Posts Tagged 'algae'

Season affects strength and direction of the interactive impacts of ocean warming and biotic stress in a coastal seaweed ecosystem

The plea for using more “realistic,” community‐level, investigations to assess the ecological impacts of global change has recently intensified. Such experiments are typically more complex, longer, more expensive, and harder to interpret than simple organism‐level benchtop experiments. Are they worth the extra effort? Using outdoor mesocosms, we investigated the effects of ocean warming (OW) and acidification (OA), their combination (OAW), and their natural fluctuations on coastal communities of the western Baltic Sea during all four seasons. These communities are dominated by the perennial and canopy‐forming macrophyte Fucus vesiculosus—an important ecosystem engineer Baltic‐wide. We, additionally, assessed the direct response of organisms to temperature and pH in benchtop experiments, and examined how well organism‐level responses can predict community‐level responses to the dominant driver, OW. OW affected the mesocosm communities substantially stronger than acidification. OW provoked structural and functional shifts in the community that differed in strength and direction among seasons. The organism‐level response to OW matched well the community‐level response of a given species only under warm and cold thermal stress, that is, in summer and winter. In other seasons, shifts in biotic interactions masked the direct OW effects. The combination of direct OW effects and OW‐driven shifts of biotic interactions is likely to jeopardize the future of the habitat‐forming macroalga F. vesiculosus in the Baltic Sea. Furthermore, we conclude that seasonal mesocosm experiments are essential for our understanding of global change impact because they take into account the important fluctuations of abiotic and biotic pressures.

Continue reading ‘Season affects strength and direction of the interactive impacts of ocean warming and biotic stress in a coastal seaweed ecosystem’

Combination of ocean acidification and warming enhances the competitive advantage of Skeletonema costatum over a green tide alga, Ulva linza

Highlights

• Coculture did not affect growth rate of U. linza but decreased it for S. costatum.

• Elevated CO2 relieved the inhibitory effect of U. linza on growth of S. costatum.

• At elevated CO2, higher temperature increased the growth rate of S. costatum.

• At elevated CO2, higher temperature reduced the growth rate of U. linza.

• Coculture did not affect respiration of U. linza but stimulated it for S. costatum.

Abstract

Red tide and green tide are two common algal blooms that frequently occur in many areas in the global oceans. The algae causing red tide and green tide often interact with each other in costal ecosystems. However, little is known on how future CO2-induced ocean acidification combined with temperature variation would affect the interaction of red and green tides. In this study, we cultured the red tide alga Skeletonema costatum and the green tide alga Ulva linza under ambient (400 ppm) and future CO2 (1000 ppm) levels and three temperatures (12, 18, 24 °C) in both monoculture and coculture systems. Coculture did not affect the growth rate of U. linza but significantly decreased it for S. costatum. Elevated CO2 relieved the inhibitory effect of U. linza on the growth of S. costatum, particularly for higher temperatures. At elevated CO2, higher temperature increased the growth rate of S. costatum but reduced it for U. linza. Coculture with U. linza reduced the net photosynthetic rate of S. costatum, which was relieved by elevated CO2. This pattern was also found in Chl a content, indicating that U. linza may inhibit growth of S. costatum via harming pigment synthesis and thus photosynthesis. In monoculture, higher temperature did not affect respiration rate of S. costatum but increased it in U. linza. Coculture did not affect respiration of U. linza but stimulated it for S. costatum, which was a signal of responding to biotic and/abiotic stress. The increased growth of S. costatum at higher temperature and decreased inhibition of U. linza on S. costatum at elevated CO2 suggest that red tides may have more advantages over green tides in future warmer and CO2-enriched oceans.

Continue reading ‘Combination of ocean acidification and warming enhances the competitive advantage of Skeletonema costatum over a green tide alga, Ulva linza’

Effects of pH on growth and biochemical responses in Agarophyton vermiculophyllum under different temperature conditions

The effects of pH (6.2, 7.2, 8.2, 9.2, and 10.2) under rising temperature (30 °C vs 20 °C) on Agarophyton vermiculophyllum growth and bio-physiology were investigated. Results showed that A. vermiculophyllum exhibited lower growth rates under elevated temperature in all pH values. Chlorophyll a, carotenoid, and phycocyanin levels were significantly enhanced by temperature elevation (p < 0.05). Enhanced H2O2 production either at lower or higher pH values correlated with lipid peroxidation (LPO) levels under elevated temperature, which suggested oxidative stress development. Oxidative damage was more severe at elevated pH values, which is confirmed by higher reactive oxygen species (ROS) levels. Compared with ambient pH 8.2 value, lower pH values under elevated temperature lead to increase activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), indicating that these enzymes played an important role to combat stress. However, decreased glutathione reductase (GR) and glutathione peroxidase (GPx) activities indicate least contribution for ROS scavenging at lower pH values. On contrary, SOD and CAT declined at elevated pH values compared with ambient pH, suggesting least contribution for ROS removal. Moreover, enhanced GR and GPx activities at elevated pH and temperature are not enough to scavenge ROS production. These data are consistent with higher H2O2 and LPO levels, and lower GST activities. Collectively, our results indicated that either pH fluctuations or elevated temperature displayed a disadvantageous influence on growth and bio-physiology of A. vermiculophyllum. Therefore, rising temperature alleviates adverse effects of seawater acidification, but it aggravates the negative effects of seawater alkalization on growth and bio-physiology of A. vermiculophyllum.

Continue reading ‘Effects of pH on growth and biochemical responses in Agarophyton vermiculophyllum under different temperature conditions’

Varying reproductive success under ocean warming and acidification across giant kelp (Macrocystis pyrifera) populations

Highlights

• Reproductive response to temperature and pH varied across populations.

• In high temperatures, only low-latitude California populations produced sporophytes.

• In low pH, all but two populations produced more eggs compared to ambient pH.

• Multiple eggs per female was the norm, not the exception.

• Gametophytes from all populations persisted in all treatments.

Abstract

Understanding how climate change may influence ecosystems depends substantially on its effects on foundation species, such as the ecologically important giant kelp (Macrocystis pyrifera). Despite its broad distribution along strong temperature and pH gradients and strong barriers to dispersal, the potential for local adaptation to climate change variables among kelp populations remains poorly understood. We assessed this potential by exposing giant kelp early life stages from genetically disparate populations in Chile and California to current and projected temperature and pH levels in common garden experiments. We observed high resistance at the haploid life stage to elevated temperatures with developmental failure appearing at the egg and sporophyte production stages among Chilean and high-latitude California populations, suggesting a greater vulnerability to climate- or ENSO-driven warming events. Additionally, populations that experience low pH events via strong upwelling, internal waves, or estuarine processes, produced more eggs per female under experimental low-pH conditions, which could increase fertilization success. These results enhance our ability to predict population extinctions and ecosystem range shifts under projected declines in ocean pH and increases in ocean temperature.

Continue reading ‘Varying reproductive success under ocean warming and acidification across giant kelp (Macrocystis pyrifera) populations’

Photosynthesis and light-dependent proton pumps increase boundary layer pH in tropical macroalgae: a proposed mechanism to sustain calcification under ocean acidification

Highlights

• Tropical calcifying macroalgae raise boundary layer pH due to photosynthesis

• Different mechanisms of inorganic carbon uptake control pH increase

• Proton pumps in light without photosynthesis appear important calcification

• Photosynthesis-driven pH increase allows calcification with ocean acidification

Abstract

Ocean acidification (OA) projections predict ocean pH to decline between 0.2 and 0.4 by 2100 with potential negative consequences for marine calcifiers without acclimation or adaption strategies to accomodate greater [H+] in seawater. Biotic control of calcified reef macroalgae thalli surface diffusive boundary layer (DBL) chemistry may overcome low pH in seawater as one strategy to accommodate OA conditions. To investigate this strategy, we examined surface DBL O2 and pH dynamics in five calcifying macroalgae (Halimeda, Udotea, Jania, Neogoniolithon, crustose coralline algae [CCA]) from the Florida Reef Tract under ambient (8.1) and low (7.65) pH using microsensors (100 μm) at the thalli surface in a flow-through flume. The role of photosynthesis and photosystem II (PSII)-independent proton pumps in controlling DBL pH were examined. Four of the five macroalgae exhibited a strong positive linear relationship between O2 production and increasing pH in the first 15–30 s of irradiance. Once a quasi-steady-state O2 concentration was reached (300 s), all species had DBL pH that were higher (0.02–0.32) than bulk seawater. The DBL pH increase was greatest at low pH and dependent on PSII. Some evidence was found for a light-dependent, but PSII-independent, proton pump. High DBL Δ pH upon illumination was likely in response to carbon concentrating mechanisms (CCMs) for photosynthesis. CCMs may be a HCO3−–H+ symport, OH– antiport or other DIC transport system, accompanied by proton efflux. HCO3– dehydration by external carbonic anhydrase (CAext) also produces OH– that can neutralize H+ in the DBL. CO2 or HCO3– uptake for photosynthesis may also engage H+/OH– fluxes as part of intracellular acid-base regulation changing DBL pH. A higher Δ pH within the DBL at low pH could be accounted for by greater CO2 diffusion and/or lower efficiencies in exporting cellular H+ across a lower concentration gradient, and/or a more efficient removal of H+ by CAext-driven dehydration of HCO3−. In the dark, Δ pH was less than in the light as these dynamics were primarily due to photosynthesis. We present a conceptual model of inorganic carbon uptake and ion transport pathways, as well as other processes associated with photosynthesis that drive DBL Δ pH and sustain tropical macroalgal calcification in the light under OA. In the dark, unless PSII-independent proton pumps are present, which do not appear to be ubiquitous amongst species, acidification processes likely dominate, resulting in CaCO3 net dissolution, particularly under OA conditions.

Continue reading ‘Photosynthesis and light-dependent proton pumps increase boundary layer pH in tropical macroalgae: a proposed mechanism to sustain calcification under ocean acidification’

Ocean acidification may threaten a unique seaweed community and associated industry in the Baltic Sea

Wild harvest of seaweed supports small-scale, high-value industries in a number of regions in the world. Information is lacking on how increasing carbon dioxide (CO2) concentrations in seawater could impact seaweeds in wild harvest situations. This study focuses on a mixed unattached loose-lying red algal community of Furcellaria lumbricalis in close association with Coccotylus truncatus that is found in the West Estonian Archipelago Sea, NE Baltic Sea. In Estonian coastal waters, the wild harvest of F. lumbricalis started in 1960s and it has since been used as raw material for furcellaran production. The aim of this study was to determine how ocean acidification may impact the balance of these two red algal species in the community. Mechanistic assessment of the carbon physiology of F. lumbricalis and C. truncatus was used to predict productivity and competitive interactions between these species in a high-CO2 world. Carbon use strategies in macroalgae were determined by analysing the natural abundances of carbon isotopes (δ13C), pH drift experiments and photosynthesis vs. dissolved inorganic carbon (DIC) curves. Photosynthesis of F. lumbricalis (operating with a CO2 concentrating mechanism or CCM) performed worse along the broader range of DIC concentrations compared to C. truncatus (non-CCM), especially those characterized under future climate conditions. Therefore, changing seawater carbon chemistry through ocean acidification has the potential to influence the balance of F. lumbricalis and C. truncatus in the community and the efficiency of the wild harvest of this community and the quality of product provided.

Continue reading ‘Ocean acidification may threaten a unique seaweed community and associated industry in the Baltic Sea’

Variability in the benefits of ocean acidification to photosynthetic rates of macroalgae without CO2-concentrating mechanisms

Increasing concentrations of surface-seawater carbon dioxide (CO2) (ocean acidification) could favour seaweed species that currently are limited for dissolved inorganic carbon (DIC). Among them, those that are unable to use CO2-concentrating mechanisms (CCMs) to actively uptake bicarbonate (HCO3–) across the plasmalemma are most likely to benefit. Here, we assess how the DIC uptake and photosynthetic rates of three rhodophytes without CCMs respond to four seawater CO2 concentrations representing pre-industrial (280 μatm), present-day (400 μatm), representative concentration pathway (RCP) emissions scenario 8.5 2050 (650 μatm) and RCP 8.5 2100 (1000 μatm). We demonstrated that the photosynthetic rates of only one species increase between the preindustrial and end-of-century scenarios, but because of differing photosynthetic quotients (DIC taken up relative to O2 evolved), all three increase their DIC uptake rates from pre-industrial or present-day scenarios to the end-of-century scenario. These variable, but generally beneficial, responses highlight that not all species without CCMs will respond to ocean acidification uniformly. This supports past assessments that, on average, this group will likely benefit from the impacts of ocean acidification. However, more concerted efforts are now required to assess whether similar benefits to photosynthetic rates and DIC uptake are also observed in chlorophytes and ochrophytes without CCMs.

Continue reading ‘Variability in the benefits of ocean acidification to photosynthetic rates of macroalgae without CO2-concentrating mechanisms’


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Ocean acidification in the IPCC AR5 WG II

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