Posts Tagged 'algae'

Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy

Ocean acidification poses a serious threat to marine calcifying organisms, yet experimental and field studies have found highly diverse responses among species and environments. Our understanding of the underlying drivers of differential responses to ocean acidification is currently limited by difficulties in directly observing and quantifying the mechanisms of bio‐calcification. Here, we present Raman spectroscopy techniques for characterizing the skeletal mineralogy and calcifying fluid chemistry of marine calcifying organisms such as corals, coralline algae, foraminifera, and fish (carbonate otoliths). First, our in vivo Raman technique is the ideal tool for investigating non‐classical mineralization pathways. This includes calcification by amorphous particle attachment, which has recently been controversially suggested as a mechanism by which corals resist the negative effects of ocean acidification. Second, high‐resolution ex vivo Raman mapping reveals complex banding structures in the mineralogy of marine calcifiers, and provides a tool to quantify calcification responses to environmental variability on various timescales from days to years. We describe the new insights into marine bio‐calcification that our techniques have already uncovered, and we consider the wide range of questions regarding calcifier responses to global change that can now be proposed and addressed with these new Raman spectroscopy tools.

Continue reading ‘Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy’

The macroalgal holobiont in a changing sea


• Macroalgae and their associated microbiota form a functional unit termed ‘holobiont’, characterized by its complex mutualistic relations. This symbiosis between macroalgae and the microbiota may be disturbed by environmental stressors, resulting in holobiont break-up.

• Current knowledge on the functional consequences of the macroalgal holobiont is limited. Although it becomes increasingly clear that the microbiota is essential for host functioning, bacteria are still considered contaminants rather than a crucial component of the holobiont, and current studies are predominantly focused on the host only.

• Macroalgae fulfil an important ecological function, and the effect of climate change on macroalgae has been a primary focus in recent algal research; however, the role of the microbiota in the hosts’ response to climate change has not yet been addressed.


When studying the effects of climate change on eukaryotic organisms we often oversee a major ecological process: the interaction with microbes. Eukaryotic hosts and microbes form functional units, termed holobionts, where microbes play crucial roles in host functioning. Environmental stress may disturb these complex mutualistic relations. Macroalgae form the foundation of coastal ecosystems worldwide and provide important ecosystem services – services they could likely not provide without their microbial associates. Still, today we do not know how environmental stress will affect the macroalgal holobiont in an increasingly changing ocean. In this review, we provide a conceptual framework that contributes to understanding the different levels at which the holobiont and environment interact, and we suggest a manipulative experimental approach as a guideline for future research.

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Temporal effects of ocean warming and acidification on coral–algal competition

While there is an ever-expanding list of impacts on coral reefs as a result of ocean warming and acidification, there is little information on how these global changes influence coral–algal competition. The present study assessed the impact of business-as-usual ocean warming and acidification conditions on the survivorship, calcification, photosynthesis and respiration of the coral–algal interaction between the macroalga Halimeda heteromorpha and the coral Acropora intermedia over 8 weeks in two seasons. The physiological responses of A. intermedia and H. heteromorpha were highly dependent on season, with both organisms demonstrating optimal rates of calcification and photosynthesis under present-day conditions in summer. Contact with H. heteromorpha did not influence A. intermedia survivorship, however did reduce long-term calcification rates. Photosynthetic rates of A. intermedia were influenced by algal contact temporally in opposing directions, with rates reduced in winter and increased in summer. Enhanced photosynthetic rates as a result of algal contact were not enough to offset the combined effects of ocean warming and acidification, which regardless of coral–algal contact, reduced survivorship, calcification and photosynthesis of A. intermedia and the calcification rates of H. heteromorpha. These findings provide experimental support for the idea that the effects of coral–algal competition are temporally variable, and help improve our understanding of how future ocean warming and acidification may alter the dynamics of coral–algal interactions.

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Review: host-pathogen dynamics of seagrass diseases under future global change


• The role of disease in global seagrass declines is largely unknown.

• Seagrass disease risk and impact may be amplified under global change.

• We review 3 groups of known seagrass pathogens: labyrinthulids, oomycetes and Phytomyxea.

• There is an urgent need to expand the field of seagrass disease research.

• We provide perspectives for future studies on seagrass-pathogen dynamics.


Human-induced global change is expected to amplify the disease risk for marine biota. However, the role of disease in the rapid global decline of seagrass is largely unknown. Global change may enhance seagrass susceptibility to disease through enhanced physiological stress, while simultaneously promoting pathogen development. This review outlines the characteristics of disease-forming organisms and potential impacts of global change on three groups of known seagrass pathogens: labyrinthulids, oomycetes and Phytomyxea. We propose that hypersalinity, climate warming and eutrophication pose the greatest risk for increasing frequency of disease outbreaks in seagrasses by increasing seagrass stress and lowering seagrass resilience. In some instances, global change may also promote pathogen development. However, there is currently a paucity of information on these seagrass pathosystems. We emphasise the need to expand current research to better understand the seagrass-pathogen relationships, serving to inform predicative modelling and management of seagrass disease under future global change scenarios.

Continue reading ‘Review: host-pathogen dynamics of seagrass diseases under future global change’

Responses of seaweeds that use CO2 as their sole inorganic carbon source to ocean acidification: differential effects of fluctuating pH but little benefit of CO2 enrichment

Laboratory studies that test the responses of coastal organisms to ocean acidification (OA) typically use constant pH regimes which do not reflect coastal systems, such as seaweed beds, where pH fluctuates on diel cycles. Seaweeds that use CO2 as their sole inorganic carbon source (non-carbon dioxide concentrating mechanism species) are predicted to benefit from OA as concentrations of dissolved CO2 increase, yet this prediction has rarely been tested, and no studies have tested the effect of pH fluctuations on non-CCM seaweeds. We conducted a laboratory experiment in which two ecologically dominant non-CCM red seaweeds (Callophyllis lambertii and Plocamium dilatatum) were exposed to four pH treatments: two static, pHT 8.0 and 7.7 and two fluctuating, pHT 8.0 ± 0.3 and 7.7 ± 0.3. Fluctuating pH reduced growth and net photosynthesis in C. lambertii, while P. dilatatum was unaffected. OA did not benefit P. dilatatum, while C. lambertii displayed elevated net photosynthetic rates. We provide evidence that carbon uptake strategy alone cannot be used as a predictor of seaweed responses to OA and highlight the importance of species-specific sensitivity to [H+]. We also emphasize the importance of including realistic pH fluctuations in experimental studies on coastal organisms.

Continue reading ‘Responses of seaweeds that use CO2 as their sole inorganic carbon source to ocean acidification: differential effects of fluctuating pH but little benefit of CO2 enrichment’

Responses to ocean acidification and diurnal temperature variation in a commercially farmed seaweed, Pyropia haitanensis (Rhodophyta)

To investigate carbon and nitrogen metabolism in Pyropia haitanensis in response to the combined conditions of ocean acidification and diurnal temperature variation, maricultured thalli were tested in acidified culture under different temperature treatments. The results showed a combined effect of ocean acidification and diurnal temperature difference on the C and N metabolism and growth of P. haitanensis. In acidifed culture, algal growth, maximum photosynthetic rate, nitrate reductase (NR) activity, amino acid (AA) content and AA score (AAS) were more significantly enhanced in seaweed under diurnal temperature variation than in seaweed at constant temperature. In acidified seawater, soluble carbohydrates in P. haitanensis increased due to greater dissolved inorganic carbon (DIC), whereas soluble proteins decreased. Under the diurnal temperature treatment, higher temperature during the light period enhanced accumulation of algal photosynthates, whereas lower temperature in the dark period reduced energy consumption, resulting in enhanced algal growth, AA content and AAS. We concluded that suitable diurnal temperature difference would be conducive to C fixation and N assimilation under ocean acidification. However, excessively high temperatures would depress algal photosynthesis and increase energy consumption, thereby exerting a negative effect on algal growth.

Continue reading ‘Responses to ocean acidification and diurnal temperature variation in a commercially farmed seaweed, Pyropia haitanensis (Rhodophyta)’

Decreasing pH affects seagrass epiphyte communities

Increasing CO2 in the atmosphere is affecting marine ecosystems, including seagrass beds. Epiphytes are a component of seagrass ecosystems. Epiphytes make a significant contribution as important primary producers in the food chain. Increasing atmospheric CO2 leads to a decrease in oceanic pH that can result in an unfavorable environment for the epiphytic community. This study was conducted to determine the effect of increasing CO2 on seagrass epiphytic communities and biomass. Using a field experiment, we manipulated dissolved carbon dioxide to 800 – 1000 ppm in line with the forecast increase in atmospheric CO2 levels in the year 2100. In situ C02 manipulations were conducted using an open-top mesocosm. The CO2 enrichment was conducted by adding CO2 at a concentration around 800 – 1000 ppm. This CO2 was injected directly using a pump and hose to the acrylic mesocosm chamber. Epiphyte community structure was affected, with an increase in the abundance of filamentous algae but a decrease in the coralline algae community in the CO2 enriched treatment units. Overall, CO2 enrichment had no effect on epiphyte biomass.

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Ocean acidification in the IPCC AR5 WG II

OUP book