Posts Tagged 'photosynthesis'

Ocean acidification effects on calcification and dissolution in tropical reef macroalgae

Net calcification rates for coral reef and other calcifiers have been shown to decline as ocean acidification (OA) occurs. However, the role of calcium carbonate dissolution in lowering net calcification rates is unclear. The objective of this study was to distinguish OA effects on calcification and dissolution rates in dominant calcifying macroalgae of the Florida Reef Tract, including two rhodophytes (Neogoniolithon strictum, Jania adhaerens) and two chlorophytes (Halimeda scabra, Udotea luna). Two experiments were conducted: (1) to assess the difference in gross (45Ca uptake) versus net (total alkalinity anomaly) calcification rates in the light/dark and (2) to determine dark dissolution (45CaCO3), using pH levels predicted for the year 2100 and ambient pH. At low pH in the light, all species maintained gross calcification rates and most sustained net calcification rates relative to controls. Net calcification rates in the dark were ~84% lower than in the light. In contrast to the light, all species had lower net calcification rates in the dark at low pH with chlorophytes exhibiting net dissolution. These data are supported by the relationship (R2 = 0.82) between increasing total alkalinity and loss of 45Ca from pre-labelled 45CaCO3 thalli at low pH in the dark. Dark dissolution of 45CaCO3-labelled thalli was ~18% higher in chlorophytes than rhodophytes at ambient pH, and ~ twofold higher at low pH. Only Udotea, which exhibited dissolution in the light, also had lower daily calcification rates integrated over 24 h. Thus, if tropical macroalgae can maintain high calcification rates in the light, lower net calcification rates in the dark from dissolution may not compromise daily calcification rates. However, if organismal dissolution in the dark is additive to sedimentary carbonate losses, reef dissolution may be amplified under OA and contribute to erosion of the Florida Reef Tract and other reefs that exhibit net dissolution.

Continue reading ‘Ocean acidification effects on calcification and dissolution in tropical reef macroalgae’

Physiological responses of Skeletonema costatum to the interactions of seawater acidification and combination of photoperiod and temperature

Ocean acidification (OA), which is a major environmental change caused by increasing atmospheric CO2, has considerable influences on marine phytoplankton. But few studies have investigated interactions of OA and seasonal changes in temperature and photoperiod on marine diatoms. In the present study, a marine diatom Skeletonema costatum was cultured under two different CO2 levels (LC, 400 μatm; HC, 1000 μatm) and three different combinations of temperature and photoperiod length (8:16 L:D with 5 ℃, 12:12 L:D with 15 ℃, 16:8 L:D with 25 ℃), simulating different seasons in typical temperate oceans, to investigate the combined effects of these factors. The results showed that specific growth rate of S. costatum increased with increasing temperature and daylength. However, OA showed contrasting effects on growth and photosynthesis under different combinations of temperature and daylength: while positive effects of OA were observed under spring and autumn conditions, it significantly decreased growth (11 %) and photosynthesis (21 %) in winter. In addition, low temperature and short daylength decreased the proteins of PSII (D1, CP47 and RubcL) at ambient pCO2 level, while OA alleviated the negative effect. These data indicated that future ocean acidification may show differential effects on diatoms in different cluster of other factors.

Continue reading ‘Physiological responses of Skeletonema costatum to the interactions of seawater acidification and combination of photoperiod and temperature’

Daily to weekly impacts of mixing and biological activity on carbonate dynamics in a large river-dominated shelf

Highlights

• We surveyed at a fixed station for 6 d at the end of ENSO 2015/2016 in summer.

• High temperature and salinity water intruded the river plume on day 3.

• Net respiration changed to net photosynthesis in the near-surface water on day 3.

• The southwesterly monsoon was disturbed, and coastal upwelling was relaxed.

• Bottom water continuously reflected a pH reduction and oxygen consumption.

Abstract

Large eutrophic river plumes can lead to hypoxic near-bottom water during summer. However, how the carbonate system in this stratified water column varies at a daily to weekly scale is still unclear. At the end of the first severe El Niño Southern Oscillation event in the 21st century during 2015/2016, high temperature, high salinity water was observed in the middle of the Pearl River plume on the northern South China Sea shelf over 6 d (July 24–29, 2016). We deployed a sensor pack (conductivity, temperature, pressure, and dissolved oxygen [DO]) along the water column each hour and took discrete samples, including total alkalinity and dissolved inorganic carbon every 3 h, to calculate pH. We observed a pH reduction rate of 0.011 pH unit·d−1 and an oxygen consumption rate of 4.4 μmol kg−1·d−1 in the near-bottom water. The temporal variations in calculated net community production rate and excess DO (measured DO – saturated DO) implied the switch in the dominance of net respiration to net photosynthesis in the near-surface water during this mixing event. We suggested that both net photosynthesis and net respiration were in the water with oversaturated DO on a short-term scale. The pH reduction and oxygen consumption rates in this study could help to estimate the level of coastal acidification and hypoxia better.

Continue reading ‘Daily to weekly impacts of mixing and biological activity on carbonate dynamics in a large river-dominated shelf’

Effects of future climate on coral-coral competition

As carbon dioxide (CO2) levels increase, coral reefs and other marine systems will be affected by the joint stressors of ocean acidification (OA) and warming. The effects of these two stressors on coral physiology are relatively well studied, but their impact on biotic interactions between corals are poorly understood. While coral-coral interactions are less common on modern reefs, it is important to document the nature of these interactions to better inform restoration strategies in the face of climate change. Using a mesocosm study, we evaluated whether the combined effects of ocean acidification and warming alter the competitive interactions between the common coral Porites astreoides and two other mounding corals (Montastraea cavernosa or Orbicella faveolata) common in the Caribbean. After 7 days of direct contact, P. astreoides suppressed the photosynthetic potential of M. cavernosa by 100% in areas of contact under both present (~28.5°C and ~400 μatm pCO2) and predicted future (~30.0°C and ~1000 μatm pCO2) conditions. In contrast, under present conditions M. cavernosa reduced the photosynthetic potential of P. astreoides by only 38% in areas of contact, while under future conditions reduction was 100%. A similar pattern occurred between P. astreoides and O. faveolata at day 7 post contact, but by day 14, each coral had reduced the photosynthetic potential of the other by 100% at the point of contact, and O. faveolata was generating larger lesions on P. astreoides than the reverse. In the absence of competition, OA and warming did not affect the photosynthetic potential of any coral. These results suggest that OA and warming can alter the severity of initial coral-coral interactions, with potential cascading effects due to corals serving as foundation species on coral reefs.

Continue reading ‘Effects of future climate on coral-coral competition’

Trophic pyramids reorganize when food web architecture fails to adjust to ocean change

As human activities intensify, the structures of ecosystems and their food webs often reorganize. Through the study of mesocosms harboring a diverse benthic coastal community, we reveal that food web architecture can be inflexible under ocean warming and acidification and unable to compensate for the decline or proliferation of taxa. Key stabilizing processes, including functional redundancy, trophic compensation, and species substitution, were largely absent under future climate conditions. A trophic pyramid emerged in which biomass expanded at the base and top but contracted in the center. This structure may characterize a transitionary state before collapse into shortened, bottom-heavy food webs that characterize ecosystems subject to persistent abiotic stress. We show that where food web architecture lacks adjustability, the adaptive capacity of ecosystems to global change is weak and ecosystem degradation likely.

Continue reading ‘Trophic pyramids reorganize when food web architecture fails to adjust to ocean change’

Effects of multiple drivers of ocean global change on the physiology and functional gene expression of the coccolithophore Emiliania huxleyi

Ongoing ocean global change due to anthropogenic activities is causing multiple chemical and physical seawater properties to change simultaneously, which may affect the physiology of marine phytoplankton. The coccolithophore Emiliania huxleyi is a model species often employed in the study of the marine carbon cycle. The effect of ocean acidification (OA) on coccolithophore calcification has been extensively studied; however, physiological responses to multiple environmental drivers are still largely unknown. Here we examined two‐way and multiple driver effects of OA and other key environmental drivers—nitrate, phosphate, irradiance, and temperature—on the growth, photosynthetic, and calcification rates, and the elemental composition of E. huxleyi. In addition, changes in functional gene expression were examined to understand the molecular mechanisms underpinning the physiological responses. The single driver manipulation experiments suggest decreased nitrate supply being the most important driver regulating E. huxleyi physiology, by significantly reducing the growth, photosynthetic, and calcification rates. In addition, the interaction of OA and decreased nitrate supply (projected for year 2100) had more negative synergistic effects on E. huxleyi physiology than all other two‐way factorial manipulations, suggesting a linkage between the single dominant driver (nitrate) effects and interactive effects with other drivers. Simultaneous manipulation of all five environmental drivers to the conditions of the projected year 2100 had the largest negative effects on most of the physiological metrics. Furthermore, functional genes associated with inorganic carbon acquisition (RubisCO, AEL1, and δCA) and calcification (CAX3, AEL1, PATP, and NhaA2) were most downregulated by the multiple driver manipulation, revealing linkages between responses of functional gene expression and associated physiological metrics. These findings together indicate that for more holistic projections of coccolithophore responses to future ocean global change, it is necessary to understand the relative importance of environmental drivers both individually (i.e., mechanistic understanding) and interactively (i.e., cumulative effect) on coccolithophore physiology.

Continue reading ‘Effects of multiple drivers of ocean global change on the physiology and functional gene expression of the coccolithophore Emiliania huxleyi’

Epiphytes provide micro-scale refuge from ocean acidification

Highlights

• OA induced bleaching and reduced metabolism in non-epiphytized coralline.

• Epiphytized corallines were less susceptible to the detrimental effects of OA.

• Epiphytized corallines had thicker diffusive boundary layer than non-epiphytized.

• Non-calcifying epiphytes provide small scale refuge from OA.

• Epiphytic refugia may protect corallines under future OA conditions.

Abstract

Coralline algae, a major calcifying component of coastal shallow water communities, have been shown to be one of the more vulnerable taxonomic groups to ocean acidification (OA). Under OA, the interaction between corallines and epiphytes was previously described as both positive and negative. We hypothesized that the photosynthetic activity and the complex structure of non-calcifying epiphytic algae that grow on corallines ameliorate the chemical microenvironmental conditions around them, providing protection from OA. Using mesocosm and microsensor experiments, we showed that the widespread coralline Ellisolandia elongata is less susceptible to the detrimental effects of OA when covered with non-calcifying epiphytic algae, and its diffusive boundary layer is thicker than when not covered by epiphytes. By modifying the microenvironmental carbonate chemistry, epiphytes, facilitated by OA, create micro-scale shield (and refuge) with more basic conditions that may allow the persistence of corallines associated with them during acidified conditions. Such ecological refugia could also assist corallines under near-future anthropogenic OA conditions.

Continue reading ‘Epiphytes provide micro-scale refuge from ocean acidification’

Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalga Pyropia haitanensis (Bangiales, Rhodophyta)

The present research investigated the effect of pCO2 levels (C), seawater temperature (T), and nutrient availability (N) on the growth and physiochemical changes in Pyropia haitanensis. With nutrient enrichment, the interaction of higher pCO2 increased relative growth rates (RGR) by 105.9% when temperature increased (22 °C) compared with the control (lower T, lower C, and lower N: LTLCLN). The higher pCO2 decreased the Pm rates at the lower temperature (18 °C), yet displayed no interaction with higher T or N levels. The higher N increased dark respiration rate (Rd) at 18 °C. At 22 °C, higher pCO2 significantly enhanced the maximum ratio of (quantum yields (Fv/Fo) and the maximum quantum yield (ψpo), while it sharply decreased the absorption of photons per active reaction center (ABS/RC) and dissipation of energy fluxes (per RC) (DIo/RC). Higher temperature obviously reduced the Fv/Fo and ψpo under ambient CO2 level. The higher pCO2 significantly increased the phycoerythrin (PE) and phycocyanin (PC) contents, while higher temperature decreased the PE contents with elevated CO2 and declined the PC content regardless of CO2 condition. At lower nutrient condition, higher pCO2 increased Chl a content. Soluble carbohydrates (SC) and soluble protein (SP) content almost was unchanged among all treatments. Our findings indicate that nutrient availability may regulate photosynthetic mechanism to offset the negative effect of future ocean warming on P. haitanensis, thereby sustaining or increasing the biomass yield of the algae.

Continue reading ‘Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalga Pyropia haitanensis (Bangiales, Rhodophyta)’

Amelioration of ocean acidification and warming effects through physiological buffering of a macroalgae

Concurrent anthropogenic global climate change and ocean acidification are expected to have a negative impact on calcifying marine organisms. While knowledge of biological responses of organisms to oceanic stress has emerged from single‐species experiments, these do not capture ecologically relevant scenarios where the potential for multi‐organism physiological interactions is assessed. Marine algae provide an interesting case study, as their photosynthetic activity elevates pH in the surrounding microenvironment, potentially buffering more acidic conditions for associated epiphytes. We present findings that indicate increased tolerance of an important epiphytic foraminifera, Marginopora vertebralis , to the effects of increased temperature (±3°C) and p CO2 (~1,000 µatm) when associated with its common algal host, Laurencia intricata . Specimens of M. vertebralis were incubated for 15 days in flow‐through aquaria simulating current and end‐of‐century temperature and pH conditions. Physiological measures of growth (change in wet weight), calcification (measured change in total alkalinity in closed bottles), photochemical efficiency (Fv/Fm ), total chlorophyll, photosynthesis (oxygen flux), and respiration were determined. When incubated in isolation, M. vertebralis exhibited reduced growth in end‐of‐century projections of ocean acidification conditions, while calcification rates were lowest in the high‐temperature, low‐pH treatment. Interestingly, association with L. intricata ameliorated these stress effects with the growth and calcification rates of M. vertebralis being similar to those observed in ambient conditions. Total chlorophyll levels in M. vertebralis decreased when in association with L. intricata , while maximum photochemical efficiency increased in ambient conditions. Net production estimates remained similar between M. vertebralis in isolation and in association with L. intricata , although both production and respiration rates of M. vertebralis were significantly higher when associated with L. intricata . These results indicate that the association with L. intricata increases the resilience of M. vertebralis to climate change stress, providing one of the first examples of physiological buffering by a marine alga that can ameliorate the negative effects of changing ocean conditions.

Continue reading ‘Amelioration of ocean acidification and warming effects through physiological buffering of a macroalgae’

Algal density alleviates the elevated CO2‐caused reduction on growth of Porphyra haitanensis (Bangiales, Rhodophyta), a species farmed in China

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO2, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO2 levels (ambient CO2, 400 ppm; elevated CO2, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L−1; medium, 2.0 g FW L−1; high, 4.0 g FW L−1]. Under ambient CO2, the relative growth rate (RGR) was 5.87% d−1, 2.32% d−1 and 1.51% d−1 in low, medium and high densities, and elevated CO2 reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (FV/FM) was higher in low than in high densities, so were the light‐utilized efficiency (α ), saturation irradiance (EK) and maximum relative electron transfer rate (rETRmax). Elevated CO2 enhanced the FV/FM in low density but not in higher densities, as well as the α, EK and rETRmax. In addition, elevated CO2 reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO2‐induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO2‐induced reduction on growth and promotion on photosynthesis indicates that rising CO2 may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters.

Continue reading ‘Algal density alleviates the elevated CO2‐caused reduction on growth of Porphyra haitanensis (Bangiales, Rhodophyta), a species farmed in China’


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Ocean acidification in the IPCC AR5 WG II

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