Posts Tagged 'review'

Impact on climate change on marine plankton with special reference to Indian seas

The seas surrounding India, namely Arabian Sea (AS) and Bay of Bengal (BoB) with their associated coastal embayments form one of the highly productive areas and biodiversity hotspots in the tropics contributing profusely to the socio-economic front of the region. Therefore, acquiring knowledge of the climate change scenario of this region and its impacts on marine ecosystems in general and planktons, in particular, is considered crucial for better resilience. In fact, several attempts have been made of late to understand the climate change impacts on plankton, corals and mangroves of this region. In this article, we tried to update the climate change scenario of Indian seas and its impact on plankton communities based on the information gathered from the peer reviewed publications and scientific reports. Results of this review have shown that the global warming generated SST (Sea Surface Temperature) rise and sea water acidification related pH fall have affected the species composition, abundance, phenology and metabolic pathways of plankton populations in this region

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Ocean acidification studies in coral reefs of Japan

Increasing anthropogenic CO2 emissions cause progressive ocean acidification, reducing the calcium carbonate saturation state and coral reef calcification rate. The future uptake of CO2 by the world ocean is predicted to reduce seawater pH by 0.3–0.5 units over the next few decades, which corresponds to a rate 100 times faster than that observed at any time during the last 20 million years. In this chapter, we discuss the effects of ocean acidification on coral reefs, which have been initially probed by culture experiments at several decreased pH conditions, being subsequently investigated by multiple stress factor experiments and field observations of acidified sites. By considering previous studies, we propose that the evaluation and prediction of future ecosystem dynamics require the development of convenient and inexpensive carbonate chemistry-related field measurement techniques such as pH logging, additionally highlighting the importance of studying two naturally acidified sites in Japan, namely, the Iwotorishima and Shikine Islands.

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Paradigm lost: ocean acidification will overturn the concept of larval-fish biophysical dispersal

Most marine ecologists have in the past 25 years changed from supporting a passive-dispersal paradigm for larval marine fishes to supporting a biophysical-dispersal paradigm wherein the behaviour of larvae plays a central role. Research shows larvae of demersal perciform fishes have considerable swimming and orientation abilities over a major portion of their pelagic larval duration. These abilities depend on sensory function, and some recent research has indicated anthropogenic acidification of the oceans will by the end of the century result in sensory dysfunction. This could strongly alter the ability of fish larvae to orientate in the pelagic environment, to locate suitable settlement habitat, to bet-hedge, and to colonize new locations. This paper evaluates the available publications on the effects of acidification on senses and behaviours relevant to dispersal of fish early life-history stages. A large majority of studies tested CO2 values predicted for the middle to end of the century. Larvae of fourteen families—all but two perciform—were studied. However, half of studies used Damselfishes (Pomacentridae), and except for swimming, most studies used settlement-stage larvae or later stages. In spite of these taxonomic and ontogenetic restrictions, all but two studies on sensory function (chemosensation, hearing, vision, detection of estuarine cues) found deleterious effects from acidification. The four studies on lateralization and settlement timing all found deleterious effects from acidification. No clear effect of acidification on swimming ability was found. If fish larvae cannot orientate due to sensory dysfunction, their dispersal will, in effect, conform to the passive dispersal paradigm. Modelling incorporating larval behaviour derived from empirical studies indicates that relative to active larvae, passive larvae will have less self-recruitment, higher median and mean dispersal distances, and lower settlement rates: further, bet hedging and colonization of new locations will decrease. The biophysical dispersal paradigm will be lost in theory and in fact, which is predicted to result in lower recruitment and less bet hedging for demersal, perciform fishes. More research is required to determine if the larvae of other Orders will be effected in the same way, or if warm- and cold-water fish faunas will be similarly effected.

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Reviews and syntheses: revisiting the boron systematics of aragonite and their application to coral calcification

The isotopic and elemental systematics of boron in aragonitic coral skeletons have recently been developed as a proxy for the carbonate chemistry of the coral extracellular calcifying fluid. With knowledge of the boron isotopic fractionation in seawater and the B / Ca partition coefficient (KD) between aragonite and seawater, measurements of coral skeleton δ11B and B / Ca can potentially constrain the full carbonate system. Two sets of abiogenic aragonite precipitation experiments designed to quantify KD have recently made possible the application of this proxy system. However, while different KD formulations have been proposed, there has not yet been a comprehensive analysis that considers both experimental datasets and explores the implications for interpreting coral skeletons. Here, we evaluate four potential KD formulations: three previously presented in the literature and one newly developed. We assess how well each formulation reconstructs the known fluid carbonate chemistry from the abiogenic experiments, and we evaluate the implications for deriving the carbonate chemistry of coral calcifying fluid. Three of the KD formulations performed similarly when applied to abiogenic aragonites precipitated from seawater and to coral skeletons. Critically, we find that some uncertainty remains in understanding the mechanism of boron elemental partitioning between aragonite and seawater, and addressing this question should be a target of additional abiogenic precipitation experiments. Despite this, boron systematics can already be applied to quantify the coral calcifying fluid carbonate system, although uncertainties associated with the proxy system should be carefully considered for each application. Finally, we present a user-friendly computer code that calculates coral calcifying fluid carbonate chemistry, including propagation of uncertainties, given inputs of boron systematics measured in coral skeleton.

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Ocean acidification

Roughly one third of anthropogenically emitted CO2 has been taken up by the oceans. When this CO2 combines with water to form H2CO3, a weak acid, water acidity increases in a process referred to as ocean acidification (OA). From the preindustrial era until present time the average pH has decreased by 0.08 units on average and it is projected to decrease a further 0.15 to 0.50 until year 2100 (IPCC RCP2.6 and RCP8.5 projections). Increased acidity hampers calcification in shell forming invertebrates, but OA also acts on a wider range of physiological processes, especially those related to cellular ion regulation, and most often non-calcifying species are equally affected. Meta-analyses show severe effects on many species of corals, echinoderms, molluscs, crustaceans, and fish at levels predicted for year 2100. Nevertheless, generalizations are presently hampered by our lack of knowledge on the variability of effects among life cycle stages, variability among taxa, how evolutionary adaptation and transgenerational effects may alleviate OA effects, and effects of OA on entire communities. Even closely related species react differently, and differences among populations of the same species separated geographically have been recorded. Also, specific life cycle stages seem to be more sensitive. In general, planktonic larvae and juveniles seem more affected than adults. Knowledge on evolutionary adaptation to OA is scarce, but the few studies that do exist indicate possible fast adaptation and buffering of OA effects by transgenerational exposure. Studies show that future OA may shift the biodiversity of entire communities. Two marine communities are of particular concern. Model studies indicate that coral reefs could be pushed beyond sustainability be the end of the century, and OA is progressing fast in the Arctic where many species are physiologically lesser capable of countering OA. OA works in concert with many other environmental stressors and knowledge on OA should be incorporated into decisions on suitable areas to protect so as to minimise effects of other stressors in habitats most vulnerable to OA.

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The future of coral reefs subject to rapid climate change: lessons from natural extreme environments

Global climate change and localized anthropogenic stressors are driving rapid declines in coral reef health. In vitro experiments have been fundamental in providing insight into how reef organisms will potentially respond to future climates. However, such experiments are inevitably limited in their ability to reproduce the complex interactions that govern reef systems. Studies examining coral communities that already persist under naturally-occurring extreme and marginal physicochemical conditions have therefore become increasingly popular to advance ecosystem scale predictions of future reef form and function, although no single site provides a perfect analog to future reefs. Here we review the current state of knowledge that exists on the distribution of corals in marginal and extreme environments, and geographic sites at the latitudinal extremes of reef growth, as well as a variety of shallow reef systems and reef-neighboring environments (including upwelling and CO2 vent sites). We also conduct a synthesis of the abiotic data that have been collected at these systems, to provide the first collective assessment on the range of extreme conditions under which corals currently persist. We use the review and data synthesis to increase our understanding of the biological and ecological mechanisms that facilitate survival and success under sub-optimal physicochemical conditions. This comprehensive assessment can begin to: (i) highlight the extent of extreme abiotic scenarios under which corals can persist, (ii) explore whether there are commonalities in coral taxa able to persist in such extremes, (iii) provide evidence for key mechanisms required to support survival and/or persistence under sub-optimal environmental conditions, and (iv) evaluate the potential of current sub-optimal coral environments to act as potential refugia under changing environmental conditions. Such a collective approach is critical to better understand the future survival of corals in our changing environment. We finally outline priority areas for future research on extreme and marginal coral environments, and discuss the additional management options they may provide for corals through refuge or by providing genetic stocks of stress tolerant corals to support proactive management strategies.

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Is ocean acidification from rising carbon dioxide a grave threat?

Global warming’ is in the news almost daily these days, but rarely do we hear about its ‘evil twin’ or ‘the other carbon dioxide (CO2) problem’, viz. ocean acidification. Global warming, caused mainly by anthropogenic CO2  emissions, is apparently accompanied by ocean acidification, which is another major growing global problem with continued increase in atmospheric CO2 levels. While there is large uncertainty in the detection and attribution of climate warming because of the large natural variability in surface temperatures, ocean acidification is relatively a certain and straight forward consequence ofrising atmospheric CO2.

Is ocean acidification a serious threat to marine life? Why is so little attention paid to this other CO2 problem? What is the present level of understanding of this problem? Has ocean acidification already manifested at least in some parts of the global oceans? What are its likely consequences? Is life on this planet headed toward extinction because of ocean acidification? What can we do to prevent ocean acidification?

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