Human CO2 emissions are modifying ocean carbonate chemistry, causing ocean acidification, and likely already impacting marine ecosystems. In particular, there is concern that coastal, benthic calcifying organisms will be negatively affected by ocean acidification, a hypothesis largely supported by laboratory studies. The inter-relationships between carbonate chemistry and marine calcifying communities in situ are complex and natural mesocosms such as tidal pools can provide useful community-level insights. In this study, we manipulated the carbonate chemistry of intertidal pools to investigate the influence of future ocean acidification on net community production (NCP) and calcification (NCC) at emersion. Adding CO2 at the start of the tidal emersion to simulate future acidification (+1500 μatm pCO2, target pH: 7.5) modified net production and calcification rates in the pools. By day, pools were fertilized by the increased CO2 (+20 % increase in NCP, from 10 to 12 mmol O2 m−2 hr−1), while there was no measurable impact on NCC. During the night, pools experienced net community dissolution (NCC < 0), even in present-day conditions, when waters were supersaturated with regards to aragonite. Adding CO2 in the pools increased nocturnal dissolution rates by 40 % (from −0.7 to −1.0 mmol CaCO3 m−2 hr−1) with no consistent impact on night community respiration. Our results suggest that ocean acidification is likely to alter temperate intertidal community metabolism on sub-daily timescales, enhancing both diurnal community production and nocturnal calcium carbonate dissolution.
Continue reading ‘Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools’Posts Tagged 'primary production'
Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools
Published 18 May 2023 Science Leave a CommentTags: algae, biological response, BRcommunity, calcification, chemistry, dissolution, field, North Atlantic, primary production, respiration
Enhalus acoroides efficiently alleviate ocean acidification by shifting modes of inorganic carbon uptake and increasing photosynthesis when pH drops
Published 3 May 2023 Science ClosedTags: algae, biogeochemistry, biological response, laboratory, North Pacific, primary production
Ocean acidification (OA) is causing increasing ecological damage, so it is worthwhile to find efficient and environmentally friendly ways to mitigate OA. The mechanism of inorganic carbon (Ci) absorption and the ability to mitigate OA of the tropical seagrass Enhalus acoroides were investigated in this study. At 2.2 mM Ci concentration, its CO2 fixation efficiency increased to 81.89 t CO2/year/Ha under pH 6.5 from 27.59 t CO2/year/Ha at pH 8.2, and even reached 88.11 t CO2/year/Ha at pH 6.5 with unlimited Ci availability, made possible by three pathways for Ci utilization, which included absorbing CO2 directly, transforming HCO3− into CO2 through extracellular carbonic anhydrase, and absorbing HCO3− directly by anion-exchange protein then transforming it to CO2 through intracellular carbonic anhydrase, as verified by inhibitor addition experiments. The carbon fixation rate increased with decreasing pH, suggesting a greater CO2 absorbing capacity for E. acoroides under acidic conditions, which further demonstrates the possibility of mitigating OA and increasing carbon fixation through conserving and restoring E. acoroides meadows. Due to the strong carbon absorption capacity of E. acoroides, it is very important to strengthen the artificial restoration of E. acoroides seagrass meadows in the environmental management of the coastline.
Continue reading ‘Enhalus acoroides efficiently alleviate ocean acidification by shifting modes of inorganic carbon uptake and increasing photosynthesis when pH drops’Short-term responses of Corallina officinalis (rhodophyta) to global-change drivers in a stressful environment of Patagonia, Argentina
Published 28 April 2023 Science ClosedTags: biological response, corals, laboratory, light, multiple factors, nutrients, physiology, primary production, South Atlantic
Over the last two decades, an increasing interest has arisen in the responses of primary producers to global-change drivers and, more recently, in the need to consider how those various drivers may interact. To understand how Corallina officinalis (hereafter Corallina) can be affected by future changing conditions, we investigated the short-term direct effects of co-occurring increased nutrient loads, solar radiation, and lower pH, assessing how these clustered drivers affected Corallina‘s overall physiological performance in a harsh Patagonian coastal environment. To describe the seasonal trend of the physiological parameters in the field, we sampled subtidal Corallina to determine their net oxygen production (NOP), pigments, and carbonate content (CC). Furthermore, we conducted seasonal 10-days experiments, simulating the conditions predicted for the year 2100 by the IPCC (RCP 8.5) —manipulating pH, nutrients, and irradiance—along with the current conditions. The pigments and carotenoids/chlorophyll-a ratio were, in general, constant in the field over the seasons; but the NOP and CC dropped in spring, when the carotenoids peaked. After the experiment, the highest carotenoid/chlorophyll-a ratio was registered in summer under both the currentand the predictedconditions and in winter under the predictedcondition. This lower physiological status was also reflected in almost all other variables. Thus, Corallina may display an acclimatation strategy to cope with high ultraviolet-radiation levels by adjusting its pigment composition to avoid photoinhibition. An understanding of how Corallina, as a habitat-forming species, will respond to future global-change may provide clues about the extent of effects on the ecosystem functions and services.
Continue reading ‘Short-term responses of Corallina officinalis (rhodophyta) to global-change drivers in a stressful environment of Patagonia, Argentina’Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change
Published 18 April 2023 Science ClosedTags: adaptation, biogeochemistry, biological response, BRcommunity, communitymodeling, corals, Indian, modeling, multiple factors, North Atlantic, North Pacific, otherprocess, primary production, regionalmodeling, South Pacific, temperature
Projecting the effects of climate change on net reef calcium carbonate production is critical to understanding the future impacts on ecosystem function, but prior estimates have not included corals’ natural adaptive capacity to such change. Here we estimate how the ability of symbionts to evolve tolerance to heat stress, or for coral hosts to shuffle to favourable symbionts, and their combination, may influence responses to the combined impacts of ocean warming and acidification under three representative concentration pathway (RCP) emissions scenarios (RCP2.6, RCP4.5 and RCP8.5). We show that symbiont evolution and shuffling, both individually and when combined, favours persistent positive net reef calcium carbonate production. However, our projections of future net calcium carbonate production (NCCP) under climate change vary both spatially and by RCP. For example, 19%–35% of modelled coral reefs are still projected to have net positive NCCP by 2050 if symbionts can evolve increased thermal tolerance, depending on the RCP. Without symbiont adaptive capacity, the number of coral reefs with positive NCCP drops to 9%–13% by 2050. Accounting for both symbiont evolution and shuffling, we project median positive NCPP of coral reefs will still occur under low greenhouse emissions (RCP2.6) in the Indian Ocean, and even under moderate emissions (RCP4.5) in the Pacific Ocean. However, adaptive capacity will be insufficient to halt the transition of coral reefs globally into erosion by 2050 under severe emissions scenarios (RCP8.5).
Continue reading ‘Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change’Projected effects of climate change on marine ecosystems in Southeast Asian seas
Published 17 April 2023 Science ClosedTags: biological response, BRcommunity, chemistry, corals, modeling, North Pacific, phytoplankton, primary production, regionalmodeling, South Pacific, zooplankton
The seas of Southeast Asia are home to some of the world’s most diverse ecosystems and resources that support the livelihoods of millions of people. Climate change will bring temperature changes, acidification and other environmental change, with uncertain consequences for human and natural systems, but there has been little regional-scale climate modelling of the marine ecosystem. We present initial dynamically downscaled projections using a biogeochemical model suitable for coastal and shelf seas. A coupled physical-biogeochemical model with a resolution of 0.1° (approximately 11 km) was used to create projections of future environmental conditions under moderate (RCP4.5) and high (RCP8.5) greenhouse gas scenarios. Changes for different parts of the region are presented, including four sensitive coastal sites of key importance for biodiversity and sustainable development: UNESCO Biosphere Reserves at Cu Lao Cham-Hoi An in Vietnam, Palawan in the Philippines and Taka Bonerate-Kepulauan Selayar in Indonesia, and coastal waters of Sabah, Malaysia, which include several marine parks. The projections show a sea that is warming by 1.1 to 2.9°C through the 21st century, with dissolved oxygen decreasing by 5 to 13 mmol m-3 and changes in many other environmental variables. The changes reach all parts of the water column and many places are projected to experience conditions well outside the range seen at the start of the century. The resulting damage to coral reefs and altered species distribution would have consequences for biodiversity, the livelihoods of small-scale fishers and the food security of coastal communities. Further work using a range of global models and regional models with different biogeochemical components is needed to provide confidence levels, and we suggest some ways forward. Projections of this type serve as a key tool for communities and policymakers as they plan how they will adapt to the challenge of climate change.
Continue reading ‘Projected effects of climate change on marine ecosystems in Southeast Asian seas’Sponge organic matter recycling: reduced detritus production under extreme environmental conditions
Published 14 April 2023 Science ClosedTags: abundance, biogeochemistry, biological response, BRcommunity, chemistry, field, multiple factors, otherprocess, oxygen, photosynthesis, physiology, phytoplankton, porifera, primary production, prokaryotes, respiration, South Pacific, temperature
Highlights
- Sponge metabolism was measured at the natural laboratory of Bouraké where sponges are naturally exposed to extreme conditions associated with tidal phase.
- The photosymbiotic HMA sponge Rhabdastrella globostellata was able to cope with extreme acidification and deoxygenation seawater.
- Photosynthetic activity of sponge symbionts was negatively affected during extreme environmental conditions.
- The sponge loop pathway was disrupted during low tide, which correlated with extreme acidification, deoxygenation and warming seawater.
Abstract
Sponges are a key component of coral reef ecosystems and play an important role in carbon and nutrient cycles. Many sponges are known to consume dissolved organic carbon and transform this into detritus, which moves through detrital food chains and eventually to higher trophic levels via what is known as the sponge loop. Despite the importance of this loop, little is known about how these cycles will be impacted by future environmental conditions. During two years (2018 and 2020), we measured the organic carbon, nutrient recycling, and photosynthetic activity of the massive HMA, photosymbiotic sponge Rhabdastrella globostellata at the natural laboratory of Bouraké in New Caledonia, where the physical and chemical composition of seawater regularly change according to the tide. We found that while sponges experienced acidification and low dissolved oxygen at low tide in both sampling years, a change in organic carbon recycling whereby sponges stopped producing detritus (i.e., the sponge loop) was only found when sponges also experienced higher temperature in 2020. Our findings provide new insights into how important trophic pathways may be affected by changing ocean conditions.
Continue reading ‘Sponge organic matter recycling: reduced detritus production under extreme environmental conditions’Photoinhibition of the picophytoplankter Synechococcus is exacerbated by ocean acidification
Published 11 April 2023 Science ClosedTags: adaptation, biological response, growth, laboratory, light, multiple factors, otherprocess, photosynthesis, physiology, phytoplankton, primary production
The marine picocyanobacterium Synechococcus accounts for a major fraction of the primary production across the global oceans. However, knowledge of the responses of Synechococcus to changing pCO2 and light levels has been scarcely documented. Hence, we grew Synechococcus sp. CB0101 at two CO2 concentrations (ambient CO2 AC:410 μatm; high CO2 HC:1000 μatm) under various light levels between 25 and 800 μmol photons m−2 s−1 for 10–20 generations and found that the growth of Synechococcus strain CB0101 is strongly influenced by light intensity, peaking at 250 μmol m−2 s−1 and thereafter declined at higher light levels. Synechococcus cells showed a range of acclimation in their photophysiological characteristics, including changes in pigment content, optical absorption cross section, and light harvesting efficiency. Elevated pCO2 inhibited the growth of cells at light intensities close to or greater than saturation, with inhibition being greater under high light. Elevated pCO2 also reduced photosynthetic carbon fixation rates under high light but had smaller effects on the decrease in quantum yield and maximum relative electron transport rates observed under increasing light intensity. At the same time, the elevated pCO2 significantly decreased particulate organic carbon (POC) and particulate organic nitrogen (PON), particularly under low light. Ocean acidification, by increasing the inhibitory effects of high light, may affect the growth and competitiveness of Synechococcus in surface waters in the future scenario.
Continue reading ‘Photoinhibition of the picophytoplankter Synechococcus is exacerbated by ocean acidification’Ocean acidification conditions and marine diatoms
Published 11 April 2023 Science ClosedTags: biological response, BRcommunity, field, morphology, photosynthesis, phytoplankton, primary production, review
Ocean acidification doesn’t just erode calcium carbonate shells. It can also slow the rate of diatoms to build their beautiful, intricate silica cell walls. Thinner walls mean lighter diatoms making the algae less able to transport carbon to the deep ocean. Diatoms are a key group of non-calcifying marine phytoplankton, responsible for ~40% of ocean productivity. Growth, cell size, and silica content are strong determinants of diatom resilience and sinking velocity; therefore, the effect of diatom species on ocean biogeochemistry is a function of its growth strategy, size, and frustule thickness. In natural environments, pH directly affects the diatom’s growth rate and therefore the timing and abundance of species. Consequently, understanding impacts of ocean acidification on diatom community structure is crucial for evaluating the sensitivity of biogeochemical cycles and ecosystem services in the world’s oceans.
Continue reading ‘Ocean acidification conditions and marine diatoms’Microbial ecosystem responses to alkalinity enhancement in the North Atlantic subtropical gyre
Published 29 July 2022 Science ClosedTags: abundance, biological response, laboratory, mitigation, North Atlantic, otherprocess, phytoplankton, primary production
In addition to reducing carbon dioxide (CO2) emissions, actively removing CO2 from the atmosphere is widely considered necessary to keep global warming well below 2°C. Ocean Alkalinity Enhancement (OAE) describes a suite of such CO2 removal processes that all involve enhancing the buffering capacity of seawater. In theory, OAE both stores carbon and offsets ocean acidification. In practice, the response of the marine biogeochemical system to OAE must be demonstrably negligible, or at least manageable, before it can be deployed at scale. We tested the OAE response of two natural seawater mixed layer microbial communities in the North Atlantic Subtropical Gyre, one at the Western gyre boundary, and one in the middle of the gyre. We conducted 4-day microcosm incubation experiments at sea, spiked with three increasing amounts of alkaline sodium salts and a 13C-bicarbonate tracer at constant pCO2. We then measured a suite of dissolved and particulate parameters to constrain the chemical and biological response to these additions. Microbial communities demonstrated occasionally measurable, but mostly negligible, responses to alkalinity enhancement. Neither site showed a significant increase in biologically produced CaCO3, even at extreme alkalinity loadings of +2,000 μmol kg−1. At the gyre boundary, alkalinity enhancement did not significantly impact net primary production rates. In contrast, net primary production in the central gyre decreased by ~30% in response to alkalinity enhancement. The central gyre incubations demonstrated a shift toward smaller particle size classes, suggesting that OAE may impact community composition and/or aggregation/disaggregation processes. In terms of chemical effects, we identify equilibration of seawater pCO2, inorganic CaCO3 precipitation, and immediate effects during mixing of alkaline solutions with seawater, as important considerations for developing experimental OAE methodologies, and for practical OAE deployment. These initial results underscore the importance of performing more studies of OAE in diverse marine environments, and the need to investigate the coupling between OAE, inorganic processes, and microbial community composition.
Continue reading ‘Microbial ecosystem responses to alkalinity enhancement in the North Atlantic subtropical gyre’Transitioning global change experiments on Southern Ocean phytoplankton from lab to field settings: insights and challenges
Published 30 June 2022 Science ClosedTags: Antarctic, biological response, BRcommunity, laboratory, light, mesocosms, molecular biology, multiple factors, nutrients, photosynthesis, physiology, phytoplankton, primary production, temperature
The influence of global change on Southern Ocean productivity will have major ramifications for future management of polar life. A prior laboratory study investigated the response of a batch-cultured subantarctic diatom to projected change simulating conditions for 2100 (increased temperature/CO2/irradiance/iron; decreased macronutrients), showed a twofold higher chlorophyll-derived growth rate driven mainly by temperature and iron. We translated this design to the field to understand the phytoplankton community response, within a subantarctic foodweb, to 2100 conditions. A 7-d shipboard study utilizing 250-liter mesocosms was conducted in March 2016. The outcome mirrors lab-culture experiments, yielding twofold higher chlorophyll in the 2100 treatment relative to the control. This trend was also evident for intrinsic metrics including nutrient depletion. Unlike the lab-culture study, photosynthetic competence revealed a transient effect in the 2100 mesocosm, peaking on day 3 then declining. Metaproteomics revealed significant differences in protein profiles between treatments by day 7. The control proteome was enriched for photosynthetic processes (c.f. 2100) and exhibited iron-limitation signatures; the 2100 proteome exposed a shift in cellular energy production. Our findings of enhanced phytoplankton growth are comparable to model simulations, but underlying mechanisms (temperature, iron, and/or light) differ between experiments and models. Batch-culture approaches hinder cross-comparison of mesocosm findings to model simulations (the latter are akin to “continuous-culture chemostats”). However, chemostat techniques are problematic to use with mesocosms, as mesozooplankton will evade seawater flow-through, thereby accumulating. Thus, laboratory, field, and modeling approaches reveal challenges to be addressed to better understand how global change will alter Southern Ocean productivity.
Continue reading ‘Transitioning global change experiments on Southern Ocean phytoplankton from lab to field settings: insights and challenges’Impact of atmospheric dry deposition of nutrients on phytoplankton pigment composition and primary production in the coastal Bay of Bengal
Published 29 June 2022 Science ClosedTags: biological response, BRcommunity, community composition, field, Indian, mesocosms, morphology, multiple factors, nutrients, photosynthesis, phytoplankton, primary production, toxicants
Atmospheric deposition of pollutants decreases pH and increases the nutrient concentration in the surface water. To examine its impact on coastal phytoplankton composition and primary production, monthly atmospheric aerosol samples were mixed with coastal waters in the microcosm experiments. These experiments suggested that the biomass of Bacillariophyceae, Dinophyceae and Chlorophyceae were increased and primary production of the coastal waters increased by 3 to 19% due to the addition of aeolian nutrients. The increase in primary production displayed significant relation with a concentration of sulphate and nitrate in the atmospheric aerosols suggesting that both decreases in pH and fertilization enhanced primary production. The impact of acidification on primary production was found to be 22%, whereas 78% was contributed by the nutrient increase. The atmospheric pollution is increasing rapidly over the northern Indian Ocean since past two decades due to rapid industrialization. Hence, it is suggested that the impact of atmospheric pollution on the coastal ecosystem must be included in the numerical models to predict possible changes in the coastal ecosystem due to climate change.
Continue reading ‘Impact of atmospheric dry deposition of nutrients on phytoplankton pigment composition and primary production in the coastal Bay of Bengal’Changing hydrographic, biogeochemical, and acidification properties in the Gulf of Maine as measured by the Gulf of Maine North Atlantic Time Series, GNATS, between 1998 and 2018
Published 8 June 2022 Science ClosedTags: abundance, biogeochemistry, calcification, chemistry, field, North Atlantic, otherprocess, photosynthesis, phytoplankton, primary production
The Gulf of Maine North Atlantic Time Series (GNATS) has been run since 1998, across the Gulf of Maine (GoM), between Maine and Nova Scotia. GNATS goals are to provide ocean color satellite validation and to examine change in this coastal ecosystem. We have sampled hydrographical, biological, chemical, biogeochemical, and bio-optical variables. After 2008, warm water intrusions (likely North Atlantic Slope Water [NASW]) were observed in the eastern GoM at 50–180 m depths. Shallow waters (<50 m) significantly warmed in winter, summer, and fall but cooled during spring. Surface salinity and density of the GoM also significantly increased over the 20 years. Phytoplankton standing stock and primary production showed highly-significant decreases during the period. Concentrations of phosphate increased, silicate decreased, residual nitrate [N*; nitrate-silicate] increased, and the ratio of dissolved inorganic nitrogen:phosphate decreased, suggesting increasing nitrogen limitation. Dissolved organic carbon (DOC) and its optical indices generally increased over two decades, suggesting changes to the DOC cycle. Surface seawater carbonate chemistry showed winter periods where the aragonite saturation (Ωar) dropped below 1.6 gulf-wide due to upward winter mixing of cool, corrosive water. However, associated with increased average GoM temperatures, Ωar has significantly increased. These results reinforce the hypothesis that the observed decrease in surface GoM primary production resulted from a switch from Labrador Sea Water to NASW entering the GoM. A multifactor analysis shows that decreasing GoM primary production is most significantly correlated to decreases in chlorophyll and particulate organic carbon plus increases in N* and temperature.
Continue reading ‘Changing hydrographic, biogeochemical, and acidification properties in the Gulf of Maine as measured by the Gulf of Maine North Atlantic Time Series, GNATS, between 1998 and 2018’Contrasting responses of phytoplankton productivity between coastal and offshore surface waters in the Taiwan Strait and the South China Sea to short-term seawater acidification
Published 8 June 2022 Science ClosedTags: biological response, BRcommunity, chemistry, field, North Pacific, photosynthesis, phytoplankton, primary production
Seawater acidification (SA) has been documented to either inhibit, enhance, or result in no effect on marine primary productivity (PP). In order to examine the effects of SA in changing environments, we investigated the influences of SA (a decrease of 0.4 pHtotal units with corresponding CO2 concentrations in the range of 22.0–39.7 µM) on PP through deck-incubation experiments at 101 stations in the Taiwan Strait and the South China Sea, including the continental shelf and slope, as well as the deep-water basin. The daily primary productivities in surface seawater under incident solar radiation ranged from 17–306 µg C (µg Chl a)−1 d−1, with the responses of PP to SA being region-dependent and the SA-induced changes varying from −88 % (inhibition) to 57 % (enhancement). The SA treatment stimulated PP in surface waters of coastal, estuarine, and shelf waters but suppressed it in the South China Sea basin. Such SA-induced changes in PP were significantly related to in situ pH and solar radiation in surface seawater but negatively related to salinity changes. Our results indicate that phytoplankton cells are more vulnerable to a pH drop in oligotrophic waters. Contrasting responses of phytoplankton productivity in different areas suggest that SA impacts on marine primary productivity are region-dependent and regulated by local environments.
Continue reading ‘Contrasting responses of phytoplankton productivity between coastal and offshore surface waters in the Taiwan Strait and the South China Sea to short-term seawater acidification’Seawater acidification exacerbates the negative effects of UVR on the growth of the bloom-forming diatom Skeletonema costatum
Published 7 June 2022 Science ClosedTags: biological response, growth, laboratory, light, morphology, multiple factors, North Pacific, photosynthesis, physiology, phytoplankton, primary production
Climate changes such as seawater acidification caused by rising atmospheric CO2 and increased ultraviolet radiation (UVR) intensity resulting from shoaling of the upper mixed layer may interact to influence the physiological performance of marine primary producers. But few studies have investigated long-term (>30 days) effects of UVR under seawater acidification conditions, along with less attention on the differential effects of long- and short-wavelength UVA. In the present study, four spectral treatments (>280, >320, >360, and >400 nm) under two pCO2 levels (400 and 1,000 μatm) were set to investigate the interactive effects of seawater acidification and UVR on the bloom-forming diatom Skeletonema costatum. The results showed that UVR decreased growth and effective quantum yield of Photosystem II (PSII) by 9%–16% and 11%–24%, respectively, but it enhanced cell sizes significantly. Long- and short-wavelength UVA showed differential effects on cell volume and the effective quantum yield of PSII, especially at the elevated CO2 level. Generally, seawater acidification depressed the effective quantum yield of PSII and cell volume by 6%–18% and 8%–39%, respectively. Additionally, the contents of key PSII proteins (D1 and D2) decreased at the elevated CO2 level. Elevated CO2 significantly increased the inhibition of UVR on growth in the >280 nm spectral treatment when compared with ambient CO2, while it showed no effects in other spectral treatments. Overall, the results indicate that the effects of seawater acidification on the ubiquitous diatom are light wavelength-dependent.
Continue reading ‘Seawater acidification exacerbates the negative effects of UVR on the growth of the bloom-forming diatom Skeletonema costatum’Effects of shellfish and macro-algae IMTA in North China on the environment, inorganic carbon system, organic carbon system, and sea–air CO2 fluxes
Published 6 May 2022 Science ClosedTags: algae, biological response, chemistry, crustaceans, field, laboratory, North Pacific, primary production
Shellfish and macro-algae integrated multi-trophic aquaculture (IMTA) contribute greatly to the sustainability of aquaculture. However, the effects of large-scale shellfish and macro-algae aquaculture on the functions of the ocean carbon sink are not clear. To clarify these effects, we studied the spatial and temporal changes of inorganic and organic carbon systems in seawater under different aquaculture modes (monoculture or polyculture of shellfish and macro-algae) in Sanggou Bay, together with the variation of other environmental factors. The results show that the summertime dissolved oxygen (DO) concentration in the shellfish culture zone was significantly lower than other zones (p < 0.05), with a minimum value of 7.07 ± 0.25 mg/L. The variation of pH and total alkalinity (TA) were large across different culture modes, and the seawater in the shellfish culture zone had the lowest pH and TA than the other zones. Seasonal environment and aquaculture modes significantly affected the variation of dissolved inorganic carbon (DIC), CO2 partial pressure (pCO2), dissolved organic carbon (DOC), and particulate organic carbon (POC) concentrations. The highest values of DIC, pCO2, and POC appeared in summer, and the lowest appeared in winter. For DOC concentration, the lowest value appeared in autumn. Spatially, DIC and pCO2 were highest in the shellfish culture zone and lowest in the macro-algae culture zone, DOC was highest in the macro-algae culture zone and lowest in the shellfish culture zone, and POC was lower in the shellfish culture zone and macro-algae culture zone and higher in the remaining zones. The results of sea–air CO2 fluxes showed that except for the shellfish culture zone during summertime, which released CO2 to the atmosphere, all culture zones were the sinks of atmospheric CO2 during the culture period, with the whole bay being a strong CO2 sink during autumn and winter. In summary, large-scale shellfish–macro-algae IMTA plays an important role in the local carbon cycle and contributes to mitigating ocean acidification and hypoxia.
Continue reading ‘Effects of shellfish and macro-algae IMTA in North China on the environment, inorganic carbon system, organic carbon system, and sea–air CO2 fluxes’The role of epiphytes in seagrass productivity under ocean acidification
Published 21 April 2022 Science ClosedTags: algae, biological response, chemistry, cnidaria, community composition, field, laboratory, Mediterranean, otherprocess, phanerogams, photosynthesis, physiology, primary production, vents
Ocean Acidification (OA), due to rising atmospheric CO2, can affect the seagrass holobiont by changing the plant’s ecophysiology and the composition and functioning of its epiphytic community. However, our knowledge of the role of epiphytes in the productivity of the seagrass holobiont in response to environmental changes is still very limited. CO2 vents off Ischia Island (Italy) naturally reduce seawater pH, allowing to investigate the adaptation of the seagrass Posidonia oceanica L. (Delile) to OA. Here, we analyzed the percent cover of different epiphytic groups and the epiphytic biomass of P. oceanica leaves, collected inside (pH 6.9–7.9) and outside (pH 8.1–8.2) the CO2 vents. We estimated the contribution of epiphytes to net primary production (NPP) and respiration (R) of leaf sections collected from the vent and ambient pH sites in laboratory incubations. Additionally, we quantified net community production (NCP) and community respiration (CR) of seagrass communities in situ at vent and ambient pH sites using benthic chambers. Leaves at ambient pH sites had a 25% higher total epiphytic cover with encrusting red algae (32%) dominating the community, while leaves at vent pH sites were dominated by hydrozoans (21%). Leaf sections with and without epiphytes from the vent pH site produced and respired significantly more oxygen than leaf sections from the ambient pH site, showing an average increase of 47 ± 21% (mean ± SE) in NPP and 50 ± 4% in R, respectively. Epiphytes contributed little to the increase in R; however, their contribution to NPP was important (56 ± 6% of the total flux). The increase in productivity of seagrass leaves adapted to OA was only marginally reflected by the results from the in situ benthic chambers, underlining the complexity of the seagrass community response to naturally occurring OA conditions.
Continue reading ‘The role of epiphytes in seagrass productivity under ocean acidification’Sensitivity of phytoplankton to climate change: direct and interactive effects of CO2 on primary production and community composition
Published 4 April 2022 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, otherprocess, physiology, phytoplankton, primary production
Marine phytoplankton constitutes about half of the primary production on Earth. It forms the base of the marine food web and is a pivotal player in the marine biological carbon pump. The primary environmental drivers that control phytoplankton growth are temperature, nutrient availability, light, and the concentration of inorganic carbon species. Ongoing climate change modifies these drivers, leading to a warming, high-CO2 ocean with altered nutrient availabilities and light regimes. Changes in phytoplankton productivity and community composition resulting from these newly emerging environmental states in the ocean have important implications for the marine ecosystem and carbon cycling.
Biogeochemical ocean models are used to investigate how marine primary production may be affected by future climate change under different emission scenarios. Phytoplankton growth rates in models are typically determined by functions describing growth dependencies on temperature, light, and nutrients. However, a large body of laboratory studies on phytoplankton responses to environmental drivers reveals two points that are usually not considered in current biogeochemical models. Firstly, phytoplankton growth can be considerably modified by the state of the carbonate system. Changes in inorganic carbon species concentrations can be either growth-enhancing (CO2(aq) and bicarbonate are substrates for photosynthesis), or growth-dampening (increasing CO2(aq) levels lead to a shift in the carbonate equilibria and result in a pH decrease, a process which is called ocean acidification). Functions describing this growth dependence of phytoplankton on the carbonate system have not been implemented in large-scale ocean biogeochemical models so far. Secondly, growth responses towards one driver can be modified if the level of another driver is changing. Functions including these so-called interactive driver effects partly exist in models (e.g. the response to varying light levels may depend on the nutrient limitation term). However, the large number of laboratory studies on multiple driver effects has never been used to constrain driver interactions in large-scale ocean biogeochemical models. This holds especially true for the findings of growth responses to driver interactions that include ocean acidification, which make up the largest share of laboratory experiments.
This thesis aims to investigate sensitivities of marine phytoplankton to changing CO2(aq) levels as well as to interactive effects between CO2 and other environmental drivers. A comprehensive and reproducible literature search in combination with a statistical analysis (Publication I) reveals that increasing CO2(aq) levels robustly dampen the growth-increasing effects of warming and improving light conditions. In addition, the results show that the calcifying phytoplankton group of coccolithophores experiences the strongest negative effects by ocean acidification compared to other phytoplankton groups. A second study (Publication II) examines the effects of mechanistically described carbonate system dependencies on primary production and community composition in a model. To this end, carbonate system dependencies of phytoplankton growth and and coccolithophore calcification are implemented into the global biogeochemical ocean model REcoM. The study shows that responses to ocean acidification cascade on growth responses to other drivers, which partly balance or counteract the direct impact of the carbonate system on growth rates. In addition, warming is identified as the main driver of the observed recent increase of coccolithophore biomass in the North Atlantic. A final study (Publication III) investigates the interactive effects between CO2 and temperature as well as between CO2 and light on phytoplankton biomass and community composition in a high emission scenario. For the parametrization in REcoM, growth responses to interacting drivers as synthesized in Publication I are used. The decrease of global future phytoplankton biomass and net community production by the end of the century is similar in simulations with and without driver interactions (-6% and -8%, respectively). However, phytoplankton responses to future climate conditions are considerably modified on a regional scale and the share of individual phytoplankton groups in the community changes both globally and regionally when accounting for multiple driver effects. Globally, diatoms and coccolithophores are impacted more and small phytoplankton less severely by future oceanic conditions when accounting for driver interactions. Future projections of the Southern Ocean phytoplankton community are modified most dramatically with the new interactive growth formulation, as diatoms and coccolithophores become less and small phytoplankton more abundant, while it is the other way round in simulations without driver interactions.
The thesis highlights 1) that the carbonate system is a critical growth-modifying driver for phytoplankton in a high-CO2 ocean, which can furthermore modify growth responses to other drivers substantially, and 2) that driver interactions have considerable effects on climate-change induced alterations in the phytoplankton community as well as on regional biomass changes in a future ocean.
Continue reading ‘Sensitivity of phytoplankton to climate change: direct and interactive effects of CO2 on primary production and community composition’Response of Cymodocea nodosa to ocean acidification and warming in the Canary Islands: direct and indirect effects
Published 24 March 2022 Science ClosedTags: biological response, BRcommunity, community composition, echinoderms, laboratory, morphology, multiple factors, North Atlantic, otherprocess, phanerogams, photosynthesis, physiology, primary production, respiration, temperature
Hightlights
- Ocean acidification increase growth and gross primary production of Cymodocea nodosa.
- The rise of temperature limited the net and gross primary production of Cymodocea nodosa.
- A positive effect of decrased pH on greater vulnerability to consumption by Paracentrotus lividus.
- A future scenario of climate change will affect metabolic rates of C.nodosa.
- Different responses to climate change have been observed by C. nodosa from Canary Islands.
Abstract
As detected in warming and ocean acidification, global change can have profound impact on marine life. Its effects on seagrasses are becoming increasingly well-known, since several studies have focused on the responses of these species to global change conditions. However a few studies have assessed the combined effect of temperature and acidification on seagrasses. Overall in this study, the combined effects of increased ocean temperature and pH levels expected at the end of this century (+5 °C and pH 7.5) on Cymodocea nodosa from Canary Islands, were evaluated for one month through manipulative laboratory experiments. Growth, net production, respiration, gross primary production, chlorophyll-a concentration and its vulnerability to herbivory were quantified. Results showed a positive effect of decreased pH on growth and gross primary production, as well as greater vulnerability to consumption by the sea urchin Paracentrotus lividus. In contrast, increased temperature limited net and gross primary production. This study shows than in future scenarios, C. nodosa from the Canary Islands may be a losing species in the global change stakes.
Continue reading ‘Response of Cymodocea nodosa to ocean acidification and warming in the Canary Islands: direct and indirect effects’Physiological control on carbon isotope fractionation in marine phytoplankton
Published 24 March 2022 Science ClosedTags: phytoplankton, primary production, review
One of the great challenges in biogeochemical research over the past half a century has been to quantify and understand the mechanisms underlying stable carbon isotope fractionation (εp) in phytoplankton in response to changing pCO2. Partly, this interest is grounded in the use of fossil photosynthetic organism remains as a proxy for past atmospheric CO2 concentrations. Phytoplankton organic carbon is depleted in 13C compared to its source because of kinetic fractionation by the enzyme RubisCO during photosynthetic carbon fixation, as well as through physiological pathways upstream of RubisCO. Moreover, other factors such as nutrient limitation, variations in light regime as well as phytoplankton culturing systems and inorganic carbon manipulation approaches may confound the influence of CO2 on εp. Here, based on experimental data compiled from the literature, we assess which underlying physiological processes cause the observed differences in εp for various phytoplankton groups in response to C-demand/C-supply and test potential confounding factors. Culturing approaches and methods of carbonate chemistry manipulation were found to best explain the differences in εp between studies, although daylength was an important predictor for εp in haptophytes. Extrapolating results from culturing experiments to natural environments and for proxy applications therefore requires caution, and it should be carefully considered whether culture methods and experimental conditions are representative of natural environments.
Continue reading ‘Physiological control on carbon isotope fractionation in marine phytoplankton’
