Posts Tagged 'algae'

The future of seaweed aquaculture in a rapidly changing world

Human activities are having increasingly negative impacts on the natural environment. The rapidly expanding human population has led to a shortage of resources and the ability to support the growing population sustainably is a major challenge for the future. Coastal environments, including natural seaweed communities, provide a range of important ecosystem services. Since seaweed aquaculture beds (SABs) provide many of the services associated with natural seaweed communities they have a potential role in providing solutions such as CO2 sequestration, provision of food and the supply of useful chemicals. However, the productivity of natural seaweed communities and SABs is under threat from the rapid changes in climate that the planet is experiencing. Here we examine the likely effects of global change, in particular elevated CO2 and ocean acidification, increased temperatures and elevated levels of UVB, on the performance of seaweeds. While it is clear that rising temperatures and elevated CO2 and their interactions with other environmental factors are likely to have profound effects on macroalgal production, such effects are likely to be species dependent. We also examine the fate of organic matter from seaweeds and the potential for using SAB productivity as a contributor to blue carbon as a strategy for amelioration of increases in anthropogenic CO2 emissions. There is considerable potential for increased drawdown of CO2 by SABs, though its effectiveness in amelioration of atmospheric CO2 increase will depend on the fate of the resulting biomass.

Continue reading ‘The future of seaweed aquaculture in a rapidly changing world’

The role of natural variability in shaping the response of coral reef organisms to climate change

Purpose of Review

We investigate whether regimes of greater daily variability in temperature or pH result in greater tolerance to ocean warming and acidification in key reef-building taxa (corals, coralline algae).

Recent Findings

Temperature and pH histories will likely influence responses to future warming and acidification. Past exposure of corals to increased temperature variability generally leads to greater thermotolerance. However, the effects of past pH variability are unclear. Variability in pH or temperature will likely modify responses during exposure to stressors, independent of environmental history. In the laboratory, pH variability often limited the effects of ocean acidification, but the effects of temperature variability on responses to warming were equivocal.


Environmental variability could alter responses of coral reef organisms to climate change. Determining how both environmental history as well as the direct impacts of environmental variability will interact with the effects of anthropogenic climate change should now be high priority.

Continue reading ‘The role of natural variability in shaping the response of coral reef organisms to climate change’

Responses of photosynthesis and CO2 concentrating mechanisms of marine crop Pyropia haitanensis thalli to large pH variations at different time scales


• A pH of 4, 5, and 9 resulted in the death of Pyropia haitanensis thalli.
• A pH of 6 and 7 increased the growth of Pyropia haitanensis thalli.
• The CO2 concentrating mechanisms may play a role in intracellular pH homeostasis.
• Actual pH variation needs to be considered in relative studies.

Wild and cultivated populations of Pyropia haitanensis have frequently experienced extremely low pH conditions in the last few decades. This could potentially threaten the development of the aquaculture of this economically important marine crop. To gain a broader perspective, we investigated the short- (4 h) and long- (7 days) term responses of CO2 concentrating mechanisms (CCMs) of P. haitanensis thalli to large variations in pH. Our study found that a pH of 4 and 5, which mimicked the decreased pH caused by acid rain, resulted in decreased photosynthesis and respiration while leading to the death of P. haitanensis thalli. Thus, acid rain would result in a decline in P. haitanensis production and threaten wild seaweed sources. However, a pH of 6 and 7 enhanced the growth of P. haitanensis thalli by > 30%, mainly because increased CO2 levels favored photosynthesis, while the algae need to effectively maintain intracellular pH homeostasis to support rapid growth rates. The contributions of extracellular carbonic anhydrases (eCAs) to photosynthetic rates remained at > 77% when pH ≥ 7, regardless of the treatment time. However, at pH 6, the contribution of eCAs to photosynthesis increased from 25% for a short-term treatment to 66% for a long-term treatment. Thus, except for work on carbon assimilation, this study proposes that the CCMs component involved in the movement and metabolism of inorganic carbon may play an important role in pH homeostasis. In addition, pH 9 also led to the death of P. haitanensis thalli, which is consistent with observations of the natural distribution of this algae and hints that P. haitanensis thalli prefer to use inorganic carbon via eCAs when pH ≥ 7. The present study suggested that the actual variation in pH experienced by marine organisms needs to be considered in the experimental design of related studies.

Continue reading ‘Responses of photosynthesis and CO2 concentrating mechanisms of marine crop Pyropia haitanensis thalli to large pH variations at different time scales’

Nutrient loading fosters seagrass productivity under ocean acidification

The effects of climate change are likely to be dependent on local settings. Nonetheless, the compounded effects of global and regional stressors remain poorly understood. Here, we used CO2 vents to assess how the effects of ocean acidification on the seagrass, Posidonia oceanica, and the associated epiphytic community can be modified by enhanced nutrient loading. P. oceanica at ambient and low pH sites was exposed to three nutrient levels for 16 months. The response of P. oceanica to experimental conditions was assessed by combining analyses of gene expression, plant growth, photosynthetic pigments and epiphyte loading. At low pH, nutrient addition fostered plant growth and the synthesis of photosynthetic pigments. Overexpression of nitrogen transporter genes following nutrient additions at low pH suggests enhanced nutrient uptake by the plant. In addition, enhanced nutrient levels reduced the expression of selected antioxidant genes in plants exposed to low pH and increased epiphyte cover at both ambient and low pH. Our results show that the effects of ocean acidification on P. oceanica depend upon local nutrient concentration. More generally, our findings suggest that taking into account local environmental settings will be crucial to advance our understanding of the effects of global stressors on marine systems.

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Effects of increased CO2 and temperature on the growth and photosynthesis in the marine macroalga Gracilaria lemaneiformis from the coastal waters of South China

The marine red macroalga Gracilaria lemaneiformis (Gracilariales, Rhodophyta) is one of the most important species for seaweed cultivation along the coastal waters of South China. In this study, G. lemaneiformis was incubated under present-day (390 ppm) or predicted-year CO2 levels (700 ppm), and under normal (20 °C) versus elevated temperatures (24 °C), to investigate possible effects of climate change conditions on the growth and photosynthesis. The chlorophyll a (Chl a), carotenoid (Car), and phycobiliprotein (PB) contents responded significantly to increased temperature under normal CO2 and high CO2 concentrations. However, CO2 enrichment in the culture had no significant impact on Chl a and Car but decreased the PB contents in G. lemaneiformis. The growth rates of G. lemaneiformis were significantly improved by increasing temperature, especially under concurrent increasing CO2 levels. Additionally, short-term exposure to high temperature stimulated the irradiance-saturated maximum photosynthetic rate (Pmax), and this stimulation was preserved with exposure to the high temperature in long-term incubations, with such stimulation being much more pronounced under normal CO2 concentrations than high CO2 concentrations. Results suggest that increased temperature exerted more pronounced effects on the growth and photosynthesis of G. lemaneiformis than increased CO2 concentrations did. We proposed that the sea cultivation of G. lemaneiformis would benefit from the ongoing climate change (increasing atmospheric CO2 concentrations and sea surface temperatures) through enhanced growth and carbon sequestration.

Continue reading ‘Effects of increased CO2 and temperature on the growth and photosynthesis in the marine macroalga Gracilaria lemaneiformis from the coastal waters of South China’

Impacts of climate change on Eucheuma-Kappaphycus farming

Climate change impacts all forms of life – including seaweeds! For farmed Eucheuma/Kappaphycus the direct and indirect impacts have caused not only physical damage to the crops but has also affected the eco-physiological, reproductive and metabolic processes of the seaweed. As a result of their importance as sources of different types of carrageenan, Eucheuma (iota)/Kappaphycus (kappa) have spread, through facilitated transfer, from its original tropical farming sites in the Philippines, across several localities in the Pacific, Atlantic and Indian Oceans. Ocean warming has caused the ‘tropicalization’ of sub-tropical waters of northeast Asia and South America, and more areas are becoming increasingly conducive to Eucheuma/Kappaphycus farming. Increases in surface seawater temperatures could have deleterious effects on reproductive capacity, including spore production, germination, recruitment and growth which, coupled with the long-practiced clonal propagation, have resulted in the declining productivity and quality of extracted colloids. Global climate change and anomalous climatic events such as El Niño and La Niña have increased the susceptibility of the selected cultivars of farmed eucheumatoids to bacterial pathogens as a result of stressful abiotic conditions which are conducive to ‘ice-ice’ disease and damaging impacts of epiphytism which have combined and literally wiped out activity in some farms. Typhoons and storms, as well as heavy rainfall during the wet season, increased in intensity by climate change, have also destroyed farms resulting in the loss of investments and income for those workers dependent on seaweed cultivation as a cash generating activity.

In addition, increased CO2 dissolution in the oceans has resulted in its acidification, coupled with exposure of the surface-cultivated seaweeds to increased UV radiation (due to ozone depletion), which could decrease the concentration of the seaweeds’ own protective pigments, thereby resulting in photo-inhibition and abiotic stresses. All of the foregoing, individually and collectively, integrate to reduce daily growth rates. Reduced pH could also lessen the spore germination capacity of cultivated eucheumatoids.

The combination of the above factors has produced an overall decline in cultivated Eucheuma/Kappaphycus production. However, the efforts of many countries to increase their total area of farming and improvement in farming techniques, ensures the world’s overall production trend for these seaweeds of industrial value to be on the rise, in general.

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Marine metal pollution and effects on seaweed species

Heavy metals are significant pollutants continuously released into the biosphere, both naturally and anthropogenically. Conceptually, metal speciation, bioavailability, and associated toxicity in marine organisms depend on a wide array of abiotic and biotic factors. Among these, pH variation is one of the most important environmental factors influencing metal speciation and toxicity. Due to this, ocean acidification is expected to modify metal speciation, altering the effects these nondegradable contaminants have on marine organisms, such as seaweeds. One clear effect of heavy metals on seaweeds is the rapid formation of reactive oxygen species (ROS). The production of ROS beyond the physiological tolerance threshold causes an oxidative stress condition that, if not attenuated, can irreversibly damage cellular constituents such as DNA/RNA, proteins, and lipids. To cope with heavy metal excess, several mechanisms exist in tolerant seaweed species, including the activation of an efficient ROS-scavenging system constituted by metal-binding compounds, antioxidant enzymes, and oxygenated polyunsaturated fatty acids, among others. Another adaptive mechanism involves the participation of ATP-binding cassette (ABC) transporter proteins in translocating a wide variety of compounds across cell membranes, including heavy metals. In contrast, an excessive heavy metal presence can inhibit photosynthesis, reduce pigment concentration and growth, induce cation losses, and disrupt gametophyte development in non-tolerant seaweed species. In a scenario of lowered ocean pH and increased heavy metal toxicity, the important roles played by non-tolerant seaweed species in structuring communities could be severely compromised, with unknown consequences for associated organisms. Therefore, in the upcoming decades, marine pollution could majorly shift and rearrange community compositions and the distributional ranges of species.

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Ocean acidification in the IPCC AR5 WG II

OUP book