Posts Tagged 'algae'

Acclimation history of elevated temperature reduces the tolerance of coralline algae to additional acute thermal stress

Increasing atmospheric CO2 is driving major environmental changes in the ocean, such as an increase in average ocean temperature, a decrease in average ocean pH (ocean acidification or OA), and an increase in the number and severity of extreme climatic events (e.g., anomalous temperature events and heatwaves). Uncertainty exists in the capacity for species to withstand these stressors occurring concomitantly. Here, we tested whether an acclimation history of ocean warming (OW) and OA affects the physiological responses of an abundant, reef-building species of crustose coralline algae (CCA), Porolithon cf. onkodes, to chronic and acute thermal stress. To address this, we exposed algae to varying temperature and pH levels for 6 weeks and this chronic treatment experiment was followed by an acute exposure to an anomalous temperature event (+4–6°C from acclimation temperature). Net photosynthetic rate was negatively affected across all treatments by increasing temperature during the acute temperature event, however, algae acclimated to the control temperature were able to maintain photosynthetic rates for +4°C above their acclimation temperature, whereas algae acclimated to elevated temperature were not. Average relative change in O2 produced resulted in a 100–175% decrease, with the largest decrease found in algae acclimated to the combined treatment of elevated temperature and reduced pH. We conclude that acclimation to chronic global change stressors (i.e., OW and OA) will reduce the tolerance of P. cf. onkodes to anomalous increases in temperature, and this may have implications for reef building processes.

Continue reading ‘Acclimation history of elevated temperature reduces the tolerance of coralline algae to additional acute thermal stress’

Exposure time modulates the effects of climate change-related stressors on fertile sporophytes and early-life stage performance of a habitat-forming kelp species

Highlight

  • Ocean warming (OW) reduced the sorus photosynthetic performance.
  • OW reduced meiospore germination rate.
  • OW and ocean acidification reduced meiospore release (MR).
  • MR is more sensitive to temperature changes than to pCO2 changes.
  • Longer exposure to OW increased the negative effects on germination rate.

Abstract

Understanding the impact of increases in pCO2 (OA) and extreme changes in temperature on marine organisms is critical to predicting how they will cope with climate change. We evaluated the effects of OA as well as warming and cooling trend temperature on early reproductive traits of Lessonia trabeculata, a foundation kelp species. Sori discs were maintained for an exposure time (ET) of 3 (T3) and 7 (T7) days to one of two contrasting pCO2 levels (450 and 1100 μatm). In addition, at each pCO2 level, they were subjected to three temperature treatments: 15 °C (control), 10 °C (cool) and 19 °C (warm). Subsequently, we compared sorus photosynthetic performance (Fv/Fm), the number of meiospores released (MR) and their germination rate (GR) after 48 h of settlement, with values obtained from sori discs not exposed (DNE) to the treatments. The Fv/Fm measured for DNE was lower than at T3 and T7 at 10 and 15 °C but not at 19 °C. Regardless of temperature, we found no significant differences between MR measured at T0 and T3 were found. MR at T7 was significantly lower at 19 °C than at 10 and 15 °C. We found only aA significant reduction in MR in response to elevated pCO2 was only found at T3. The GR of meiospores released by DNE and then maintained for 48 h to 19 °C decreased significantly by ∼33 % when compared with those maintained for the same time at 10 and 15 °C. A similar, but more drastic reduction (∼54 %) in the GR was found in meiospores released by sori discs exposed for T3 and maintained for 48 h to 19 °C. We suggest that OA and warming trend will threaten the early establishment of this species with further consequences for the functioning of the associated ecosystem.

Graphical abstract

Under laboratory conditions were investigated the combined effect of pCO2, temperature and the exposure time on sorus photosynthetic performance (Fv/Fm) and meiospore performance (release and germination rate) of a habitat-forming kelp Lessonia trabeculata. The results suggest that important traits such as sorus photosynthetic performance, meiospores released and germination rate can be affected by those stressors and by the extent to which the sori are exposed. We concluded that ocean warming and ocean acidification might threaten the early establishment of this species with further consequences for the ecosystem functioning, goods and services in coastal environments.

Continue reading ‘Exposure time modulates the effects of climate change-related stressors on fertile sporophytes and early-life stage performance of a habitat-forming kelp species’

The Bouraké semi-enclosed lagoon (New Caledonia). A natural laboratory to study the life-long adaptation of a coral reef ecosystem to climate change-like conditions

According to current experimental evidence, coral reefs could disappear within the century if CO2 emissions remain unabated. However, recent discoveries of diverse and high cover reefs that already thrive under extreme conditions seem to contradict these projections. Volcanic CO2 vents, semi-enclosed lagoons and mangrove estuaries are unique study sites where one or more ecologically relevant parameters for life in the oceans are close or even worse than currently projected for the year 2100. These natural analogues of future conditions hold new hope for the future of coral reefs and provide unique natural laboratories to explore how reef species could keep pace with climate change. To achieve this, it is essential to characterize their environment as a whole, and accurately consider all possible environmental factors that may differ from what is expected in the future and that may possibly alter the ecosystem response.

In this study, we focus on the semi-enclosed lagoon of Bouraké (New Caledonia, SW Pacific Ocean) where a healthy reef ecosystem thrives in warm, acidified and deoxygenated water. We used a multi-scale approach to characterize the main physical-chemical parameters and mapped the benthic community composition (i.e., corals, sponges, and macroalgae). The data revealed that most physical and chemical parameters are regulated by the tide, strongly fluctuate 3 to 4 times a day, and are entirely predictable. The seawater pH and dissolved oxygen decrease during falling tide and reach extreme low values at low tide (7.2 pHT and 1.9 mg O2 L−1 at Bouraké, vs 7.9 pHT and 5.5 mg O2 L−1 at reference reefs). Dissolved oxygen, temperature, and pH fluctuates according to the tide of up to 4.91 mg O2 L−1, 6.50 °C, and 0.69 pHT units on a single day. Furthermore, the concentration of most of the chemical parameters was one- to 5-times higher at the Bouraké lagoon, particularly for organic and inorganic carbon and nitrogen, but also for some nutrients, notably silicates. Surprisingly, despite extreme environmental conditions and altered seawater chemical composition, our results reveal a diverse and high cover community of macroalgae, sponges and corals accounting for 28, 11 and 66 species, respectively. Both environmental variability and nutrient imbalance might contribute to their survival under such extreme environmental conditions. We describe the natural dynamics of the Bouraké ecosystem and its relevance as a natural laboratory to investigate the benthic organism’s adaptive responses to multiple stressors like future climate change conditions.

Continue reading ‘The Bouraké semi-enclosed lagoon (New Caledonia). A natural laboratory to study the life-long adaptation of a coral reef ecosystem to climate change-like conditions’

Tidal action and macroalgal photosynthetic activity prevent coastal acidification in an eutrophic system within a semi-desert region

Highlights

  • Macroalgal photosynthesis (MP) controls daily pH variability during low tide.
  • Environmental factors control pH variability at seasonal scale.
  • Ulva lactuca photosynthetic activity increased the pH of seawater.
  • Macrotidal action and MP prevent coastal acidification in an eutrophic system.

Abstract

Nutrient input drive macroalgal blooms and increases in photosynthetic activity in coastal ecosystems. An intense macroalgal photosynthetic activity can increase the surrounding pH and it could prevent the acidification that often follows an eutrophication process. We tested this hypothesis with field sampling and experiments in a macrotidal (up to 9 m in amplitude) coastal system within a semi-desert region with contrasting eutrophic conditions and Ulva lactuca blooms in the northern Argentinean Patagonia (San Antonio Bay). Our results indicate that daily pH variability during low tide could be controlled by the photosynthetic activity of Ulva lactuca under eutrophic conditions. At seasonal scale, the pH variations were related to environmental features, particularly seawater temperature. Both environmental (i.e. high solar radiation, negligible freshwater inputs and, large tidal action) and anthropogenic nutrient inputs into the studied area promote the Ulva lactuca blooms, which in turn increases the surrounding pH in well oxygenated seawater through the intense photosynthetic activity. Our study shows that eutrophication instead of being a driver of acidification, could contribute to its prevention in well oxygenated marine coastal systems located within semi-desert regions.

Continue reading ‘Tidal action and macroalgal photosynthetic activity prevent coastal acidification in an eutrophic system within a semi-desert region’

Seasonal photophysiological performance of adult western Baltic Fucus vesiculosus (Phaeophyceae) under ocean warming and acidification

Shallow coastal marine ecosystems are exposed to intensive warming events in the last decade, threatening keystone macroalgal species such as the bladder wrack (Fucus vesiculosus, Phaeophyceae) in the Baltic Sea. Herein, we experimentally tested in four consecutive benthic mesocosm experiments, if the single and combined impact of elevated seawater temperature (Δ + 5°C) and pCO2 (1100 ppm) under natural irradiance conditions seasonally affected the photophysiological performance (i.e., oxygen production, in vivo chlorophyll a fluorescence, energy dissipation pathways and chlorophyll concentration) of Baltic Sea Fucus. Photosynthesis was highest in spring/early summer when water temperature and solar irradiance increases naturally, and was lowest in winter (December to January/February). Temperature had a stronger effect than pCO2 on photosynthetic performance of Fucus in all seasons. In contrast to the expectation that warmer winter conditions might be beneficial, elevated temperature conditions and sub-optimal low winter light conditions decreased photophysiological performance of Fucus. In summer, western Baltic Sea Fucus already lives close to its upper thermal tolerance limit and future warming of the Baltic Sea during summer may probably become deleterious for this species. However, our results indicate that over most of the year a combination of future ocean warming and increased pCO2 will have slightly positive effects for Fucus photophysiological performance.

Continue reading ‘Seasonal photophysiological performance of adult western Baltic Fucus vesiculosus (Phaeophyceae) under ocean warming and acidification’

Elevated CO2 influences competition for growth, photosynthetic performance and biochemical composition in Neopyropia yezoensis and Ulva prolifera

Highlights

  • The growth of Neopyropia yezoensis was significantly inhibited by Ulva prolifera.
  • Elevated CO2 enhanced the resistance of N. yezoensis to the effect of U. prolifera.
  • Elevated CO2 increased the competitive ability of U. prolifera.

Abstract

The occurrence of various marine macroalgae in the same niche will inevitably lead to interspecific competition due to similar environmental requirements. With the increasing global atmospheric CO2 concentration, the resulting ocean acidification can potentially influence competition among macroalgae in the future. Neopyropia yezoensis (Rhodophyta, formerly Pyropia yezoensis) and the epiphytic alga Ulva prolifera (Chlorophyta) were selected for investigating competition among macroalgae grown under different CO2 conditions. The results showed that when cultured with U. proliferaN. yezoensis‘ growth rate was significantly inhibited along with a sharp decrease in net photosynthetic rate. Although CO2 decreased the growth rate of N. yezoensis, it enhanced the resistance of the alga to the allelopathic effect of U. prolifera. While no difference was found between U. prolifera grown in monoculture and biculture, strong competitive ability was observed. CO2 could enhance this ability with higher net photosynthetic rate. However, CO2 significantly inhibited the carotenoid synthesis in both plants. This inhibition in N. yezoensis was more pronounced in the presence of U. prolifera. Biculture promoted the accumulation of soluble protein in N. yezoensis while it inhibited the process in U. prolifera. In addition, it enhanced the inhibitory effect of acidification on soluble carbohydrates of both plants. Elevated CO2 levels alleviated the competition between N. yezoensis and U. prolifera, but the latter can become the more competitive epiphytic alga which can impact the future of nori culture.

Continue reading ‘Elevated CO2 influences competition for growth, photosynthetic performance and biochemical composition in Neopyropia yezoensis and Ulva prolifera’

Elevated pCO2 reinforces preference among intertidal algae in both a specialist and generalist herbivore

Highlights

  • Elevated pCO2 influences growth and chemical composition of some intertidal algae.
  • Herbivore preference is reinforced by resilience of preferred alga to pCO2 exposure.
  • Preference is also influenced by changes in lesser-preferred algal species.
  • Specialist and generalist feeding may be indirectly affected by ocean acidification.

Abstract

Ocean acidification (OA) can induce changes in marine organisms and species interactions. We examined OA effects on intertidal macroalgal growth, palatability, and consumption by a specialist crab (Pugettia producta) and a generalist snail (Tegula funebralis) herbivore. Moderate increases in pCO2 increased algal growth in most species, but effects of pCO2 on C:N and phenolic content varied by species. Elevated pCO2 had no effect on algal acceptability to herbivores, but did affect their preference ranks. Under elevated pCO2, electivity for a preferred kelp (Egregia menziesii) and preference rankings among algal species strengthened for both P. producta and T. funebralis, attributable to resilience of E. menziesii in elevated pCO2 and to changes in palatability among less-preferred species. Preferred algae may therefore grow more under moderate pCO2 increases in the future, but their appeal to herbivores may be strengthened by associated shifts in nutritional quality and defensive compounds in other species.

Continue reading ‘Elevated pCO2 reinforces preference among intertidal algae in both a specialist and generalist herbivore’

Increased light availability modulates carbon and nitrogen accumulation in the macroalga Gracilariopsis lemaneiformis (Rhodophyta) in response to ocean acidification

Highlights

  • The effects of light and elevated pCO2 on Gracilariopsis were examined.
  • Ocean acidification enhanced algal biomass, photosynthesis and total C/N ratios.
  • Increasing light and elevated pCO2 lowered nutritional quality of G. lemaneiformis.

Abstract

The economically important red macroalga Gracilariopsis lemaneiformis has demonstrated positive ecological functions in nutrient bioextraction efficiency and high harvestable biomass, as well as being a food and agar source owing to its richness in proteins and polysaccharides. Carbon dioxide (CO2)-induced ocean acidification has resulted in mixed nutrient compound accumulations in this marine autotroph. G. lemaneiformis also experiences light variations resulting from self-shading and varied cultivation depths. Therefore, a factorial coupling experiment was conducted to examine how growth, photosynthesis performance, soluble cell components and metabolic enzyme-driven activities respond to light availability changes and CO2 enrichment. The ocean acidification enhanced the growth characteristics, total carbon/nitrogen ratios and metabolic nutrient accumulation processes in G. lemaneiformis regardless of the light level. Photosynthetic performances, including relative electron transport rate and maximum photochemical quantum yield, were increased by high pCO2 concentrations, resulting in soluble carbohydrate accumulation. The carbon and nitrogen accumulations might result from variations in carbonic anhydrase and nitrate reductase activities under high pCO2 conditions. The soluble protein and free amino acids contents declined in response to CO2 elevation, and this effect was more pronounced as the light intensity increased. Thus, future climate changes may cause greater algal biomass accumulations, but they may negatively affect the cell composition and nutritional quality of G. lemaneiformis.

Continue reading ‘Increased light availability modulates carbon and nitrogen accumulation in the macroalga Gracilariopsis lemaneiformis (Rhodophyta) in response to ocean acidification’

An intertidal life: combined effects of acidification and winter heatwaves on a coralline alga (Ellisolandia elongata) and its associated invertebrate community

Highlights

  • Coralline alga create a microhabitat with mitigating effect on ocean acidification
  • Temperature is the major driver of changes in the invertebrate reef community
  • Winter heatwaves and acidified conditions alter invertebrates community structure
  • Algal reef communities become dominated by opportunistic taxa

Abstract

In coastal marine ecosystems coralline algae often create biogenic reefs. These calcareous algal reefs affect their associated invertebrate communities via diurnal oscillations in photosynthesis, respiration and calcification processes. Little is known about how these biogenic reefs function and how they will be affected by climate change. We investigated the winter response of a Mediterranean intertidal biogenic reef, Ellisolandia elongate exposed in the laboratory to reduced pH conditions (i.e. ambient pH – 0.3, RCP 8.5) together with an extreme heatwave event (+1.4°C for 15 days). Response variables considered both the algal physiology (calcification and photosynthetic rates) and community structure of the associated invertebrates (at taxonomic and functional level). The combination of a reduced pH with a heatwave event caused Ellisolandia elongata to significantly increase photosynthetic activity. The high variability of calcification that occurred during simulated night time conditions, indicates that there is not a simple, linear relationship between these two and may indicate that it will resilient to future conditions of climate change.

In contrast, the associated fauna were particularly negatively affected by the heatwave event, which impoverished the communities as opportunistic taxa became dominant. Local increases in oxygen and pH driven by the algae can buffer the microhabitat in the algal fronds, thus favouring the survival of small invertebrates.

Continue reading ‘An intertidal life: combined effects of acidification and winter heatwaves on a coralline alga (Ellisolandia elongata) and its associated invertebrate community’

Carbonate chemistry and temperature dynamics in an alga dominated habitat

Recent works have begun to explore the magnitude and frequency of localized changes in seawater chemistry in shallow water systems, where the effects of warming and acidification are still unpredictable. In a Mediterranean shallow coastal site, we empirically characterized the diel, seasonal, and annual pattern of pH, temperature, and associated chemical changes on one Ellisolandia elongata ‘corniche’, (i.e. a coastal algal biogenic reef). Local benthic metabolism together with temperature, were two of the main drivers for the carbonate system variation over diel and seasonal cycles. During the 12-month study, a total of seven heatwave events were recorded (two of which occurred in winter) with the longest lasting 11 days. The present study highlights the importance of improving the knowledge of changes and dynamics occurring at local scale, by extending in situ data acquisition at shallow coastal sites, in order to better assess the impacts of climate change on both environment and ecosystems.

Continue reading ‘Carbonate chemistry and temperature dynamics in an alga dominated habitat’

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