algae Archives - Ocean Acidification

Posts Tagged 'algae'

Decline of a distinct coral reef holobiont community under ocean acidification

Published 22 April 2024 Science Leave a Comment
Tags: algae, annelids, biological response, BRcommunity, bryozoa, chemistry, cnidaria, corals, laboratory, molecular biology, physiology, porifera, prokaryotes, sediment, South Pacific

Background

Microbes play vital roles across coral reefs both in the environment and inside and upon macrobes (holobionts), where they support critical functions such as nutrition and immune system modulation. These roles highlight the potential ecosystem-level importance of microbes, yet most knowledge of microbial functions on reefs is derived from a small set of holobionts such as corals and sponges. Declining seawater pH — an important global coral reef stressor — can cause ecosystem-level change on coral reefs, providing an opportunity to study the role of microbes at this scale. We use an in situ experimental approach to test the hypothesis that under such ocean acidification (OA), known shifts among macrobe trophic and functional groups may drive a general ecosystem-level response extending across macrobes and microbes, leading to reduced distinctness between the benthic holobiont community microbiome and the environmental microbiome.

Results

We test this hypothesis using genetic and chemical data from benthic coral reef community holobionts sampled across a pH gradient from CO₂ seeps in Papua New Guinea. We find support for our hypothesis; under OA, the microbiome and metabolome of the benthic holobiont community become less compositionally distinct from the sediment microbiome and metabolome, suggesting that benthic macrobe communities are colonised by environmental microbes to a higher degree under OA conditions. We also find a simplification and homogenisation of the benthic photosynthetic community, and an increased abundance of fleshy macroalgae, consistent with previously observed reef microbialisation.

Conclusions

We demonstrate a novel structural shift in coral reefs involving macrobes and microbes: that the microbiome of the benthic holobiont community becomes less distinct from the sediment microbiome under OA. Our findings suggest that microbialisation and the disruption of macrobe trophic networks are interwoven general responses to environmental stress, pointing towards a universal, undesirable, and measurable form of ecosystem change.

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Ocean acidification significantly alters the trace element content of the kelp, Saccharina latissima

Published 17 April 2024 Science Leave a Comment
Tags: algae, biological response, chemistry, laboratory, North Atlantic, performance, physiology

Highlights

Exposure of S. latissima to higher concentrations of pCO₂ caused a significant increase in the content and subcellular heterogeneity of iodine and arsenic in kelp.
The iodine-to‑calcium and bromine-to‑calcium ratios of kelp increased significantly under high CO₂.
High CO₂ significantly reduced levels of copper and cadmium in kelp tissue.
The elemental content of seaweeds used as food should be carefully monitored as climate change accelerates this century.

Abstract

Seaweeds are ecosystem engineers that can serve as habitat, sequester carbon, buffer ecosystems against acidification, and, in an aquaculture setting, represent an important food source. One health issue regarding the consumption of seaweeds and specifically, kelp, is the accumulation of some trace elements of concern within tissues. As atmospheric CO₂ concentrations rise, and global oceans acidify, the concentrations of elements in seawater and kelp may change. Here, we cultivated the sugar kelp, Saccharina latissima under ambient (~400 μatm) and elevated pCO₂ (600–2400 μatm) conditions and examined the accumulation of trace elements using x-ray powder diffraction, sub-micron resolution x-ray imaging, and inductively coupled plasma mass spectrometry. Exposure of S. latissima to higher concentrations of pCO₂ and lower pH caused a significant increase (p < 0.05) in the iodine and arsenic content of kelp along with increased subcellular heterogeneity of these two elements as well as bromine. The iodine-to‑calcium and bromine-to‑calcium ratios of kelp also increased significantly under high CO₂/low pH (p < 0.05). In contrast, high CO₂/low pH significantly reduced levels of copper and cadmium in kelp tissue (p < 0.05) and there were significant inverse correlations between concentrations of pCO₂ and concentrations of cadmium and copper in kelp (p < 0.05). Changes in copper and cadmium levels in kelp were counter to expected changes in their free ionic concentrations in seawater, suggesting that the influence of low pH on algal physiology was an important control on the elemental content of kelp. Collectively, these findings reveal the complex effects of ocean acidification on the elemental composition of seaweeds and indicate that the elemental content of seaweeds used as food must be carefully monitored as climate change accelerates this century.

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A laboratory study of the increasing competitiveness of Karenia mikimotoi under rising CO2 scenario

Published 3 April 2024 Science Closed
Tags: algae, biological response, community composition, laboratory, morphology, multiple factors, North Pacific, otherprocess, physiology, phytoplankton, temperature

Highlights

Rising CO₂ level promoted the growth of Karenia mikimotoi.
Rising CO₂ weakened allelopathic effects of Ulva pertusa on K. mikimotoi.
High CO₂ level disturbed the synthesis of free fatty acids in U. pertusa, decreasing its allelopathic effects.
Rising CO₂ increases the outbreak risk of K. mikimotoi.

Abstract

Ocean acidification (OA) driven by elevated carbon dioxide (CO₂) levels is expected to disturb marine ecological processes, including the formation and control of harmful algal blooms (HABs). In this study, the effects of rising CO₂ on the allelopathic effects of macroalgae Ulva pertusa to a toxic dinoflagellate Karenia mikimotoi were investigated. It was found that high level of CO₂ (1000 ppmv) promoted the competitive growth of K. mikimotoi compared to the group of present ambient CO₂ level (420ppmv), with the number of algal cell increased from 32.2 × 10⁴ cells/mL to 36.75 × 10⁴ cells/mL after 96 h mono-culture. Additionally, rising CO₂ level weakened allelopathic effects of U. pertusa on K. mikimotoi, as demonstrated by the decreased inhibition rate (50.6 % under the original condition VS 34.3 % under the acidified condition after 96 h co-culture) and the decreased reactive oxygen species (ROS) level, malondialdehyde (MDA) content, antioxidant enzymes activity (superoxide dismutase (SOD), peroxidase (POD), glutathione peroxidase (GPX), glutathione reductase (GR) and catalase (CAT) and non-enzymatic antioxidants (glutathione (GSH) and ascorbic acid (ascorbate, vitamin C). Indicators for cell apoptosis of K. mikimotoi including decreased caspase-3 and -9 protease activity were observed when the co-cultured systems were under rising CO₂ exposure. Furthermore, high CO₂ level disturbed fatty acid synthesis in U. pertusa and significantly decreased the contents of fatty acids with allelopathy, resulting in the allelopathy weakening of U. pertusa. Collectively, rising CO₂ level promoted the growth of K. mikimotoi and weakened allelopathic effects of U. pertusa on K. mikimotoi, indicating the increased difficulties in controlling K. mikimotoi using macroalgae in the future.

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Examining the effects of elevated CO2 on the growth kinetics of two microalgae, Skeletonema dohrnii (Bacillariophyceae) and Heterosigma akashiwo (Raphidophyceae)

Published 26 March 2024 Science Closed
Tags: abundance, algae, biological response, growth, North Pacific, otherprocess, photosynthesis, phytoplankton

Carbon dioxide (CO₂) serves as the primary substrate for the photosynthesis of phytoplankton, forming the foundation of marine food webs and mediating the biogeochemical cycling of C and N. We studied the effects of CO₂ variation on the Michaelis-Menten equations and elemental composition of Skeletonema dohrnii and Heterosigma akashiwo. CO₂ functional response curves were conducted from 100 to 2000 ppm. The growth of both phytoplankton was significantly affected by CO₂, but in different trends. The growth rate of S. dohrnii increased as CO₂ levels rose up to 400 ppm before reaching saturation. In contrast to S. dohrnii, the growth rate of H. akashiwo increased with CO₂ increasing up to 1000 ppm, and then CO₂ saturated. In addition, H. akashiwo showed a slower growth rate than S. dohrnii for all CO₂ concentrations, aside from 1000 ppm, and the Michaelis-Menten equations revealed that the half-saturation constant of H. akashiwo was higher than S. dohrnii. An increase in CO₂ concentration was seen to significantly affected the POC: Chl-a of both S. dohrnii and H. akashiwo, however, the effects on their elemental composition were minimal. Overall, our findings indicate that H. akashiwo had a more positive reaction to elevated CO₂ than S. dohrnii, and with higher nutrient utilization efficiency, while S. dohrnii exhibited higher carbon fixation efficiency, which is in line with their respective carbon concentrating mechanisms. Consequently, elevated CO₂, either alone or in combination with other limiting factors, may significantly alter the relative relationships between these two harmful algal blooms (HAB) species over the next century.

Continue reading ‘Examining the effects of elevated CO2 on the growth kinetics of two microalgae, Skeletonema dohrnii (Bacillariophyceae) and Heterosigma akashiwo (Raphidophyceae)’

Adverse environmental perturbations may threaten kelp farming sustainability by exacerbating enterobacterales diseases

Published 25 March 2024 Science Closed
Tags: algae, biological response, community composition, field, laboratory, light, molecular biology, morphology, mortality, multiple factors, North Pacific, otherprocess, physiology, prokaryotes, protists, reproduction

Globally kelp farming is gaining attention to mitigate land-use pressures and achieve carbon neutrality. However, the influence of environmental perturbations on kelp farming remains largely unknown. Recently, a severe disease outbreak caused extensive kelp mortality in Sanggou Bay, China, one of the world’s largest high-density kelp farming areas. Here, through in situ investigations and simulation experiments, we find indications that an anomalously dramatic increase in elevated coastal seawater light penetration may have contributed to dysbiosis in the kelp Saccharina japonica’s microbiome. This dysbiosis promoted the proliferation of opportunistic pathogenic Enterobacterales, mainly including the genera Colwellia and Pseudoalteromonas. Using transcriptomic analyses, we revealed that high-light conditions likely induced oxidative stress in kelp, potentially facilitating opportunistic bacterial Enterobacterales attack that activates a terrestrial plant-like pattern recognition receptor system in kelp. Furthermore, we uncover crucial genotypic determinants of Enterobacterales dominance and pathogenicity within kelp tissue, including pathogen-associated molecular patterns, potential membrane-damaging toxins, and alginate and mannitol lysis capability. Finally, through analysis of kelp-associated microbiome data sets under the influence of ocean warming and acidification, we conclude that such Enterobacterales favoring microbiome shifts are likely to become more prevalent in future environmental conditions. Our study highlights the need for understanding complex environmental influences on kelp health and associated microbiomes for the sustainable development of seaweed farming.

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Changes in isotope fractionation during nitrate assimilation by marine eukaryotic and prokaryotic algae under different pH and CO2 conditions

Published 13 March 2024 Science Closed
Tags: algae, biological response, nitrogen fixation, physiology

The impact of environmental factors on nitrogen (N) and oxygen (O) isotope effects during algal nitrate assimilation causes uncertainty in the field application of sedimentary N isotope records and nitrate isotopes to understand the marine nitrogen cycle. Ocean acidification is predicted to change nitrogen cycling including nitrate assimilation, but how N and O isotope effects during algal nitrate assimilation vary in response to changes in seawater pH and partial pressure CO₂ (pCO₂) remains unknown. We measured N and O isotope effects during nitrate assimilation and physiological states of the marine diatom Thalassiosira weissflogii and Synechococcus under different pH (8.1 or 7.8) and pCO₂ (400 or 800 μatm) conditions. Low pH and/or high pCO₂ equally decreased N and O isotope effects during nitrate assimilation by diatoms possibly due to reducing cellular nitrate efflux/uptake ratio and decreased isotope effects for nitrate uptake, whereas they did not affect those by Synechococcus with low intracellular nitrate concentration and limited nitrate efflux. Our results provide compelling experimental evidence showing different changes in N and O isotope effects during nitrate assimilation by marine eukaryotic and prokaryotic phytoplankton at low pH and/or high pCO₂. These findings suggest new insight into environmental controls on variability in the isotope effect during algal nitrate assimilation, and have implications for improving a predictive understanding of N and O isotope tools in acidified oceans.

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Increased light intensity enhances photosynthesis and biochemical components of red macroalga of commercial importance, Kappaphycus alvarezii, in response to ocean acidification

Published 12 March 2024 Science Closed
Tags: algae, biological response, laboratory, light, multiple factors, North Pacific, photosynthesis, physiology

Highlights

Effects of light availability and pCO₂ on Kappaphycus alvarezii were examined.
Moderate increases in light intensity and pCO₂ had positive effects on K. alvarezii.
OA and high light promoted carbon accumulation, but they had negative impacts on nitrogen.

Abstract

The concentration of atmospheric carbon dioxide (CO₂) has increased drastically over the past several decades, resulting in the pH of the ocean decreasing by 0.44 ± 0.005 units, known as ocean acidification (OA). The Kappaphycus alvarezii (Rhodophyta, Solieriaceae), is a commercially and ecologically important red macroalga with significant CO₂ absorption potential from seawater. The K. alvarezii also experienced light variations from self-shading and varied cultivation depths. Thus, the aim of present study was to investigate the effects of two pCO₂ levels (450 and 1200 ppmv) and three light intensities (50, 100, and 150 μmol photons·m⁻²·s⁻¹) on photosynthesis and the biochemical components in K. alvarezii. The results of the present study showed that a light intensity of 50 μmol photons·m⁻²·s⁻¹ was optimal for K. alvarezii photosynthesis with 0.663 ± 0.030 of F_v/F_m and 0.672 ± 0.025 of F_v’/F_m’. Phycoerythrin contents at two pCO₂ levels decreased significantly with an increase in light intensity by 57.14–87.76%, while phycocyanin contents only decreased from 0.0069 ± 0.001 mg g⁻¹ FW to 0.0047 ± 0.001 mg g⁻¹ FW with an increase in light intensity at 1200 ppmv of pCO₂. Moreover, moderate increases in light intensity and pCO₂ had certain positive effects on the physiological performance of K. alvarezii, specifically in terms of increasing soluble carbohydrate production. Although OA and high light levels promoted total organic carbon accumulation (21.730 ± 0.205% DW) in K. alvarezii, they had a negative impact on total nitrogen accumulation (0.600 ± 0.017% DW).

Continue reading ‘Increased light intensity enhances photosynthesis and biochemical components of red macroalga of commercial importance, Kappaphycus alvarezii, in response to ocean acidification’

Quantifying the impacts of multiple stressors on the production of marine benthic resources

Published 11 March 2024 Science Closed
Tags: abundance, algae, biogeochemistry, biological response, BRcommunity, chemistry, communityMF, laboratory, mesocosms, methods, modeling, mollusks, morphology, mortality, multiple factors, North Atlantic, nutrients, otherprocess, performance, physiology, regionalmodeling, temperature

Coastal ecosystems are among the most heavily affected by climate change and anthropogenic activities, which impacts their diversity, productivity and functioning and puts many of the key ecosystem services that they provide at risk. Although empirical studies have moved beyond single-stressor-single-species experiments with limited extrapolation potential and have increasingly investigated the cumulative effects of simultaneously occurring multiple stressors, consistent generalities have not yet been identified. Upscaling from controlled experiments to natural ecosystems, therefore, remains an unsolved challenge. Disentangling the independent and cumulative effects of multiple stressors across different levels of biological complexity, revealing the underlying mechanisms and understanding how coastal ecosystems may respond to predicted scenarios of global change is critical to manage and protect our natural capital.

In this thesis, I advance multiple stressor research by applying complementary approaches to quantify the impact of multiple stressors on marine benthic resources and thereby help predict the consequences of expected climate change for coastal habitats. First, I present the newly developed experimental platform QIMS (Quantifying the Impacts of Multiple Stressors) that overcomes some of the shortfalls of previous multiple stressor research (Chapter 2). Second, in a novel empirical study, I investigate the independent and combined effects of moderate ocean warming and acidification on the functioning and production of mussels and algae, considering the effects of interspecific interactions in the presence or absence of the respective other species (Chapter 3). Third, I synthesise monitoring data from Dublin Bay (representative of a typical metropolitan estuary) using conditional interference and a Bayesian Network model and provide alternative system trajectories according to different climate change scenarios. From this new model, I deepen the understanding of the complex linkages between environmental conditions and the diversity and functioning of Dublin Bay to support local decision making and management (Chapter 4).

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Physiological impacts of CO2-Induced acidification and UVR on invasive alga Caulerpa racemosa

Published 11 March 2024 Science Closed
Tags: algae, biological response, laboratory, light, Mediterranean, multiple factors, photosynthesis, physiology

Anthropogenically increasing atmospheric CO₂ causes changes in the carbon chemistry of seawater. With these changes, the HCO₃⁻ and CO₂ concentration of seawater increases, while the pH decreases. CO₂-induced ocean acidification by interacting with ultraviolet radiation (UVR) affects the metabolic pathways of seaweeds such as photosynthesis, growth, and nutrient uptake in a species-specific manner. This study was designed to determine the future ecological success of Caulerpa racemosa, an invasive species in the Mediterranean. In laboratory culture, C. racemosa was exposed to CO₂-induced low pH (pH: 7.7) with or without UVR (UVA: 1.2 W m⁻²; UVB: 0.55 W m⁻²) and its physiological responses were investigated. Maximum quantum yield of photosystem-II (F_v/F_m) and light utilization efficiency (α) of C. racemosa was negatively affected by low pH and UVR. However, low pH increased the rETR_max (maximum relative electron transfer rate) of C. racemosa. This increased rETR_max indicated that the photosynthesis of C. racemosa was not photosynthetically saturated at the ambient inorganic carbon pool. This could be an advantage in competing with other species in the predicted future ocean acidification. The combined effect of low pH and UVR affected the rETR_max of C. racemosa in different ways along with the incubation time. The synergistic effect observed in the first two weeks turned into an antagonistic effect in the last two weeks. The data obtained from this study suggest that incubation time is the most effective factor in the response of C. racemosa to CO₂-induced low pH and moderate-level UVR. In addition, our results support the hypothesis that C. racemosa may be one of the species that will benefit from CO₂-induced ocean acidification.

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Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming

Published 4 March 2024 Science Closed
Tags: algae, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, photosynthesis, physiology, temperature

Ocean acidification and warming caused by elevated CO₂ are urgent problems facing the marine ecological environment. With the strengthening of environmental governance in China, anthropogenic inputs of terrestrial phosphorus into the coastal ocean have drastically decreased, resulting in frequent phosphorus deficiency in seawater. These environmental factors in the future may affect algal growth, photosynthesis and yield. As an important economic macroalga suitable for large-scale cultivation, Gracilariopsis lemaneiformis is also potentially affected by the coupling of ocean acidification, warming and phosphorus deficiency. In this study, G. lemaneiformis was cultured outdoors under two pCO₂ levels (LC, 400 μatm; HC, 1000 μatm), two temperatures (LT, 20 ℃; HT, 24 ℃) and two phosphorus concentrations (LP, 0.1 μmol L⁻¹; HP, 10 μmol L⁻¹) to investigate its growth and photosynthetic performance. The results showed that LP significantly decreased the relative growth rates (RGR) and the maximum photosynthesis rate (P_m) of G. lemaneiformis both under LC and HC conditions. Under P depletion condition, the effects of warming and ocean acidification on the growth and photosynthetic performance of G. lemaneiformis showed an opposite trend, that is, HC caused a decrease in the growth, P_m, maximum relative electron transfer rate (rETR_max) and light utilization efficiency (α) from the rapid light response curve of G. lemaneiformis, and HT improved these parameters. Under LP condition, HC significantly inhibited the RGR of G. lemaneiformis in the LT group but had no significant effect on RGR in the HT group. Additionally, under LP condition, HC insignificantly affected PE and PC contents in the LT group, but significantly reduced these contents in the HT group. These findings suggest that phosphorus deficiency results in a decline in the growth of G. lemaneiformis and, under LP condition, the inhibition effect of ocean acidification on the growth of G. lemaneiformis could be mitigated by warming. This study provides scientific guidance for the field cultivation and selective breeding of G. lemaneiformis in phosphorus-deficient seawater under global climate change.

Continue reading ‘Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming’

Turf algae drives coral bioerosion under high CO2

Published 20 February 2024 Science Closed
Tags: abundance, algae, biogeochemistry, biological response, BRcommunity, calcification, chemistry, communityMF, corals, dissolution, field, laboratory, morphology, multiple factors, North Pacific, otherprocess, photosynthesis, respiration, temperature, vents

Turf algal prevalence will increase in coral ecosystems under ocean acidification yet their contribution towards the ongoing and projected degradation of reefs is often overlooked. Turf algal settlement was induced on exposed coral skeleton adjacent to live coral tissue to investigate coral-turf algal interactions through a combination of laboratory and field transplantation (shallow volcanic CO₂ seep) experiments across two temperature regimes. Here, we show that turf algae are competitively favored over corals under high pCO₂ conditions. Turf algae-associated biological activity locally acidified the microenvironment overlying the exposed coral skeleton, leading to its bioerosion. Increases in coral-turf algal interactions could shift coral ecosystems towards net dissolution and should be integrated into global accretion models when considering future carbonate budgets under climate change.

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Physiological responses of Caulerpa spp. (with different dissolved inorganic carbon physiologies) to ocean acidification

Published 1 February 2024 Science Closed
Tags: algae, biological response, growth, laboratory, photosynthesis, physiology, primary production, South Pacific

Caulerpa is a widely distributed genus of chlorophytes (green macroalgae) which are important for their dietary, social and coastal ecosystem value. Ocean acidification (OA) threatens the future of marine ecosystems, favouring macroalgal species that could benefit from increased seawater carbon dioxide (CO₂) concentrations. Most macroalgae species possess CO₂ concentrating mechanisms (CCMs) that allow active uptake of bicarbonate (HCO₃⁻). Those species without CCMs are restricted to using CO₂, which is currently the least abundant species of dissolved inorganic carbon (DIC) in seawater. Thus, macroalgae without CCMs are predicted to be likely benefit from OA. Caulerpa is one of the rare few genera that have species both with and without CCMs. The two most common Caulerpa species in New Zealand are C. geminata (possesses a CCM) and C. brownii (non-CCM). We investigated the responses of growth, photo-physiology and DIC utilisation of C. geminata and C. brownii to four mean seawater pH treatments (8.03, 7.93, 7.83 and 7.63) that correspond to changes in pH driven by increases in pCO₂ simulating future OA. There was a tendency for the mean growth rates for C. brownii (non-CCM) to increase under lower pH, and the growth rates of C. geminata (CCM) to decline with lower pH, although this was not statistically significant. However, this is likely because variability in growth rates also increased as seawater pH declined. There were few other differences in physiology of both species with pH, although there was tendency for greater preference for CO₂ over HCO₃⁻ uptake in the CCM species with declining seawater pH. This study demonstrates that DIC-use alone does not predict macroalgal responses to OA.

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Season influences interspecific responses of canopy-forming kelps to future warming and acidification at high latitude

Published 26 January 2024 Science Closed
Tags: algae, biological response, growth, laboratory, morphology, multiple factors, North Pacific, performance, physiology, temperature

Variability in primary producers’ responses to environmental change may buffer higher trophic levels against shifts in basal resource composition. Then again, in instances where there is a lack of functional redundancy because consumers rely on a few species to meet their energetic requirements at specific times of the year, altered community production dynamics may significantly impact food web resilience. In high-latitude kelp forests, a complementary annual phenology of seaweed production supports coastal marine consumers’ metabolic needs across large seasonal variations in their environment. Yet, marine consumers in these systems may face significant metabolic stress under the pronounced low pH conditions expected in future winters, particularly if they lack the resources to support their increased energetic demands. In this study, we investigate how the growth and nutritional value of three dominant, coexisting macroalgal species found in subpolar kelp forests will respond to ocean acidification and warming in future winter and summer seasons. We find that the three kelps Macrocystis pyrifera, Hedophyllum nigripes, and Neoagarum fimbriatum differ in their vulnerability to future environmental conditions, and that the seasonal environmental context of nutrient and light availability shapes these responses. Our results suggest that poleward fringe populations of M. pyrifera may be relatively resilient to anticipated ocean warming and acidification. In contrast, ocean warming conditions caused a decrease in the biomass and nutritional quality of both understory kelps. Considering the unique production phenology of H. nigripes, we emphasize that negative impacts on this species in future winters may be of consequence to consumer energetics in this system. This work highlights how interspecific variation in autotrophs’ responses to global change can disrupt the diversity and phenological structure of energy supply available to higher trophic levels.

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Early stage ecological communities on artificial algae showed no difference in diversity and abundance under ocean acidification

Published 24 January 2024 Science Closed
Tags: abundance, algae, annelids, biological response, BRcommunity, calcification, chemistry, community composition, crustaceans, echinoderms, field, Mediterranean, mesocosms, mitigation, mollusks, otherprocess, photosynthesis, protists, respiration

Marine habitat-forming species create structurally complex habitats that host macroinvertebrate communities characterized by remarkable abundance and species richness. These habitat-forming species also play a fundamental role in creating favourable environmental conditions that promote biodiversity. The deployment of artificial structures is becoming a common practice to help offset habitat loss although with mixed results. This study investigated the suitability of artificial flexible turfs mimicking the articulated coralline algae (mimics) as habitat providers and the effect of ocean acidification (OA) on early stage ecological communities associated to flexible mimics and with the mature community associated to Ellisolandia elongata natural turfs. The mimics proved to be a suitable habitat for early stage communities. During the OA mesocosms experiment, the two substrates have been treated and analysed separately due to the difference between the two communities. For early stage ecological communities associated with the mimics, the lack of a biologically active substrate does not exacerbate the effect of OA. In fact, no significant differences were found between treatments in crustaceans, molluscs and polychaetes diversity and abundance associated with the mimics. In mature communities associated with natural turfs, buffering capability of E. elongata is supporting different taxonomic groups, except for molluscs, greatly susceptible to OA.

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High nutrient availability modulates photosynthetic performance and biochemical components of the economically important marine macroalga Kappaphycus alvarezii (Rhodophyta) in response to ocean acidification

Published 24 January 2024 Science Closed
Tags: algae, biological response, laboratory, multiple factors, North Pacific, nutrients, photosynthesis, physiology

Increased atmospheric CO₂ concentrations not only change the components of inorganic carbon system in seawater, resulting in ocean acidification, but also lead to decreased seawater pH, resulting in ocean acidification. Consequently, increased inorganic carbon concentrations in seawater provide a sufficient carbon source for macroalgal photosynthesis and growth. Increased domestic sewage and industrial wastewater discharge into coastal areas has led to nutrient accumulation in coastal seawaters. Combined with elevated pCO₂ (1200 ppmv), increased nutrient availability always stimulates the growth of non-calcifying macroalgae, such as red economical macroalga Gracilariopsis lemaneiformis. Here, we evaluated the interactive effects of nutrients with elevated pCO₂ on the economically important marine macroalga Kappaphycus alvarezii (Rhodophyta) in a factorial 21-day coupling experiment. The effects of increased nutrient availability on photosynthesis and photosynthetic pigments of K. alvarezii were greater than those of pCO₂ concentration. The highest F_v/F_m values (0.660 ± 0.019 and 0.666 ± 0.030, respectively) were obtained at 2 μmol L⁻¹ of NO₃–N at two pCO₂ levels. Under the elevated pCO₂ condition, the Chl-a content was lowest (0.007 ± 0.004 mg g⁻¹) at 2 μmol L⁻¹ of NO₃–N and highest (0.024 ± 0.002 mg g⁻¹) at 50 μmol L⁻¹ of NO₃–N. The phycocyanin content was highest (0.052 ± 0.012 mg g⁻¹) at 150 μmol L⁻¹ of NO₃–N under elevated pCO₂ condition. The malondialdehyde content declined from 32.025 ± 4.558 nmol g⁻¹ to 26.660 ± 3.124 nmol g⁻¹ with the increased nutrients at under low pCO₂. To modulate suitable adjustments, soluble biochemical components such as soluble carbohydrate, soluble protein, free amino acids, and proline were abundantly secreted and were likely to protect the integrity of cellular structures under elevated nutrient availability. Our findings can serve as a reference for cultivation and bioremediation methods under future environmental conditions.

Continue reading ‘High nutrient availability modulates photosynthetic performance and biochemical components of the economically important marine macroalga Kappaphycus alvarezii (Rhodophyta) in response to ocean acidification’

Biochemical adaptability of the relationship between tropical hard corals and photosynthetic symbiotic algae under climate change

Published 23 January 2024 Science Closed
Tags: adaptation, algae, BRcommunity, corals, otherprocess, performance, review

Tropical coral reefs, a vital component of the global marine ecosystem, are currently under threat from climate change factors such as rising temperatures, ocean acidification, and extreme weather events. High temperatures induce coral bleaching, resulting in the loss of their energy supply and an acceleration of metabolic rates, rendering them more vulnerable. Ocean acidification affects the formation of calcium carbonate skeletons in symbiotic algae and decreases photosynthetic efficiency, further exacerbating the risk of damage to the symbiotic algae in high-temperature conditions. Extreme weather events directly cause physical damage to corals and alter marine environments, reducing their chances of survival. This review focuses on the impact of climate change on the biochemical adaptability between tropical hard corals and photosynthetic symbiotic algae, exploring their ecological relationship, the influence of climate change on this relationship, and the adaptive mechanisms. Understanding the adaptive mechanisms between hard corals and symbiotic algae is crucial for developing conservation strategies and management plans to maintain the functionality and biodiversity of coral reef ecosystems. It also aids in ensuring the survival and prosperity of this delicate relationship under the challenges posed by climate change, allowing future generations to continue enjoying the magnificence of tropical coral reefs.

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Paleoceanographic importance of tri- and di-unsaturated alkenones through the early phase of Cretaceous Oceanic Anoxic Event 2 from southern high latitudes of the proto-Indian Ocean

Published 17 January 2024 Science Closed
Tags: algae, biological response, field, Indian, paleo, physiology, sediment

Alkenones are biomarkers derived exclusively from species of haptophyte algae. The relative abundance of di- to tri-unsaturated C₃₇ alkenones expressed as U^K’₃₇ is widely applied as a sea surface paleotemperature proxy for Cenozoic marine sediments. However, the absence of alkatrienones prior to the Eocene has precluded application of the U^K’₃₇ proxy for assessment of Cretaceous paleoclimates. Herein, we report a C₄₀ alkatrienone (tetraconta-9E, 16E, 23E-trien-3-one; C_40:3 Et) in deep-sea sediments from southern high latitudes (International Ocean Discovery Program: IODP site U1516). This discovery extends the geologic record of alkatrienones to the late Cenomanian, ∼70 million years earlier than previous reports. The parallel occurrence of higher abundances of a C₄₀ alkadienone (tetraconta-16E, 23E-dien-3-one; C_40:2 Et) allowed calculation of the U^K’₄₀ unsaturation index, comparable to U^K’₃₇. Stratigraphic variations in the δ¹³C of C_40:2 Et revealed an elevated (∼1.5 ‰) positive carbon isotope excursion (CIE) relative to those observed in carbonate from other OAE2 sequences likely reflecting a decrease in global pCO₂. The U^K’₄₀ profile suggests a concurrent drop in sea surface temperature associated with the decline in pCO₂ during the early phase of OAE2. The timing of these environmental perturbations in the southern high latitude of the proto-Indian Ocean suggests they were triggered by volcanism associated with large igneous province (LIP) formation.

Continue reading ‘Paleoceanographic importance of tri- and di-unsaturated alkenones through the early phase of Cretaceous Oceanic Anoxic Event 2 from southern high latitudes of the proto-Indian Ocean’

Thermal fluctuations and CO2 enrichment synergistically accelerate biomass yield of Neopyropia yezoensis

Published 15 January 2024 Science Closed
Tags: algae, biological response, growth, laboratory, multiple factors, North Pacific, photosynthesis, physiology, temperature

Due to the rising atmospheric pCO₂, the greenhouse effect in the natural environment has intensified, leading to ocean acidification and frequently extreme temperature events. Limited research has been conducted on the effects of near-shore temperature fluctuations and ocean acidification on macroalgae. In this study, Neopyropia yezoensis (Bangiales, Rhodophyta) was cultured under two CO₂ concentrations (LC: 400 μatm and HC: 1000 μatm) and three temperature conditions (10 ℃, 14 ℃, and fluctuation: increased from 10 ℃ to 14 ℃ and then decreased back to 10 ℃ with a fluctuation of 1 ℃ per day). The growth, chlorophyll fluorescence, photosynthetic pigments, and soluble carbohydrate of N. yezoensis were measured. The results showed that the relative growth rate, rETR_max, contents of chlorophyll a, phycoerythrin, and carotenoid in the thalli increased at 14 ℃ and thermal fluctuation, while the content of soluble carbohydrate were inhibited. Moreover, the effect of pCO₂ on growth was significant only under temperature fluctuation. Even when the temperature dropped to 10 ℃, the physiological responses of N. yezoensis were still promoted by the thermal fluctuation condition. These findings indicate that the yield and quality of N. yezoensis could potentially improve in the future warming scenarios, and changes observed in N. yezoensis could serve as an early indicator for global climate change.

Continue reading ‘Thermal fluctuations and CO2 enrichment synergistically accelerate biomass yield of Neopyropia yezoensis’

The impacts of climate change on the reproduction of native and invasive kelps

Published 5 January 2024 Science Closed
Tags: algae, biological response, community composition, laboratory, morphology, mortality, multiple factors, North Pacific, otherprocess, reproduction, temperature

Climate change represents a threat to coastal marine ecosystems through variable effects on community structure and function due to increasing mean sea-surface temperatures (SST), marine heatwaves, variation in salinity, and ocean acidification. Among the most at risk species are California kelps, which have already experienced significant die-offs over the past several years as a result of elevated SST and urchin grazing. However, the effects of these stresses on the very sensitive microscopic kelp life stage (gametophyte) are much less understood. Gametophytes are generally less resilient to changes in abiotic conditions, so global environmental change could result in drastic changes in kelp forest community structure and composition via impacts on this life stage. My dissertation research used manipulative laboratory experiments to investigate the interacting role of abiotic stressors on kelp reproduction and community compositions, specifically, the growth and survival of early kelp life stages. My first chapter focused on the effects of climate-driven temperature increases and ocean acidification on bull kelp (Nereocystis luetkeana) gametophytes from Point Arena, CA (Korabik et al. 2023). From 2014 to 2016, the largest marine heatwave in history appeared off the coast of California resulting in large kelp die off events. In this chapter, I asked how increased temperature and lowered pH impact the survival of bull kelp gametophytes and the production of juvenile bull kelp sporophytes. My results showed that increased temperature resulted in a significant decrease in the survival of gametophytes and a lower number of juveniles produced, whereas lowered pH only had a significant effect on the production of juveniles, slowing their rate of development. These results indicate that the predicted increase of marine heatwaves could have devastating effects on the persistence of bull kelp forest ecosystems. My second chapter considered the interacting effects of climate driven changes in temperature and salinity and interactions with the invasive seaweed (Sargassum muticum) on the growth and survival of giant kelp (Macrocystis pyrifera) gametophytes from Tomales Bay, CA. In my experiments, I tested: 1) how different salinities and temperatures impact giant kelp early life stages from different sources within Tomales Bay, 2) how the presence of invasive Sargassum propagules affect giant kelp gametophyte development, and 3) how the combined effects of salinity, temperature, and Sargassum presence affect giant kelp early life stages. My results indicate that 1) the presence of Sargassum had little effect on the survival of giant kelp gametophytes, 2) Sargassum accelerated development of giant kelp juvenile sporophytes, and 3) high temperatures resulted in the greatest reduction of giant kelp gametophyte survival. These results imply that giant kelp reproduction and presence within estuaries is more influenced by temperature than salinity and microscopic-stage competition with invasive species. My third chapter examined the effects of increased temperature and lowered salinities on invasive Wakame (Undaria pinnatifida) gametophytes in the San Francisco Bay. Previous studies have shown that low salinity can limit the distribution of Undaria, but there is no information about these effects on gametophyte stages. Using a full factorial design, I exposed Undaria gametophytes to five salinity conditions ranging from low to ambient salinity and two temperatures representing pre-2013 temperature maxima in San Francisco and maximum increased temperatures experienced under the 2014-2016 marine heatwave. I found that Undaria microstages were unable to survive below 20 psu and generally survived better under warmer temperatures of 18°C. Climate change in California is predicted to result in higher temperatures and reduced annual rainfall in drought years, which may facilitate future northward expansion of Wakame populations. With this research, I can better predict the impacts of climate change on kelp ecosystems to help coastal managers prioritize future protection efforts. Early life stages are often the most vulnerable to stress, and in this era of rapid climate change, understanding early life stage responses to stress will allow scientists and managers to better work towards the protection of our planet.

Continue reading ‘The impacts of climate change on the reproduction of native and invasive kelps’

Physio-biochemical and metabolomic analyses of the agarophyte Gracilaria salicornia indicates its tolerance to elevated pCO2 levels

Published 14 December 2023 Science Closed
Tags: abundance, algae, biological response, growth, Indian, laboratory, otherprocess, photosynthesis, physiology

Gracilaria salicornia is an agar-producing red macroalga commonly found growing in the intertidal and upper subtidal on various substrates with distribution across the Indo-Pacific. The ability of G. salicornia to survive under harsh conditions suggests potential use as a candidate for sustainable farming and alternative source of livelihood for the local coastal communities under future climate conditions. An earlier study investigated the effects of future predicted pCO₂ level on the photosynthesis and respiration of G. salicornia but studies on the metabolomic responses of this alga to constant elevated pCO₂ level is lacking. Here, elevated pCO₂ level was simulated on G. salicornia for 14 days to compare its growth, photosynthetic efficiency, pigment content, agar properties and metabolite composition under current pCO₂ level (∼pH 8.1) and end-of-century future-predicted (∼pH 7.8) pCO₂ level. The observed biomass growth, coupled with unaffected photosynthetic parameters and agar-related properties underscore G. salicornia’s ability to adapt to higher pCO₂ levels. The modulation of metabolites showcases the alga’s adaptive strategies at elevated pCO₂ whereby stress-mediating compounds such as gallic acid and oxalic acid were increased while stress-indicating metabolites such as serine, glycine, and ascorbic acid did not show significant changes. Interestingly, the metabolome profile imply that the alga regulates its metabolism according to culture duration rather than the pCO₂ level.

Continue reading ‘Physio-biochemical and metabolomic analyses of the agarophyte Gracilaria salicornia indicates its tolerance to elevated pCO2 levels’

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