Posts Tagged 'Indian'

The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt

The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region, provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Water samples for phytoplankton enumeration were collected from the upper 30 m during two cruises, the first to the South Atlantic sector (Jan–Feb 2011; 60 °W–15 °E and 36–60 °S) and the second in the South Indian sector (Feb–Mar 2012; 40–120 °E and 36–60 °S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Sub-Tropical, Polar, and Sub-Antarctic Fronts. The influence of environmental parameters, such as sea-surface temperature (SST), salinity, carbonate chemistry (i.e., pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macro-nutrients (i.e., nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB, was assessed statistically. Nanophytoplankton (cells 2–20 μm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, the coccolithophore Emiliania huxleyi and the diatoms Fragilariopsis nana, F. pseudonana and Pseudonitzschia sp. were the most dominant and widely distributed species. A combination of SST, macro-nutrient concentrations and pCO2 were the best statistical descriptors of biogeographic variability of biomineralizing species composition between stations. Emiliania huxleyi occurred in the silicic acid-depleted waters between the Sub-Antarctic Front and the Polar Front, indicating a favorable environment for this coccolithophore in the GCB after spring diatom blooms remove silicic acid to limiting levels. After full consideration of variability in carbonate chemistry and temperature on the distribution of nanoplankton in the GCB, we find that temperature remains the dominant driver of biogeography in a large proportion of the modern Southern Ocean.

Continue reading ‘The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt’

Assessing phytoplankton community structure in relation to hydrographic parameters and seasonal variation (Pre and Post Monsoon)

The present study is conducted to assess hydrographical parameters, phytoplankton composition and the relationship between physicochemical parameters and phytoplankton assemblages along Chabahar coastal waters, South coast of Iran. Based on the collected samples from four stations, all the hydrographical parameters such as sea surface temperature, salinity, pH, DO and nitrate, inorganic phosphate, silicate, and phytoplankton assemblages were studied for five months (from April 2014 to August 2014). A total of 165 phytoplankton groups/taxa were observed in which the Dinophyceae formed the dominant group in all seasons. During the pre-monsoon season, Dinophyceae (56.5%) was the most abundant phytoplankton group followed by Bacillariophyceae (40.8%), Cyanophyceae (1.7 %) and Dictyochophyceae (0.8%). Meanwhile, in the post-monsoon season, Dinophyceae was dominant (49.5%), followed by Bacillariophyceae (46.7%), Cyanophyceae (1.8%), and Dictyochophyceae (1.8%). The highest phytoplankton density was in mid-May (19584953± 345182 cell per litter) and the lowest was in late July (163928± 1790 cells per liter). Salinity, nitrate, phosphate, silicate showed significant variation (p<0.05) among seasons while pH, seawater temperature, dissolve oxygen did not show significant differences in all stations over the study periods (p<0.05). Phytoplankton density correlated positively with water temperature and salinity. Results showed an increased concentration in phytoplankton density during Pre-monsoon season followed by Post-monsoon and monsoon season.

Continue reading ‘Assessing phytoplankton community structure in relation to hydrographic parameters and seasonal variation (Pre and Post Monsoon)’

Intertidal oysters reach their physiological limit in a future high-CO2 world

Sessile marine molluscs living in the intertidal zone experience periods of internal acidosis when exposed to air (emersion) during low tide. Relative to other marine organisms, molluscs have been identified as vulnerable to future ocean acidification; however, paradoxically it has also been shown that molluscs exposed to high CO2 environments are more resilient compared with those molluscs naive to CO2 exposure. Two competing hypotheses were tested using a novel experimental design incorporating tidal simulations to predict the future intertidal limit of oysters in a high-CO2 world; either high-shore oysters will be more tolerant of elevated PCO2 because of their regular acidosis, or elevated PCO2 will cause high-shore oysters to reach their limit. Sydney rock oysters, Saccostrea glomerata, were collected from the high-intertidal and subtidal areas of the shore and exposed in an orthogonal design to either an intertidal or a subtidal treatment at ambient or elevated PCO2, and physiological variables were measured. The combined treatment of tidal emersion and elevated PCO2 interacted synergistically to reduce the haemolymph pH (pHe) of oysters, and increase the PCO2 in the haemolymph (Pe,CO2) and standard metabolic rate. Oysters in the intertidal treatment also had lower condition and growth. Oysters showed a high degree of plasticity, and little evidence was found that intertidal oysters were more resilient than subtidal oysters. It is concluded that in a high-CO2 world the upper vertical limit of oyster distribution on the shore may be reduced. These results suggest that previous studies on intertidal organisms that lacked tidal simulations may have underestimated the effects of elevated PCO2.

Continue reading ‘Intertidal oysters reach their physiological limit in a future high-CO2 world’

Variation in calcification rate of Acropora downingi relative to seasonal changes in environmental conditions in the northeastern Persian Gulf

There is a strong interest in understanding how coral calcification varies with changing environmental conditions, especially given the projected changes in temperature and aragonite saturation due to climate change. This study explores in situ variation in calcification rates of Acropora downingi in the northeastern Persian Gulf relative to seasonal changes in temperature, irradiance and aragonite saturation state (Ωarag). Calcification rates of A. downingi were highest in the spring and lowest in the winter, and intra-annual variation in calcification rate was significantly related to temperature (r2 = 0.30) and irradiance (r2 = 0.36), but not Ωarag (r2 = 0.02). Seasonal differences in temperature are obviously confounded by differences in other environmental conditions and vice versa. Therefore, we used published relationships from experimental studies to establish which environmental parameter(s) (temperature, irradiance, and/or Ωarag) placed greatest constraints on calcification rate (relative to the maximum spring rate) in each season. Variation in calcification rates was largely attributable to seasonal changes in irradiance and temperature (possibly ~57.4 and 39.7% respectively). Therefore, we predict that ocean warming may lead to increased rates of calcification during winter, but decelerate calcification during spring, fall and especially summer, resulting in net deceleration of calcification for A. downingi in the Persian Gulf.

Continue reading ‘Variation in calcification rate of Acropora downingi relative to seasonal changes in environmental conditions in the northeastern Persian Gulf’

Variation in carbonate system and air-water CO2 flux during summer in the Mahanadi Estuary, India

The carbonate system of water of the inner estuary and near shore in the Mahanadi estuary, Bay of Bengal, India was studied in summer season of 2014. Physicochemical parameters like temperature, pH, salinity, total alkalinity (TA), dissolved inorganic carbon (DIC), total organic carbon (TOC) and chlorophyll a (chl a) were measured in order to study their role in controlling the CO2 flux. The estuary acted as a sink for atmospheric CO2 triggered by the allochthonous organic carbon input. The average CO2 flux was recorded as -0.36±13.29 μmol/m2h in inner estuary and -10.36±2.00 μmol/m2h in near shore region. The temperature and salinity were found to be significantly and positively correlated with fCO2 (water) indicating their deterministic role in influencing air-water CO2 flux.

Continue reading ‘Variation in carbonate system and air-water CO2 flux during summer in the Mahanadi Estuary, India’

Biomarker response of climate change-induced ocean acidification and hypercapnia studies on brachyurian crab Portunus pelagicus

A laboratory level microcosm analysis of the impacts of ocean acidification on the environmental stress biomarkers in Portunus pelagicus (Linneaus 1758)exposed to a series of pH regimes expected in the year 2100 (pH 7.5 and 7.0) and leakage from a sub-seabed carbon dioxide storage site (pH 6.5 – 5.5) was carried out. Levels of the antioxidant enzyme catalase, the phase II detoxification enzyme, glutathione S. transferase, the lipid peroxidation biomarker, malondialdehyde, acetylcholinesterase, and reduced glutathione were estimated in the tissues of the exposed animals to validate theses enzymes as biomarkers of Hypercapnia. The integrated biomarkers indicated a stress full environment in all animals except those exposed to the control seawater (pH 8.1). The reducing pH was also observed to be highly lethal to the animals exposed to lower pH levels which were obvious from the rate of mortality in a short term of exposure. The present study substantiates the role of biomarkers as an early warning of ocean acidification at a sub-lethal level.

Continue reading ‘Biomarker response of climate change-induced ocean acidification and hypercapnia studies on brachyurian crab Portunus pelagicus’

Coral reefs and people in a high-CO2 world: where can science make a difference to people?

Reefs and People at Risk

Increasing levels of carbon dioxide in the atmosphere put shallow, warm-water coral reef ecosystems, and the people who depend upon them at risk from two key global environmental stresses: 1) elevated sea surface temperature (that can cause coral bleaching and related mortality), and 2) ocean acidification. These global stressors: cannot be avoided by local management, compound local stressors, and hasten the loss of ecosystem services. Impacts to people will be most grave where a) human dependence on coral reef ecosystems is high, b) sea surface temperature reaches critical levels soonest, and c) ocean acidification levels are most severe. Where these elements align, swift action will be needed to protect people’s lives and livelihoods, but such action must be informed by data and science.

An Indicator Approach

Designing policies to offset potential harm to coral reef ecosystems and people requires a better understanding of where CO2-related global environmental stresses could cause the most severe impacts. Mapping indicators has been proposed as a way of combining natural and social science data to identify policy actions even when the needed science is relatively nascent. To identify where people are at risk and where more science is needed, we map indicators of biological, physical and social science factors to understand how human dependence on coral reef ecosystems will be affected by globally-driven threats to corals expected in a high-CO2 world. Western Mexico, Micronesia, Indonesia and parts of Australia have high human dependence and will likely face severe combined threats. As a region, Southeast Asia is particularly at risk. Many of the countries most dependent upon coral reef ecosystems are places for which we have the least robust data on ocean acidification. These areas require new data and interdisciplinary scientific research to help coral reef-dependent human communities better prepare for a high CO2 world.

Continue reading ‘Coral reefs and people in a high-CO2 world: where can science make a difference to people?’


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