Seagrass ecosystem is one of the most productive ecosystems in coastal waters providing numerous ecological functions and supporting a large biodiversity. However, various anthropogenic stressors including climate change are impacting these vulnerable habitats. Here, we investigated the independent and combined effects of ocean warming and ocean acidification on plant–herbivore interactions in a tropical seagrass community. Direct and indirect effects of high temperature and high pCO2 on the physiology of the tropical seagrass Thalassia hemprichii and sea urchin Tripneustes gratilla were evaluated. Productivity of seagrass was found to increase under high pCO2, while sea urchin physiology including feeding rate decreased particularly under high temperature. The present study indicated that future climate change will affect the bottom-up and top-down balance, which potentially can modify the ecosystem functions and services of tropical seagrass ecosystems.
Ocean acidification (OA) is negatively affecting calcification in a wide variety of marine organisms. These effects are acute for many tropical scleractinian corals under short-term experimental conditions, but it is unclear how these effects interact with ecological processes, such as competition for space, to impact coral communities over multiple years. This study sought to test the use of individual-based models (IBMs) as a tool to scale up the effects of OA recorded in short-term studies to community-scale impacts, combining data from field surveys and mesocosm experiments to parameterize an IBM of coral community recovery on the fore reef of Moorea, French Polynesia. Focusing on the dominant coral genera from the fore reef, Pocillopora, Acropora, Montipora and Porites, model efficacy first was evaluated through the comparison of simulated and empirical dynamics from 2010–2016, when the reef was recovering from sequential acute disturbances (a crown-of-thorns seastar outbreak followed by a cyclone) that reduced coral cover to ~0% by 2010. The model then was used to evaluate how the effects of OA (1,100–1,200 µatm pCO2) on coral growth and competition among corals affected recovery rates (as assessed by changes in % cover y−1) of each coral population between 2010–2016. The model indicated that recovery rates for the fore reef community was halved by OA over 7 years, with cover increasing at 11% y−1 under ambient conditions and 4.8% y−1 under OA conditions. However, when OA was implemented to affect coral growth and not competition among corals, coral community recovery increased to 7.2% y−1, highlighting mechanisms other than growth suppression (i.e., competition), through which OA can impact recovery. Our study reveals the potential for IBMs to assess the impacts of OA on coral communities at temporal and spatial scales beyond the capabilities of experimental studies, but this potential will not be realized unless empirical analyses address a wider variety of response variables representing ecological, physiological and functional domains.
Global change driven by anthropogenic carbon emissions is altering ecosystems at unprecedented rates, especially coral reefs, whose symbiosis with algal endosymbionts ise particularly vulnerable to increasing ocean temperatures and altered carbonate chemistry. Here, we assess the physiological responses of the coral holobiont (animal host + algal symbiont) of three Caribbean coral species from two reef environments after exposure to simulated ocean warming (28, 31 °C), acidification (300 – 3290 μatm), and the combination of stressors for 93 days. We used multidimensional analyses to assess how multiple coral holobiont physiological parameters respond to ocean acidification and warming. Our results demonstrate significantly diminishing holobiont physiology in S. siderea and P. astreoides in response to projected ocean acidification, while future warming elicited severe declines in P. strigosa. Offshore S. siderea fragments exhibited higher physiological plasticity than inshore counterparts, suggesting that this offshore population has the capacity to modulate their physiology in response to changing conditions, but at a cost to the holobiont. Plasticity of P. strigosa and P. astreoides was not clearly different between natal reef environments, however, temperature evoked a greater plastic response in both species. Interestingly, while these species exhibit unique physiological responses to ocean acidification and warming, when data from all three species are modeled together, convergent stress responses to these conditions are observed, highlighting the overall sensitivities of tropical corals to these stressors. Our results demonstrate that while ocean warming is a severe acute stressor that will have dire consequences for coral reefs globally, chronic exposure to acidification may also impact coral physiology to a greater extent than previously assumed. The variety of responses to global change we observe across species will likely manifest in altered Caribbean reef assemblages in the future.
Coccolithophores are unicellular phytoplanktonic organisms characterized by a covering of calcite plates, the coccoliths, which are produced intracellularly. These calcifiers, as one of the main planktonic functional groups, play an important role in the inorganic carbon cycle and possibly as ballast that sinks organic carbon to the deep-sea. Most efforts to understanding coccolithophore response to ocean acidification (OA) –or the raise in atmospheric CO2 reduces ocean pH and saturation states (Ω) of CaCO3– have been through lab experiments, mostly using a small set of strains of the cosmopolitan, easily cultivated species Emiliania huxleyi. This species is especially interesting because it is young (~ 291,000 years) and has adapted to a wide range of marine environments. However, it is not the only coccolithophore and even within that species there is a lot of phenotypic and genetic diversity and diverse responses to OA in the lab. Despite the efforts made it is unclear how the physiological effects under controlled conditions translate to community-level responses in the field. This thesis aimed to contribute to understanding this issue by studying the distribution, composition and realized niches of coccolithophore assemblages and E. huxleyi morphotypes in contrasting pCO2/pH/Ωcalcite environments of the Eastern South Pacific, and to evaluate the responses of different E. huxleyi23 morphotypes to targeted pCO2/pH levels set in the lab. For this, the coccolithophores were surveyed in a coastal-oceanic section, mesotrophic waters, upwelling systems, and fjords-channels of Patagonia. From a total of 40 species, E. huxleyi was the most prevalent (30-100 % relative abundance). Within this taxon, several morphotypes has been described as stable in culture and genetically differentiated (e.g., the A and R morphotypes). The moderately-calcified A morphotype dominated the E. huxleyi populations being only surpassed by the R hyper-calcified morphotype in upwelling systems with high pCO2/low pH. This abrupt shift in the composition of E. huxleyi populations suggested that these coastal environments hold genetic reservoirs for their adaptation to OA. Therefore, the hypothesis was tested that these forms are adapted to resist high pCO2/low pH conditions. Unexpectedly, the morphotypes from the Eastern South Pacific were not more sensitive than the R hyper-calcified strains from neighboring high pCO2/low pH waters (lowering growth rates and PIC/POC ratios). On the other hand, realized-niche analysis showed that the A morphotype has a broader niche that is more tolerant to environmental-change (i.e., generalist) than the R morphotype’s niche, specialized to high pCO2/low pH waters. The lack of evidence for local adaptation to high pCO2/low pH conditions in E. huxleyi, might be explained by a narrow unimodal niche response to Ωcalcite revealed by niche analysis that was not tested experimentally. Alternatively, the R hyper-calcified morphotype might be selected by an unidentified condition particular to the Eastern South Pacific that correlates with temperature, salinity, and Ωcalcite of its realized-niche. Overall, despite their rapid turnover and large population sizes, oceanic planktonic microorganisms do not necessarily exhibit adaptations to high-pCO2 upwelled waters, and this ubiquitous coccolithophore may be near the limit of its capacity to adapt to ongoing OA.
Symbiosis establishment is a milestone in the life cycles of most broadcast-spawning corals; however, it remains largely unknown how initial symbiont infection is affected by ocean warming and acidification, particularly for massive corals. This study investigated the combined effects of elevated temperature (29 vs. 31 °C) and pCO2 (~ 450 vs. ~ 1000 μatm) on the recruits of a widespread massive coral, Platygyra daedalea. Results showed that geometric diameter and symbiosis establishment were unaffected by high pCO2, while elevated temperature significantly reduced successful symbiont infection by 50% and retarded the geometric diameter by 6%. Although neither increased temperature, pCO2, nor their interaction affected survival or algal pigmentation of recruits, there was an inverse relationship between symbiont infection rates and survivorship, especially at high temperatures, possibly as a result of oxidative stress caused by algal symbionts under increased temperature. Intriguingly, the proportion of Durusdinium did not increase in recruits at 31 °C, while recruits reared under high pCO2 hosted less Breviolum and more Durusdinium, indicating a high degree of plasticity of early symbiosis and contrasting to the previous finding that heat stress usually leads to the prevalence of thermally tolerant Durusdinium in coral recruits. These results suggest that ocean warming is likely to be more deleterious for the early success of P. daedalea than ocean acidification and provide insights into our understanding of coral-algal symbiotic partnerships under future climatic conditions.
The sponge-associated microbial community contributes to the overall health and adaptive capacity of the sponge holobiont. This community is regulated by the environment and the immune system of the host. However, little is known about the effect of environmental stress on the regulation of host immune functions and how this may, in turn, affect sponge–microbe interactions. In this study, we compared the bacterial diversity and immune repertoire of the demosponge, Neopetrosia compacta, and the calcareous sponge, Leucetta chagosensis, under varying levels of acidification and warming stress based on climate scenarios predicted for 2100. Neopetrosia compacta harbors a diverse microbial community and possesses a rich repertoire of scavenger receptors while L. chagosensis has a less diverse microbiome and an expanded range of pattern recognition receptors and immune response-related genes. Upon exposure to RCP 8.5 conditions, the microbiome composition and host transcriptome of N. compacta remained stable, which correlated with high survival (75%). In contrast, tissue necrosis and low survival (25%) of L. chagosensis was accompanied by microbial community shifts and downregulation of host immune-related pathways. Meta-analysis of microbiome diversity and immunological repertoire across poriferan classes further highlights the importance of host–microbe interactions in predicting the fate of sponges under future ocean conditions.
Ocean acidification has been broadly recognised to have effects on the structure and functioning of marine benthic communities. The selection of tolerant or vulnerable species can also occur during settlement phases, especially for calcifying organisms which are more vulnerable to low pH–high pCO2 conditions. Here, we use three natural CO2 vents (Castello Aragonese north and south sides, and Vullatura, Ischia, Italy) to assess the effect of a decrease of seawater pH on the settlement of Mollusca in Posidonia oceanica meadows, and to test the possible buffering effect provided by the seagrass. Artificial collectors were installed and collected after 33 days, during April–May 2019, in three different microhabitats within the meadow (canopy, bottom/rhizome level, and dead matte without plant cover), following a pH decreasing gradient from an extremely low pH zone (pH < 7.4), to ambient pH conditions (pH = 8.10). A total of 4659 specimens of Mollusca, belonging to 57 different taxa, were collected. The number of taxa was lower in low and extremely low pH conditions. Reduced mollusc assemblages were reported at the acidified stations, where few taxa accounted for a high number of individuals. Multivariate analyses revealed significant differences in mollusc assemblages among pH conditions, microhabitat, and the interaction of these two factors. Acanthocardia echinata, Alvania lineata, Alvania sp. juv, Eatonina fulgida, Hiatella arctica, Mytilys galloprovincialis, Musculus subpictus, Phorcus sp. juv, and Rissoa variabilis were the species mostly found in low and extremely low pH stations, and were all relatively robust to acidified conditions. Samples placed on the dead matte under acidified conditions at the Vullatura vent showed lower diversity and abundances if compared to canopy and bottom/rhizome samples, suggesting a possible buffering role of the Posidonia on mollusc settlement. Our study provides new evidence of shifts in marine benthic communities due to ocean acidification and evidence of how P. oceanica meadows could mitigate its effects on associated biota in light of future climate change.
Prior to fertilization, mothers provision their oocytes with mRNA that regulates the early stages of development and may additionally include transcripts for proteins that support embryonic stress response early on. At some point during embryogenesis, however, these maternal transcripts are degraded as zygotic transcription activates and intensifies during a phenomenon known as the maternal-to-zygotic transition (MZT). Some evidence suggests that as the MZT progresses, and the effects of maternal transcripts are waning while the zygotic expression is being established, offspring of marine broadcast spawners become more vulnerable to environmental perturbations. In light of escalating threats to marine broadcast spawners, it is critical to understand their reproduction and development, which are essential processes for species resilience by repopulating and replenishing existing populations. Reef building corals, in particular, are under threat from multiple stressors at the local and global scales. Mass mortality has occurred in recent years due to a series of marine heatwaves. In addition, there is chronic stress occurring in the form of ocean acidification, or the decline in pH in surface waters due to the uptake of atmospheric carbon dioxide of anthropogenic origin. Here, we characterize the function of maternal mRNAs, the timeline of the MZT, and sensitivity of gene expression to ocean acidification (OA) in the reef- building coral, Montipora capitata to investigate role of the MZT in embryonic stress response in reef-building corals.
Global change, including rising temperatures and acidification, threatens corals globally. Although bleaching events reveal fine-scale patterns of resilience, traits enabling persistence under global change remain elusive. We conducted a 95-d controlled-laboratory experiment investigating how duration of exposure to warming (~28, 31°C), acidification (pCO2 ~ 343 [present day], ~663 [end of century], ~3109 [extreme] μatm), and their combination influences physiology of reef-building corals (Siderastrea siderea, Pseudodiploria strigosa) from two reef zones on the Belize Mesoamerican Barrier Reef System. Every 30 d, net calcification rate, host protein and carbohydrate, chlorophyll a, and symbiont density were quantified for the same coral individual to characterize acclimation potential under global change. Coral physiologies of the two species were differentially affected by stressors and exposure duration was found to modulate these responses. Siderastrea siderea exhibited resistance to end of century pCO2 and temperature stress, but calcification was negatively affected by extreme pCO2. However, S. siderea calcification rates remained positive after 95 d of extreme pCO2 conditions, suggesting acclimation. In contrast, P. strigosa was more negatively influenced by elevated temperatures, which reduced most physiological parameters. An exception was nearshore P. strigosa, which maintained calcification rates under elevated temperature, suggesting local adaptation to the warmer environment of their natal reef zone. This work highlights how tracking coral physiology across various exposure durations can capture acclimatory responses to global change stressors.
Coral reef community composition, function, and resilience have been altered by natural and anthropogenic stressors. Future anthropogenic ocean and coastal acidification (together termed “acidification”) may exacerbate this reef degradation. Accurately predicting reef resilience requires an understanding of not only direct impacts of acidification on marine organisms but also indirect effects on species interactions that influence community composition and reef ecosystem functions. In this 28-day experiment, we assessed the effect of acidification on coral–algal, coral–sponge, and algal–sponge interactions. We quantified growth of corals (Siderastrea radians), fleshy macroalgae (Dictyota spp.), and sponges (Pione lampa) that were exposed to local summer ambient (603 μatm) or elevated (1105 μatm) pCO2 seawater. These species are common to hard-bottom communities, including shallow reefs, in the Florida Keys. Each individual was maintained in isolation or paired with another organism. Coral growth (net calcification) was similar across seawater pCO2 and interaction treatments. Fleshy macroalgae had increased biomass when paired with a sponge but lost biomass when growing in isolation or paired with coral. Sponges grew more volumetrically in the elevated seawater pCO2 treatment (i.e., under acidification conditions). Although these results are limited in temporal and spatial scales due to the experimental design, they do lend support to the hypothesis that acidification may facilitate a shift towards increased sponge and macroalgae abundance by directly benefiting sponge growth which in turn may provide more dissolved inorganic nitrogen to macroalgae in the Florida Keys.
Oyster microbiomes are integral to healthy function and can be altered by climate change conditions. Genetic variation among oysters is known to influence the response of oysters to climate change and may ameliorate any adverse effects on oyster microbiome, however, this remains unstudied. Nine full-sibling selected breeding lines of the Sydney rock oyster (Saccostrea glomerata) were exposed to predicted warming (ambient = 24°C, elevated = 28°C) and ocean acidification (ambient pCO2 = 400, elevated pCO2 = 1000 µatm) for four weeks. The haemolymph bacterial microbiome was characterised using 16S rRNA (V3-V4) gene sequencing and varied among oyster lines in the control (ambient pCO2, 24°C) treatment. Microbiomes were also altered by climate change dependent on oyster lines. Bacterial α-diversity increased in response to elevated pCO2 in two selected lines, while bacterial β-diversity was significantly altered by combinations of elevated pCO2 and temperature in four selected lines. Climate change treatments caused shifts in the abundance of multiple Amplicon Sequence Variants (ASVs) driving change in the microbiome of some selected lines. We show that oyster genetic background may influence the Sydney rock oyster haemolymph microbiome under climate change and that future assisted evolution breeding programs to enhance resilience should consider the oyster microbiome.
The sponge-associated microbial community contributes to the overall health and adaptive capacity of the sponge holobiont. This community is regulated by the environment, as well as the immune system of the host. However, little is known about the effect of environmental stress on the regulation of host immune functions and how this may, in turn, affect sponge-microbe interactions. In this study, we compared the microbiomes and immune repertoire of two sponge species, the demosponge, Neopetrosia compacta and the calcareous sponge, Leucetta chagosensis, under varying levels of acidification and warming stress. Neopetrosia compacta harbors a diverse bacterial assemblage and possesses a rich repertoire of scavenger receptors while L. chagosensis has a less diverse microbiome and an expanded range of pattern recognition receptors and proteins with immunological domains. Upon exposure to warming and acidification, the microbiome and host transcriptome of N. compacta remained stable, which correlated with high survival. In contrast, the bacterial community of L. chagosensis exhibited drastic restructuring and widespread downregulation of host immune-related pathways, which accompanied tissue necrosis and mortality. Differences in microbiome diversity and immunological repertoire of diverse sponge groups highlight the central role of host-microbe interactions in predicting the fate of sponges under future ocean conditions.
In the oligotrophic waters of the Mediterranean Sea, during the stratification period, the microbial loop relies on pulsed inputs of nutrients through atmospheric deposition of aerosols from both natural (Saharan dust) and anthropogenic origins. While the influence of dust deposition on microbial processes and community composition is still not fully constrained, the extent to which future environmental conditions will affect dust inputs and the microbial response is not known. The impact of atmospheric wet dust deposition was studied both under present and future (warming and acidification) environmental conditions through experiments in 300 L climate reactors. Three dust addition experiments were performed with surface seawater collected from the Tyrrhenian Sea, Ionian Sea and Algerian basin in the Western Mediterranean Sea during the PEACETIME cruise in May–June 2017. Top-down controls on bacteria, viral processes and community, as well as microbial community structure (16S and 18S rDNA amplicon sequencing) were followed over the 3–4 days experiments. Different microbial and viral responses to dust were observed rapidly after addition and were most of the time higher when combined to future environmental conditions. The input of nutrients and trace metals changed the microbial ecosystem from bottom-up limited to a top-down controlled bacterial community, likely from grazing and induced lysogeny. The composition of mixotrophic microeukaryotes and phototrophic prokaryotes was also altered. Overall, these results suggest that the effect of dust deposition on the microbial loop is dependent on the initial microbial assemblage and metabolic state of the tested water, and that predicted warming, and acidification will intensify these responses, affecting food web processes and biogeochemical cycles.
The effects of seagrass on microalgal assemblages under experimentally elevated temperatures (28°C) and CO2 partial pressures (pCO2; 800 μatm) were examined using coral reef mesocosms. Concentrations of nitrate, ammonium, and benthic microalgal chlorophyll a (chl-a) were significantly higher in seagrass mesocosms, whereas phytoplankton chl-a concentrations were similar between seagrass and seagrass-free control mesocosms. In the seagrass group, fewer parasitic dinoflagellate OTUs (e.g., Syndiniales) were found in the benthic microalgal community though more symbiotic dinoflagellates (e.g., Cladocopium spp.) were quantified in the phytoplankton community. Our results suggest that, under ocean acidification conditions, the presence of seagrass nearby coral reefs may (1) enhance benthic primary productivity, (2) decrease parasitic dinoflagellate abundance, and (3) possibly increase the presence of symbiotic dinoflagellates.
Globally, kelp forests are threatened by multiple stressors, including increasing grazing by sea urchins. With coastal upwelling predicted to increase in intensity and duration in the future, understanding whether kelp forest and urchin barren urchins are differentially affected by upwelling-related stressors will give insight into how future conditions may affect the transition between kelp forests and barrens. We assessed how current and future-predicted changes in the duration and magnitude of upwelling-associated stressors (low pH, dissolved oxygen, and temperature) affected the performance of purple sea urchins (Strongylocentrotus purpuratus) sourced from rapidly-declining bull kelp (Nereocystis leutkeana) forests and nearby barrens and maintained on habitat-specific diets. Kelp forest urchins were of superior condition to barrens urchins, with ~ 6–9 times more gonad per body mass. Grazing and condition in kelp forest urchins were more negatively affected by distant-future and extreme upwelling conditions, whereas grazing and survival in urchins from barrens were sensitive to both current-day and all future-predicted upwelling, and to increases in acidity, hypoxia, and temperature regardless of upwelling. We conclude that urchin barren urchins are more susceptible to increases in the magnitude and duration of upwelling-related stressors than kelp forest urchins. These findings have important implications for urchin population dynamics and their interaction with kelp.
Amphibolis antarctica seagrass meadows, and their associated calcifying epiphytes, are abundant on Australia’s west coast, but have declined in recent years due to anthropogenic factors such as marine heatwaves, damaging fishing practices and increased turbidity resulting from eutrophication which causes light limitation. Burning fossil fuels has increased the flux of CO2 in to the ocean, lowering surface seawater pH, and making more carbon available for photosynthetic life. There are benefits of increasing CO2 for those seagrasses that are carbon limited, as this alleviates their energetic use of carbon concentrating mechanisms (CCM’S) which are less efficient, and more energy costly than passive diffusion of CO2 across cell walls. This study used pulse amplitude modulation fluorometry to quantify relative electron transport rates (rETR) at a range of pH levels both above and below current ocean pH of 8.1, and found that A. antarctica has significantly decreased rETR at pH treatments of 7.81 and 7.61. Calcifying epiphytes on A. antarctica also had a significant drop in rETR at the lower pH treatments. There was also significantly lowered rETR at higher pH treatments, likely the result of carbon limitation. These results from the lower pH tests may have profound implications for A. antarctica meadows under ocean acidification. A decline in these meadows would cause the loss of ecosystem services provided by them, such as carbon storage and sequestration, commercial fisheries and a decline the abundance of biodiversity that they support.
Bacteria are essential in the maintenance and sustainment of marine environments (e.g., benthic systems), playing a key role in marine food webs and nutrient cycling. These microorganisms can live associated as epiphytic or endophytic populations with superior organisms with valuable ecological functions, e.g., seagrasses. Here, we isolated, identified, sequenced, and exposed two strains of the same species (i.e., identified as Cobetia sp.) from two different marine environments to different nutrient regimes using batch cultures: (1) Cobetia sp. UIB 001 from the endemic Mediterranean seagrass Posidonia oceanica and (2) Cobetia sp. 4B UA from the endemic Humboldt Current System (HCS) seagrass Heterozostera chilensis. From our physiological studies, both strains behaved as bacteria capable to cope with different nutrient and pH regimes, i.e., N, P, and Fe combined with different pH levels, both in long-term (12 days (d)) and short-term studies (4 d/96 h (h)). We showed that the isolated strains were sensitive to the N source (inorganic and organic) at low and high concentrations and low pH levels. Low availability of phosphorus (P) and Fe had a negative independent effect on growth, especially in the long-term studies. The strain UIB 001 showed a better adaptation to low nutrient concentrations, being a potential N2-fixer, reaching higher growth rates (μ) than the HCS strain. P-acquisition mechanisms were deeply investigated at the enzymatic (i.e., alkaline phosphatase activity, APA) and structural level (e.g., alkaline phosphatase D, PhoD). Finally, these results were complemented with the study of biochemical markers, i.e., reactive oxygen species (ROS). In short, we present how ecological niches (i.e., MS and HCS) might determine, select, and modify the genomic and phenotypic features of the same bacterial species (i.e., Cobetia spp.) found in different marine environments, pointing to a direct correlation between adaptability and oligotrophy of seawater.
Mangrove–coral habitat is characterized by heterogeneity in the physical environment that allows it to be out of equilibrium with open ocean conditions, resulting in differentiation of local physical, chemical, and biological attributes. This chapter highlights how some mangrove habitats can act as alternate refuges for corals during climate threats, particularly increasing seawater temperature, high levels of solar radiation, and ocean acidification. Coastal ecosystems are interconnected and so any change in one coastal ecosystem will have an impact on other ecosystems. Similarly, recovery and resilience of coastal ecosystems like coral reefs depend on the degree of connectivity and support from the neighboring coastal ecosystems such as seagrass beds. Therefore, healthy seagrass beds are especially vital for the resilience of coral reefs, as they support the coral communities to adapt to climate change impacts. Corals compete with seaweeds for space on the reef. When corals are healthy, the coral–seaweed competition reaches a balance. But, if the corals are not able to do well because of smothering like eutrophication or climate change induced impacts, then seaweeds can take over. Our study results suggest that coral reefs may become increasingly susceptible to seaweed proliferation under ocean acidification. Though the functional links of mangroves, seagrasses, and coral reefs have been studied, their conservation and management aspects due to connectivity and their importance for humans is yet to be understood. Importance of interconnectivity in biodiversity richness is illustrated by presenting the bioresource availability in the existing heterogeneous coral reef, seagrass, and mangrove habitats of the Neil Island, the Andamans and studies on the interactions among them are essential for conservation and management of such precious ecosystems.
Highlights Elevated temperature has a greater effect on calcifying algae populations than pCO2. Southern and central populations already live close to their thermal and stress limits, while northern populations appear as the most resilient to environmental changes. Light calcification is the most valuable physiological process and is prioritized in populations throughout the geographical gradient in…
In marine ecosystems, fluctuations in surface-seawater carbon dioxide (CO2), significantly influence the whole metabolism of marine algae, especially during the early stages of macroalgal development. In this study, the response of the green alga Ulva fasciata for elevating ocean acidification was investigated using four levels of pCO2 ∼280, 550, 750 and 1050 µatm. Maximum growth rate (6.6 % day-1), protein (32.43 %DW) and pigment (2.9 mg/g) accumulation were observed at pCO2-550 with an increase of ∼2-fold compared to control. On the other hand, lipid and carbohydrate contents recorded their maximum production (4.23 and 46.96 %DW, respectively) at pCO2-750 while control showed 3.70 and 42.37 %DW, respectively. SDS-PAGE showed the presence of unique bands in response to pCO2, especially at 550 µatm. Dominant associated bacteria was shifted from Halomonas hydrothermalis of control to Vibrio toranzoniae at pCO2-1050. These findings suggest that ocean acidification at 550 µatm might impose noticeable effects on growth, protein, pigments, and protein profile of U. fasciata, which could be a good source for fish farming. While, pCO2-750 was recommended for energetic purpose, due to its high lipid and carbohydrate contents.