here. This study was carried out during the Pre-Southwest Monsoon (April-May) to the Late Southwest Monsoon (August) period in 2014. During the sampling period, large hydrographical transformation was evident in the study area (off Alappuzha, Southwest coast of India); warmer Pre-Southwest Monsoon water column condition got transformed into cooler and nitrate-rich hypoxic waters during the Southwest Monsoon (June-August) due to intense coastal upwelling. Copepods were present in the study area throughout the sampling period with a noticeable increase in their abundance during the Southwest Monsoon. On the other hand, the first appearance of Noctiluca in the sampling location was during the Early Southwest Monsoon (mid-June) and thereafter their abundance increased towards the Peak Southwest Monsoon. The grazing experiments carried out as per the food removal method showed noticeable differences in the feeding preferences of Noctiluca and copepods, especially on the different size fractions of phytoplankton. Noctiluca showed the highest positive electivity for the phytoplankton micro-fraction (av. 0.49 ± 0.04), followed by nano-fraction (av. 0.17 ± 0.04) and a negative electivity for the pico-fraction (av. -0.66 ± 0.06). In total ingestion of Noctiluca, micro-fraction contribution (83.7%) was significantly higher compared to the nano- (15.7%) and pico-fractions (0.58%). On the other hand, copepods showed the highest positive electivity for the phytoplankton nano-fraction (av. 0.38 ± 0.04) followed by micro- (av. -0.17 ± 0.05) and pico-fractions (av. -0.35 ± 0.05). Similarly, in total ingestion of copepods, nano-fraction (69.7%) was the highest followed by micro- (28.9%) and pico-fractions (1.37%). The grazing pressure of Noctiluca on the total phytoplankton was found to be 27.7% of the standing stock and 45.6% of the production, whereas in the case of copepods, it was 9.95% of the standing stock and 16.6% of the production. The study showed that the grazing pressure of Noctiluca on the total phytoplankton as well as larger phytoplankton fraction was 2.8- and 8-folds higher than that of the copepods. This suggests the leading role of Noctiluca as an effective grazer of larger phytoplankton along the southwest west coast of India, especially during the Peak/Late Southwest Monsoon.

Dissolved methane in Indian freshwater reservoirs.

Emission of methane (CH4), a potent greenhouse gas, from tropical reservoirs is of interest because such reservoirs experience conducive conditions for CH4 production through anaerobic microbial activities. It has been suggested that Indian reservoirs have the potential to emit as much as 33.5 MT of CH4 per annum to the atmosphere. However, this estimate is based on assumptions rather than actual measurements. We present here the first data on dissolved CH4 concentrations from eight freshwater reservoirs in India, most of which experience seasonal anaerobic conditions and CH4 buildup in the hypolimnia. However, strong stratification prevents the CH4-rich subsurface layers to ventilate CH4 directly to the atmosphere, and surface water CH4 concentrations in these reservoirs are generally quite low (0.0028-0.305 µM). Moreover, only in two small reservoirs substantial CH4 accumulation occurred at depths shallower than the level where water is used for power generation and irrigation, and in the only case where measurements were made in the outflowing water, CH4 concentrations were quite low. In conjunction with short periods of CH4 accumulation and generally lower concentrations than previously assumed, our study implies that CH4 emission from Indian reservoirs has been greatly overestimated.

Cecembia lonarensis gen. nov., sp. nov., a haloalkalitolerant bacterium of the family Cyclobacteriaceae, isolated from a haloalkaline lake and emended descriptions of the genera Indibacter, Nitritalea and Belliella.

A novel Gram-staining-negative, rod-shaped, non-motile bacterium, designated strain LW9(T), was isolated from a water sample collected from Lonar Lake of Buldhana district, Maharashtra, India. Colonies and broth cultures were reddish orange due to the presence of carotenoid pigments. Strain LW9(T) was positive for catalase, ornithine decarboxylase and lysine decarboxylase activities and negative for gelatinase, oxidase, urease and lipase activities. The predominant fatty acids were iso-C(15 : 0) (31.3 %), iso-C(16 : 0) (9.3 %), anteiso-C(15 : 0) (7.3 %), iso-C(16 : 1) H (6.1 %), summed feature 3 (comprising C(16 : 1)ω7c/C(16 : 1)ω6c; 5.9 %), iso-C(17 : 1)ω9c (5.4 %) and iso-C(17 : 0) 3-OH (5.0 %). Strain LW9(T) contained MK-7 as the major respiratory quinone. The polar lipids consisted of phosphatidylethanolamine, two unidentified aminolipids and seven unidentified lipids. The DNA G+C content of strain LW9(T) was 40.5 mol%. 16S rRNA gene sequence analysis indicated that the type strains of Indibacter alkaliphilus and Aquiflexum balticum, two members of the family Cyclobacteriaceae (phylum 'Bacteroidetes') were the most closely related strains with sequence similarities of 93.0 and 94.0 %, respectively. Other members of the family Cyclobacteriaceae showed sequence similarities <93.0 %. Based on these phenotypic characteristics and on phylogenetic inference, strain LW9(T) is proposed as the representative of novel species in a new genus, Cecembia lonarensis gen. nov., sp. nov. The type strain of the type species, Cecembia lonarensis, is LW9(T) (= CCUG 58316(T) = KCTC 22772(T)). Emended descriptions of the genera Indibacter, Nitritalea and Belliella are also proposed.

Variations in some environmental characteristics including C and N stable isotopic composition of suspended organic matter in the Mandovi estuary.

Chemical and isotopic (δ13C and δ15N) investigation of the Mandovi estuary along the Indian west coast affected strongly by the seasonal monsoon cycle was carried out. The Mandovi estuary is a major waterway for Goa and extensively used for transportation of iron and manganese ore. In addition, with large population centers as well as agricultural fields located on its shores, the estuary is assumed to have been influenced by human activities. Measurements of chemical and isotopic parameters made in the lower part of the estuary during the southwest (SW) monsoon and post-monsoon seasons reveal distinct changes, and it is observed that despite considerable enrichment of macronutrients during the SW monsoon, productivity of the estuary (phytoplankton biomass), as inferred from the chlorophyll-a content, is not as high as expected. This is due to occurrences of high turbidity and cloud cover that limits photosynthetic productivity. The isotopic characterization (C and N isotopes) of suspended organic matter produced/transported during the monsoon and post-monsoon seasons of year 2007 provides a baseline dataset for future isotopic studies in such type of tropical estuaries.

Retraction. Cecembia lonarensis gen. nov., sp. nov., a novel haloalkalitolerant bacterium of the family Cyclobacteriaceae, isolated from a haloalkaline lake and emended descriptions of the genera Indibacter, Nitritalea, Belliella and Aquiflexum.

The authors would like to retract this publication in order to improve the chemotaxonomic data as it has become apparent that there are inconsistencies in the data presented in this paper. This paper has been retracted from IJSEM Papers in Press and will not be published in print in IJSEM.

Denitrifying bacterial community composition changes associated with stages of denitrification in oxygen minimum zones.

Denitrification in the ocean is a major sink for fixed nitrogen in the global N budget, but the process is geographically restricted to a few oceanic regions, including three oceanic oxygen minimum zones (OMZ) and hemipelagic sediments worldwide. Here, we describe the diversity and community composition of microbes responsible for denitrification in the OMZ using polymerase chain reaction, sequence and fragment analysis of clone libraries of the signature genes (nirK and nirS) that encode the enzyme nitrite reductase, responsible for key denitrification transformation steps. We show that denitrifying assemblages vary in space and time and exhibit striking changes in diversity associated with the progression of denitrification from initial anoxia through nitrate depletion. The initial denitrifying assemblage is highly diverse, but succession on the scale of 3-12 days leads to a much less diverse assemblage and dominance by one or a few phylotypes. This progression occurs in the natural environment as well as in enclosed incubations. The emergence of dominants from a vast reservoir of rare types has implications for the maintenance of diversity of the microbial population and suggests that a small number of microbial dominants may be responsible for the greatest rates of transformations involving nitrous oxide and global fixed nitrogen loss. Denitrifying blooms, driven by a few types responding to episodic environmental changes and distributed unevenly in time and space, are consistent with the sampling effect model of diversity-function relationships. Canonical denitrification thus appears to have important parallels with both primary production and nitrogen fixation, which are typically dominated by regionally and temporally restricted blooms that account for a disproportionate share of these processes worldwide.

The next generation of iron fertilization experiments in the Southern Ocean.

Of the various macro-engineering schemes proposed to mitigate global warming, ocean iron fertilization (OIF) is one that could be started at short notice on relevant scales. It is based on the reasoning that adding trace amounts of iron to iron-limited phytoplankton of the Southern Ocean will lead to blooms, mass sinking of organic matter and ultimately sequestration of significant amounts of atmospheric carbon dioxide (CO2) in the deep sea and sediments. This iron hypothesis, proposed by John Martin in 1990 (Martin 1990 Paleoceanography 5, 1-13), has been tested by five mesoscale experiments that provided strong support for its first condition: stimulation of a diatom bloom accompanied by significant CO2 drawdown. Nevertheless, a number of arguments pertaining to the fate of bloom biomass, the ratio of iron added to carbon sequestered and various side effects of fertilization, continue to cast doubt on its efficacy. The idea is also unpopular with the public because it is perceived as meddling with nature. However, this apparent consensus against OIF is premature because none of the published experiments were specifically designed to test its second condition pertaining to the fate of iron-induced organic carbon. Furthermore, the arguments on side effects are based on worst-case scenarios. These doubts, formulated as hypotheses, need to be tested in the next generation of OIF experiments. We argue that such experiments, if carried out at appropriate scales and localities, will not only show whether the technique will work, but will also reveal a wealth of insights on the structure and functioning of pelagic ecosystems in general and the krill-based Southern Ocean ecosystem, in particular. The outcomes of current models on the efficacy and side effects of OIF differ widely, so data from adequately designed experiments are urgently needed for realistic parametrization. OIF is likely to boost zooplankton stocks, including krill, which could have a positive effect on recovery of the great whale populations. Negative effects of possible commercialization of OIF can be controlled by the establishment of an international body headed by scientists to supervise and monitor its implementation.