Posts Tagged 'photosynthesis'

Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment

Climate change threatens the survival of scleractinian coral from exposure to concurrent ocean warming, acidification and deoxygenation; how corals can potentially adapt to this trio of stressors is currently unknown. This study investigates three coral species (Acropora muricata, Acropora pulchra and Porites lutea) dominant in an extreme mangrove lagoon (Bouraké, New Caledonia) where abiotic conditions exceed those predicted for many reef sites over the next 100 years under climate change and compared them to conspecifics from an environmentally more benign reef habitat. We studied holobiont physiology as well as plasticity in coral-associated microorganisms (Symbiodiniaceae and bacteria) through ITS2 and 16S rRNA sequencing, respectively. We hypothesised that differences in coral-associated microorganisms (Symbiodiniaceae and bacteria) between the lagoonal and adjacent reef habitats may support coral host productivity and ultimately the ability of corals to live in extreme environments. In the lagoon, all coral species exhibited a metabolic adjustment of reduced photosynthesis-to-respiration ratios (P/R), but this was accompanied by highly divergent coral host-specific microbial associations. This was substantiated by the absence of shared ITS2-type profiles (proxies for Symbiodiniaceae genotypes). We observed that ITS2 profiles originating from Durusdinium taxa made up < 3% and a novel Symbiodinium ITS2 profile A1-A1v associated with A. pulchra. Bacterial community profiles were also highly divergent in corals from the lagoonal environment, whereas corals from the reef site were consistently dominated by Hahellaceae, Endozoicomonas. As such, differences in host–microorganism associations aligned with different physiologies and habitats. Our results argue that a multitude of host–microorganism associations are required to fulfill the changing nutritional demands of corals persisting into environments that parallel climate change scenarios.

Continue reading ‘Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment’

Impacts of elevated temperature and pCO2 on the brooded larvae of Pocillopora damicornis from Luhuitou Reef, China: evidence for local acclimatization

In this study, we tested whether larvae brooded by the reef coral Pocillopora damicornis from a naturally extreme and highly variable environment are preadapted to cope with predicted increases in temperature and pCO2. We exposed larvae to two temperatures (29 vs. 30.8 °C) crossed with two pCO2 levels (~ 500 vs. ~ 1000 μatm) in a full-factorial experiment for 5 d. Larval performance was assessed as dark respiration (RD), net and gross photosynthesis (PN and PG, respectively), survival, settlement, and the activity of carbonic anhydrase (CA), the central enzyme involved in photosynthesis. The results showed that RD was unaffected by either elevated temperature or pCO2, while elevated temperature and/or pCO2 stimulated PN and PG and increased the ratios of PN to RD, indicating a relatively higher autotrophic capacity. Consequently, larval survivorship under elevated temperature and/or pCO2 was consistently 14% higher than that under the control treatment. Furthermore, elevated temperature and pCO2 did not affect host CA activity, but synergistically enhanced symbiont CA activity, contributing greatly to the stimulated photosynthetic capacity. These results suggest that brooded larvae of P. damicornis larvae from Luhuitou may be preadapted to cope with projected warming and ocean acidification. More generally, it appears that corals from highly variable environments may have increased resilience to the widespread climate change.

Continue reading ‘Impacts of elevated temperature and pCO2 on the brooded larvae of Pocillopora damicornis from Luhuitou Reef, China: evidence for local acclimatization’

Recruits of the temperate coral Oculina arbuscula mimic adults in their resilience to ocean acidification

Ocean acidification has been investigated extensively in scleractinian corals, but studies on different life stages of the same species are lacking. We investigated the response of recruits of the temperate coral Oculina arbuscula to increased CO2 concentrations, a species whose adults show significant tolerance to elevated concentrations of CO2. Specifically, we exposed small colonies (5-12 mm diameter) to 475, 710, and 1261 ppm CO2 for 75 d in the laboratory to address the hypothesis that, like adults, the health of O. arbuscula recruits is not affected by increased CO2 concentrations. Calcification rates were monitored regularly during the experiment, while mortality, respiration rates, photosynthetic rates, algal symbiont densities, and soluble protein were quantified at the end. As predicted, CO2 concentration did not impact survival, algal densities, or soluble protein concentrations in O. arbuscula recruits. In contrast, both calcification rates and photosynthesis:respiration ratios tended to be lower at higher CO2. Comparing the results of this study on recruits with published studies on adults suggested that both life stages exhibit a similar non-linear response to CO2 concentration, whereby recruits may be unable to counter the increased energetic cost of calcification that occurs at the highest CO2. Based on these results and environmental monitoring showing that mean pCO2 is increasing by ~2.4% yr-1 in the waters off Georgia, USA, we conclude that O. arbuscula recruits may begin to exhibit depressed calcification rates within the current century if CO2 emissions are not reduced.

Continue reading ‘Recruits of the temperate coral Oculina arbuscula mimic adults in their resilience to ocean acidification’

Combined effects of temperature, irradiance and pH on Teleaulax amphioxeia (Cryptophyceae) physiology and feeding ratio for its predator Mesodinium rubrum (Ciliophora)

The cryptophyte Teleaulax amphioxeia is a source of plastids for the ciliate Mesodinium rubrum and both organisms are members of the trophic chain of several species of Dinophysis. It is important to better understand the ecology of organisms at the first trophic levels before assessing the impact of principal factors of global change on Dinophysis spp. Therefore, combined effects of temperature, irradiance and pH on growth rate, photosynthetic activity and pigment content of a temperate strain of T. amphioxeia were studied using a full factorial design (central composite design 23*) in 17 individually controlled bioreactors. The derived model predicted an optimal growth rate of T. amphioxeia at a light intensity of 400 µmol photons · m‐2 · s‐1, more acidic pH (7.6) than the current average and a temperature of 17.6°C. An interaction between temperature and irradiance on growth was also found, while pH did not have any significant effect. Subsequently, to investigate potential impacts of prey quality and quantity on the physiology of the predator, M. rubrum was fed two separate prey: predator ratios with cultures of T. amphioxeia previously acclimated at two different light intensities (100 and 400 µmol photons · m‐2 · s‐1). M. rubrum growth appeared to be significantly dependant on prey quantity while effect of prey quality was not observed. This multi‐parametric study indicated a high potential for a significant increase of T. amphioxeia in future climate conditions but to what extent this would lead to increased occurrences of Mesodinium spp. and Dinophysis spp. should be further investigated.

Continue reading ‘Combined effects of temperature, irradiance and pH on Teleaulax amphioxeia (Cryptophyceae) physiology and feeding ratio for its predator Mesodinium rubrum (Ciliophora)’

Influence of fluctuating irradiance on photosynthesis, growth and community structure of estuarine phytoplankton under increased nutrients and acidification

Highlights

• Global change impact was assessed in post-bloom estuarine phytoplankton communities.

• Future scenario of higher nutrients and lower pH favored the growth of phytoplankton.

• Growth and photosynthesis were negatively affected by mixing in the marine community.

• Marine are more vulnerable than river communities under mixing in a Future scenario.

• Such effects can alter the trophic web of this highly productive area of Patagonia.

Abstract

Estuaries represent the interface between riverine and marine ecosystems and they are among the most productive areas on Earth; thus it is of utmost importance to understand their functioning in a global change scenario. So far, it is virtually unknown how the interaction between nutrient inputs, acidification and fluctuating light regimes could alter photosynthesis, growth, and phytoplankton structure in the end members (i.e., river and sea) of estuaries. Using the Chubut river estuary (Argentina) as a model ecosystem, we conducted experimentation during the austral summer (i.e., the windy season, February of 2016) with both, river and seawater phytoplankton communities to assess these topics. We evaluated the impact of fluctuating irradiance (static vs. mixed conditions) using short- (<one day) and mid-term acclimation (five days) and mimicking scenarios of higher acidification and nutrients (Future) as compared with an unmodified Present. The growth of both communities increased significantly under the Future as compared to the Present scenario, but mixing decreased growth only in seawater phytoplankton. Small centric diatoms (mainly Thalassiosira spp.) co-dominated with unidentified flagellates in the seawater, but the relative abundance of diatoms was higher in the Future as compared with the Present scenario. Diatoms and cryptophytes co-dominated in the river at the end of the experiments for both static and mixed conditions. Net primary productivity (NPP) decreased in the Future scenario and this was coupled with higher inhibition (k) of photosystem II (PSII), in both communities. Our results indicate that fluctuating irradiance, under a future global change scenario, as simulated here, has a significant impact on the structure and growth of seawater phytoplankton, together with increases in photochemical inhibition and decreases in NPP. However, these changes are much smaller in the river phytoplankton. Thus, the overall effects of mixing on the trophodynamics of the area will be more important at the sea than in the river end of the estuary.

Continue reading ‘Influence of fluctuating irradiance on photosynthesis, growth and community structure of estuarine phytoplankton under increased nutrients and acidification’

Global environmental changes negatively impact temperate seagrass ecosystems

The oceans are increasingly affected by multiple aspects of global change, with substantial impacts on ecosystem functioning and food-web dynamics. While the effects of single factors have been extensively studied, it has become increasingly evident that there is a need to unravel the complexities related to a multiple stressor environment. In a mesocosm experimental study, we exposed a simplified, multi-trophic seagrass ecosystem (composed of seagrass, two shrimp species, and two intermediate predatory fish species) to three global change factors consisting of simulated storm events (Storms), heat shocks (Heat), and ocean acidification (OA), and the combination of all three factors (All). The most striking result indicated that when all factors were combined, there was a negative influence at all trophic levels, while the treatments with individual factors revealed species-specific response patterns. It appeared, however, that single factors may drive the multi-stressor response. All single factors (i.e., Storms, Heat, and OA) had either negative, neutral, or positive effects on fish and shrimp, whereas no effect was recorded for any single stressor on seagrass plants. The findings demonstrate that when several global change factors appear simultaneously, they can have deleterious impacts on seagrass ecosystems, and that the nature of factors and food-web composition may determine the sensitivity level of the system. In a global change scenario, this may have serious and applicable implications for the future of temperate seagrass ecosystems.

Continue reading ‘Global environmental changes negatively impact temperate seagrass ecosystems’

The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)

Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial, light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 µatm) and future (1000 µatm) pCO2 levels under a constant as well as a dynamic light, simulating more realistic light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimize its photophysiology for effective light usage during both low- and high-light periods. This photoacclimative response, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla is able to maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, M. pusilla is likely to cope well with future conditions in the Arctic Ocean.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)’


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