Posts Tagged 'primary production'

Effects of nearshore processes on carbonate chemistry dynamics and ocean acidification

Time series from open ocean fixed stations have robustly documented secular changes in carbonate chemistry and long-term ocean acidification (OA) trends as a direct response to increases in atmospheric carbon dioxide (CO2). However, few high-frequency coastal carbon time series are available in reef systems, where most affected tropical marine organisms reside. Seasonal variations in carbonate chemistry at Cheeca Rocks (CR), Florida, and La Parguera (LP), Puerto Rico, are presented based on 8 and 10 years of continuous, high-quality measurements, respectively. This dissertation synthesizes autonomous and bottle observations to model carbonate chemistry and to understand how physical and biological processes affect seasonal carbonate chemistry at both locations. The autonomous carbonate chemistry and oxygen observations are used to examine a mass balance approach using a 1-D model to determine net rates of ecosystem calcification and production (NEC and NEP) from communities close (<5km) to the buoys. The results provide evidence to suggest that seasonal response between benthic metabolism and seawater chemistry at LP is attenuated relative to that at CR because their differences in benthic cover and how benthic metabolism modifies the water chemistry. Simple linear trends cannot explain the feedback between metabolism and reef water chemistry using long-term observations over natural variations. The effects of community production on partial pressure of CO2 (pCO2sw) make these interactions complex at short- and long-term scales. Careful consideration should be taken when inferring local biogeochemical processes, given that pCO2sw (and presumably pH) respond on much shorter time and local scales than dissolved inorganic carbon (DIC) and total alkalinity (TA). The observations highlight the need for more comprehensive observing systems that can reliably measure both the fast-response (pCO2sw, pH) and slow-response (DIC) carbon pools.

Continue reading ‘Effects of nearshore processes on carbonate chemistry dynamics and ocean acidification’

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’

A multistressor model of carbon acquisition regulation for macroalgae in a changing climate

It is widely hypothesized that noncalcifying macroalgae will be more productive and abundant in increasingly warm and acidified oceans. Macroalgae vary greatly in the magnitudes and interactions of responses of photosynthesis and growth to multiple stressors associated with climate change. A knowledge gap that exists between the qualitative “macroalgae will benefit” hypothesis and the variable outcomes observed is regulation of physiological mechanisms that cause variation in the magnitudes of change in primary productivity, growth, and their covariation. In this context, we developed a model to quantitatively describe physiological responses to coincident variation in temperature, carbonate chemistry and light supply in a representative bicarbonate‐using marine macroalga. The model is based on Ulva spp., the best understood dissolved inorganic carbon uptake mechanism among macroalgae, with data enabling synthesis across all parameters. At boundary layer pH < 8.7 most inorganic carbon is taken up through the external carbonic anhydrase (CAext) mechanism under all conditions of photosynthetic photon flux density, temperature, and boundary layer thickness. Each 0.1 unit decline in pH causes a 20% increase in the fraction of diffusive uptake of CO2 thereby lessening reliance on active transport of bicarbonate. Modeled downregulation of anion exchange‐mediated active bicarbonate transport associated with a 0.4 unit decline in pH under ocean acidification is consistent with enhanced growth up to 4% per day without increasing photosynthetic rate. The model provides a means to quantify magnitudes of change in productivity under factorial combinations of changing temperature, CO2, and light supply anticipated as climate changes.

Continue reading ‘A multistressor model of carbon acquisition regulation for macroalgae in a changing climate’

Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change

Coastal and intertidal habitats are at the forefront of anthropogenic influence and environmental change. The species occupying these habitats are adapted to a world of extremes, which may render them robust to the changing climate or more vulnerable if they are at their physiological limits. We characterized the diurnal, seasonal and interannual patterns of flux in biogeochemistry across an intertidal gradient on a temperate sandstone platform in eastern Australia over 6 years (2009–2015) and present a synthesis of our current understanding of this habitat in context with global change. We used rock pools as natural mesocosms to determine biogeochemistry dynamics and patterns of eco‐stress experienced by resident biota. In situ measurements and discrete water samples were collected night and day during neap low tide events to capture diurnal biogeochemistry cycles. Calculation of pHT using total alkalinity (TA) and dissolved inorganic carbon (DIC) revealed that the mid‐intertidal habitat exhibited the greatest flux over the years (pHT 7.52–8.87), and over a single tidal cycle (1.11 pHT units), while the low‐intertidal (pHT 7.82–8.30) and subtidal (pHT 7.87–8.30) were less variable. Temperature flux was also greatest in the mid‐intertidal (8.0–34.5°C) and over a single tidal event (14°C range), as typical of temperate rocky shores. Mean TA and DIC increased at night and decreased during the day, with the most extreme conditions measured in the mid‐intertidal owing to prolonged emersion periods. Temporal sampling revealed that net ecosystem calcification and production were highest during the day and lowest at night, particularly in the mid‐intertidal. Characterization of biogeochemical fluctuations in a world of extremes demonstrates the variable conditions that intertidal biota routinely experience and highlight potential microhabitat‐specific vulnerabilities and climate change refugia.

Continue reading ‘Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change’

Photosynthetic performances of marine microalgae under influences of rising CO2 and solar UV radiation

Marine photosynthesis contributes approximately half of the global primary productivity. Ocean climate changes, such as increasing dissolved CO2 in seawater and consequently declining pH (known as ocean acidification, OA), may alter marine photosynthetic performance. There are numerous studies on the effects of OA on photosynthetic organisms, but controversial findings indicate positive, neutral, and negative influences. Most of the studies so far have been conducted under controlled conditions that ignored the presence of solar UV radiation. Increased CO2 availability may play a fertilizing role, while the concurrent pH drop may exert pressure on microalgal cells, especially during the night period. It is known that elevated CO2 concentrations downregulate CO2-concentrating mechanisms (CCMs), and intracellular concentrations of dissolved inorganic carbon in diatoms grown under elevated CO2 levels can be much lower than that in low CO2-grown ones. Such a reduced CO2 availability within cells in response to increased CO2 in the water can lead to enhanced photorespiration due to an increased O2 to CO2 ratio around the carboxylating and oxygenating enzyme, RuBisCO. Therefore, negative and positive effects of OA may depend on light levels, since the saved energy due to downregulation of CCMs can benefit growth under light-limited conditions but enhance photoinhibition under light-excessive conditions. OA affects metabolic pathways in phytoplankton. It augments ß-oxidation and the citric acid cycle, which accumulates toxic phenolic compounds. In the upper mixed layer, phytoplankton are exposed to excessive PAR and UV radiation (UVR). The calcareous incrustations of calcified microalgae, known to shield the organisms from UVR, are thinned due to OA, exposing the cells to increased solar UV and further inhibiting their calcification and photosynthesis, reflecting a compounded impact. Such UV and OA interactive effects are expected to reduce primary productivity in oligotrophic pelagic surface waters. In this chapter, we review and analyze recent results on effects of OA and UV and their combined effects on marine photosynthesis of microalgae, which falls in the context of marine photosynthesis under changing ocean environments and multiple stressors.

Continue reading ‘Photosynthetic performances of marine microalgae under influences of rising CO2 and solar UV radiation’

Model simulation of seasonal growth of Fucus vesiculosus in its benthic community

Numerical models are a suitable tool to quantify impacts of predicted climate change on complex ecosystems but are rarely used to study effects on benthic macroalgal communities. Fucus vesiculosus L. is a habitat‐forming macroalga in the Baltic Sea and alarming shifts from the perennial Fucus community to annual filamentous algae are reported. We developed a box model able to simulate the seasonal growth of the Baltic Fucus–grazer–epiphyte system. This required the implementation of two state variables for Fucus biomass in units of carbon (C) and nitrogen (N). Model equations describe relevant physiological and ecological processes, such as storage of C and N assimilates by Fucus, shading effects of epiphytes or grazing by herbivores on both Fucus and epiphytes, but with species‐specific rates and preferences. Parametrizations of the model equations and required initial conditions were based on measured parameters and process rates in the near‐natural Kiel Outdoor Benthocosm (KOB) experiments during the Biological Impacts of Ocean Acidification project. To validate the model, we compared simulation results with observations in the KOB experiment that lasted from April 2013 until March 2014 under ambient and climate‐change scenarios, that is, increased atmospheric temperature and partial pressure of carbon dioxide. The model reproduced the magnitude and seasonal cycles of Fucus growth and other processes in the KOBs over 1 yr under different scenarios. Now having established the Fucus model, it will be possible to better highlight the actual threat of climate change to the Fucus community in the shallow nearshore waters of the Baltic Sea.

Continue reading ‘Model simulation of seasonal growth of Fucus vesiculosus in its benthic community’

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’

Combined effects of global climate change and nutrient enrichment on the physiology of three temperate maerl species

Made up of calcareous coralline algae, maerl beds play a major role as ecosystem engineers in coastal areas throughout the world. They undergo strong anthropogenic pressures, which may threaten their survival. The aim of this study was to gain insight into the future of maerl beds in the context of global and local changes. We examined the effects of rising temperatures (+3°C) and ocean acidification (−0.3 pH units) according to temperature and pH projections (i.e., the RCP 8.5 scenario), and nutrient (N and P) availability on three temperate maerl species (Lithothamnion corallioides, Phymatolithon calcareum, and Lithophyllum incrustans) in the laboratory in winter and summer conditions. Physiological rates of primary production, respiration, and calcification were measured on all three species in each treatment and season. The physiological response of maerl to global climate change was species‐specific and influenced by seawater nutrient concentrations. Future temperature–pH scenario enhanced maximal gross primary production rates in P. calcareum in winter and in L. corallioides in both seasons. Nevertheless, both species suffered an impairment of light harvesting and photoprotective mechanisms in winter. Calcification rates at ambient light intensity were negatively affected by the future temperature–pH scenario in winter, with net dissolution observed in the dark in L. corallioides and P. calcareum under low nutrient concentrations. Nutrient enrichment avoided dissolution under future scenarios in winter and had a positive effect on L. incrustans calcification rate in the dark in summer. In winter conditions, maximal calcification rates were enhanced by the future temperature–pH scenario on the three species, but P. calcareum suffered inhibition at high irradiances. In summer conditions, the maximal calcification rate dropped in L. corallioides under the future global climate change scenario, with a potential negative impact on CaCO3 budget for maerl beds in the Bay of Brest where this species is dominant. Our results highlight how local changes in nutrient availability or irradiance levels impact the response of maerl species to global climate change and thus point out how it is important to consider other abiotic parameters in order to develop management policies capable to increase the resilience of maerl beds under the future global climate change scenario.

Continue reading ‘Combined effects of global climate change and nutrient enrichment on the physiology of three temperate maerl species’

The effect of elevated CO2 on the production and respiration of a Sargassum thunbergii community: a mesocosm study

Approximately one‐third of anthropogenic carbon dioxide is absorbed into the ocean and causes it to become more acidic. The Intergovernmental Panel on Climate Change (IPCC) suggested that the surface ocean pH, by the year 2100, would drop by a further 0.3 and 0.4 pH units under RCP (Representative Concentration Pathway) 6.0 and 8.5 climate scenarios. The macroalgae communities that consisted of Sargassum thunbergii and naturally attached epibionts were exposed to fluctuations of ambient and manipulated pH (0.3–0.4 units below ambient pH). The production and respiration in S. thunbergii communities were calculated from dissolved oxygen time‐series recorded with optical dissolved oxygen sensors. The pH, irradiance, and dissolved oxygen occurred in parallel with diurnal (day/night) patterns. According to net mesocosm production – photosynthetically active radiation (PAR) model, the saturation and compensation PAR, the mean maximum gross mesocosm production (GMP), and daily mesocosm respiration were higher in the CO2 enrichment, than in the ambient condition, while the mean of photosynthetic coefficient was similar. In conclusion, elevated CO2 stimulated oxygen production and consumption of S. thunbergii communities in the mesocosm. Furthermore, the sensitivity of the GMP of the S. thunbergii community to irradiance was reduced, and achieved maximum production rate at higher PAR. These positive responses to CO2 enrichment suggest that S. thunbergii communities may thrive in under high CO2 conditions.

Continue reading ‘The effect of elevated CO2 on the production and respiration of a Sargassum thunbergii community: a mesocosm study’

Seasonal variability of calcium carbonate precipitation and dissolution in shallow coral reef sediments

Shallow, permeable calcium carbonate (CaCO3) sediments make up a large proportion of the benthic cover on coral reefs and account for a large fraction of the standing stock of CaCO3. There have been a number of laboratory, mesocosm, and in situ studies examining shallow sediment metabolism and dissolution, but none of these have considered seasonal variability. Advective benthic chambers were used to measure in situ net community calcification (NCC) rates of CaCO3 sediments on Heron Island, Australia (Great Barrier Reef) over an annual cycle. Sediments were, on average, net precipitating during the day and net dissolving at night throughout the year. Night dissolution rates (−NCCNIGHT) were highest in the austral autumn and lowest in the austral winter driven by changes in respiration (R) and to a lesser extent temperature and Ωarag/pH. Similarly, precipitation during the day (+NCCDAY) was highest in March and lowest in winter, driven primarily by benthic net primary production (NPP) and temperature. On average, sediments were net precipitating over a diel cycle (NCC24h) but shifted to net dissolving in July and December. This shift was largely caused by the differential effects of seasonal cycles in organic metabolism and carbonate chemistry on NCCDAY and NCCNIGHT. The results from this study highlight the large variability in sediment CaCO3 dynamics and the need to include repeated measurements over different months and seasons, particularly in shallow reef systems that can experience large swings in light, temperature, and carbonate chemistry.

Continue reading ‘Seasonal variability of calcium carbonate precipitation and dissolution in shallow coral reef sediments’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,376,941 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book