Posts Tagged 'Indian'

pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios

The increasing atmospheric CO2 concentration in the last few decades has resulted in a decrease in oceanic pH. In this study, we assessed the natural variability of pH in coastal waters off Goa, eastern Arabian Sea. pHT showed large variability (7.6–8.1) with low pH conditions during south‐west monsoon (SWM), and the variability is found to be associated with upwelling rather than freshwater runoff. Considering that marine biota inhabiting dynamic coastal waters off Goa are exposed to such wide range of natural fluctuations of pH, an acidification experiment was carried out. We studied the impact of low pH on the local population of sea urchin Stomopneustes variolaris (Lamarck, 1816). Sea urchins were exposed for 210 days to three treatments of pHT: 7.96, 7.76 and 7.46. Our results showed that S. variolaris at pHT 7.96 and 7.76 were not affected, whereas the ones at pHT 7.46 showed adverse effects after 120 days and 50% mortality by 210 days. However, even after exposure to low pH for 210 days, 50% organisms survived. Under low pH conditions (pHT 7.46), the elemental composition of sea urchin spines exhibited deposition of excess Sr2+ as compared to Mg2+ ions. We conclude that although the sea urchins would be affected in future high CO2 waters, at present they are not at risk even during the south‐west monsoon when low pH waters reside on the shelf.

Continue reading ‘pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios’

Configuration and skill assessment of the coupled biogeochemical model for the carbonate system in the Bay of Bengal

Highlights

  • A coupled physical-biogeochemical model (ROMS-PISCES) has been set up for the Bay of Bengal region to emulate the carbonate chemistry of this region.
  • The model has been run and rigorously evaluated using the available data sets and 8 statistical indices have been used to evaluate model skills.
  • The effect of wind stress and E-P has been evaluated through two numerical experiments, which uses two different bulk formulae to calculate the wind stresses.
  • The model is excellent in simulating the spatial heterogeneity and temporal variation of all the carbonate parameters thus giving a basis for further studies like the effect of physical dynamics, forecasting, etc.

Abstract

The Bay of Bengal is a semi-enclosed ocean basin situated in the eastern part of the North Indian Ocean. Though the physical dynamical features of the Bay of Bengal have been studied and measured in detail, the carbonate chemistry of this basin has been less explored, and very few reliable data-sets exist. This paucity of data has emerged as a major challenge in modeling and understanding the carbonate system parameters for this region. In this study, a coupled physical-biogeochemical (ROMS-PISCES) model has been configured and run to emulate the surface carbonate system parameters (DIC, TALK, pCO2, and pH) for the Bay of Bengal region. Model skill assessment analysis has been performed using available observational data-sets. Two different numerical experiments have been performed (WB indicating the use of default bulk formulae of ROMS to calculate wind stress and WoB indicating the calculated wind stresses of QuikSCAT climatology product using different bulk formula), to understand which one reproduces the carbonate parameters better. Both the numerical experiments are rigorously compared for physical as well as carbonate system parameters. The numerical experiments have been passed through exhaustive statistical analysis by comparing it with the observed data-sets. The temperature, the primary driver affecting pH and pCO2 has been reproduced by both the experiments excellently, and the correlation value is more than 0.9 with RAMA buoy data (15o N, 90o E). The salinity, when compared with the NIOA climatology data, shows that the WoB experiment has better captured both the spatial and temporal variation of salinity. Both the numerical experiments have been compared individually with three sets of observed carbonate data. The WoB run has been found to emulate carbonate system parameters satisfactorily than the WB run. The pCO2 and pH show a good positive correlation with RAMA data and the values are 0.87, and 0.93, respectively.

 

Continue reading ‘Configuration and skill assessment of the coupled biogeochemical model for the carbonate system in the Bay of Bengal’

Status of corals along the Sindh coast of Pakistan: prevailing environmental conditions, their impacts on community structure and conservation approaches

Highlights

• Describes status of corals along the Sindh coast of Pakistan.

• Prevailing physico-chemical conditions in coastal waters of Sindh, Pakistan.

• Impacts of physico-chemical conditions on corals distribution patterns.

• Existing threats and future conservation plans.

Abstract

Reef system across the globe is facing serious anthropogenic threats and impacts. The present study describes the status of corals, prevailing stresses and their impacts on community structure along the Sindh coast of Pakistan. In the current study, 21 species of hard corals were recorded. All together, 50 live coral species recorded from the coastal waters of Pakistan. High diversity occurred at Churna Island (15 species). A little bit patch reef formation was observed at Churna Island (dive sites 2 and 3) while scattered colonies were recorded in coastal habitats. Porites species were found dominating both in coastal and offshore environments. Overall, temperature and nutrient concentrations were found to be fluctuating than what corals prefer, however, pH concentrations were found in normal ranges. Calcium, carbon and oxygen were recorded as major elements incorporated in coral skeletons. Possible causes of limited coral fauna and a confined distribution pattern appeared to be linked with local factors (strong wave action, high nutrient concentrations, temperature fluctuations, past geological events, reversal monsoon and overfishing) rather than global changes. Other impacts, for example diving tourism, coral mining or collection for ornaments or sale are minor. Prevailing stresses, increase in the construction of local infrastructure in coastal areas and unmanaged tourism indicates that in future, the level of pollution will further increase in coastal areas. As a result, a further shift in community structure will occur and it appears that only Porites will survive in the coastal waters of Pakistan. Future protection efforts should focus on regular monitoring and establishing of an effective Marine Protected Area at least around the shallow habitats of the Churna Island.

Continue reading ‘Status of corals along the Sindh coast of Pakistan: prevailing environmental conditions, their impacts on community structure and conservation approaches’

Vulnerability and resilience of tropical coastal ecosystems to ocean acidification

Ocean acidification leads to a wide variety of responses from tropical coastal ecosystems. Coral reefs are most vulnerable with most coral species exhibiting declining calcification rates with decreasing pH and carbonate chemistry parameters. Some corals show resilience to acidification likely due to active physiological regulation of their calcifying fluid. Other calcifying organisms, such as some foraminifera and coccolithophores, exhibit negative responses, whereas some symbiont-bearing calcifiers respond positively, to increasing acidification. Seagrasses and brown macroalgae thrive under acidified conditions, with increasing rates of primary productivity. Some tropical coastal fish species are resilient, and in some species, respond positively, to acidification. Some tropical species show complex, nonlinear responses to declining pH and carbonate chemistry. Factors that influence the ability of a species to adapt to and/or resist acidification include food supply, nutrient availability, temperature, diet, interactions with symbionts and other organisms and species and community diversity. Interactive effects of ocean acidification with other climate change parameters, such as elevated temperature, play an important but poorly understood role in determining the resilience and vulnerability of tropical coastal species, communities and ecosystems. Some short-lived species can undergo acclimation and/or adaptive evolution to increase fitness in the face of acidification. Biota living in tropical estuarine and nearshore environments, such as mangroves, seagrasses and intertidal and subtidal inshore benthos, are unlikely to be significantly affected by future acidification as such environments exhibit very wide variations in water and sediment pH and carbonate chemistry. Nearly all tropical coastal environments exhibit significant CO2 efflux to the atmosphere due to pCO2 and [CO32-] oversaturation caused by high rates of respiration and factors linked to fluvial discharge. Except for coral reefs, most calcifying organisms and upwelling regions, tropical estuarine and inshore ecosystems unaffected by eutrophication and other anthropogenic problems should be resilient to future acidification.

Continue reading ‘Vulnerability and resilience of tropical coastal ecosystems to ocean acidification’

Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients (update)

Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of δ11B of calcite tests to seawater pH. However, our knowledge of the relationship between δ11B and pH remains incomplete for many taxa. Thus, to expand the potential scope of application of this proxy, we report δ11B data for seven different species of planktonic foraminifera from sediment core tops. We utilize a method for the measurement of small samples of foraminifera and calculate the δ11B-calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or without sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia menardii, and Globorotalia tumida, including for unstudied core tops and species. These taxa have diverse ecological preferences and are from sites that span a range of oceanographic regimes, including some that are in regions of air–sea equilibrium and others that are out of equilibrium with the atmosphere. The sensitivity of δ11Bcarbonate to δ11Bborate (e.g., Δδ11Bcarbonate∕Δδ11Bborate) in core tops is consistent with previous studies for T. sacculifer and G. ruber and close to unity for N. dutertrei, O. universa, and combined deep-dwelling species. Deep-dwelling species closely follow the core-top calibration for O. universa, which is attributed to respiration-driven microenvironments likely caused by light limitation and/or symbiont–host interactions. Our data support the premise that utilizing boron isotope measurements of multiple species within a sediment core can be utilized to constrain vertical profiles of pH and pCO2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pumps.

Continue reading ‘Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients (update)’

Short-term responses to ocean acidification: effects on relative abundance of eukaryotic plankton from the tropical Timor Sea

Anthropogenic carbon dioxide (CO2) emissions drive climate change and pose one of the major challenges of our century. The effects of increased CO2 in the form of ocean acidification (OA) on the communities of marine planktonic eukaryotes in tropical regions such as the Timor Sea are barely understood. Here, we show the effects of high CO2 (pCO2=1823±161 μatm, pHT=7.46±0.05) versus in situ CO2 (pCO2=504±42 μatm, pHT=7.95±0.04) seawater on the community composition of marine planktonic eukaryotes immediately and after 48 hours of treatment exposure in a shipboard microcosm experiment. Illumina sequencing of the V9 hypervariable region of 18S rRNA (gene) was used to study the eukaryotic community composition. Down-regulation of extracellular carbonic anhydrase occurred faster in the high CO2 treatment. Increased CO2 significantly suppressed the relative abundances of eukaryotic operational taxonomic units (OTUs), including important primary producers. These effects were consistent between abundant (DNA-based) and active (cDNA-based) taxa after 48 hours, e.g., for the diatoms Trieres chinensis and Stephanopyxis turris. Effects were also very species-specific among the different diatoms. The microbial eukaryotes showed adaptation to the CO2 treatment over time, but many OTUs were adversely affected by decreasing pH. OA effects might fundamentally impact the base of marine biodiversity, suggesting unpredictable outcomes for food web functioning in the future ocean.

Continue reading ‘Short-term responses to ocean acidification: effects on relative abundance of eukaryotic plankton from the tropical Timor Sea’

Variation of pCO2 concentrations induced by tropical cyclones “Wind-Pump” in the middle-latitude surface oceans: a comparative study

The Bermuda Testbed Mooring (BTM) and Bay of Bengal Ocean Acidification (BOBOA) mooring measurements were used to identify changes in the partial pressure of CO2 at the sea surface (pCO2sea) and air-sea CO2 fluxes (FCO2) associated with passage of two tropical cyclones (TCs), Florence and Hudhud. TC Florence passed about 165 km off the BTM mooring site with strong wind speeds of 24.8 m s–1 and translation speed of 7.23 m s–1. TC Hudhud passed about 178 km off the BOBOA mooring site with wind speeds of 14.0 m s–1 and translation speed of 2.58 m s–1. The present study examined the effect of temperature, salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), air-sea CO2 flux, and phytoplankton chlorophyll a change on pCO2sea as a response to TCs. Enhanced mixed layer depths were observed due to TCs-induced vertical mixing at both mooring sites. Decreased pCO2sea (–15.16±5.60 μatm) at the BTM mooring site and enhanced pCO2sea (14.81±7.03 μatm) at the BOBOA mooring site were observed after the passage of Florence and Hudhud, respectively. Both DIC and TA are strongly correlated with salinity in the upper layer of the isothermal layer depth (ILD). Strong (weak) vertical gradient in salinity is accompanied by strong (weak) vertical gradients in DIC and TA. Strong vertical salinity gradient in the upper layer of the ILD (0.031 psu m–1), that supply much salinity, dissolved inorganic carbon and total alkalinity from the thermocline was the cause of the increased pCO2sea in the BOBOA mooring water. Weak vertical salinity gradient in the upper layer of the ILD (0.003 psu m–1) was responsible for decreasing pCO2sea in the BTM mooring water. The results of this study showed that the vertical salinity gradient in the upper layer of the ILD is a good indicator of the pCO2sea variation after the passages of TCs.

Continue reading ‘Variation of pCO2 concentrations induced by tropical cyclones “Wind-Pump” in the middle-latitude surface oceans: a comparative study’

State and trends of Australia’s oceans: ocean acidification

The pH and aragonite saturation state of surface seawaters around Australia
are influenced by the large-scale circulation, and superimposed on this are the
effects of seasonal changes due largely to biological activity and temperature
change. Maximum values of aragonite saturation state tend to develop over
summer-early autumn, while pH values are typically greatest in winter.
Biological production contributes to increases of both pH and aragonite
saturation state in the spring-summer, while warming acts to increase the
saturation state and decrease pH. Seasonal ranges of both variables are
already estimated to be outside the ranges that many of Australia’s marine
ecosystems are likely to have experienced in the late 1800s.

Continue reading ‘State and trends of Australia’s oceans: ocean acidification’

State and trends of Australia’s ocean report: ocean acidification and calcifying zooplankton

There is no evidence of a decline in calcifying zooplankton at the IMOS National
Reference Stations over the past 10 years, suggesting ocean acidification
over this time span is unlikely to be having a substantial impact on calcifying
zooplankton. However, there is some evidence that calcifying zooplankton
might at Maria Island and Yongala be sensitive to the aragonite saturation state
at the range of values currently observed.

Continue reading ‘State and trends of Australia’s ocean report: ocean acidification and calcifying zooplankton’

Evaluation of heterotrophic bacteria associated with healthy and bleached corals of Gulf of Kutch, Gujarat, India for siderophore production and their response to climate change factors

Highlights

• Comparison of siderophore production by healthy and bleached coral associated microbes.

• Catecholate type of siderophore is mainly produced by coral associated microbes.

• Adapting ability of healthy and bleached coral isolates in changing climate.

• Significant effect of lowering pH and increasing temperature on growths and siderophore production of coral associated bacteria.

Abstract

Bacteria are known to play a crucial role in coral health but their mechanisms are unclear. Siderophore production could be one of the mechanisms by which they benefit or harm the corals. Bacteria produce siderophore to adapt in harsh conditions, such as nutrient limiting and competing environments such as coral surface. In the present study, siderophore producing ability of microbes associated with healthy and bleached corals is evaluated as both healthy and bleached coral surface provide a different environment concerning nutrients and competitions. Total of 129 siderophore-producing bacteria associated with two healthy (n = 66 isolates) and bleached coral (n = 63) species (Porites spp. and Turbinaria spp.) from the Gulf of Kutch (GoK), Gujarat (India) are screened and compared. No relation between coral health status and siderophore producing ability of microbes is observed (one-way ANOVA, p = 0.67). All the isolates are positive to catecholate type of siderophore which has the strongest affinity for limiting iron. The study also explores the growth and siderophore production behavior of healthy and bleached coral isolates at decreasing pH and temperature rise as they are the important factors that affects the solubility of nutrients and thus, the structure and functioning of the microbes. Isolates from bleached corals showed an increase in growth even at pH 6, whereas the growth of healthy coral isolates reduces at pH 6. Temperature rise is negatively correlated to growth and siderophore production by all isolates except Bacillus sp. PH26. Combined low pH and temperature rise stress, negatively affect growth and siderophore production of coral-associated microbes with Bacillus sp. PH26 as exception. General correlation trend of bacterial growth and siderophore production is positive. The isolates showing exceptional behavior might be possibly beneficial or harmful to the coral health. Thus, growth and siderophore production of microbes under changing climate conditions might be used as preliminary tools to screen beneficial and pathogenic microbes of corals from opportunistic microbes. This screening would reduce the number of possible candidates for in-situ and in-vitro microcosm experiments to understand the role of siderophore producing microbes in coral health. Overall, pH and temperature have a significant impact on coral-associated microbial growth and siderophore production, which ultimately impact the coral health and disease as the microbes form an integral part of coral holobiont. The study laid the foundation for future studies to understand the role of siderophore producing bacteria in coral health in the global climate-changing era.

Continue reading ‘Evaluation of heterotrophic bacteria associated with healthy and bleached corals of Gulf of Kutch, Gujarat, India for siderophore production and their response to climate change factors’


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Ocean acidification in the IPCC AR5 WG II

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