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Climate change and ocean acidification effects on seagrass and marine macroalgae
Global Change Biology
Abstract
Although seagrasses and marine macroalgae (macro-autotrophs) play critical ecological roles in reef, lagoon, coastal and open-water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro-autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO2 ], and lower carbonate [CO3 (2-) ] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO2 ]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro-autotroph photosynthesis is overwhelmingly C3 (≥ 85%) with most species capable of utilizing HCO3 (-) ; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO2 -only users, lead us to conclude that photosynthetic and growth rates of marine macro-autotrophs are likely to increase under elevated [CO2 ] similar to terrestrial C3 species. In the tropics, many species live close to their thermal limits and will have to up-regulate stress-response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO2 ] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO2 ] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO2 ] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H(+) and DIC. These fluxes control micro-environments that promote calcification over dissolution and may be more important than CaCO3 mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO2 ocean; therefore, it is critical to elucidate the research gaps identified in this review.
... Seagrasses are considered critical species of the marine ecosystem due to their contribution to stabilizing the coastal ecosystems [1][2][3] by stabilizing the sediment, preventing coastal erosion and protecting shorelines. They are significant carbon sinks due to their high productivity, crucial in sequestering a substantial portion of atmospheric carbon dioxide. ...
... Studies have shown that the global extinction rate of seagrasses was approximately 1% per year before 1940 but has increased to 7% per year in recent times [1,3,9]. It has been determined that between 13% and 38% of Posidonia oceanica seagrass beds along the Mediterranean coasts have been lost since the 1960s [6]. ...
... According to the RCP 2.6 scenario, the pH value of the oceans is expected to decrease to 8.05 in 2100, and the water temperature is expected to increase by 1°C. In the RCP 8.5 scenario, the Experimental Strategies on Climate Change Impacts: Climate Chamber Approach for Seagrass Meadows pH value of the ocean surface water in 2100 is expected to decrease by 0.3-0.4 units to 7.8, and the water temperature is expected to increase by 3.7°C [3,17,19,20]. As a result of the expected 0.3-0.4 ...
Seagrasses are vital to marine ecosystems, providing stability to coastal areas, acting as significant carbon sinks and supporting biodiversity. However, environmental changes, particularly climate change, are threatening seagrass habitats. The global extinction rate of seagrasses has increased significantly, with notable losses in the Mediterranean Sea. This decline is attributed to pollution, climate change, and rising temperatures, which impact seagrass growth, reproduction, and survival. To study these effects, climate chamber systems simulating future climate scenarios were used. These systems, including aquariums and transparent bags, allow for controlled adjustments of climate variables such as CO2 concentration, temperature, and pH. Fieldwork conducted in Aliağa, İzmir, involved setting up these systems and collecting samples of the seagrass Cymodocea nodosa. The study revealed that aquarium systems were more stable and controllable than bag systems in field conditions. The findings underscore the importance of climate chamber systems in understanding the ecological impact of climate change on seagrasses. These systems provide valuable insights for developing conservation strategies and managing marine ecosystems. Accurate simulation of future conditions is crucial for predicting and mitigating the effects of global warming on seagrass meadows and marine biodiversity
... In submerged aquatic vegetation (e.g., macroalgal habitat), photosynthetic organisms utilize both gaseous CO 2 and HCO 3 as carbon source for photosynthesis. Due to the significantly slower diffusion rate of CO 2 gas in water compared to the atmosphere (approximately 10,000 times slower), marine macroalgae have evolved carbon-concentrating mechanisms (CCMs) and can utilize not only CO 2 but also HCO 3 from dissolved inorganic carbon (C T ) for photosynthesis (Giordano et al. 2005;Koch et al. 2013). Therefore, research on carbon assimilation is highly complex, as it requires an understanding of varied photosynthetic mechanisms (i.e., CCMs), but it is very important due to its association with climate change issues (Koch et al. 2013;Kim et al. 2016). ...
... Due to the significantly slower diffusion rate of CO 2 gas in water compared to the atmosphere (approximately 10,000 times slower), marine macroalgae have evolved carbon-concentrating mechanisms (CCMs) and can utilize not only CO 2 but also HCO 3 from dissolved inorganic carbon (C T ) for photosynthesis (Giordano et al. 2005;Koch et al. 2013). Therefore, research on carbon assimilation is highly complex, as it requires an understanding of varied photosynthetic mechanisms (i.e., CCMs), but it is very important due to its association with climate change issues (Koch et al. 2013;Kim et al. 2016). ...
... Therefore, the photosynthetic rate could increase with higher CO₂ concentrations because photorespiration is reduced due to more efficient CO₂ fixation by Rubisco activity. Additionally, the down-regulation of CCMs under OA conditions provides an energy efficiency advantage by saving the energy required for CCM operation, as U. ohnoi increases its preference for diffusive CO₂ (Kim et al. 2013a;Koch et al. 2013;Kang et al. 2021;. Thus, while improved CO₂ affinity at higher CO₂ levels enhances C T assimilation, this may not lead to significant changes in PQ because net O₂ evolution also increases as oxygen consumption through respiration decreases. ...
Recently there has been a rapid increase in interest regarding the CO2 removal capacity of seaweed, leading to a focus on photosynthesis research. Because direct measuring the dissolved inorganic carbon (CT) uptake rate is challenging, the use of the photosynthetic quotient (PQ), which converts oxygen evolution to carbon fixation, has proven effective. However, PQ is highly sensitive to various environmental factors, including climate change (warming and acidification). This study aimed to investigate the impact of climate change conditions on the PQ of Ulva ohnoi, namely, control (CONT: 271 µatm CO2 & 20°C), acidification (OA: 526 µatm CO2 & 20°C), warming (OW: 307 µatm CO2 & 25°C), and greenhouse (GR: 634 µatm CO2 & 25°C). The PQ was determined through an incubation experiment, where simultaneous measurements of O2 evolution and CT uptake rates were conducted in a seawater medium. The average PQ values were consistently above 1 across all treatments, with the highest PQ values observed in the CONT (1.67 ± 0.03) and the lowest in the OW (1.16 ± 0.04). While increased CO2 levels and light intensity did not affect the PQ value, higher temperatures had a significant impact on the PQ of U. ohnoi. Consequently, it can be expected that increased temperatures will lead to a decrease in PQ, resulting in increased CT uptake compared to O2 evolution. Estimating CT uptake based on O2 evolution may, therefore, lead to an overestimation of the CT uptake rate when applying theoretical PQ.
... Photosynthetic activity in many marine macroalgae is constrained by limited dissolved inorganic carbon (DIC) concentrations, primarily due to the low saturation of seawater carbon dioxide (CO₂) (Koch et al., 2013). The relatively low concentrations of aqueous CO₂, compared with the macroalgae's demand for inorganic carbon, hinder the optimization of photosynthesis. ...
... This reduction in the DBL facilitates transport of DIC, enhancing photosynthetic efficiency Hurd et al., 2011). Additionally, pH affects the chemical equilibrium and speciation of DIC in the surrounding water, influencing the availability of CO₂ and HCO₃ − (Raven & Beardall, 2003;Koch et al., 2013). In areas with high water motion, macroalgae may have greater access to DIC due to increased mixing and delivery of these compounds, which further influences their ability to photosynthesize and grow (Mass et al., 2010;Cornwall et al., 2012). ...
... In recent years, numerous studies have focused on the response of marine macroalgae to OA, which has greatly improved our understanding of the biological repercussions of OA (Koch et al., 2013). However, insufficient attention has been paid to noncalcareous species, particularly fleshy species, which are of significant ecological and economic value in coastal aquaculture. ...
... Different lowercase letters above the bar indicate significant differences between treatments. macroalgae, exhibit diverse growth and physiological responses (Koch et al., 2013) which usually depend on the energy balance between synthesis and consumption (Häder and Gao, 2023). Considering the complex marine environment caused by global changes and local environmental variations, the responses of macroalgal growth and photosynthesis to OA exhibit interspecific differences (Ji and Gao, 2021). ...
To investigate the effects of ocean acidification (OA) and nitrogen limitation on macroalgae growth and photophysiological responses, Gracilariopsis lemaneiformis was cultured under two main conditions: ambient (Low CO2, LC, 390 μatm) and CO2 enriched (High CO2, HC, 1000 μatm), with low (LN, 7 μmol L⁻¹) and high (HN, 56 μmol L⁻¹) nitrate. High CO2 levels decreased growth under both LN and HN treatments. HC reduced Chl a, carotenoids, phycoerythrin (PE), and phycocyanin (PC) under HN conditions, while only Chl a decreased under LN conditions. NO3 ⁻ uptake rate was restricted under LN compared to HN, while HC enhanced it under HN. Net photosynthetic O2 evolution rates did not differ between CO2 and nitrate treatments. Dark respiration rates were higher under HN, further boosted by HC. The stimulated effective quantum yield (Y(II)) corresponded to decreased non-photochemical quenching (NPQ) under HN conditions. Nitrate, not CO2, showed significant effects on the relative electron transport rate (rETRmax), light use efficiency (α) and saturation light intensity (Ik) that with lowered rETRmax and α under LN culture. Our results indicate that OA may negatively affect Gracilariopsis lemaneiformis growth and alter its photophysiological performance under different nutrient conditions.
... Seagrasses may benefit from acidification because it reduces the cost of carbon intake for photosynthesis, however, there is little evidence that CO2 enrichment increases seagrass production (Koch et al., 2013). Acidification can have an impact on related species, as well as community consequences on seagrass meadows. ...
Ocean acidification (OA) causes an increase in carbon dioxide (CO2) and a reduction in the pH of ocean waters. This chapter reviews the current literature to investigate the adverse effects of OA on fish health and marine ecosystem dynamics. OA poses serious threats to marine biodiversity and ecosystem dynamics. Fish experience severe physiological problems such as impaired growth, development, tissue damage, Impaired behavioral changes, sensory and brain functions, and disruption in predator-prey interactions due to acidification with a 74% decline in survival rates of egg and larval stages. Besides affecting fish, OA also affects marine ecosystem dynamics: reducing calcification rates in calcifying species, increasing seagrass production, causing effects on habitat-forming species, and disrupting the food web. Vulnerable species, such as coral reef fish, show high sensitivity, risking the stability of their habitats. The United Nations recognized the OA as a threat to marine biodiversity through the Convention on Biodiversity. The future research needs to focus on understanding fish and marine animals' adaptive mechanisms to OA, its interaction with other stressors, and global collaboration to address the underlying causes of OA.
... Climate change is having a profound effect on life in the oceans, including warming oceans, rising sea levels, ocean acidification, changing ocean currents and productivity, and shifts in species distribution and abundance. Annual average Arctic sea ice extent has decreased between 3.5% and 4.1% per decade, with September sea ice extent decreasing between 10.7% and 15.9% per decade [16] (see Fig. 2). Coastal areasare also vulnerable to the effects of ocean warming. ...
Climate change is exerting profound effects on marine climates, significantly impacting oceanic ecosystems and the species that inhabit them. Rising global temperatures lead to increased ocean warming, causing thermal expansion and contributing to sea level rise. This warming disrupts marine life, affecting breeding cycles, migration patterns, and food availability. Additionally, the increased absorption of carbon dioxide by oceans results in acidification, which harms coral reefs, shellfish, and other calcifying organisms. Melting polar ice caps and glaciers contribute to habitat loss for species like polar bears and penguins, while altering ocean currents and weather patterns. These changes exacerbate the frequency and intensity of extreme weather events, such as hurricanes and typhoons, further stressing marine environments. Climate change also affects the distribution and abundance of fish stocks, threatening global fisheries and the livelihoods dependent on them. Understanding and mitigating the impacts of climate change on marine climates is crucial for preserving biodiversity, ensuring food security, and maintaining the health of our planet's oceans.
... Seagrasses are one of the most valuable ecosystems in terms of the services provided (Costanza et al., 1997) and they contribute to the functioning of estuaries as habitat, by altering sediment dynamics, and through their tight link with water quality. For instance, these primary producers both influence, and are influenced by, water column nutrients (Valiela, 1995;Lincoln et al., 2021), carbon (Koch et al., 2013), sediment (Walter et al., 2020), and dissolved oxygen (DO) (Long et al., 2020). Because of their influence on carbon and DO, seagrass conservation and restoration are proposed mitigation strategies for ocean acidification and hypoxia (referred to together as OAH), which are threats characterized by water that is acidified (CO 2 -rich, low pH) and low DO, respectively (Feely et al., 2016). ...
Seagrass beds provide important ecosystem services and are valued, in part, for their potential to mediate stressors such as ocean acidification and hypoxia (OAH) for sensitive species. However, the susceptibility of seagrasses to anthropogenic impacts and recent declines motivate the need to better understand the drivers of seagrass and the water quality consequences that occur with variation in seagrass abundance. To meet this need, we leveraged existing monitoring data (water quality and seagrass), hydrodynamic circulation model, and biogeochemical model framework with seagrass submodel, to produce a biophysical model of Coos Bay estuary, Oregon, U.S. The model includes biogeochemical processes involving water quality, plankton, seagrass, and sediment-water interactions. Ecosystem models like this are useful for evaluating complex estuarine systems because they allow us to extend our understanding of system dynamics beyond existing observations and perform experiments to identify the processes driving observed patterns. We used the biophysical model of Coos Bay to evaluate the dynamics of water quality and native eelgrass (Zostera marina) under three eelgrass abundance scenarios (zero eelgrass, current extent, and maximum observed extent) to elucidate the relationship between eelgrass and OAH. Including eelgrass in the Coos Bay model produced results that more closely resembled water quality observations - dissolved oxygen (DO) and pH were more dynamic in simulations with eelgrass, often having both higher highs and lower lows. While there were some areas of the estuary where DO improved with the addition of eelgrass to the model there was overall a small net increase in harmful DO conditions (based on a salmon physiological threshold). In contrast, ocean acidification conditions, pH and calcium carbonate saturation state for aragonite (Ω), were improved (based on oyster requirements) with the addition of eelgrass - although the magnitude of improvement differed seasonally and spatially. Our new model represents a useful tool - one which accounts for and controls the relevant physical and biogeochemical processes - to evaluate conditions that confer resilience or enhance vulnerability to OAH in an important Pacific Northwest coastal estuary and results can inform the OAH-related dynamics occurring in other eastern boundary current estuaries.
... Thermal sensitivity of macroalgae was found to vary by species, population, site, life stage, and life history (Fredersdorf et al., 2009;Savva et al., 2018;Wieters et al., 2013;Zou and Gao, 2013). Moreover, thermal sensitivity is also influenced by many other physical environmental factors, such as light intensity, light quality, salinity, pH, and CO 2 concentration (Koch et al., 2013;Liu et al., 2018;Rautenberger et al., 2015;Zou et al., 2018). Consequently, an ex situ experiment is used to exclude the effects of other environmental factors when investigating thermal sensitivity. ...
Calcifying macroalgae play a critical role in coastal ecosystems, but rising sea temperatures pose a significant threat to their survival. This study aims to investigate the thermal sensitivity of the three marine macroalgal species Padina boryana, Halimeda opuntia , and H. macroloba . Photosynthetic performance, metabolism, pigment content, and oxidative stress–related parameters were measured at temperatures of 28°C, 32°C, 36°C, and 40°C and the thermal performance curves (TPCs) were determined for F v /F m , F v /F 0 , ϕPSII, and oxygen production to assess maximum rate (R max ), optimum temperature (T opt ), critical thermal maximum (CT max ), and thermal safety margin (TSM) of these three macroalgal species. The results showed that 40°C had the most negative effect on all three species with P. boryana demonstrating better performance compared to both Halimeda species. TPCs from photosynthetic performance revealed thermal sensitivity variations by species and P. boryana exhibited a broader thermal tolerance range compared to Halimeda . On the other hand, TPCs of oxygen production provided similar CT max values. Based on TPC projections, all three species might survive future ocean warming and marine heatwaves, though these conditions will have significant effects, with P. boryana showing greater tolerance than both Halimeda species. This study highlights the differential thermal responses and sensitivities of these macroalgae, contributing to understanding their potential resiliencies under future climate change scenarios.
... In the case of M. pyrifera, a stimulatory effect of warming on photosynthetic activity was observed, as evidenced by an increase in net/ gross-P max , quantum efficiency and ETRr in comparison to the control treatment. In other seaweeds, photosynthesis can be stimulated by rising temperatures until signs of metabolic stress appear when warming exceeds physiological tolerance thresholds (Eggert 2012; Koch et al. 2013). Within the photosynthetic machinery, some thermally sensitive reactions from light-harvesting to carbon fixation (e.g., electron transport, photophosphorylation, Rubisco activity) can be accelerated by warming (Collén and Davison 1999; Bischof and Rautenberger 2012; Müller et al. 2012). ...
The kelps Eisenia arborea, Macrocystis pyrifera, and Pterygophora californica are foundation species in the Eastern North Pacific, with their latitudinal limits extending to the Baja California peninsula (Mexico). In comparison to the other species, E. arborea exhibits a higher level of thermo-tolerance. This is attributable to the fact that its southernmost populations are located in warmer waters, and are able to persist thermal anomalies associated with marine heatwaves (MHWs) and ENSO. The objective of this study was to ascertain whether the physiological responses of gametophytes mirror this apparent difference in thermo-tolerances among these species. A laboratory experiment was conducted, by which the photobiology and respiration of gametophytes of the three species were compared when exposed to warm conditions simulating a MHW (20 ⁰C for six days), followed by a post-MHW phase (14 ⁰C for six days). The increase in temperature had no impact on the photosynthetic capacities of the three species; however, it did result in an elevated respiratory activity, which consequently led to an increase in the compensation irradiance. Subsequent to the termination of the warming period, E. arborea did not exhibit signs of physiological stress, while the photosynthetic capacities of M. pyrifera underwent a decline. The respiration rates and compensation irradiance of E. arborea and M. pyrifera recovered, but not in P. californica. The apparent absence of metabolic stress in E. arborea following the cessation of warming suggests a higher degree of resistance to MHWs. This enhanced physiological resilience in gametophytes can contribute to the observed elevated thermal resistance in E. arborea, and underscore its acclimation capacity in the face of warming events.
... In the past few decades, an increase in pCO 2 has been predicted to enhance carbon fixation and photosynthesis in fleshy algae, potentially resulting in algal blooms. However, more recent work has shown that this is not always the case and the response of algae to higher pCO 2 is speciesspecific (Koch et al. 2013). In this study, G. changii was cultivated under current (~ pH 8.1) and future projected pH (~ pH 7.8) and pCO 2 conditions, simulating the SSP3-7.0 ...
Metabolomics offers valuable insights into the final stages of biological processes within organisms and holds promise for environmental monitoring. The escalating levels of anthropogenic CO2 due to industrialization are projected to raise atmospheric pCO2 to levels exceeding 1000 ppm by 2100. The ocean absorbs approximately 30% of this increase in CO2, altering seawater chemistry and decreasing pH levels. In this study, untargeted gas chromatography-mass spectrometry (GC–MS) complemented by physio-biochemical analyses, was utilized to explore the impact of elevated pCO2 on the growth, photosynthesis, agar yield and quality, and metabolite composition of the red alga Gracilaria changii. Although elevated pCO2 did not increase the growth rate of G. changii, an increase in the photosynthetic electron transport rate suggests that photosynthetic carbon assimilation was enhanced. The extra photosynthate was used for other cellular processes including proton export to regulate cellular pH homeostasis given the excess H⁺ in the environment, rather than being invested in new tissue growth. Thymine emerged as a key metabolite influenced by elevated pCO2 in G. changii. Pathway analysis unveiled significant impacts on amino acid synthesis pathways in G. changii at high pCO2. The concentration of compounds such as dopamine and glutamic acid, which are known to be triggered during stress response and provide antipathogenic bioactivity, increased in thalli cultured at higher pCO2. Heatmap analysis indicates d-3 as the turning point for G. changii cultivated at higher pCO2, where the macroalgae begin to regulate their metabolites to alleviate abiotic stresses from higher pCO2 and to maintain essential metabolic functions.
... Climate change causes continuous oceanic warming and changes the carbon cycle process, which also affects the concentration and dissolution of oxygen in seawater (Barange et al., 2018). The low oxygen area in sea area will expand with the ongoing oceanic warming and changes in carbon dioxide concentration under the trend of the climate change; these effects may threaten marine species that need high dissolved oxygen levels (Koch et al., 2013;Fu et al., 2018). T. murphyi has a high demand for dissolved oxygen in seawater, which may also be one of the reasons why the spatial variation of T. murphyi suitable habitat is affected by different climate change scenarios (Arcos et al., 2001). ...
As an economically crucial species in the southeast Pacific Ocean, understanding the spatiotemporal distribution changes of the habitat of Trachurus murphyi under the influence of climate change is essential for effective resource assessment and management. The spatiotemporal changes in suitable habitats of T. murphyi under three climate change scenarios (SSP126, SSP370, and SSP585) of Phase 6 of the Coupled Model Intercomparison Project (CMIP6) were explored based on key environmental factors affecting the potential distribution of the species in a habitat suitability index (HSI) model. Results show that seawater temperature would increase under different scenarios, while the mixed layer depths would decrease under SSP370 and SSP585 scenarios but vary slightly under the SSP126 scenario, which is similar to the variation in different climate periods. The positive difference in seawater temperature will be distributed in the central, southern, and offshore regions of Chile, and the negative difference in mixed layer depths be accounted for a large region. Under different climate scenarios, the HSI value for fishing ground and the overall proportion of suitable habitat area of T. murphyi will be decreased over the forecasted period. The suitable habitat of T. murphyi is concentrated in the 42°S–47°S area and will move to the southwest in different climate periods. Based on short-term climate change, the proportion of suitable habitat areas in the high seas of Chile is larger than in the exclusive economic zone under medium- and long-term climate change under different scenarios. The results of the gravity center of suitable T. murphyi habitat indicates that the spatial distribution of T. murphyi might be related to variations in oceanic currents. These findings provide insights for the effective fisheries resource management of T. murphyi in the Southeast Pacific Ocean.
... At first sight, it would be predicted that aquatic photoautotrophs without, or with a weak, CCM, and thus showing a low affinity for CO 2 or HCO 3 − use in Ci acquisition, might show improved performance in the higher CO 2 environments of the future [65,[119][120][121]. ...
The diffusive availability of CO2 for photosynthesis is orders of magnitude lower in water than in air. This, and the low affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) for CO2, implies that most marine photoautotrophs (cyanobacteria, microalgae, macroalgae and marine angiosperms or seagrasses) would be severely restricted were they to rely only on dissolved CO2 for their photosynthetic performance. On the other hand, the ~120 times higher concentration of bicarbonate (HCO3⁻) makes this inorganic carbon (Ci) form more available for utilisation by marine photosynthesisers. The most common way in marine macrophytes to utilise HCO3⁻ is to convert it to CO2 within acidic micro-zones of diffusion boundary layers (DBLs), including the cell walls, as catalysed by an outwardly acting carbonic anhydrase (CA). This would then generate an intra-chloroplastic (or for cyanobacteria intra-carboxysomal) CO2-concentrating mechanism (CCM). Some algae (e.g., the common macroalgae Ulva spp.) and most cyanobacteria and microalgae feature direct HCO3⁻ uptake as the most efficient CCM, while others (e.g., some red algae growing under low-light conditions) may rely on CO2 diffusion only. We will in this contribution summarise our current understanding of photosynthetic carbon assimilation of submerged marine photoautotrophs, and in particular how their ‘biophysical’ CCMs differ from the ‘biochemical’ CCMs of terrestrial C4 and Crassulacean Acid Metabolism (CAM) plants (for which there is very limited evidence in cyanobacteria, algae and seagrasses).
... Fleshy macroalgal species are expected to be more resilient to increased CO 2 concentrations compared to calcified species because the former do not experience dissolution and have access to more CO 2 for photosynthesis (Koch et al. 2013), which has been supported by modelling (Schlenger et al. 2021). However, experiments have shown that the consequences of OA appear to be species-specific. ...
Increases in atmospheric CO 2 have led to more CO 2 entering the world’s oceans, decreasing the pH in a process called ’ocean acidification’. Low pH has been linked to impacts on macroalgal growth and stress, which can alter palatability to herbivores. Two common and ecologically important macroalgal species from the western Antarctic Peninsula, the unpalatable Desmarestia menziesii and the palatable Palmaria decipiens , were maintained under three pH treatments: ambient (pH 8.1), near future (7.7) and distant future (7.3) for 52 days and 18 days, respectively. Discs of P. decipiens or artificial foods containing extracts of D. menziesii from each treatment were presented to the amphipod Gondogeneia antarctica in feeding choice experiments. Additionally, G. antarctica exposed to the different treatments for 55 days were used in a feeding assay with untreated P. decipiens . For D. menziesii , extracts from the ambient treatment were eaten significantly more by weight than the other treatments. Similarly, P. decipiens discs from the ambient and pH 7.7 treatments were eaten more than those from the pH 7.3 treatment. There was no significant difference in the consumption by treated G. antarctica . These results suggest that ocean acidification may decrease the palatability of these macroalgae to consumers but not alter consumption by G. antarctica .
... These species support ecosystem productivity, create structural habitat, act as ecological engineers (sensu Jones et al., 1994), and underpin a multitude of ecosystem services. In coastal marine ecosystems, foundation species such as kelps (Graham et al., 2007;Steneck et al., 2002), corals (De'ath et al., 2012;Hoegh-Guldberg et al., 2007;Hughes et al., 2003), seagrasses (Koch et al., 2013;Serrano et al., 2021;Short & Neckles, 1999), mangroves (Alongi, 2015;Ward et al., 2016), and oysters (Beck et al., 2011), among others, are experiencing marked changes in distribution and dynamics in response to gradual and episodic changes in water temperature (e.g., marine heatwaves, MHW) and other anthropogenic stressors. These spatial and temporal responses in such population attributes as abundance, productivity, and demographic and genetic structure are complex because of the interactions among multiple simultaneously changing environmental and ecological drivers (e.g., Crain et al., 2008;Hewitt et al., 2016). ...
Marine foundation species are critical for the structure and functioning of ecosystems and constitute the pillar of trophic chains while also providing a variety of ecosystem services. In recent decades, many foundation species have declined in abundance, sometimes threatening their current geographical distribution. Kelps (Laminariales) are the primary foundation species in temperate coastal systems worldwide. Kelp ecosystems are notoriously variable, challenging the identification of key factors controlling their dynamics. Identification of these drivers is key to predicting the fate of kelp ecosystems under climatic change and to informing management and conservation decisions such as restoration. Here, we used in situ data from long‐term monitoring programs across 1350 km of coast spanning multiple biogeographic regions in the state of California (USA) to identify the major regional drivers of density of two dominant canopy‐forming kelp species and to elucidate the spatial and temporal scales over which they operate. We used generalized additive mixed models to identify the key drivers of density of two dominant kelp species (Nereocystis luetkeana and Macrocystis pyrifera) across four ecological regions of the state of California (north, central, southwest, and southeast) and for the past two decades (2004–2021). The dominant drivers of kelp density varied among regions and species but always included some combination of nitrate availability, wave energy and exposure, density of purple sea urchins, and temperature as the most important predictors. These variables explained 63% of the variability of bull kelp in the northern and central regions, and 45% and 51.4% of the variability in giant kelp for the central/southwest and southeast regions, respectively. These large‐scale analyses infer that a combination of lower nutrient availability, changes in wave energy and exposure, and increases in temperature and purple sea urchin counts have contributed to the decline of kelp observed in the last decade. Understanding the drivers of kelp dynamics can be used to identify regional patterns of historical stability and periods of significant change, ultimately informing resource management and conservation decisions such as site selection for kelp protection and restoration.
... An increase in CO 2 levels leads to ocean acidification, affecting seaweed physiology. Acidified conditions alter nutrient uptake, reduce photosynthetic efficiency, and impact growth (Koch et al. 2013;Gao et al. 2018). Research on acidification effects and the development of adaptive strategies are crucial. ...
Marine macroalgae cultivation predominantly depends on plant-based material from natural waters of the sea and vegetative methods from previous harvests as well. However, this prevalent method poses drawbacks, including physiological variations within the seed stock and a decrease in genetic diversity, resulting in diminished growth rates and other by-products of cultivated seaweeds. Addressing these limitations is crucial, necessitating the developing of a sustainable and scalable approach to generate high-quality plantlets within the seaweed cultivation community and research teams. Recent strides in tissue culture and micropropagation techniques offer promising solutions, enhancing seed supply and facilitating the efficient cultivation of uniform seedlings. Diverse seaweed species have succeeded in culture and regenerating into new plantlets through techniques like protoplast, callus, and regeneration. Among various cultivation methods, vegetative and spore-based methods are considered the conventional ones. While vegetative fragments have proven their efficiency for species such as Kappaphycus, Gracilaria, Gelidiella, and Gelidium, challenges include significant seed material consumption and reduced vigor across successive generations. Conversely, reproductive cells have demonstrated utility for species with robust reproductive potential, such as Pyropia, Ulva, Saccharina, and Undaria. This chapter will discuss possible ways to increase the reproductive rate and sporulation through the natural life cycle by manipulation of abiotic factors. Nonetheless, optimization of these conditions requires extensive experimentation due to species-specific requirements, variations in plant age, and physiological backgrounds.
... Elevated pCO 2 resulted in a significant increase in P gross rate of L. pygmaeum, although the CO 2 fertilisation effect on P net was observed only in some treatment combinations (e.g., in high nutrients under low light and under low nutrients and high light) (Figure 3a), and for both metrics (P gross , P net ), the pattern suggested a parabolic response. This response implies that photosynthesis is limited by dissolved inorganic carbon, as shown in CCA recruits (Ordoñez et al. 2019) and adults (Hofmann, Koch, and de Beer 2016), and non-calcareous algae (Koch et al. 2013). The precise pathway by which elevated pCO 2 enhances photosynthesis in L. pygmaeum was not investigated in our study but may have involved relaxation of the carbon concentrating mechanisms (CCM) activity (Cornwall et al. 2013) and increased uptake of CO 2 via diffusive gradients, as suggested for P. onkodes (Bergstrom et al. 2020). ...
The global problem of ocean acidification and localised decline in water quality are major threats to coral reefs worldwide. This study examined the individual and interactive impacts of global and local stressors by investigating the effects of increased seawater p CO 2 , elevated nutrient concentrations and reduced light levels on linear growth and metabolic rates of the common branching crustose coralline alga Lithophyllum cf. pygmaeum . We found complex interactions between factors on algal growth and photosynthetic rates, but overall, growth was significantly enhanced by p CO 2 enrichment under all light and nutrient combinations. This is the first study to report a positive growth response in coralline algae to elevated p CO 2 using linear extension methods. In contrast, the combination of reduced light levels and high nutrient concentrations simulating poor water quality conditions reduced algal growth rates by up to 67% (compared to individuals exposed to high light, low nutrients and elevated p CO 2 ). Decreased light levels reduced linear growth, P gross and P net rates by 33%, 18% and 24%, respectively, highlighting the critical role of light in coralline algal physiology. We suggest that poor water quality may counteract any CO 2 fertilisation effect under ocean acidification conditions on the growth of coralline algae, and this has implications for coral reef conservation as it emphasises the importance of improving water quality to maintaining coral reef functions. These results further highlight the need for multifactorial experiments to better understand the interplay between global and local processes on coralline algae growth.
... Low temperatures can slow down cellular metabolism, impeding photosynthesis and nutrient synthesis, thereby reducing growth rates (Pereira et al. 2005). Prolonged exposure to low temperatures can induce adverse reactions in algae, suppressing growth and reproductive capacity, and may even trigger a dormant state (Koch et al. 2013;Xu et al. 2021). ...
Pyropia kinositae, a recently discovered species in the northern Yellow Sea, could be an ideal species for offshore Pyropia cultivation in northern regions. This study aims to explore the effects of different temperatures and light intensities on the growth and physiological-biochemical characteristics of P. kinositae to determine the optimal conditions for its blade growth. The results showed that under low temperature (LT: 8 °C) conditions, high light intensity (25% of natural light) significantly inhibited the growth of P. kinositae; the highest relative growth rate of P. kinositae was observed at 12.5% of natural light intensity. Under high temperatures (HT: 12 °C), low light intensity (6.25%, 3.125% of natural light) was more favorable for the growth of P. kinositae, while high light intensity suppresses the maximum quantum yield (Fv/Fm) of P. kinositae. LT was more conducive to the accumulation of chlorophyll a (Chl a), carotenoid (Car), phycoerythrin (PE), and phycocyanin (PC). Under HT conditions, the effect of light intensity on Chl a and Car was insignificant, but low light intensity favored the synthesis of PE and PC. UV-absorbing compounds, mycosporine-like amino acids (MAAs), decreased with decreasing light intensity. In conclusion, temperature and light intensity significantly impacted on the growth and physiological and biochemical characteristics of P. kinositae, with an interactive effect on the accumulation of various photosynthetic pigments. The results provide insights into better cultivation management and improve the productivity of this economical macroalgae.
... These meadows provide numerous essential ecosystem services. Seagrasses are thought to benefit from ocean acidification, as they can utilize both CO₂ and HCO₃⁻ for photosynthesis, although they have a higher affinity for CO₂ and are often carbon-limited [6][7]. Additionally, evidence from natural volcanic CO₂ vents at Ischia, Panarea Islands, and Basiluzzo Islet-where conditions of natural acidification occur-indicates a correlation between increased dissolved inorganic carbon (DIC) and enhanced net primary production [8]. ...
The dissolution of CO2 in seawater as bicarbonate ions (HCO₃⁻) offers a promising alternative to geological storage, provided the process ensures long-term stability and avoids harming marine ecosystems. Storing CO2 in the form of bicarbonate ions could remain effective for geologic timescales, potentially up to 10,000 years [1–3]. This approach involves treating natural seawater by mixing it with pre-equilibrated seawater solutions produced from the reaction of CO2 with Ca(OH)2, adjusted to maintain the same pH as seawater. Recent research [4] has shown that the resulting bicarbonate-rich solution is stable, but concerns persist regarding its potential environmental impacts. While alkalinity itself does not directly affect marine biology, its increase significantly alters pH and the concentrations of key ions and molecules, such as those in the carbonate system, which can directly influence biological processes. The extent of modifications to seawater carbonate chemistry depends on the amount of alkalinity added per unit volume and the rate at which this volume mixes with surrounding waters. The rate at which perturbed seawater equilibrates with the atmosphere is also a critical factor. Seagrasses, marine angiosperms that evolved from terrestrial plants and returned to the sea during the Cretaceous period (approximately 140 to 100 million years ago), play a vital role in marine ecosystems. Seagrass meadows are among the most productive ecosystems on Earth, with an average primary productivity ranging from 394 to 1200 g C m⁻² y⁻¹. These meadows provide numerous essential ecosystem services. Seagrasses are thought to benefit from ocean acidification, as they can utilize both CO₂ and HCO₃⁻ for photosynthesis, although they have a higher affinity for CO₂ and are often carbon-limited [6–7]. Additionally, evidence from natural volcanic CO₂ vents at Ischia, Panarea Islands, and Basiluzzo Islet—where conditions of natural acidification occur—indicates a correlation between increased dissolved inorganic carbon (DIC) and enhanced net primary production [8]. Building on existing literature, this analysis will explore the potential co-benefits of increased bicarbonate concentrations for seagrasses, aiming to assess how these benefits could enhance seagrass health and growth. It will also evaluate the opportunity to integrate this technology with Nature-Based Solutions, such as seagrass restoration, to maximize ecosystem resilience and climate mitigation efforts.
... The current pH of global ocean surface water is 8.1. In the RCP 8.5 scenario, the pH is expected to drop by 0.3 to 0.4 units, reaching 7.8 by 2100, while the water temperature is projected to rise by 3.7 °C (Orr et al., 2005;Martin et al., 2008;Koch et al., 2013;IPCC, 2014). ...
... The availability of nutrients, sometimes in excess, is also a factor that impacts seagrass survival. Although seagrasses themselves can improve water quality in aquaculture (de los Santos et al., 2020), they are at risk from eutrophication, especially under increasing thermal stress from anthropogenic climate change (Pazzaglia et al., 2020;Koch et al., 2012;Marbà and Duarte, 2009;Short and Neckles,1999). These factors fluctuate over time and may influence the success rates of different restoration methods. ...
... 1969;Gee and Niyogi 2017;Jensen et al. 2019). For some algae, e.g., the diatom Thalassiosira weissflogii and the green alga Udotea flabellum, they not only have a biophysical CCM but also a biochemical CCM; the latter is defined as one where an initial fixation of Ci transports into C 4 acid supporting C 4 photosynthesis (Koch et al. 2013;Reinfelder et al. 2000;Reiskind and Bowes 1991). In diatom C 4 photosynthesis, HCO 3 − transported into the cytoplasm is fixed to C 4 acid by phosphoenolpyruvate carboxylase (PEPC), then the products transported to chloroplasts, decarboxylated by phosphoenolpyruvate carboxykinase (PEPCK) to produce CO 2 (Reinfelder et al. 2000). ...
CO 2 concentration mechanisms (CCMs) are important in maintaining the high efficiency of photosynthesis of marine algae. Aquatic photoautotrophs have two types of CCMs: biophysical CCMs, based on the conversion of inorganic carbon, and biochemical CCMs, based on the formation of C 4 acid intermediates. However, the contribution of biophysical and biochemical CCMs to algal carbon fixation remains unclear. Here, we used ethoxyzolamide (EZ) inhibitors of carbonic anhydrase and 3-mercaptopicolinic acid (MPA) inhibitors for phosphoenolpyruvate carboxykinase to examine the importance of biophysical and biochemical CCMs in photosynthesis of the green macroalga Ulva prolifera . The culture experiments showed that the carbon fixation of the species declined when EZ inhibited the biophysical CCM, while the increase in cyclic electron flow around the photosystem I indicated a more active biochemical CCM, contributing to ~ 50% of total carbon fixation. The biophysical CCM was also reinforced when MPA inhibited the biochemical CCM. In a comparison, the biophysical CCM can compensate for almost 100% of total carbon fixation. The results indicate that biophysical CCMs dominate the process of carbon fixation of U. prolifera while biochemical CCM plays a supporting role. Our results provide evidence of a complementary coordination mechanism between the biophysical and biochemical CCMs that promotes the efficiency of photosynthesis of U. prolifera , an efficient mechanism to boost the alga’s bloom.
... Although CO 2 addition can be a powerful tool to increase algal growth rates, the associated acidification of seawater can increase an alga's sensitivity to other stressors. This has been observed in studies that focused on the interaction between ocean warming and ocean acidification (OA), where OA caused a shift in the optimum temperature range of certain algae (Koch et al., 2013). Because of this, it has been hypothesized that high CO 2 conditions could narrow the optimal temperature range of A. taxiformis. ...
The red alga Asparagopsis taxiformis has recently been recognized for its unique ability to significantly reduce methane emissions from ruminant animals when fed in small quantities. The main obstacle in using this seaweed as a methane‐mitigating feed supplement is the lack of commercially available biomass. Little is known about how best to grow this red alga on a commercial scale, as there are few published studies that have investigated the factors that influence growth, physiology, and overall performance. This study examined the effects of temperature and CO 2 enrichment on the growth, photophysiology, and concentration of bromoform, the secondary metabolite largely responsible for methane reduction in A. taxiformis . A series of single and multifactor closed culture experiments were conducted on A. taxiformis collected, isolated, and cultured from populations in Southern California. We identified the optimal temperature range to be between 22 and 26°C, with significant short‐term stress observed below 15°C and above 26°C. Carbon dioxide addition resulted in increased performance, when accounting for growth per CO 2 use. In general, we observed the highest bromoform concentrations in algae with the highest growth rates, but these results varied among experiments. These findings indicate that through environmental control and by addressing limiting resources, significant increases in biomass production and quality can be achieved.
... In addition, declines in abundance and the redistribution of coastal macroalgae (brown seaweed in particular) on a global scale have been attributed to anthropogenic pressure and climate change (see examples reviewed in e.g. [8][9][10][11]). ...
... The complex consequences caused by these problems urgently need to be interpreted from a network perspective (Cheung et al. 2013;Fossheim et al. 2015;Duarte et al. 2020;Pecuchet et al. 2020). For instance, ocean acidification, leading to changes in the concentration of carbon dioxide in seawater, affects the pH value (Koch et al. 2013), directly impacting the formation of coral exoskeletons dependent on calcification, thus influencing reef-building processes. Consequently, a large number of tropical marine organisms that rely on coral reefs as habitats are indirectly affected (Wilson et al. 2008). ...
Aim
In complex networks, the degree distribution varies and provides an insight into the general structure of the system. For example, it may show scale‐free characteristics of the network, indicating higher vulnerability against non‐random disturbances. However, investigating its spatio‐temporal variability, degree distribution in marine food webs remains an unresolved issue. In this paper, we focus on describing the global variability of degree distribution in marine food webs.
Location
Global.
Methods
We studied 105 marine food webs. By Kolmogorov–Smirnov test, and kernel density estimation, we determined the degree distribution of each food web, described its spatio‐temporal pattern and quantified the correlation between relevant parameters as a function of the scale‐free property of the degree distribution.
Results
Marine food webs around the globe did not strictly exhibit scale‐free characteristics in most regions, and only below 5% of the food webs entered the “strongest fit” level of the scale‐free network. We also find food webs in the polar regions indicate relatively high goodness‐of‐fit to scale‐free networks. The upwelling ecosystem related to ocean currents is prone to form a scale‐free web, which exhibits periodic scale‐free characteristics. The ecosystem types with relatively ‘low fit’ levels were mainly concentrated in the ecosystems heavily influenced by human activities.
Main Conclusions
This research will enhance the research in terms of (a) classifying degree distribution in marine food webs; (b) revealing the variability in the spatial pattern of particular distributions, for example, the scale‐free characteristics and (c) exploring the distribution of in‐degree in space, quantifying the proportion of generalist and specialist species, as a potential indicator of adaptive potential of ecosystems. This research contributes to our understanding of the scale‐free features of marine food webs globally. It also offers a real systems‐based conservation approach to assess the spatial heterogeneity of the structural vulnerability of marine ecosystems.
... The observed increase in SST has several detrimental effects on P. oceanica meadows, affecting the productivity in terms of rhizome length, rhizome width and biomass (Stipcich et al. 2022a), the growth rate (Marín-Guirao et al. 2019;Guerrero-Meseguer et al. 2020) and also its nutritional value (Stipcich et al. 2023a). Under high stress levels, key physiological processes such as photosynthesis and respiration are also altered, since they are among the most heat-sensitive in higher plants (Lee et al. 2007;Koch et al. 2013;Marín-Guirao et al. 2016). Temperature effects on P. oceanica plants are highly dependent on local environmental conditions, which modulate the ability of plants to cope with single and multiple stressors (Savva et al. 2018;Jahnke et al. 2019;Pazzaglia et al. 2020;Stipcich et al. 2022b;Santillán-Sarmiento et al. 2023). ...
Marine Heat Waves (MHWs) occurrence has been increasing in the Mediterranean Sea. The effects of field simulated MHWs of different intensity (medium and high temperature) on the transcriptome expression of the endemic seagrass Posidonia oceanica were evaluated considering different origins of the plant. The aim of the study was reached through a common garden transplant experiment in the North-west of Sardinia (Italy), where two P. oceanica meadows characterized by different thermal regimes (cold and warm) were chosen. MHWs were simulated in front of a power plant, that creates a natural laboratory by releasing warm water in the sea. Differential gene expression and GO enrichment analyses highlighted differences in the transcriptomic profiles of plants from cold and warm environments suggesting that the MHWs induced different levels of stress due to different tolerance to the heat event. Plants from both origins activated processes to achieve protein homeostasis, but only cold plants activated an antioxidant defense and altered sugar metabolism, both indicators of heat stress. Within plants of the same origin, a different response to MHW intensity was also detected: while warm plants showed the most complex response at high temperature rather than at medium temperature, cold plants seemed to better cope with the medium temperature intensity rather than with high temperature.
... Makroalga merupakan tumbuhan tingkat rendah yang memiliki batang, akar dan daun yang belum terdeferensiasi sehingga untuk membedakannya seringkali bagian makroalga disebut dengan thallus (menyerupai). Berdasarkan kandungan pigmennya, makroalga terbagi menjadi 3 divisi yakni Chlorophyta (alga hijau), Rhodophyta (alga merah) dan Phaeophyta (alga cokelat) (Koch et al., 2013). Chlorophyta didominasi pigmen hijau dan mengandung klorofil a dan b, Rhodophyta didominasi pigmen merah dan mengandung klorofil a dan d serta Phaeophyta didominasi pigmen cokelat dan mengandung klorofil a dan c (Gavino & Trono, 1997). ...
Information on macroalgae species and their distribution in the coastal areas of Kolaka Regency is extremely limited. This research is a preliminary study of macroalgae species found along the coast of Kolaka Regency, conducted in the waters of Tanggetada Village. The research applied the belt transect method and 1 x 1 m quadrats using a 50 m long line transect with a placement interval of each quadrat of 5 m, which was repeated 3 times with a distance of 50 m between line transects. The results showed that 20 species of macroalgae, namely Caulerpa verticillata, Caulerpa racemosa, Dyctiosphaeria versluysii, Dyctiosphaeria cavernosa, Udotea sp., Halimeda opuntia, Halimeda macroloba, Halimeda sp., Boodlea composita, Gelidiella acerosa, Hormophysa triquetra, Sargassum sp., Lobophora variegata, Padina minor, Liagora sp., Avrainvillea obscura, Gracillaria coronopifolia, Valonia aegagropila, Acanthophora spicifera, and Dictyota dichotoma, come from 3 group, namely 11 species from the Chlorophyta, 5 species from the Rhodophyta, and 4 species from the Phaeophyta. Water conditions in Tanggetada village still support macroalgae growth. Further research with a wider scale is needed in the observation area to reach the coral reef area and an overview of the ecological index of macroalgae in the Tanggetada village. Keywords: Macroalgae Divisi; Macroalgae Species; Tanggetada; Water conditions Abstrak Informasi yang tersedia mengenai spesies makroalga dan distribusinya di wilayah pesisir Kabupaten Kolaka masih sangat terbatas. Penelitian ini merupakan studi pendahuluan mengenai spesies makroalga yang ditemukan di sepanjang pesisir Kabupaten Kolaka, yang dilakukan di perairan Desa Tanggetada. Penelitian dilaksanakan menggunakan metode belt transect dan kuadrat 1 x 1 m menggunakan transek garis sepanjang 50 m dengan interval penempatan setiap kuadrat sebesar 5 m yang diulangi sebanyak 3 kali ulangan dengan jarak antar transek garis sebesar 50 m. Hasil penelitian menemukan 20 jenis makroalga yaitu Caulerpa verticillata, Caulerpa racemosa, Dyctiosphaeria versluysii, Dyctiosphaeria cavernosa, Udotea sp., Halimeda opuntia, Halimeda macroloba, Halimeda sp., Boodlea composita, Gelidiella acerosa, Hormophysa triquetra, Sargassum sp., Lobophora variegata, Padina minor, Liagora sp., Avrainvillea obscura, Gracillaria coronopifolia, Valonia aegagropila, Acanthophora spicifera dan Dictyota dichotoma yang berasal dari dari 3 kelompok yakni 11 jenis dari Chlorophyta, 5 jenis dari Rhodophyta dan 4 jenis dari Phaeophyta. Nilai rata-rata kondisi perairan Desa Tanggetada masih termasuk dalam kisaran nilai optimum untuk mendukung pertumbuhan makroalga. Namun demikian, penelitian ini masih membutuhkan penelitian lanjutan dengan skala area pengamatan yang lebih luas hingga mencapai daerah terumbu karang untuk menggambarkan indeks ekologi makroalga yang berada di Pesisir Tanggetada. Kata kunci : Divisi Makroalga; Jenis Makroalga; Kondisi perairan;Tanggetada
Seagrass plays a vital role in marine ecosystems by providing food and shelter, maintaining water quality, protecting the coastline, and maintaining nutrient cycling and oxygen content. However, due to the climate change and tourism activities, seagrass around the world is facing high stress and degradation. Therefore, a systematic study is required to analyse the impact on seagrass. This study aims to analyse stress in the Thalassia hemprichii species in Benoa Bay, Bali, given Bali’s tourism industry and Benoa Bay’s popularity for water sports. Field data were collected at 96 locations, and the leaf samples were analysed for leaf pigments. The study, Chlorophyll-a (Chl-a), chlorophyll-b (Chl-b), total chlorophyll, and total carotenoids were analysed using standard protocols. Total chlorophyll ranged from 0.502 to 1.906 mg/g while the total carotenoids ranged from 0.224 to 1.018 mg/g. The lowest chlorophyll levels were found in tourism hotspots like Sanur and Benoa harbour, while these regions also exhibited higher carotenoid levels. This suggests high stress in these areas, possibly due to high-speed boat traffic. The study could be further improved by quantifying other environmental parameters like water quality and temperature to understand the root causes. However, the study provides baseline information for the conservation of Benoa Bay.
Seagrasses, considered one of the most important carbon sinks in the world, face multiple threats, with climate change being the most significant. In addition to providing a habitat for other aquatic vertebrates and invertebrates, they play a crucial role in marine ecosystems by preventing sediment erosion and acting as primary producers. According to climate scenarios established by the Intergovernmental Panel on Climate Change (IPCC), understanding how these species will respond to seawater temperature and pH changes is essential for planning mitigation strategies. Climate chambers are used in both marine and laboratory environments to investigate the efects of these scenarios on marine organisms. In climate chamber systems, the molecular responses of these species under various stress conditions can be determined by analyzing expression changes in target genes. Tis chapter methodologically details stress-based gene expression studies conducted on Cymodocea nodosa using microcosm systems.
Aquaculture ponds have emerged as a significant contributor to greenhouse gas (GHG) emissions. We measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions in ponds, all located in Jiangsu Province, with different fish and management practices over an entire cycle. All ponds emitted these gases, with higher CH4 and N2O levels during fish growth than stocking period. The highest CH4 and N2O fluxes were found in the Crucian carp (Carassius auratus) pond with up to 16,512 ± 3015 μmol/(m2·h) and 5.54 ± 0.31 μmol/(m2·h), respectively. CH4 was the primary contributor to the global warming potential in traditional earthen ponds, accounting for an average contribution rate of 87.7 %. The dissolved oxygen (DO) concentration was the water quality parameter that most significantly influenced the CO2 flux, while pH acted as its primary regulator. The GHG emission intensity per unit of fish production in traditional earthen ponds was 197 times higher than that in in-pond raceway systems. Largemouth bass (Micropterus salmoides) and Crucian carp ponds exhibited CH4 diffusion fluxes at the sediment-water interface, which were > 20 times higher than those at the water-air interface. Our results further suggest that stocking density and feed amount significantly influence the variations in GHG emissions among the ponds with the in-pond raceway system having low carbon emissions and being high yield aquaculture system compared to traditional earthen ponds. The water depth and DO concentration can be manipulated to reduce GHG emissions across the various interfaces.
Sharks are important species that occupy different niches and trophic levels due to their biological and behavioural variability. It makes them a key element for conservation measures in marine environments. Among several stressors, climate changes put pressure on species in different ways (direct and indirect) and intensities. Understanding how changes may affect shark species is essential to evaluate measures that reduce the impact on shark populations and help them to adapt to a future climatic scenario. The aim was to identify the levels of vulnerability for Northern and Northeastern Brazil sharks to climate change based on a semiquantitative method of ecological risk assessment. Temperature and UV light were, respectively, the most concerning direct and indirect effects for sharks. In general, most of the assessed species have moderate chances of surviving the pressure caused by climate change. Carcharhinus porosus , Mustelus higmani and Isogomphodon oxyrhyncus were the most vulnerable assessed species. Coastal and estuarine sharks had high rates of exposure and high vulnerability indexes to climate change. Coastal and inshore species generally has high habitat specificity and latitudinal limitation, which worsens its ability to adapt to the new climate scenario. Both parameters may be a crucial factor in preserving coastal shark populations. Continental shelf habitats are commonly affected by other human stressors, such as fishing, waste contamination and destruction of tidal vegetation. In this way, region‐specific conservation measures can reduce bycatch and increase reproductive efficiency, increasing the likelihood of coastal sharks surviving climate change. There is still little knowledge about the synergistic effect between human pressure and climate change. However, it is necessary to take measures to preserve the coastal and estuarine environments, so that the biota of these areas show favourable conditions for survival.
To mitigate global warming, seaweeds or marine algae are expected to capture carbon dioxide directly from the atmosphere. With the aim to transplant it to the coastal areas in the future, we tried to culture a brown algae Sargassum horneri, which is frequently found in the coastal area in Japan at a low cost using composted sewage sludge as a locally available nutrient source. As a fundamental study, we mixed 1 L seawater and 10 g composted sewage sludge and collected its supernatant as composted sewage sludge (CSS) extract. Then, the brown algae was grown at 20 °C in the seawater mixed with CSS extract at 0%, 1%, 10%, and 20% for seven weeks, replacing the mixture of seawater and CSS extract every week. As the result, the algal growth was observed only in the seawater with 1% CSS extract, achieving the maximum values of full length and fresh weight which were 1.2 and 2.1 times larger than those in the seawater without CSS extract, respectively. On the other hand, the extract application at 10% and 20% to the seawater significantly inhibited the algal growth, probably due to the oversupplies of ammonium and phosphorus from CSS. The algae grown in the seawater with 1% CSS extract had photosynthetic pigments at the comparable concentrations to those grown in the seawater without CSS extract, while they had less contents of heavy metals. These results revealed the potential of CSS to supply nutrients for seaweed growth but the size of brown algae grown in this study was not enough for its transplantation to the coastal areas, motivating further studies to use CSS more effectively.
Seagrass meadows are vital carbon sinks, but their function is threatened by rapid decline, driving restoration efforts to enhance coastal recovery and carbon removal. The capacity of these restored seagrass as carbon sources or sinks depends largely on organic carbon metabolism and carbonate dynamics. In this study, we employed ex situ core incubation to investigate the metabolic rates of replanted seagrasses (SG), including gross primary productivity (GPP), community respiration (R), net ecosystem metabolism (NEM), and net ecosystem calcification (NEC) in SG and surrounding bare sediments (BS). SG exhibited higher GPP (26.0 ± 1.0 mmol O2 m-2 h-1 vs 0.7 ± 0.1 mmol O2 m-2 h-1) and NEM (208.2 ± 6.3 mmol O2 m-2 d-1 vs 20.1 ± 2.8 mmol O2 m-2 d-1) than BS, indicating their potential as carbon sinks by shifting benthic metabolism towards a more autotrophic state. In contrast, SG showed higher daytime carbonate production and nighttime carbonate dissolution, which could offset each other, resulting in no significant difference in NEC between SG and BS. In summary, our results found that the SG exhibited significantly higher NEM compared to BS, while no significant difference was found for NEC. Consequently, the net effect on the carbon uptake capacity of the restored seagrass is likely increased, primarily due to the higher NEM. Our findings highlight the ecological significance of seagrass restoration in mitigating climate change through carbon removal. Ex situ core incubation method allows for the simultaneous measurement of organic and inorganic carbon metabolism. While ex situ core incubation enhances feasibility, in situ assessments are still necessary to validate the results and ensure a comprehensive understanding of seagrass ecosystem dynamics.
Photosynthetic organisms have an enormous influence on our environment through their effects on the development of other life on Earth and the way they alter the planet's geology and geochemistry. This book takes a unique approach by examining the evolutionary history of the major groups of aquatic photoautotrophs in the context of the ecophysiological characteristics that have allowed them to adapt to the challenges of life in water and thrive under past and present environmental conditions. The important role played by aquatic photoautotrophs on a planet undergoing unprecedented anthropogenic-induced change is also highlighted, in chapters on their critical function in mitigating environmental change through their physiological processes, and on the role of algae in biotechnology. This invaluable resource will be appreciated by researchers and advanced students interested in the biodiversity and evolutionary physiology of the full range of aquatic photoautotrophs, and their interaction with the environment.
Photosynthetic organisms have an enormous influence on our environment through their effects on the development of other life on Earth and the way they alter the planet's geology and geochemistry. This book takes a unique approach by examining the evolutionary history of the major groups of aquatic photoautotrophs in the context of the ecophysiological characteristics that have allowed them to adapt to the challenges of life in water and thrive under past and present environmental conditions. The important role played by aquatic photoautotrophs on a planet undergoing unprecedented anthropogenic-induced change is also highlighted, in chapters on their critical function in mitigating environmental change through their physiological processes, and on the role of algae in biotechnology. This invaluable resource will be appreciated by researchers and advanced students interested in the biodiversity and evolutionary physiology of the full range of aquatic photoautotrophs, and their interaction with the environment.
Photosynthetic organisms have an enormous influence on our environment through their effects on the development of other life on Earth and the way they alter the planet's geology and geochemistry. This book takes a unique approach by examining the evolutionary history of the major groups of aquatic photoautotrophs in the context of the ecophysiological characteristics that have allowed them to adapt to the challenges of life in water and thrive under past and present environmental conditions. The important role played by aquatic photoautotrophs on a planet undergoing unprecedented anthropogenic-induced change is also highlighted, in chapters on their critical function in mitigating environmental change through their physiological processes, and on the role of algae in biotechnology. This invaluable resource will be appreciated by researchers and advanced students interested in the biodiversity and evolutionary physiology of the full range of aquatic photoautotrophs, and their interaction with the environment.
The fishery of the western rock lobster, Panulirus cygnusGeorge, 1962, is Australia’s most valuable wild-caught single-species fishery. Recruitment in some regions of the fishery was observed to be significantly lower than expected after the 2010/2011 West Australian marine heatwave that caused extensive disturbance of dominant coastal habitats. This event generated interest in the study of the factors influencing survival and recruitment of post-larval benthic P. cygnus after settlement. The habitat associations of the highly cryptic post-settlement early-juveniles were previously unknown, with only anecdotal observations of individuals within limestone crevices in nearshore habitats. Our study used early-juveniles derived from ongoing monitoring of puerulus settlement to examine their habitat association mechanism in mesocosm experiments. Comparison of common nearshore habitat assemblages (bare sand, limestone crevices, and seagrasses (Posidonia and Amphibolis) at varying seagrass densities) found that most early-juveniles associated strongly with Amphibolis assemblages at high stem densities (~2,100 stems m–2). A shift in association between Amphibolis fronds and stems at high stem density to Amphibolis-shaded sand and leaf debris at low stem density indicated active habitat selection by early-juveniles. Habitat choices were tested with the scents of prey items and habitat types within Amphibolis assemblages using Y-maze bioassays. No significant olfactory choices were found, suggesting that habitat associations may be driven by multiple cues. Our study provides new laboratory-based insights into the habitat association of early-juvenile P. cygnus and suggests changes in seagrass assemblage identity and density are likely to be important. Further experimentation is needed to define the cues driving these patterns. The impact of habitat change on recruitment in this important fishery remains unknown and should be an objective of future research.
El cambio climático global está generando afectaciones importantes en los organismos que habitan los ambientes marinos, las macroalgas presentan cambios en su metabolismo, fenología y distribución que se han estudiado con más frecuencia en tiempos recientes debido a la tropicalización de las zonas templadas y polares, cambios en el pH de los océanos y su consecuente acidificación. El presente trabajo ofrece un panorama general del impacto del cambio climático en las macroalgas marinas, así como de algunas de las adaptaciones que estas han desarrollado para su sobrevivencia.
Ecological Dynamics in the Face of Climate Change: Exploring Organisms, Habitats, and Behavioural Adaptations is a comprehensive exploration of the profound impacts of climate change on ecosystems and living things. It encompasses a broad spectrum of topics, from the pivotal role of microorganisms in combating global warming to the dramatic changes in marine ecosystems and the surge of invasive species.
This book covers the following topics:
1. Microorganisms’ response to global warming and permafrost behavior
2. Links between antibiotic resistance and climate change
3. The role of phytoplankton in marine ecosystems
4. Impact on seagrass meadows and benthic ecosystems
5. Advantages of invasive species and their effects on the ecosystem
6. Impacts of global warming on floristic diversity, medicinal plants, insects, amphibians, and reptiles
This publication is an invaluable resource for gaining insights into the intricate ecological transformations triggered by climate change and the adaptive mechanisms employed by living organisms to navigate these challenges. It is an essential reference for scientists and environmental enthusiasts, offering a comprehensive guide for individuals seeking to delve into the complex interplay between nature and its impact on human existence.
Ocean acidification (OA), caused by the rising concentration of atmospheric CO2, leads to changes in the marine carbonate system. This, in turn, affects the physiological processes of phytoplankton. In response to increased pCO2 levels, marine microalgae modulate their physiological responses to meet their energy and metabolic requirements. Nitrogen metabolism is a critical metabolic pathway, directly affecting the growth and reproductive capacity of marine microorganisms. Understanding the molecular mechanisms that regulate nitrogen metabolism in microalgae under OA conditions is therefore crucial. This study aimed to investigate how OA affects the expression profiles of key genes in the nitrogen metabolic pathway of the marine diatom Skeletonema costatum. Our findings indicate that OA upregulates key genes involved in the nitrogen metabolic pathway, specifically those related to nitrate assimilation and glutamate metabolism. Moreover, pCO2 has been identified as the predominant factor affecting the expression of these genes, with a more significant impact than pH variations in S. costatum. This research not only advances our understanding of the adaptive mechanisms of S. costatum in response to OA but also provides essential data for predicting the ecological consequences of OA on marine diatoms.
Organismal phenotyping to identify fitness traits is transforming our understanding of adaptive responses and ecological interactions of species within changing environments. Here we present a portable Multi-Taxa Phenotyping (MTP) system that can retrieve a suite of metabolic and photophysiological parameter across light, temperature, and/or chemical gradients, using real time bio-optical (oxygen and chlorophyll a fluorescence) measurements. The MTP system integrates three well-established technologies for the first time: an imaging Pulse Amplitude Modulated (PAM) chlorophyll a fluorometer, custom-designed well plates equipped with optical oxygen sensors, and a thermocycler. We demonstrate the ability of the MTP system to distinguish phenotypic performance characteristics of diverse aquatic taxa spanning corals, mangroves and algae based on metabolic parameters and Photosystem II dynamics, in a high-throughput capacity and accounting for interactions of different environmental gradients on performance. Extracted metrics from the MTP system can not only provide information on the performance of aquatic taxa exposed to differing environmental gradients, but also provide predicted phenotypic responses of key aquatic organisms to environmental change. Further work validating how rapid phenotyping tools such as the MTP system predict phenotypic responses to long term environmental changes in situ are urgently required to best inform how these tools can support management efforts.
This study was carried out to determine the amounts of heavy metals in Silver Catfish and water samples collected from the Ogbogoro section of the new Calabar River in Nigeria. Measure key water quality parameters, such as pH, temperature, salinity, conductivity, total suspended solids, and Total dissolved solids. Dissolved oxygen levels were assessed using the Winkler method, turbidity was determined using a Secchi disc. Metals in fish tissue were analysed using a spectrophotometer, including copper, zinc, cadmium, chromium, nickel, lead, iron, and cobalt. These findings suggest that fish have increased levels of Pb, Cd, and Cr, posing possible ecological and human health hazards. Water quality measures such as pH, dissolved oxygen, and conductivity were also found to vary. To address these findings, it is recommended to establish regular monitoring programs, enforce strict environmental regulations, and implement mitigation measures to reduce heavy-metal inputs. This research contributes to the understanding of heavy metal contamination in Southern Nigeria and provides recommendations for policymakers, resource managers, and local communities to protect and sustainably regulate river ecosystems. Continuous monitoring and study are required to understand the long-term trends and possible effects of heavy-metal pollution caused by heavy metals.
Climate models predict increases in frequency of summer heat waves. In Europe, such events have already caused declines in seagrass meadows, highlighting the importance of short-term responses of local communities to climate stress. Understanding the variability among populations along the European thermal gradient in response to heat waves is crucial for seagrass conservation and management. Using a mesocosm we compared effects of a simulated heat wave on the photophysiology of Zostera marina populations coming from low (43 degrees N, Adriatic Sea) and high latitudes (56 degrees N, North and Baltic Seas). Measurements before, during and up to 4 wk after the heat wave included photophysiological parameters derived from light response curves generated by PAM fluorometry and gene expression using qRT-PCR. In all 3 populations, initial exposures to thermal stress were characterized by increases in dark adapted effective quantum yield (Y-0), maximum electron transfer rate of PSII (ETRmax) and slope of the light response curve (alpha), coinciding with upregulations of the gene superoxidase dismutase [Mn]. With continuation of the heat wave these initial effects disappeared, demonstrated by declines in Y-0, ETRmax and alpha relative to controls. Z. marina from the Adriatic suffered from the simulated heat wave as much as its high-latitude counterparts. However, we also demonstrate slight photophysiological differences between the populations during the recovery phase, where performance of high-latitude populations continued declining even after water temperatures returned to control levels, while photochemical activity fully recovered in the Adriatic population. These results might draw the attention of future studies and seagrass conservation efforts.
Photosynthetic rates of many marine macroalgae are saturated by the present day inor-ganic carbon (Ci) composition of seawater, while those of seagrasses (or marine angiosperms) are CO1-limited. In this study we attempted to simulate the Ci conditions of near-shore seawater during the time that seagrasses colonised the sea (in the Cretaceous), and compare the photosynthetic performance of representatives of the 2 plant groups under those versus present day conditions. The results show that the seagrasses have an affinity for Ci at least as high as the algae under the low pH and high C02/HC03' concentration ratios simulating near-shore areas of the Cretaceous seas, indicating that their photosynthetic capacity then matched that of macroalgae. However, in the high pH and high COz/HCO?-ratlos of today, their a f f ~ n ~ t y for Ci is lower than that of the macroalgae, and it is suggested that this deficiency renders them a lower ability for Ci utilisation. This situat~on may possibly be reversed again as global CO2 levels of the atmosphere and, consequently, of near-shore marine habi-tats increase in the future.
Temperature is a major factor determining the natural distribution of plants, and the success and timing of agricultural crops. Habitats occupied by plants show dramatic differences in temperature during the period of active growth, ranging from just above freezing in polar or alpine areas to over 50 °C in the hottest deserts. Moreover, in many habitats the same individual plant is subjected to wide seasonal variations in temperature and even diurnal temperature fluctuations may be considerable.
The mechanisms by which marine angiosperms, or seagrasses, utilize external inorganic carbon (Ci) include, in addition to uptake of CO2 formed spontaneously from HCO3–: (i) extracellular carbonic anhydrasemediated conversion of HCO3– to CO2 at normal seawater pH, or in acid zones created by H⁺ extrusion, and (ii) H⁺-driven utilization (direct uptake?) of HCO3–. The latter mechanism was recently indicated for Zostera marina, Halophila stipulaceaand Ruppia maritima, and manifested itself as a sensitivity of photosynthesis to buffers, as well as a relative insensitivity to acetazolamide under buffer-free conditions, especially at high pH.
Seagrasses have until recently been viewed as having Ci utilization systems that are less ‘efficient’ than macroalgae, and this has, for example, led to the thought that future rises in atmospheric and thus dissolved CO2 would have a stronger effect on seagrasses than on macroalgae. However, most of the experiments leading to such conclusions were carried out in the laboratory on detached leaves, and buffers were used to keep HCO3–/CO2 ratios stable during Ci additions. The revelation that seagrass photosynthesis is sensitive to buffers as well as to physical perturbations, has led to new experiments in which initial pH values are set by appropriate HCO3–/CO32–ratios, and/or O2 measurements on leaf pieces are replaced with pulse amplitude-modulated fluorometry on whole, attached leaves, often in situ. Under such conditions, the photosynthetic responses of seagrasses to Ci match those obtained for macroalgae. Thus, the paradigm of ‘inefficient’ Ci utilization by seagrasses as compared with macroalgae may no longer be valid. Consequently, it seems that the generally observed high productivity of seagrass beds may have its background in very efficient, H⁺-driven, means of HCO3– utilization.
Calcified macroalgae are distributed in marine habitats from polar to tropical latitudes and from intertidal shores to the deepest reaches of the euphotic zone. These algae play critical ecological roles including being key to a range of invertebrate recruitment processes, functioning as autogenic ecosystem engineers through provision of three-dimensional habitat structure, as well as contributing critical structural strength in coral reef ecosystems. Calcified macroalgae contribute significantly to the deposition of carbonates in coastal environments. These organisms are vulnerable to human-induced changes resulting from land and coastal development, such as altered patterns of sedimentation, nutrient enrichment through sewage and agricultural run-off, and are affected by coastal dredging and aquaculture. The consequences of increasing sea surface temperatures and fundamental changes in the carbon chemistry of seawater due to CO2 emissions from anthropogenic activities will have serious impacts on calcifying macroalgae. It is not yet understood how interactions between a range of variables acting at local and global scales will influence the viability of calcifying macroalgae and associated ecosystems. Research is urgently needed on all aspects of the taxonomy, biology and functional ecology of calcifying macroalgae. Without an understanding of the species present, measurement of change and understanding species-specific responses will not be possible.
Aquatic angiosperms are derived from terrestrial ancestors and appear to have re-invaded water on many occasions. While removing problems of water supply and reducing the need for supporting tissue, freshwaters have a potentially low and fluctuating supply of CO2 for photosynthesis, as well as generally low light. This paper reviews the structural, morphological, physiological, and biochemical features of freshwater macrophytes in the context of maximising net carbon uptake underwater, and discusses how inorganic carbon may influence macrophyte ecology. Submerged leaves tend to have a low photosynthetic capacity on an area basis, matching the low rates of supply of CO2 and light. Morphological and structural strategies to overcome potential carbon limitation include possession of aerial or floating leaves, and lacunal connexions to high concentrations of sedimentary CO2 via the roots. Physiological and biochemical strategies include crassulacean acid metabolism, C4-like metabolism in Hydrilla and Egeria, and the ability to use HCO3–. The activity of all these can be regulated by environmental conditions to maximize growth rate. Use of HCO3–. is the most widespread carbon acquisition strategy, present in about half of the tested submerged angiosperms. It is more common in lakes of high alkalinity and in the elodeid growth form.
http://www.nhm.ac.uk/business-centre/publishing/books/botany/seaweeds/index.html
Coral communities worldwide are undergoing intense degradation in response to natural and human distur- bances, and many reef systems have already experienced significant declines in live coral cover associated with an increase in macroalgal abundance. Here, we document the seasonal dynamics of the macroalgal communities of the Northern Florida Reef Tract, providing a baseline for long-term studies of coral-algal competition in the area. Both macroalgal biomass and percent cover on reefs showed an increasing trend from January to July, when both light and temperature conditions were favorable for growth. Maximum percent cover (56.7 %) was found in July and minimum levels in December (25.8 %). During these peaks in algal cover, many corals were completely covered by dense mats of algae. Two genera, Halimeda and Dictyota, represented the largest proportion (77299 %) of the total algal biomass. In the summer, Dictyota spp. dominated the algal com- munity, occupying up to 40 % of the reef bottom with a dry biomass of up to 20 g.m22. In addition, two species, Stypopodium zonale and Trichogloea requienii, showed a significant bloom in April 1998, covering a significant percentage of the bottom (up to 25 %) at an inshore reef. Species that exhibited rapid space monopolization on Florida reefs, such as Dictyota spp. and Stypopodium zonale, also showed rapid growth in microcosm and field growth studies. No correlations were found between fish grazer abundance and algal biomass or percent cover, indicating that present grazer population abundance and composition are not adequate to prevent space monopolization and coral overgrowth by algae such as Dictyota spp. and Halimeda spp. Only a continued monitoring effort will determine whether the seasonal dynamics of the algal community may result in the decline of coral populations in the Northern Florida Reef Tract.
The acid base relations of plant (including algal) environments are complex, comprising geological processes as modified by biology including, especially over the last 200 years, man. Some habitats (e.g. high intertidal rockpools and some freshwater bodies) have pH variations of up to three units over a did l cycle as a result of photosynthesis and respiration. Other habitats, e.g. nutrient-poor open ocean habitats, have did l variations that are more than an order of magnitude smaller. Anthropogenic influences on acid base relations of different habitats include the input to the atmosphere of gases that dissolve to produce acidic solutions. The quantitatively predominant gas is CO2, but SO2, NOx and NHy (via nitrification) can also be significant. The influence of the acidic gases in aquatic habitats (including the upper layers of peat bogs) and on terrestrial photosynthetic organisms alters the inorganic carbon speciation and pH around the photosynthetic cells. The calcified coralline marine red macroalgae, with benthic and unattached (maerl) life forms, have extracellular calcification; their calcification rate will decline in the future, with a more CO2-rich ocean and decreasing CO32- concentrations. The marine planktonic coccolithophores have intracellular calcification, though the coccoliths themselves occur externally. While many coccolithophores show decreased calcification with increasing external CO2 and the attendant decrease in external CO32-, this is not universal. For both coralline red algae and coccolithophores the external CaCO3 will dissolve when seawater becomes undersaturated with respect to the relevant crystal form of CaCO3. Overall, the effects of increased CO2 alone are negligible or result in increased growth of non-calcified algae, while there is most generally a decreased growth of calcified algae.
The primary productivity of four species of crustose coralline algae was measured as a function of depth (0-18 m) and irradiance on samples collected from and growing upon the windward coral reef at Lizard Island, northern Great Barrier Reef, Australia. Significantly higher productivities were measured in the field than in the laboratory. Maximum gross oxygen production in situ varied from 12.8 to 22.8 mmol m(-2) h(-1); dark respiration consumed between 2.7 and 4.5 mmol O-2 m(-2) h(-1). Integration of photosynthesis-irradiance models with half sine curve approximations of whole-day iffadiance yielded estimated in situ net productivities of 15-132 mmol O-2 m(-2) d(-1). When multiplied by previously determined photosynthetic quotients, in situ net carbon fixation was estimated to vary from 0.2 to 1.3 g m(-2) d(-1). Multiplying these rates by measured surface relief factors of 3.1 for the reef crest and 5.0 for the windward slope yielded estimated contributions to reef organic production of 0.9-5 g C (net) planar m(-2) d(-1) over the depth interval 0-18 m, given 100% cover. These data suggest that crustose coralline algae make a larger contribution to organic production on coral reefs than has been thought to this time. A curvilinear model is presented that enables their primary productivity to be estimated from measurements of in situ irradiance at the solar zenith.
... dioxide in the atmosphere and Chamberlin2 suggested a variety of geological processes that could affect atmospheric carbon dioxide concentra- tions ... established values for surface ocean pH and alkalinity, it is possible to calculate aqueous CO2 and atmospheric pCO2. ...
At light saturation, rate of photosynthesis increased with temperature to a maximum at 30oC (temperature optimum), then decreased sharply. At lower light intensities the temperature optimum decreased. The initial slope of the photosynthesis-irradiance curve was similar at temperatures from 5-30oC but was reduced at 35oC. The irradiance at light saturation and at the light compensation point increased linearly with temperature from 5-30oC and 5-35oC, respectively. The increased compensation irradiance at higher temperatures implies that H. tasmanica has a greater light requirement during summer and is more susceptible to short-term decreases in irradiance levels during summer than during winter. -from Author
In algae and cyanobacteria, calcification is always associated with biosynthetic products and, where analyses have been made, these products have been found to consist predominantly of polysaccharide, although no specific polymer seems to be associated with calcification. Two aspects of the mineralization merit special consideration: photosynthesis has long been considered the main driving force causing a depletion in aqueous carbon dioxide and an increase in CO32−. Photosynthesis will always favour calcification and the magnitude of the effect will depend upon photosynthetic rates and the lengths of diffusion paths for the ions and molecules involved in calcification. Second, at the ocean surface the precipitation of calcium carbonate is thermodynamically favoured even in the absence of photosynthesis, which may indicate either a widespread evolution of calcification inhibitors or absence of suitable catalysts. Today, the majority of aquatic plants remain uncalcified.
The concentration of CO2 ([CO2]) in the atmosphere is projected to exceed 550 ppm by 2050. C3 plants respond directly to growth at elevated [CO2] by stimulation of photosynthesis and reduced stomatal conductance. The stimulation of photosynthesis is the result of increased velocity of carboxylation of CO2 by Rubisco and inhibition of the competing oxygenation reaction. Long-term exposure of C3 plants to elevated [CO2] can also lead to photosynthetic acclimation in which allocation of resources to components of the photosynthetic machinery, including Rubisco, is altered to optimize metabolic efficiency. The decrease in stomatal conductance that occurs in all plants at elevated [CO2] can reduce canopy water use and indirectly enhance carbon gain by ameliorating drought stress. However, canopy micrometeorology constrains reductions in water use at the whole-plant level compared to the leaf level. C4 photosynthesis is not directly stimulated by free-air concentration enrichment (FACE) of CO2 in the field. However, reduced water use can indirectly enhance carbon gain by ameliorating stress in times and places of drought. There are commonalities and important distinctions between plant responses to growth at elevated [CO2] under FACE versus controlled environment chambers. In FACE experiments: (1) the enhancement of photosynthesis and productivity by elevated [CO2] is sustained over time; (2) the decrease in carboxylation capacity and leaf N characteristic of photosynthetic acclimation to elevated [CO2] is consistent with an optimization of metabolic efficiency rather than a general down-regulation of metabolism, and (3) the enhancement effect of elevated [CO2] is greatest for photosynthesis, intermediate for biomass accumulation, and lowest for crop yield. Plant responses to elevated [CO2] have the potential to influence the global carbon cycle and climate in the future, but the complexity of scaling from the leaf to whole plant, canopy, ecosystem and biosphere make it unclear to what extent this will be realized. Elevated [CO2] will probably offset some of the future losses in crop yield caused by increased temperature and drought stress, but not to the extent previously thought. Expanding FACE experimentation to consider multiple elements of global change across a wider geographic range and more ecosystem types should be a priority if we are to minimize the problems, and maximize the benefits, of climate change impacts on ecosystem good and services.
Publisher Summary This chapter discusses the morphological and cytological aspects of algal calcification. The deposition of calcium salts may occur either extra, inter, or intracellularly. The calcium carbonate is deposited as either the aragonite or the calcite crystal isomorph, and mixtures of the two isomorphs do not occur. The CaCO 3 -impregnated cell walls in algae make them important sediment and reef-forming organisms. The cell walls of vegetative cells, with the exception of the walls of the genicula, hair cells, and the walls of some cells surrounding the conceptacles, contain extensive deposits of the calcite crystal isomorph of CaCO 3 mixed with some magnesium carbonate. Crystal formation basically requires two steps— namely, crystal nucleation and crystal growth (crystallization). Algae, in general, secrete a wide range of organic molecules, and it is possible that these molecules inhibit CaCO 3 nucleation and therefore, calcification. Calcium carbonate is not the only mineral deposit formed by algae. Aside from the large and delicately sculpted deposits of silica formed by diatoms and some other algae, algae also deposits calcium oxalate, barium sulfate, and more rarely other mineral salts.
The calcium carbonate deposits of Cyanophyte, Charophyte, Chlorophyte, Phaeophyte and Rhodophyte algae have been studied with the scanning electron microscope. The SEM permitted in situ observation of these deposits, which allowed the crystal structure and the organization of the crystalline deposits to be observed. The CaCO3 was deposited either as argonite or calcite. The CaCO3 depositing algae can be grouped into three major groups according to the organization and site of deposition of the crystals. The first group (Group A) exhibits extreme organization and the CaCO3 is deposited on an organic matrix within the cell. The deposits of algae of Group B are formed within the cell wall or mucilage and also show some organization. The deposits of algae of Group C are completely extracellular and exhibit no organization.
The algae examined at Pivers Island, Beaufort, were the Chlorophytan Codium fragile var. tomentosoides, and four Phaeophytans: Dictyota dichotoma, Padina vickersii (Dictyotales), Sargassum filipendula (Fucales: Sargassaceae) and Fucus vesiculosus (Fucales: Fucaceae). The intertidal F. vesiculosus differs from the other four, subtidal algae in the C4-like or CAM-like traits of having a higher affinity for inorganic C (saturated by normal sea-water concentrations), a greater capacity for HCO3- and in the occurrence of low-amplitude CAM-like diel changes in titratable acidity. These characteristics suggest a higher capacity to fix inorganic C from ambient inorganic C on the basis of biomass or tissue N in the intertidal than in the normally submersed algae. They also point out the excess of photosynthetic capacity in the subtidal algae over what can be expressed in full sunlight in normal sea-water inorganic C concentration during steady state photosynthesis. Natural abundance 13C/12C ratio measurements on S. filipendula (haptophytic) with a pleustophytic Sargassum sp. from the Gulf Stream are consistent with greater boundary layer limitation on inorganic C acquisition for the pleustophyte. -from Authors
Extracellular calcification by the giant celled alga Chara corallina may involve active Ca2+ extrusion from the cell in exchange for protons. The following evidence is presented: CaCO3 incrustations accrete largely along the inside, facing the cell, as revealed by X-ray microanalysis using Sr2+ and Mn2+ as tracers for new mineralization. Inward proton currents are inhibited by the Ca2+ transport antagonists Gd3+ and La3+. Low Ca2+ concentrations inhibit pH banding and photosynthesis, and solutions of low Ca2+ activity support more photosynthesis in the presence of additional buffered calcium. The ratio of calcification to photosynthesis in moderately alkaline solutions containing sufficient calcium remains stable at about 1.0 independent of solution Ca2+ concentration. Ion specific microelectrodes placed close to the calcified surface sometimes detect increases in Ca2+ activity coincident with decreases in proton activity. As the pCa of solution increases, the maximum pH observed at the alkaline surface increases, as does the maximum solution pH which supports electrochemical currents by the cell. Combinations of extracellular pH and pCa approach the calculated thermodynamic limits for ATP driven 2 H+/ Ca2+ exchange against the cytosol.
Numerous methods have been employed to ascertain whether Ascophyllum nodosum exhibits the characteristics of photorespiration. Different oxygen concentrations appear to have little effect on the apparent rate of photosynthesis, the alga displays low CO2 compensation points in air and water, postillumination CO2 bursts (and O2 ‘gulps’) were not observed in either environment, and ¹⁴CO2 evolution into a CO2-free atmosphere was inhibited in the light compared with that observed in the dark. Suggestions that photosynthetic quotients can be used as an indicator of the photorespiratory state were found to be unsuitable as determinations of the total inorganic carbon concentration from pH measurements were found to be inconsistent which resulted in variable apparent photosynthetic quotient values. Thus photorespiration is suppressed in Ascophyllum nodosum and it is suggested that the mechanism is based on an inorganic carbon transport pump.
The deposition of CaCO3 by algae (calcification) is a widespread phenomenon and the deposits of either aragonite or calcite may be extra‐, inter‐, or intracellular. This variability in location and crystal isomorph suggests that different calcification mechanisms operate in different algal groups. Despite this difference, all algal calcification systems have some common features. These include the need for a suitable CaCO3‐crystal nucleation mechanism and the stimulation of calcification by photosynthesis. The physiology and biochemistry of algal calcification are discussed in relation to the above processes and compared to noncalcareous algae.
The severity of the impact of elevated atmospheric pCO2 to
coral reef ecosystems depends, in part, on how seawater pCO2
affects the balance between calcification and dissolution of carbonate
sediments. Presently, there are insufficient published data that relate
concentrations of pCO2 and CO32-
to in situ rates of reef calcification in natural settings to accurately
predict the impact of elevated atmospheric pCO2 on
calcification and dissolution processes. Rates of net calcification and
dissolution, CO32- concentrations, and
pCO2 were measured, in situ, on patch reefs, bare sand, and
coral rubble on the Molokai reef flat in Hawaii. Rates of calcification
ranged from 0.03 to 2.30 mmol CaCO3 m-2
h-1 and dissolution ranged from -0.05 to -3.3 mmol
CaCO3 m-2 h-1.
Calcification and dissolution varied diurnally with net calcification
primarily occurring during the day and net dissolution occurring at
night. These data were used to calculate threshold values for
pCO2 and CO32- at which rates of
calcification and dissolution are equivalent. Results indicate that
calcification and dissolution are linearly correlated with both
CO32- and pCO2. Threshold
pCO2 and CO32- values for
individual substrate types showed considerable variation. The average
pCO2 threshold value for all substrate types was
654±195 μatm and ranged from 467 to 1003 μatm. The average
CO32- threshold value was 152±24
μmol kg-1, ranging from 113 to 184 μmol
kg-1. Ambient seawater measurements of pCO2
and CO32- indicate that
CO32- and pCO2 threshold values
for all substrate types were both exceeded, simultaneously, 13% of the
time at present day atmospheric pCO2 concentrations. It is
predicted that atmospheric pCO2 will exceed the average
pCO2 threshold value for calcification and dissolution on the
Molokai reef flat by the year 2100.
The acid—base relations of plant (including algal) environments are complex, comprising geological processes as modified by biology including, especially over the last 200 years, man. Some habitats (e.g. high intertidal rockpools and some freshwater bodies) have pH variations of up to three units over a diel cycle as a result of photosynthesis and respiration. Other habitats, e.g. nutrient-poor open ocean habitats, have diel variations that are more than an order of magnitude smaller. Anthropogenic influences on acid—base relations of different habitats include the input to the atmosphere of gases that dissolve to produce acidic solutions. The quantitatively predominant gas is CO 2 , but SO 2 , NO x and NH y (via nitrification) can also be significant. The influence of the acidic gases in aquatic habitats (including the upper layers of peat bogs) and on terrestrial photosynthetic organisms alters the inorganic carbon speciation and pH around the photosynthetic cells. The calcified coralline marine red macroalgae, with benthic and unattached (maerl) life forms, have extracellular calcification; their calcification rate will decline in the future, with a more CO 2 -rich ocean and decreasing CO 3 2- concentrations. The marine planktonic coccolithophores have intracellular calcification, though the coccoliths themselves occur externally. While many coccolithophores show decreased calcification with increasing external CO 2 and the attendant decrease in external CO 3 2- , this is not universal. For both coralline red algae and coccolithophores the external CaCO 3 will dissolve when seawater becomes undersaturated with respect to the relevant crystal form of CaCO 3 . Overall, the effects of increased CO 2 alone are negligible or result in increased growth of non-calcified algae, while there is most generally a decreased growth of calcified algae.
Experiments on short-term photosynthesis in H(14)CO3 (-) (2-5 s) using various species of different algal classes resulted in predominant (14)C-labelling (>90% of total (14)C-incorporation) of phosphorylated compounds. The percentage of malate and aspartate usually accounts for distinctly less than 10% of the total (14)C-labelling. These findings are consistent with data from enzymatic analyses, since 97-100% of the carboxylation capacity is due to ribulose-1.5-biphosphate carboxylase (EC 4.1.1.39) in Rhodophyceae and Chlorophyceae. Phaeophyceae are generally characterized by considerable activity of phosphoenolpyruvate carboxykinase (EC 4.1.1.32): at least 10% of carboxylation is confined to this enzyme. Similar ratios are obtained when rates of photosynthesis and of light-independent CO2-fixation are compared. Activity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) could not be detected in the species investigated. The results are discussed with emphasis on the pathway of photosynthetic carbon assimilation in marine algae.
The Mediterranean Sea, one of the regions warming fastest under climate
change, harbours lush seagrass (Posidonia oceanica) meadows that form
the basis for a key ecosystem in the region. Recent field results have
shown that increased maximum annual seawater temperature in the
Mediterranean has already led to increased seagrass mortality. Here we
project the trajectory of P. oceanica meadows under the warming expected
in the western Mediterranean through the twenty-first century to
conclude that warming will lead to the functional extinction of P.
oceanica meadows by the middle of this century (year 2049+/-10) even
under a relatively mild greenhouse-gas emissions scenario. Efforts to
alleviate local stresses adding to the loss of P. oceanica meadows will
have a limited effect in conserving the meadows under climate change.
Efforts to mitigate climate change are urgently needed to preserve this
key ecosystem.
The influence of Mg2+ ions on the ion-activity product of calcium and carbonate dissolved in seawater has been investigated. The present approach is based mainly on: (1) the preponderance of this element in the marine system; (2) the observations by Weyl (1965), Jansen and Kitano (1963), and more recently by Plummer and Mackenzie (1974) on the higher solubility of magnesian calcite relative to pure calcite; and (3) the inferences drawn from our laboratory studies on the Ca2+—Mg2+ ion-exchange behaviour on surfaces of pure calcite. From these considerations, the pK value corresponding to a calcite containing 12 mole% of MgCO, has been estimated to be 7.7± 0.1 at 20°C. This value has serious reflections on the extent of saturation of seawater with respect to calcium-carbonate polymorphs. The reassessed degree of carbonate saturation for an average warm-surface ocean turns out to be only between 1.0 and 2.2.
The photosynthetic capacity of submerged Ulva sp. when utilizing CO2 and HCO−3 as exogenous carbon forms has been investigated and compared with ambient carbon concentrations in sea water. Saturating concentrations of HCO− 3 and CO2 were 1200 and 100 μM, respectively at saturating light, and photosynthetic rates under such conditions averaged 700 μmolO2·gDW−1 ·h−1. The HCO−3 concentration of sea water (≈2500μM), was thus found to be saturating for photosynthesis of Ulva. At the CO2 concentration of sea water (≈ 10 μM), the contribution of this carbon form to photosynthesis could be 27% at the most. Under conditions of slow water movement, the relative importance of CO2 utilization would probably be minimized in favour of HCO−3 utilization. It is concluded that HCO−3 uptake is not limiting photosynthesis for Ulva under natural conditions.
Six marine macroalgae and two angiosperms were examined for their ability to use HCO
3-and CO2 for photosynthesis. All species used HCO
3-despite wide taxonomic differences. They also used HCO
3-with high affinity: natural HCO
3-concentrations (2.2 mM) were close to saturation, and the apparent half-saturation constants were low, i.e. K1/2 (HCO
3-)=0.54 to 0.80 mM HCO
3-. Expressed as a ratio, the affinity for CO2 relative to HCO
3-under rate-limiting concentrations was about 2 for the marine species compared to much higher values, 5.4 to 101, among freshwater species examined previously. This difference was due to a higher affinity for HCO
3-among marine species, whereas the affinity for CO2 was in the same range for marine and freshwater species, i.e. K1/2 (CO2)=0.08 to 0.30 mM. The high affinity for HCO
3-of marine species is consistent with the high and constant availability of HCO
3-and the low availability of CO2 in seawater. In freshwaters, availability of HCO
3-and CO2 varies considerably, depending on habitat. The difference in HCO
3-affinity may be due to different electrogenic ionpumps and thus mechanisms of HCO
3--use, operating in freshwater and marine species. Photosynthetic rates in natural seawater were close to maximum at atmospheric equilibrium (pH 8.2 to 8.4) and declined at high pH approaching zero between pH 9.5 and 10.5. This reduction may be due to the conversion of HCO
3-to CO
3-, followed by CaCO3 precipitation, and/or to a direct pH-effect. Ulva lactuca and Enteromorpha sp. retained photosynthetic activity at the highest pH tested (10.5), consistent with the high pH recorded in mats of these species.
The effects of total dissolved inorganic carbon (DIC), free carbon dioxide [CO2(aq)], and bicarbonate (HCO
3-) concentrations on net photosynthetic oxygen evolution of the marine angiosperm Thalassia testudinum Banks ex König collected from Biscayne Bay (1988) and from Tampa Bay (1990), Florida, USA, were examined. Rates of photosynthesis declined by 85% from pH 7.25 to 8.75 in buffered seawater media with constant DIC concentration (2.20 mM), suggesting a strong influence of CO2(aq) concentration. A plateau in the pH-response curve between pH 7.75 and 8.50 indicated possible utilization of HCO
3-. Responses of photosynthesis measured in buffered seawater media of varying DIC concentrations (0.75 to 13.17 mM) and pH (7.8 to 8.61) demonstrated that photosynthesis is rate-limited at ambient DIC levels. Photosynthesis increased in media with increasing HCO
3-concentrations but near-constant CO2(aq) levels, confirming HCO
3-assimilation. Calculated half-saturation constants (K
s
)for CO2(aq) and HCO
3-indicated a high affinity for the former [K
s
(CO2)=3 to 18 μM] and a much lower affinity for the latter [K
s
(HCO
3-)=1.22 to 8.88 mM]. Calculated V
max values for HCO
3-were generally higher than those for CO2(aq), suggesting relatively efficient HCO
3-utilization, despite the apparent low affinity for this carbon form.
The effects of elevated CO2 and temperature on photosynthesis and calcification in the calcifying algae Halimeda macroloba and Halimeda cylindracea and the symbiont-bearing benthic foraminifera Marginopora vertebralis were investigated through exposure to a combination of four temperatures (28 degrees C, 30 degrees C, 32 degrees C, and 34 degrees C) and four CO2 levels (39, 61, 101, and 203 Pa; pH 8.1, 7.9, 7.7, and 7.4, respectively). Elevated CO2 caused a profound decline in photosynthetic efficiency (F-V : F-M), calcification, and growth in all species. After five weeks at 34 degrees C under all CO2 levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. significantly decreased in 203 Pa, 32 degrees C and 34 degrees C treatments, but Chl a and Chl c(2) concentration in M. vertebralis was not affected by temperature alone, with significant declines in the 61, 101, and 203 Pa treatments at 28 degrees C. Significant decreases in F-V : F-M in all species were found after 5 weeks of exposure to elevated CO2 (203 Pa in all temperature treatments) and temperature (32 degrees C and 34 degrees C in all pH treatments). The rate of oxygen production declined at 61, 101, and 203 Pa in all temperature treatments for all species. The elevated CO2 and temperature treatments greatly reduced calcification (growth and crystal size) in M. vertebralis and, to a lesser extent, in Halimeda spp. These findings indicate that 32 degrees C and 101 Pa CO2, are the upper limits for survival of these species on Heron Island reef, and we conclude that these species will be highly vulnerable to the predicted future climate change scenarios of elevated temperature and ocean acidification.
The primary productivity of four species of crustose coralline algae was measured as a function of depth (0-18 m) and irradiance on samples collected from and growing upon the windward coral reef at Lizard Island, northern Great Barrier Reef, Australia. Significantly higher productivities were measured in the field than in the laboratory. Maximum gross oxygen production in situ varied from 12.8 to 22.8 mmol m 22 h 21 ; dark respiration consumed between 2.7 and 4.5 mmol O2 m 22 h 21 . Integration of photosynthesis-irradiance models with half sine curve ap- proximations of whole-day irradiance yielded estimated in situ net productivities of 15-132 mmol O2 m 22 d 21 . When multiplied by previously determined photosynthetic quotients, in situ net carbon fixation was estimated to vary from 0.2 to 1.3 g m 22 d 21 . Multiplying these rates by measured surface relief factors of 3.1 for the reef crest and 5.0 for the windward slope yielded estimated contributions to reef organic production of ;0.9-5 g C (net) planar m 22 d 21 over the depth interval 0-18 m, given 100% cover. These data suggest that crustose coralline algae make a larger contribution to organic production on coral reefs than has been thought to this time. A curvilinear model is presented that enables their primary productivity to be estimated from measurements of in situ irradiance at the solar zenith.
A generalized physicochemical model of the response of marine organisms’ calcifying fluids to CO2-induced ocean acidification is proposed. The model is based upon the hypothesis that some marine calcifiers induce calcification by elevating pH, and thus ΩA, of their calcifying fluid by removing protons (H+). The model is explored through two end-member scenarios: one in which a fixed number of H+ is removed from the calcifying fluid, regardless of atmospheric pCO2, and another in which a fixed external–internal H+ ratio ([H+]E/[H+]I) is maintained. The model is able to generate the full range of calcification response patterns observed in prior ocean acidification experiments and is consistent with the assertion that organisms’ calcification response to ocean acidification is more negative for marine calcifiers that exert weaker control over their calcifying fluid pH. The model is empirically evaluated for the temperate scleractinian coral Astrangia poculata with in situ pH microelectrode measurements of the coral’s calcifying fluid under control and acidified conditions. These measurements reveal that (1) the pH of the coral’s calcifying fluid is substantially elevated relative to its external seawater under both control and acidified conditions, (2) the coral’s [H+]E/[H+]I is approximately the same under control and acidified conditions, and (3) the coral removes fewer H+ from its calcifying fluid under acidified conditions than under control conditions. Thus, the carbonate system dynamics of A. poculata’s calcifying fluid appear to be most consistent with the fixed [H+]E/[H+]I end-member scenario. Similar microelectrode experiments performed on additional taxa are required to assess the model’s general applicability.