Posts Tagged 'review'

Invited review – the effects of anthropogenic abiotic stressors on the sensory systems of fishes

Graphical abstract.


  • Conditions in abiotic factors of oceans and freshwater habitats are changing quickly due to anthropogenic activity.
  • Low pH impairs olfaction and vision, alters otolith growth, and affects CNS functioning.
  • High temperatures increase the signalling speed of nerves, alters sensory processing, and increases ROS in the CNS.
  • Low oxygen impairs energy production, nerve conduction speed, negatively affects vision and causes apoptosis in the brain.


Climate change is a growing global issue with many countries and institutions declaring a climate state of emergency. Excess CO2 from anthropogenic sources and changes in land use practices are contributing to many detrimental changes, including increased global temperatures, ocean acidification and hypoxic zones along coastal habitats. All senses are important for aquatic animals, as it is how they can perceive and respond to their environment. Some of these environmental challenges have been shown to impair their sensory systems, including the olfactory, visual, and auditory systems. While most of the research is focused on how ocean acidification affects olfaction, there is also evidence that it negatively affects vision and hearing. The effects that temperature and hypoxia have on the senses have also been investigated, but to a much lesser extent in comparison to ocean acidification. This review assembles the known information on how these anthropogenic challenges affect the sensory systems of fishes, but also highlights what gaps in knowledge remain with suggestions for immediate action.

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The history of chemical concepts and field studies of CO2 in seawater: a tribute to Kurt Buch (1881–1967)

This review of the research on the marine CO2 system spans the time between the mid-19th century and the first years after World War II. It covers the period from the first attempts to determine the amount of CO2 dissolved in seawater to the first complete physico-chemical characterization of the marine CO2 system. The development of the latter was significantly influenced by the theoretical and experimental work of the Finnish chemical oceanographer Kurt Buch (1881–1967) during the first half of the 20th century. To acknowledge his outstanding achievements in Chemical Oceanography, this review is dedicated to him.

The first part of our discussion is organized along the characteristic variables of the marine CO2 system. The analytical procedures that led successively to the definition of total CO2, alkalinity (“neutral carbonate”), the CO2 partial pressure (“CO2 tension”) and pH are briefly described. We trace the attempts to connect these variables quantitatively through the mass action law. After several failed attempts, CO2 dissociation constants were finally determined with the support of the International Council for the Exploration of the Sea (1931). Their results constituted the basis of the marine CO2 studies conducted after World War II.

The second focus of our review refers to the various field studies, including early measurements of total CO2 and alkalinity during Norwegian (1878) and Danish expeditions (1895/96) in the North Atlantic and Arctic Ocean and the first measurements of surface water pCO2 in the North Atlantic, in 1902. Furthermore, we acknowledge the achievements of the German Atlantic expedition (1925–1927) for the characterization of the vertical and horizontal distribution of pH, pCO2 and CaCO3 saturation in the Atlantic Ocean. Among Buch’s field studies of the CO2 system, we consider the Finnish monitoring program, in which pH and alkalinity were measured at over 70 stations in the northern Baltic Sea.

Whenever it is appropriate, we show the connection between past scientific ideas, concepts and knowledge with current efforts and developments concerning the understanding of the marine carbon cycle and its response to increasing atmospheric CO2.

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Editorial: microbial response to a rapidly changing marine environment: global warming and ocean acidification, volume II


Warming and acidification are representative of ongoing pronounced changes in the world’s oceans today. Increasing sea water temperature adjusts basal metabolic rates or physiological status of marine organisms (Reid et al., 2019), and potentially forces some species to shift their distribution ranges (Benedetti et al., 2021). Ocean acidification results in physiological stress of organisms, inhibits their growth, and decreases biological calcification rates, although the degree and direction of these effects vary among taxonomic groups. For this Research Topic, we have focused on the responses of microbial communities. As a vital component of the marine ecosystem microbes play pivotal roles, not only in pathways of energy transfer through the food web but also in global biogeochemical cycles (e.g., Falkowski and Raven, 2013). This Research Topic was conceived to contribute to the understanding of present and future changes in microbial communities in recognition of ongoing warming and acidifying oceanic conditions.

The first volume of this Research Topic on Microbial response to a rapidly changing marine environment: Global warming and ocean acidification was launched in 2020 with a total of 10 articles published, covering the wide scope of physiological and ecological responses of diverse taxonomic groups to environmental changes in a range of geographic regions, as summarized in our Editorial (Yun et al., 2021). Due to the success of the first volume, we launched volume II of the Research Topic in 2021. We now add a total of 11 new fascinating articles of which many expand our knowledge on specific aspects of physiological responses to environmental changes. Several articles focused on the alterations of dissolved organic matter (DOM) by bacteria and algae under warming and acidifying conditions, and other works used ecological and model based approaches to examine spatio-temporal dynamics.

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Can marine hydrothermal vents be used as natural laboratories to study global change effects on zooplankton in a future ocean?

It is claimed that oceanic hydrothermal vents (HVs), particularly the shallow water ones, offer particular advantages to better understand the effects of future climate and other global change on oceanic biota. Marine hydrothermal vents (HVs) are extreme oceanic environments that are similar to projected climate changes of the earth system ocean (e.g., changes of circulation patterns, elevated temperature, low pH, increased turbidity, increased bioavailability of toxic compounds. Studies on hydrothermal vent organisms may fill knowledge gaps of environmental and evolutionary adaptations to this extreme oceanic environment. In the present contribution we evaluate whether hydrothermal vents can be used as natural laboratories for a better understanding of zooplankton ecology under a global change scenario.

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Climate change: stressor on marine buffer system

Oceans are natural carbonate buffer systems and work as a carbon sink in the environment which is much larger than the atmospheric and terrestrial carbon content. The global carbon cycle is maintained by the continuous gaseous exchange during photosynthesis and respiration. The atmospheric CO2 also gets dissolved into the ocean water and forms weak carbonic acid. Thus, ocean water is a mixture of various numerous weak acids and bases and stays in contact with the atmosphere and other minerals as sediments. All of them together make the ocean an excellent buffer for neutralizing small changes in its composition. But the recent increase in industrialization and anthropogenic activities are causing the increase in atmospheric CO2 and climate change. More atmospheric CO2 is being dissolved in ocean water and carbon is being released from oceanic carbon sink making the ocean more acidic. Since industrialization, ocean water pH has dropped by 0.1 unit which indicated approximately a 30% increase in hydrogen ion concentration and 16% decrease in carbonate ion concentration relative to the preindustrial value. As a result of ocean acidification, there are devastating effects on ocean biota. An increase in sea surface temperature and deoxygenation are other climate change-related stressors on the ocean system.

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Ocean acidification and aquacultured seaweeds: progress and knowledge gaps

This systematic review aimed to synthesise the existing studies regarding the effects of ocean acidification (OA) on seaweed aquaculture. Ocean acidification scenarios may increase the productivity of aquacultured seaweeds, but this depends on species-specific tolerance ranges. Conversely, seaweed productivity may be reduced, with ensuing economic losses. We specifically addressed questions on: how aquacultured seaweeds acclimatise with an increase in oceanic CO2; the effects of OA on photosynthetic rates and nutrient uptake; and the knowledge gaps in mitigation measures for seaweed farming in OA environments. Articles were searched by using Google Scholar, followed by Scopus and Web of Science databases, limiting the publications from 2001 to 2022. Our review revealed that, among all the OA-related studies on macroalgae, only a relatively small proportion (n < 85) have examined the physiological responses of aquacultured seaweeds. However, it is generally agreed that these seaweeds cannot acclimatise when critical biological systems are compromised. The existing knowledge gaps regarding mitigation approaches are unbalanced and have overly focused on monitoring and cultivation methods. Future work should emphasise effective and implementable actions against OA while linking the physiological changes of aquacultured seaweeds with production costs and profits.

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Chapter 10 – Carbonate chemistry, carbon cycle, and its sequestration in aquatic system

Carbon is the universal currency used by biota to store and expend energy. Oceans act as a reservoir for almost 30% of the atmospheric carbon dioxide. The oceans store carbon in three forms: dissolved inorganic carbon (CO2 , HCO3, and CO32−), dissolved organic carbon (both small and large organic molecules), and particulate organic carbon (live organisms or fragments of dead plants and animals). They also store it in the form of black carbon (BC). Carbon keeps on exchanging between the aquatic and terrestrial ecosystems via atmosphere. Inorganic carbon is absorbed and released at the interface of the ocean’s surface and surrounding air, through the process of diffusion. This exchange of inorganic carbon takes place only in the form of CO 2, which forms carbonate when dissolved in seawater. The formation of carbonate allows oceans to take up and store a much larger amount of carbon than would be possible if dissolved CO2 remained in that form. Carbon is also cycled through the ocean by the biological processes of photosynthesis, respiration, and decomposition of aquatic plants. The changes in the chemistry of the ocean due to acidification have a great impact on marine life as well as corals and foraminifera. Since the concentration of carbon dioxide has increased rapidly in the last few decades, it becomes crucial for us to fully understand the carbonate processes and the various source and sink of carbon in the aquatic system in order to mitigate the negative effects of global warming and climate change.

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Report on ocean acidification monitoring in the Western Indian Ocean

Carbon dioxide (CO2) emissions from human activities are largely absorbed by the ocean, accounting for about one-third of the total emissions over the past 200 years from the combustion of fossil fuels, the production of cement, and changes in land use (Sabine et al., 2004). The uptake of CO2 by the ocean benefits society by moderating the rate of climate change but also causes unprecedented changes to ocean chemistry, decreasing the pH of the water and leading to a suite of chemical changes collectively known as ocean acidification. Like climate change, ocean acidification is a growing global problem that will intensify with continued CO2 emissions and has the potential to change marine ecosystems and affect benefits to society.

The chemistry of the ocean is changing at an unprecedented rate and magnitude due to anthropogenic carbon dioxide emissions; the rate of change exceeds that which has occurred for at least the past hundreds of thousands of years. Unless anthropogenic CO2 emissions are substantially curbed, or atmospheric CO2 is controlled by some other means, the average pH of the ocean will continue to fall. Ocean acidification has demonstrated impacts on many marine organisms. While the ultimate consequences are still unknown, there is a risk of ecosystem change that may threaten coral reefs, fisheries, protected species, and other natural resources of value to society.

Since the start of the Industrial Revolution, the average pH of ocean surface waters has decreased by about 0.1 units, from about 8.2 to 8.1. Model predictions show an additional 0.2–0.3 drop in pH by the end of the century, even under optimistic scenarios. Perhaps more important is that the rate of this change exceeds any known change in ocean chemistry for at least 800,000 years. The major changes in ocean chemistry caused by increasing atmospheric CO2 are well understood and can be precisely calculated, despite some uncertainty resulting from biological feedback processes.

However, the direct biological effects of ocean acidification are less certain and will vary among organisms, with some coping well and others not at all. The long-term consequences of ocean acidification for marine biota are unknown, but changes in many ecosystems and the services they provide to society appear likely based on current understanding.

In response to these concerns, WIOMSA launched ocean acidification projects in six countries: Kenya, Mauritius, Mozambique, Seychelles, South Africa and Tanzania, with the support of the Swedish International Development Cooperation Agency and institutional partners in the WIO region. The research provides a baseline that will foster the development of an integrated science strategy for ocean acidification monitoring, research and impact assessment. It presents a review of the current state of knowledge on ocean acidification in the WIO region and identifies the gaps in information required to improve understanding and address the consequences of ocean acidification.

The report consists of seven chapters. Chapter 1 introduces the subject of ocean acidification and chapters 2 to 7 summarize the esults of ocean acidification monitoring in the six countries that participated in the four-year monitoring project. Lessons learned and recommendations are presented for each country.

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Chapter 11 – Mediterranean Sea general biogeochemistry

This chapter gives an overview of the general biogeochemistry in the Mediterranean Sea explaining the particularities of the main biogeochemical variables and the physical, biological, and geochemical processes driving their distribution in the main basins of this marginal sea. Each subsection focuses on one essential variable, starting from dissolved oxygen and following inorganic nutrients, dissolved organic carbon and the CO2 system. A brief overview on the utility of those biogeochemical variables to identify water masses is also given. The chapter concludes with a summary of the projections and threats on biogeochemistry in the Mediterranean Sea under different future climate change scenarios.

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Ocean acidification and sea warming-toward a better comprehension of its consequences

Climate change, rigorously heralded more than thirty years ago as a real threat, has become the most pressing and pernicious global problem for the entire planet. In conjunction with local impacts such as fishing, eutrophication or the invasion of alien species, to give just a few examples, the acidification of the oceans and the warming of the sea began to show its effects more than twenty years ago. These signals were ignored at the time by the governing bodies and by the economic stakeholders, who now see how we must run to repair the huge inflicted damage. Today, different processes are accelerating, and the thermodynamic machine has definitely deteriorated. We see, for example, that the intensity and magnitude of hurricanes and typhoons has increased. Most models announce more devastation of flash floods and a decomposition in the water cycle, which are factors directly affecting ecosystems all over the world. Important advances are also observed in the forecasting of impacts of atmospheric phenomena in coastal areas with more and more accurate models. Rising temperatures and acidification already affect many organisms, impacting the entire food chain. All organisms, pelagic or benthic, will be affected directly or indirectly by climate change at all depths and in all the latitudes. The impact will be non-homogeneous. In certain areas it will be more drastic than in others, and the visualization of such impacts is already ongoing. Some things may be very evident, such as coral mortalities in tropical areas or in the surface waters of the Mediterranean, while others may be less visible, such as changes in microelement availability affecting plankton productivity. In fact, primary productivity in microalgae, macroalgae and phanerogams is already beginning to feel the impact of warmer, stratified and nutrient-poor waters in many parts of the planet. Nutrients are becoming less available, temperature is rising above certain tolerance limits and water movement (turbulence) may change in certain areas favoring certain species of microplankton instead of others. All these mechanisms, together with light availability (which, in principle, is not drastically changing except for the cloudiness), affect the growth of the organisms that can photosynthesize and produce oxygen and organic matter for the rest of the trophic chain. That shift in productivity completely changes the rest of the food chain. In the Arctic or Antarctic, the problem is slightly different. Life depends on the dynamics of ice that is subject to seasonal changes. But winter solidification and summer dissolution is undergoing profound changes, causing organisms that are adapted to that rhythm of ice change to be under pressure. The change is more evident in the North Pole, but is also visible in the South pole, where the sea ice cover has also dramatically changed. In the chapter there is also a mention about the general problem of the water currents and their profound change do greenhouse gas effects. The warming of the waters and their influence on the marine currents are also already affecting the different ocean habitats. The slowdown of certain processes is causing an acceleration in the deoxygenation of the deepest areas and therefore an impact on the fragile communities of cold corals that populate large areas of our planet. Many organisms will be affected in their dispersion and their ability to colonize new areas or maintain a connection between different populations. The rapid adaptations to these new changes are apparent. Nature is on its course of restart from these new changes, but in this transitional phase the complexity and interactions that have taken thousands or millions of years to form can fade away until a new normal is consolidated.

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Climate change impacts on the coral reefs of the UK Overseas Territory of the Pitcairn Islands: resilience and adaptation considerations

The coral reefs of the Pitcairn Islands are in one of the most remote areas of the Pacific Ocean, and yet they are exposed to the impacts of anthropogenic climate change. The Pitcairn Islands Marine Protected Area was designated in 2016 and is one of the largest in the world, but the marine environment around these highly isolated islands remains poorly documented. Evidence collated here indicates that while the Pitcairn Islands’ reefs have thus far been relatively sheltered from the effect of warming sea temperatures, there is substantial risk of future coral decalcification due to ocean acidification. The projected acceleration in the rate of sea level rise, and the reefs’ exposure to risks from distant ocean swells and cold-water intrusions, add further uncertainty as to whether these islands and their reefs will continue to adapt and persist into the future. Coordinated action within the context of the Pitcairn Islands Marine Protected Area can help enhance the resilience of the reefs in the Pitcairn Islands. Options include management of other human pressures, control of invasive species and active reef interventions. More research, however, is needed in order to better assess what are the most appropriate and feasible options to protect these reefs.

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Ocean acidification around the UK and Ireland


What is already happening

  • Atmospheric CO2 exceeded 414 ppm in 2021 and has continued to increase by approximately 2.4 ppm per year over the last decade. The global ocean absorbs approximately a quarter of anthropogenic carbon dioxide (CO2) emissions annually.
  • The North Atlantic Ocean contains more anthropogenic CO2 than any other ocean basin, and surface waters are experiencing an ongoing decline in pH (increasing acidity). Rates of acidification in bottom waters are occurring faster at some locations than in surface waters.
  • Some species are already showing effects from ocean acidification when exposed to short-term fluctuations and could be used as indicator species for long-term impacts on marine ecosystems.

What could happen in the future

  • Models project that the average continental shelf seawater pH will continue to decline to year 2050 at similar rates to the present day, with rates then increasing in the second half of the century, depending on the emissions scenario.
  • The rate of pH decline in coastal areas is projected to be faster in some areas (e.g. Bristol Channel) than others, such as the Celtic Sea.
  • Under high-emission scenarios, it is projected that bottom waters on the North-West European Shelf seas will become corrosive to more soluble forms of calcium carbonate (aragonite). Episodic undersaturation events are projected to begin by 2030.
  • By 2100, up to 90% of the north-west European shelf seas may experience undersaturation for at least one month of each year.
  • High levels of nearshore variability in carbonate chemistry may mean that some coastal species have a higher adaptative capacity than others. However, all species are at increased risk from extreme exposure episodes.
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Global decrease in heavy metal concentrations in brown algae in the last 90 years

Graphical abstract


  • A decline in metal pollution in algae is widespread in coastal ecosystems worldwide.
  • Decrease in algae concentrations may not also occur in seawater but in bioavailability.
  • Decreases began from 70’s coinciding with the implementation of environmental policies.
  • Legislation and ocean acidification can impact on the heavy metal content in algae.


In the current scenario of global change, heavy metal pollution is of major concern because of its associated toxic effects and the persistence of these pollutants in the environment. This study is the first to evaluate the changes in heavy metal concentrations worldwide in brown algae over the last 90 years (>15,700 data across the globe reported from 1933 to 2020). The study findings revealed significant decreases in the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb and Zn of around 60–84% (ca. 2% annual) in brown algae tissues. The decreases were consistent across the different families considered (Dictyotaceae, Fucaceae, Laminariaceae, Sargassaceae and Others), and began between 1970 and 1990. In addition, strong relationships between these trends and pH, SST and heat content were detected. Although the observed metal declines could be partially explained by these strong correlations, or by adaptions in the algae, other evidences suggest an actual reduction in metal concentrations in oceans because of the implementation of environmental policies. In any case, this study shows a reduction in metal concentrations in brown algae over the last 50 years, which is important in itself, as brown algae form the basis of many marine food webs and are therefore potential distributors of pollutants.

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Unraveling cellular and molecular mechanisms of acid stress tolerance and resistance in marine species: new frontiers in the study of adaptation to ocean acidification

Graphical abstract


  • OA poses a threat to marine life, although some taxa can tolerate low seawater pH.
  • Different responses at cellular and molecular level observed in marine organisms
  • Role of ABC transporter proteins towards acid stress tolerance and resistance
  • Understanding cellular mechanisms of acid stress tolerance to unravel OA impacts


Since the industrial revolution, fossil fuel combustion has led to a 30 %-increase of the atmospheric CO2 concentration, also increasing the ocean partial CO2 pressure. The consequent lowered surface seawater pH is termed ocean acidification (OA) and severely affects marine life on a global scale. Cellular and molecular responses of marine species to lowered seawater pH have been studied but information on the mechanisms driving the tolerance of adapted species to comparatively low seawater pH is limited. Such information may be obtained from species inhabiting sites with naturally low water pH that have evolved remarkable abilities to tolerate such conditions. This review gathers information on current knowledge about species naturally facing low water pH conditions and on cellular and molecular adaptive mechanisms enabling the species to survive under, and even benefit from, adverse pH conditions. Evidences derived from case studies on naturally acidified systems and on resistance mechanisms will guide predictions on the consequences of future adverse OA scenarios for marine biodiversity.

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Voltage-gated proton channels explain coccolithophore sensitivity to ocean acidification

Coccolithophores are unicellular photosynthetic plankton that perform extraordinary feats in ionic homeostasis to fabricate intricate nano-patterned plates made of calcium carbonate (CaCO3) crystals called coccoliths (1). Outside marine science communities, coccolithophores are less known than animal calcifiers such as shellfish or the cnidarians that form coral reefs. However, coccolithophores are one of Earth’s greatest biological producers of CaCO3. The production and sinking of coccoliths play complex roles in ocean carbon cycles, helping carry organic carbon to the deep sea as well serving on a geological scale to help the ocean buffer CO2 fluctuations (23). Unlike other calcifying organisms, where precipitation of CaCO3 is extracellular, coccolithophores calcify in special intracellular Golgi-derived coccolith vesicles. To do this, they maintain among the greatest fluxes of Ca2+ and H+ known for any cell ions which would be toxic if allowed to accumulate in the cytoplasm (1). In PNAS, Kottmeier et al. (4) demonstrate how they rely on voltage-gated proton channels to expel H+ released by CaCO3 precipitation, which also offers a way forward to resolving disparate results from two decades of research on coccolithophore sensitivity to ocean acidification.

Approximately a third of human CO2 emissions are absorbed by the ocean, resulting in ocean acidification. As CO2 dissolves in the sea it reacts with water to form carbonic acid, generating H+ (decreasing pH) and perturbing a set of interlocked equilibria involving CO2, HCO3, CO32−, H+, and Ca2+ by increasing [HCO3], decreasing [CO32−], and lowering the saturation states of alternative forms of CaCO3 (5). The inorganic chemistry is complex but comparatively well known. The response of calcifying organisms should be simple to predict if it depended only on the tendency of CaCO3 to precipitate or dissolve in seawater: Organisms such as coccolithophores which produce calcite, the more stable form of CaCO3, should be less sensitive to ocean acidification compared to organisms like many corals which produce less-stable forms such as aragonite.

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Assessing the future carbon budget through the lens of policy-driven acidification and temperature targets

Basing a future carbon budget on warming targets is subject to uncertainty due to uncertainty in the relationship between carbon emissions and warming, and may not prevent dangerous change throughout the entire climate system. Here, we use a climate emulator to constrain a future carbon budget that is more representative by using a combination of both warming and ocean acidification targets. The warming targets considered are the Paris Agreement targets of 1.5 and 2°C; the acidification targets are -0.17 and -0.21 pH units informed by aragonite saturation states. Considering acidification targets in conjunction with warming targets is found to narrow the uncertainty in the future carbon budget, especially in situations where the acidification target is more stringent than, or of similar stringency to, the warming target. Considering a strict combination of the two more stringent targets (both targets of 1.5°C warming and -0.17 acidification must be met), the carbon budget ranges from -74.0 to 129.8PgC. This reduces uncertainty in the carbon budget from 286.2PgC to 203.8PgC (29%). Assuming an emissions rate held constant since 2021 (which is a conservative assumption), the budget towards both targets was either spent by 2019, or will be spent by 2026.

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Reviews and syntheses: carbon biogeochemistry of Indian estuaries

The goal of this review is to provide a comprehensive overview of the magnitude and drivers of carbon cycling dynamics in the major estuaries of India. Data from a total of 32 estuaries along the Bay of Bengal (BB) and the Arabian Sea (AS) were compiled from the literature and re-analysed based on changes in season (wet vs. dry) and marine end-members (e.g., BB vs. AS). The estuaries are generally undersaturated in dissolved oxygen relative to the atmosphere and strongly influenced by local and regional precipitation patterns. Speciation of the dissolved inorganic carbon (DIC) pool is dominated by bicarbonate and primarily variability in DIC is controlled by a combination of carbonate weathering, the degree of precipitation, the length of the estuaries, in situ respiration, and mixing. Carbonate dissolution had the largest influence on DIC during the wet season, while respiration was the primary control of DIC variability in the estuaries connected with BB during the dry season. Interestingly, the influence of anaerobic metabolism on DIC is observed in the oxygenated mangrove dominated estuaries, which we hypothesize is driven by porewater exchange in intertidal sediments. Dissolved organic carbon (DOC) generally behaves non-conservatively in the studied estuaries. The DOC-particulate organic carbon (POC) inter-conversion and DOC mineralization are evident in the BB during the dry season and AS estuaries, respectively. The wet season δ13CPOC shows dominance of freshwater algae, C3 plant material, as well as marine organic matter in POC. However, anthropogenic inputs are evident in some estuaries in eastern India during the dry season. POC respiration was identified in the AS; however, a link between POC and CH4 is identified throughout both the regions. pCO2 is controlled principally by respiration with freshwater discharge only playing a marginal important role in the BB. The AS estuaries act as a CO2 source to the atmosphere; however, the BB estuaries vary between a source and sink. POC together with methanotrophy and dam abundance appear to control CH4 concentrations, and all of the studied estuaries act as a CH4 source to the atmosphere. Additionally, anthropogenic inputs and groundwater exchange also show potential influences in some cases. The Indian estuaries contribute 2.62 % and 1.09 % to the global riverine DIC and DOC exports to the ocean, respectively. The total CO2 and CH4 fluxes from Indian estuaries are estimated as ~9718 Gg yr-1 and 3.27 Gg yr-1, which contributes ~0.67 % and ~0.12 %, respectively, to global estimates of estuarine greenhouse gas emissions. While a qualitative idea on the major factors controlling the carbon biogeochemistry in India is presented through this work, a more thorough investigation including rate quantification of the above-mentioned mechanisms is essential for precise accounting of the C budget of Indian estuaries.

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High sclerobiont calcification in marginal reefs of the eastern tropical Pacific

Graphical abstract.

A sclerobiont is any organism capable of fouling hard substrates. Sclerobionts have recently received attention due to their notable calcium carbonate contributions to reef structures and potential to offset drops in carbonate budgets in degraded reefs. However, due to their encrusting nature, it is difficult to quantify net calcium carbonate production at the level of individual taxonomic groups, and knowledge regarding the main environmental factors that regulate their spatial distributions is limited. In addition, the material types used to create experimental substrates, their orientations, and their overall deployment times can influence settlement and the composition of the resulting communities. Thus, comparative evaluations of these variables are necessary to improve future research efforts. In this study, we used calcification accretion units (CAUs) to quantify the calcium carbonate contributions of sclerobionts at the taxonomic group level and evaluated the effects of two frequently used materials [i.e., polyvinyl chloride (PVC) and terracotta (TCT) tiles] on the recruitment and calcification of the sclerobiont community in the tropical Mexican Pacific and the Midriff Island Region of the Gulf of California over 6 and 15 months [n = 40; 5 CAUs x site (2) x deployment time (2) x material type (2)]. The net sclerobiont calcification rate (mean ± SD) reached maximum values at six months and was higher in the Mexican Pacific (2.15 ± 0.99 kg m−2 y−1) than in the Gulf of California (1.70 ± 0.67 kg m−2 y−1). Moreover, the calcification rate was slightly higher on the PVC-CAUs compared to that of the TCT-CAUs, although these differences were not consistent at the group level. In addition, cryptic microhabitats showed low calcification rates when compared to those of exposed microhabitatsCrustosecoralline algae and barnacles dominated the exposed experimental surfaces, while bryozoans, mollusks, and serpulid polychaetes dominated cryptic surfaces. Regardless of the site, deployment time, or material type, barnacles made the greatest contributions to calcimass production (between 41 and 88%). Our results demonstrate that the orientation of the experimental substrate, and the material to a lesser extent, influence the sclerobiont community and the associated calcification rate. Upwelling-induced surface nutrient levels, low pH levels, and the aragonite saturation state (ΩAr) limit the early cementation of reef-building organisms in the tropical Mexican Pacific and promote high bioerosion rates in corals of the Gulf of California. Our findings demonstrate that sclerobionts significantly contribute to calcium carbonate production even under conditions of high environmental variability.

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Threats to Australia’s oceans and coasts: a systematic review

Graphical abstract.


  • Threats to Australia’s oceans and coasts described in the academic literature from 2010 to 2020 were systematically reviewed.
  • 307 threats were identified across three categories, with most threats in the group “environmental and human-induced threats”.
  • Threats were described as impacting environmental (68%), economic (14%), socio-cultural (12%), and Indigenous (6%) values.
  • Only 45 of the 226 papers (20%) discussed multiple threats.
  • Findings highlight the cumulative and multi-faceted threats facing Australian oceans and coasts that must be addressed.


Oceans and coasts provide important ecosystem, livelihood, and cultural values to humans and the planet but face current and future compounding threats from anthropogenic activities associated with expanding populations and their use of and reliance on these environments. To respond to and mitigate these threats, there is a need to first systematically understand and categorise them. This paper reviewed 226 articles from the period 2010–2020 on threats to Australia’s oceans and coasts, resulting in the identification of a total of 307 threats. Threats were grouped into three broad categories — threats from use and extraction; environmental and human-induced threats; and policy and socio-political threats —then ranked by frequency. The most common ‘threats from use and extraction’ were recreational activities, non-point source pollution, and urban development; the most common ‘environmental and human-induced threat’ was increased temperatures; and the most common ‘policy and socio-political threat’ was policy gaps and failures (e.g., a lack of coastal climate adaptation policies). The identification of threats across all three categories increased over time; however, the identification of ‘threats from use and extraction’ increased most rapidly over the last four years (2017–2020). Threats were most often described for their impacts on environmental values (68%), followed by economic (14%), socio-cultural (12%), and Indigenous (6%) values. Only 45 of the 226 papers (20%) discussed multiple threats. The threats facing Australia’s oceans and coasts are rising, cumulative, and multi-faceted, and the inherent tensions between varied uses, along with intensification of uses that derive short-term anthropogenic benefit, will continue to degrade the ecological sustainability of ocean and coastal systems if actions are not taken.

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Impact of climate change on Arctic macroalgal communities

The Arctic region faces a warming rate that is more than twice the global average. Seaice loss, increase in precipitation and freshwater discharge, changes in underwater light, and amplification of ocean acidification modify benthic habitats and the communities they host. Here we synthesize existing information on the impacts of climate change on the macroalgal communities of Arctic coasts. We review the shortand long-term changes in environmental characteristics of shallow hard-bottomed Arctic coasts, the floristics of Arctic macroalgae (description, distribution, life-cycle, adaptations), the responses of their biological and ecological processes to climate change, the resulting winning and losing species, and the effects on ecosystem functioning. The focus of this review is on fucoid species, kelps, and coralline algae which are key ecosystem engineers in hard-bottom shallow areas of the Arctic, providing food, substrate, shelter, and nursery ground for many species. Changes in seasonality, benthic functional diversity, food-web structure, and carbon cycle are already occurring and are reshaping Arctic benthic ecosystems. Shallow communities are projected to shift from invertebrate-to algal-dominated communities. Fucoid and several kelp species are expected to largely spread and dominate the area with possible extinctions of native species. A considerable amount of functional diversity could be lost impacting the processing of land-derived nutrients and organic matter and significantly altering trophic structure and energy flow up to the apex consumers. However, many factors are not well understood yet, making it difficult to appreciate the current situation and predict the future coastal Arctic ecosystem. Efforts must be made to improve knowledge in key regions with proper seasonal coverage, taking into account interactions between stressors and across species.

Continue reading ‘Impact of climate change on Arctic macroalgal communities’

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