Coral reefs worldwide are threatened by climate change effects like increasing ocean warming and ocean acidification. These increased pressures cause a dysbiosis between the coral host, algal endosymbionts, and associated coral microbiome that results in the coral host expelling algal endosymbionts, leaving the coral host with a stark white ‘bleached’ appearance. Without their endosymbionts, coral hosts are forced to sustain themselves energetically with heterotrophy instead of relying on the autotrophic carbon and energy sources that once came from the algal endosymbionts. When this response, termed ‘coral bleaching’, happens reef-wide during an extreme wave of increased ocean temperatures, this is called a mass Coral Bleaching Event. The frequency and intensity of mass Coral Bleaching events are increasing around the world, forcing corals to acclimatize to survive. This dissertation investigates the physiological and genomic mechanisms underlying acclimatization and increased stress tolerance in two common, reef-building corals: Montipora capitata and Pocillopora acuta. In three chapters, I present findings that support phenotypic plasticity and increased stress tolerance in M. capitata and hypothesize the mechanisms contributing to this. In Chapter 1, I conducted an ex-situ experiment that mimicked an environmentally realistic, extended heatwave and ocean acidification scenario in a factorial design of increased temperature and increased pCO2 conditions for a two-month stress period and a two-month recovery period. Both species’ physiological states were significantly challenged but M. capitata displayed a more favorable photosynthetic rate to antioxidant capacity ratio and associated with more thermally tolerant symbionts. Although M. capitata survived at higher rates than P. acuta, physiological state was still significantly impacted after two months of recovery, suggesting that marine heatwaves likely induce physiological legacies that may impact performance during the next, inevitable heatwave. In Chapter 2, I further investigated P. acuta’s stress response from Chapter 1 at a genomic level. We sought to test the effects of environmental stressors on gene body DNA methylation patterns to elucidate how environmentally sensitive and dynamic DNA methylation changes are in invertebrates. However, when analyzing gene expression data, our team found that polyploidy was prevalent in our samples, which convoluted our ability to test environmental effect in addition to polyploidy structure. We found that DNA methylation patterns followed polyploidy genetic lineage with diploid corals exhibiting the highest levels of DNA methylation despite lower gene expression levels of epigenetic machinery proteins. Despite significant DNA methylation pattern differences between polyploidies, P. acuta populations still severely declined in increased stress conditions (outlined in Chapter 1), suggesting that regardless of differential gene body methylation and ploidy status, this species may be ultimately too sensitive to future ocean conditions. In Chapter 3, I further investigated the genomic mechanisms underlying stress response in Montipora capitata, by directly comparing bleached (‘Susceptible’) and non-bleached (‘Resistant’) phenotypes of conspecific pairs. We found very little genetic diversity among our samples suggesting there is no effect of genetic structure on phenotypic variation in this context. ‘Resistant’ corals were characterized by association with more thermally tolerant symbionts, lower gene expression variability, higher gene body methylation levels on genes involved in death and stress response, and a more robust cellular stress response. The results of all three chapters suggest that both physiological and genomic stats impact bleaching susceptibility and phenotype and that not one mechanism may act alone to produce a particular phenotype. This dissertation aids in elucidating the mechanisms of stress response in reef-building corals, ultimately guiding our current knowledge of phenotypic variation in the face of climate change.
Continue reading ‘Elucidating the mechanisms of stress tolerance in reef-building coral holobionts’Posts Tagged 'growth'
Elucidating the mechanisms of stress tolerance in reef-building coral holobionts
Published 21 September 2023 Science ClosedTags: abundance, algae, biological response, corals, growth, laboratory, molecular biology, mortality, multiple factors, otherprocess, photosynthesis, physiology, temperature
Ocean acidification affects the response of the coastal coccolithophore Pleurochrysis carterae to irradiance
Published 21 September 2023 Science ClosedTags: biological response, growth, laboratory, light, multiple factors, North Pacific, photosynthesis, physiology, phytoplankton, primary production
The ecologically important marine phytoplankton group coccolithophores have a global distribution. The impacts of ocean acidification on the cosmopolitan species Emiliania huxleyi have received much attention and have been intensively studied. However, the species-specific responses of coccolithophores and how these responses will be regulated by other environmental drivers are still largely unknown. To examine the interactive effects of irradiance and ocean acidification on the physiology of the coastal coccolithophore species Pleurochrysis carterae, we carried out a semi-continuous incubation experiment under a range of irradiances (50, 200, 500, 800 μmol photons m−2 s−1) at two CO2 concentration conditions of 400 and 800 ppm. The results suggest that the saturation irradiance for the growth rate was higher at an elevated CO2 concentration. Ocean acidification weakened the particulate organic carbon (POC) production of Pleurochrysis carterae and the inhibition rate was decreased with increasing irradiance, indicating that ocean acidification may affect the tolerating capacity of photosynthesis to higher irradiance. Our results further provide new insight into the species-specific responses of coccolithophores to the projected ocean acidification under different irradiance scenarios in the changing marine environment.
Continue reading ‘Ocean acidification affects the response of the coastal coccolithophore Pleurochrysis carterae to irradiance’Ocean acidification reduces iodide production by the marine diatom Chaetoceros sp. (CCMP 1690)
Published 13 September 2023 Science ClosedTags: biological response, growth, Indian, laboratory, physiology, phytoplankton
Highlights
- Ocean acidification had no effect on growth rates of the diatom Chaetoceros sp. CCMP (1690) but higher cell yield under high CO2.
- Ocean acidifcation has the potential to inhibit the diatom-mediated iodate to iodide reduction process.
- Iodide production was decoupled from iodate uptake and refute the proposed link between iodide produced and cell membrane permeability.
Abstract
Phytoplankton in marine surface waters play a key role in the global iodine cycle. The biologically-mediated iodide production under future scenarios is limited. Here we compare growth, iodate to iodide conversion rate and membrane permeability in the diatom Chaetoceros sp. (CCMP 1690) grown under seawater carbonate chemistry conditions projected for 2100 (1000 ppm) and pre-industrial (280 ppm) conditions. We found no effect of CO2 on growth rates, but a significantly higher cell yield under high CO2, suggesting sustained growth from relief from carbon limitation. Cell normalised iodate uptake (16.73 ± 0.92 amol IO3− cell−1) and iodide production (8.61 ± 0.15 amol I− cell−1) was lower in cultures grown at high pCO2 than those exposed to pre-industrial conditions (21.29 ± 2.37 amol IO3− cell−1, 11.91 ± 1.49 amol I− cell−1, respectively). Correlating these measurements with membrane permeability, we were able to ascertain that iodide conversion rates were not linked to cell permeability and that the processes of mediated iodate loss and diatom-iodide formation are decoupled. These findings are the first to implicate OA in driving a potential shift in diatom-mediated iodate reduction. If our results are indicative of diatom-mediated iodine cycling in 2100, future surface ocean conditions could experience reduced rates of iodide production by Chaetoceros spp., potentially lowering iodide concentrations in ocean regions dominated by this group. These changes have the potential to impact ozone cycling and new particle formation in the atmosphere.
Continue reading ‘Ocean acidification reduces iodide production by the marine diatom Chaetoceros sp. (CCMP 1690)’The combined effect of pH and dissolved inorganic carbon concentrations on the physiology of plastidic ciliate Mesodinium rubrum and its cryptophyte prey
Published 13 September 2023 Science ClosedTags: biological response, growth, laboratory, North Atlantic, photosynthesis, physiology, phytoplankton, protists
Ocean acidification is caused by rising atmospheric partial pressure of CO2 (pCO2) and involves a lowering of pH combined with increased concentrations of CO2 and dissolved in organic carbon in ocean waters. Many studies investigated the consequences of these combined changes on marine phytoplankton, yet only few attempted to separate the effects of decreased pH and increased pCO2. Moreover, studies typically target photoautotrophic phytoplankton, while little is known of plastidic protists that depend on the ingestion of plastids from their prey. Therefore, we studied the separate and interactive effects of pH and DIC levels on the plastidic ciliate Mesodinium rubrum, which is known to form red tides in coastal waters worldwide. Also, we tested the effects on their prey, which typically are cryptophytes belonging to the Teleaulax/Plagioslemis/Geminigera species complex. These cryptophytes not only serve as food for the ciliate, but also as a supplier of chloroplasts and prey nuclei. We exposed M. rubrum and the two cryptophyte species, T. acuta, T. amphioxeia to different pH (6.8 – 8) and DIC levels (∼ 6.5 – 26 mg C L-1) and assessed their growth and photosynthetic rates, and cellular chlorophyll a and elemental contents. Our findings did not show consistent significant effects across the ranges in pH and/or DIC, except for M. rubrum, for which growth was negatively affected only by the lowest pH of 6.8 combined with lower DIC concentrations. It thus seems that M. rubrum is largely resilient to changes in pH and DIC, and its blooms may not be strongly impacted by the changes in ocean carbonate chemistry projected for the end of the 21th century.
Continue reading ‘The combined effect of pH and dissolved inorganic carbon concentrations on the physiology of plastidic ciliate Mesodinium rubrum and its cryptophyte prey’Differential reaction norms to ocean acidification in two oyster species from contrasting habitats
Published 6 September 2023 Science ClosedTags: adaptation, biological response, growth, laboratory, mollusks, morphology, mortality, North Atlantic, otherprocess, physiology
Ocean acidification (OA), a consequence of the increase in anthropogenic emissions of carbon dioxide, causes major changes in the chemistry of carbonates in the ocean with deleterious effects on calcifying organisms. The pH/pCO2 range to which species are exposed in nature is important to consider when interpreting the response of coastal organisms to OA. In this context, emerging approaches, which assess the reaction norms of organisms to a wide pH gradient, are improving our understanding of tolerance thresholds and acclimation potential to OA. In this study, we decipher the reaction norms of two oyster species living in contrasting habitats: the intertidal oyster Crassostrea gigas and the subtidal flat oyster Ostrea edulis, which are two economically and ecologically valuable species in temperate ecosystems. Six-month-old oysters of each species were exposed in common garden for 48 days to a pH gradient ranging from 7.7 to 6.4 (total scale). Both species are tolerant down to a pH of 6.6 with high plasticity in fitness-related traits such as survival and growth. However, oysters undergo remodelling of membrane fatty acids to cope with decreasing pH along with shell bleaching impairing shell integrity and consequently animal fitness. Finally, our work reveals species-specific physiological responses and highlights that intertidal C. gigas seems to have a better acclimation potential to rapid and extreme OA changes than O. edulis. Overall, our study provides important data about the phenotypic plasticity and its limits in two oyster species, which is essential for assessing the challenges posed to marine organisms by OA.
Continue reading ‘Differential reaction norms to ocean acidification in two oyster species from contrasting habitats’Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)
Published 30 August 2023 Science ClosedTags: biological response, growth, laboratory, mollusks, mortality, multiple factors, North Pacific, physiology, salinity
Highlights
- Salinity and pH tolerance ranges were identified for Mactra chinensis Philippi juveniles in laboratory tests.
- Survival rates were significantly reduced at extreme pH and salinity.
- Low pH and salinity induced oxidative stress, decreasing antioxidant enzyme activities.
Abstract
The study investigated the impact of salinity and pH changes on the survival, growth, and antioxidant enzyme activity in Mactra chinensis Philippi (1.00 ± 0.10 cm shell length, 0.75±0.04 cm shell height), a marine clam species. Juveniles were exposed to various pH levels (5.4 – 9.6) and salinities (5 – 35 psu) for up to 20 days at 19 ± 0.5 ˚C. The individual effect of salinity and pH on juveniles were evaluated under pH 8.0 and salinity 30 psu, respectively. The results indicated that the highest survival rates were observed at pH 8.0 (85%, salinity = 30 psu) and salinity 30 psu (95%, pH = 8.0). The survival rates were significantly reduced at extreme pH (≤ 7.2; ≥ 8.4) and salinities (≤ 15; 35 psu). Additionally, oxidative stress was observed in clams exposed to low pH and salinity as indicated by the decreased activities of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). Notably, no significant difference in relative growth rates was observed between salinity 25 and 30 psu, between pH 7.8/8.4 and pH 8.0. Our results provide information on potential impact of pH and salinity changes on economically important bivalve species and may be used to optimize pH and salinity in aquaculture.
Continue reading ‘Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)’Physiological responses of scallops and mussels to environmental variability: implications for future shellfish aquaculture
Published 25 August 2023 Science ClosedTags: adaptation, biological response, chemistry, field, growth, mollusks, morphology, North Pacific, otherprocess
Highlights
- High acclimatization capability in mussels and scallops
- Growth rates, δ13C, δ15N, and shell strength differed between seasons and depths.
- Mussels and scallops had higher growth rates at 5 m than 30 m.
- Shell strength changed with depth in mussels but not in the scallops.
- Differences in nutritional sources between depths are higher in winter than spring.
Abstract
Puget Sound (Washington, USA) is a large estuary, known for its profitable shellfish aquaculture industry. However, in the past decade, scientists have observed strong acidification, hypoxia, and temperature anomalies in Puget Sound. These co-occurring environmental stressors are a threat to marine ecosystems and shellfish aquaculture. Our research assesses how environmental variability in Puget Sound impacts two ecologically and economically important bivalves, the purple-hinge rock scallop (Crassodoma gigantea) and Mediterranean mussel (Mytilus galloprovincialis). Our study examines the effect of depth and seasonality on the physiology of these two important bivalves to gain insight into ideal grow-out conditions in an aquaculture setting, improving the yield and quality of this sustainable protein source. To do this, we used Hood Canal (located in Puget Sound) as a natural multiple-stressor laboratory, which allowed us to study acclimatization capacity of shellfish in their natural habitat and provide the aquaculture industry information about differences in growth rate, shell strength, and nutritional sources across depths and seasons. Bivalves were outplanted at two depths (5 and 30 m) and collected after 3.5 and 7.5 months. To maximize mussel and scallop growth potential in an aquaculture setting, our results suggest outplanting at 5 m depth, with more favorable oxygen and pH levels. Mussel shell integrity can be improved by placing out at 5 m, regardless of season, however, there were no notable differences in shell strength between depths in scallops. For both species, δ13C values were lowest at 5 m in the winter and δ15N was highest at 30 m regardless of season. Puget Sound’s combination of naturally and anthropogenically acidified conditions is already proving to be a challenge for shellfish farmers. Our study provides crucial information to farmers to optimize aquaculture grow-out as we begin to navigate the impacts of climate change.
Continue reading ‘Physiological responses of scallops and mussels to environmental variability: implications for future shellfish aquaculture’Examining the reproductive success of bull kelp (Nereocystis luetkeana, Phaeophyceae, Laminariales) in climate change conditions
Published 10 August 2023 Science ClosedTags: algae, biological response, growth, laboratory, mortality, multiple factors, North Pacific, reproduction, temperature
Climate change is affecting marine ecosystems in many ways, including raising temperatures and leading to ocean acidification. From 2014 to 2016, an extensive marine heat wave extended along the west coast of North America and had devastating effects on numerous species, including bull kelp (Nereocystis luetkeana). Bull kelp is an important foundation species in coastal ecosystems and can be affected by marine heat waves and ocean acidification; however, the impacts have not been investigated on sensitive early life stages. To determine the effects of changing temperatures and carbonate levels on Northern California’s bull kelp populations, we collected sporophylls from mature bull kelp individuals in Point Arena, CA. At the Bodega Marine Laboratory, we released spores from field-collected bull kelp, and cultured microscopic gametophytes in a common garden experiment with a fully factorial design crossing modern conditions (11.63 ± 0.54°C and pH 7.93 ± 0.26) with observed extreme climate conditions (15.56 ± 0.83°C and 7.64 ± 0.32 pH). Our results indicated that both increased temperature and decreased pH influenced growth and egg production of bull kelp microscopic stages. Increased temperature resulted in decreased gametophyte survival and offspring production. In contrast, decreased pH had less of an effect but resulted in increased gametophyte survival and offspring production. Additionally, increased temperature significantly impacted reproductive timing by causing female gametophytes to produce offspring earlier than under ambient temperature conditions. Our findings can inform better predictions of the impacts of climate change on coastal ecosystems and provide key insights into environmental dynamics regulating the bull kelp lifecycle.
Continue reading ‘Examining the reproductive success of bull kelp (Nereocystis luetkeana, Phaeophyceae, Laminariales) in climate change conditions’Seasonal production dynamics of high latitude seaweeds in a changing ocean: implications for bottom-up effects on temperate coastal food webs
Published 10 August 2023 Science ClosedTags: algae, biological response, BRcommunity, calcification, chemistry, dissolution, field, growth, laboratory, light, morphology, multiple factors, North Pacific, otherprocess, phanerogams, photosynthesis, physiology, primary production, temperature
As the oceans absorb excess heat and CO2 from the atmosphere, marine primary producers face significant changes to their abiotic environments and their biotic interactions with other species. Understanding the bottom-up consequences of these effects on marine food webs is essential to informing adaptive management plans that can sustain ecosystem and cultural services. In response to this need, this dissertation provides an in-depth consideration of the effects of global change on foundational macroalgal (seaweed) species in a poorly studied, yet highly productive region of our world’s oceans. To explore how seaweeds within seasonally dynamic giant kelp forest ecosystems will respond to ocean warming and acidification, I employ a variety of methods: year-round environmental monitoring using an in situ sensor array, monthly subtidal community surveys, and a series of manipulative experiments. I find that a complementary phenology of macroalgal production currently characterizes these communities, providing complex habitat and a nutritionally diverse energy supply to support higher trophic levels throughout the year. I also find that future ocean warming and acidification will lead to substantial shifts in the phenology, quantity and quality of macroalgal production in these systems. My results suggest that the giant kelp Macrocystis pyrifera may be relatively resilient to the effects of global change in future winter and summer seasons at high latitudes. In contrast, the calcifying coralline algae Bossiella orbigniana and Crusticorallina spp. and the understory kelps Hedophyllum nigripes and Neoagarum fimbriatum will experience a suite of negative impacts, especially in future winter conditions. The resulting indirect effects on macroalgal-supported coastal food webs will be profound, with projected reductions in habitat and seasonal food supply on rocky reefs. Coming at a time of heightened interest in seaweed production potential at high latitudes, this dissertation provides a comprehensive evaluation of the future of these foundational organisms in a changing environment.
Continue reading ‘Seasonal production dynamics of high latitude seaweeds in a changing ocean: implications for bottom-up effects on temperate coastal food webs’A bone morphogenetic protein regulates the shell formation of Crassostrea gigas under ocean acidification
Published 8 August 2023 Science ClosedTags: biological response, growth, laboratory, molecular biology, mollusks, North Pacific
Bone morphogenetic proteins (BMPs) are key factors controlling osteoblast differentiation, which have been proved to be involved in the hard tissue formation of marine mollusks. In the present study, a member of BMPs gene (CgBMP7) was identified from Pacific oyster Crassostrea gigas (C. gigas) with the aim to understand its possible role in the regulation of shell formation under ocean acidification (OA) conditions. The open reading frame (ORF) of CgBMP7 was of 1254 bp encoding a polypeptide of 417 amino acids. The deduced amino acid sequence of CgBMP7 was comprised of one signal peptide, one prodomain and one TGF-β domain, which shared 21.69%-61.10% identities with those from other species. The mRNA transcript of CgBMP7 was ubiquitously expressed in all the tested tissues of adult oysters with a higher expression level in mantle, notably highest in the middle fold of the three folds of mantle. The expression level of bone morphogenetic protein type I receptor (CgBMPR1B) mRNA was also highest in the MF and up-regulated dramatically post recombinant BMP7 protein (rCgBMP7) stimulation. After the blockage of BMPR1B with inhibitor LDN193189 (LDN), the mRNA expression level and phosphorylation level of CgSmad1/5/8 in mantle were decreased, and the mRNA expression level of CgCaM and Cgengrailed-1 were down-regulated significantly. During the oysters were exposed to acidified seawater for weeks, the expression levels of CgBMP7, CgBMPR1B and CgSmad1/5/8 in the middle fold of mantle decreased significantly (p < 0.01) at the 4th week, and CgCaM and Cgengrailed-1 also exhibited the same variable expression patterns as CgBMP7. In addition, the growth of shell in the treatment group (pH 7.8) was slower than that in the control group (pH 8.1). These results collectively indicated that BMP7 was able to trigger the BMPR-Smad signaling pathway and involved in controlling the formation of oyster calcified shell under OA conditions.
Continue reading ‘A bone morphogenetic protein regulates the shell formation of Crassostrea gigas under ocean acidification’The effect of differences pH of waters on the growth rate of seagrass of Cymodocea rotundata (in Indonesian)
Published 20 July 2023 Science ClosedTags: biological response, growth, laboratory, phanerogams, physiology, South Pacific
The continued use of fossil fuels will increase the concentration of carbon dioxide (CO2) in the atmosphere. Ocean acidification occurs due to CO2 in the atmosphere diffusing into the oceans. The oceans are able to absorb CO2 in the atmosphere as much as 35 % more which causes a decrease in ocean pH. Seagrass Cymodocea rotundata is a type of seagrass that can be found growing in tropical waters. This situation raises concerns about the possible impact on the growth of seagrass C. rotundata. This study aims to analyze the content of nitrate, phosphate and potassium and the growth of seagrass C. rotundata which includes the growth of leaves, rhizomes and roots of C. rotundata against differences in pH. The study used an experimental method with a completely randomized design using a random table. A total of 15 jars with a diameter of 20 cm and a height of 25 cm were used with 3 treatments, each treatment was repeated 5 times. The results of the linear regression test showed that pH had an effect on nitrate concentrations, and had a strong effect on phosphate and potassium concentrations. The highest growth rate of C. rotundata seagrass leaves in the control ranged from 0.50–1.29 mm/day while the lowest at low pH ranged from 0.07–0.73 mm/day. The growth rate of seagrass rhizomes horizontally and vertically was highest at low pH while the lowest was at control pH. The highest growth rate of seagrass roots at low pH ranged from 0.20–0.90 mm/day. while the lowest was in the control ranged from 0.13–0.43 mm/day. pH also affects the growth rate of leaves, rhizomes and seagrass roots of C. rotundata. The lower the pH, the lower the leaf growth rate, in contrast to rhizomes and roots, the lower the pH, the higher the growth rate.
Continue reading ‘The effect of differences pH of waters on the growth rate of seagrass of Cymodocea rotundata (in Indonesian)’Effects of climate change and eutrophication on photosynthesis and carbon-concentrating mechanisms: surprising diversity among reef algae
Published 19 July 2023 Science ClosedTags: algae, biological response, chemistry, growth, laboratory, multiple factors, North Pacific, nutrients, photosynthesis, physiology, primary production
Increased anthropogenic CO2 emission since the start of the Industrial Revolution has brought a changing climate and various threats to coastal ecosystems including ocean warming, ocean acidification (OA), and sea level rise. Coral reef ecosystems are especially vulnerable to the climate change, because ocean warming and acidification decrease calcification and increase bleaching in coral. In addition to these impacts of climate change, coastal ecosystems are already experiencing local anthropogenic impacts such as chronic eutrophication and continuing arrival of new invasive species. In Hawai‘i, large-scale blooms of both native and invasive macroalgae are often observed in the region with coastal eutrophication by land-based anthropogenic nutrient input. Predicting the effects of OA (increased CO2 concentration in the ocean) on algae is not straightforward because many algae are already equipped with carbon-concentrating mechanisms (CCMs) with which algae can increase their internal CO2 concentration for photosynthesis. Further, nutrient availability especially that of the macronutrient, nitrogen (N) could alter the operation of algal CCMs because CCMs involve specific, large proteins such as ribulose-1,5-biphosphate carboxylase-oxygenase (RUBISCO) and carbonic anhydrases (CA). This study experimentally investigated how OA and eutrophication, independently and synergistically, affect photosynthesis and CCMs in common Hawaiian reef algae. Algae can quickly change their maximum photosynthetic rates and CCMs when grown under elevated CO2 and N. Further, we found a surprising diversity among reef algae in how they react to elevated CO2 and N with their CCMs. The results of this study suggest that many Hawaiian algae will thrive under future climate change conditions, and OA and eutrophication will likely work in their favor, accelerating the phase shift from coral-dominated to macroalgal-dominated reefs in unpredictably faster paces and with players that are not easily predicted.
Continue reading ‘Effects of climate change and eutrophication on photosynthesis and carbon-concentrating mechanisms: surprising diversity among reef algae’The effects of ocean change drivers on the ecophysiology of the mottled brittle star Ophionereis fasciata
Published 18 July 2023 Science ClosedTags: biological response, calcification, dissolution, echinoderms, growth, laboratory, mesocosms, mortality, multiple factors, performance, physiology, South Pacific, temperature
Global ocean environments are rapidly changing, posing a substantial threat to the viability of marine populations due to the co-occurrence of different changing ocean (CO) drivers, such as ocean warming (OW) and ocean acidification (OA). In order to persist, marine species undergo some combination of acclimation and adaptation in response to these changes. Understanding such responses is essential to measure and predict the magnitude and direction of environmental changes, leading to the development of different approaches to understanding the links and interactions between biological processes and abiotic environmental conditions. A series of long-term mesocosm experiments have been conducted using adult Ophionereis fasciata as a model to investigate the physiological response and trade-offs of marine organisms to ocean acidification, ocean warming and the combined effect of both drivers. A scenario-based approach was adopted to elucidate the primary physiological responses to conditions currently experienced by this species in its tidally influenced habitat (21-24°C and pH 7.75-7.4) as well as changes expected to occur in the near future due to CO (+2.5 ℃ and -0.36 pH by 2100). Long-term exposure to OW and OA conditions affected survival, metabolic rate, regeneration and growth rates, calcification/dissolution and the righting response of O. fasciata. Temperature changes clearly impacted these aspects of the mottled brittle star, while changes in pH had more subtle or no effect. Our results indicate that for most of the assessed ecophysiological traits, there are no significant interactive effects of OA and OW. Moreover, temperature was the dominant driver, with a greater impact regarding the magnitude and quantity of the affected processes. However, the exposure to a combination of high temperature and low pH produced complex responses in terms of survival and calcification/dissolution. Finally, we documented the first report of symbionts associated with O. fasciata: an obligate amphipod parasite and a facultative commensal polychaete. Our findings indicate that the mottled brittle star will need to cope with CO conditions in context with the predictions made for New Zealand waters, with a potential impact on its performance and survival, as well as its distribution and ecological interactions.
Continue reading ‘The effects of ocean change drivers on the ecophysiology of the mottled brittle star Ophionereis fasciata’Physiological response of an Antarctic cryptophyte to increasing temperature, CO2, and irradiance
Published 12 July 2023 Science ClosedTags: abundance, Antarctic, biogeochemistry, biological response, growth, laboratory, light, multiple factors, otherprocess, photosynthesis, phytoplankton, primary production, temperature
The Southern Ocean, a globally important CO2 sink, is one of the most susceptible regions in the world to climate change. Phytoplankton of the coastal shelf waters around the Western Antarctic Peninsula have been experiencing rapid warming over the past decades and current ongoing climatic changes will expose them to ocean acidification and high light intensities due to increasing stratification. We conducted a multiple-stressor experiment to evaluate the response of the still poorly studied key Antarctic cryptophyte species Geminigera cryophila to warming in combination with ocean acidification and high irradiance. Based on the thermal growth response of G. cryophila, we grew the cryptophyte at suboptimal (2°C) and optimal (4°C) temperatures in combination with two light intensities (medium light: 100 μmol photons m−2 s−1 and high light [HL]: 500 μmol photons m−2 s−1) under ambient (400 μatm pCO2) and high pCO2 (1000 μatm pCO2) conditions. Our results reveal that G. cryophila was not susceptible to high pCO2, but was strongly affected by HL at 2°C, as both growth and carbon fixation were significantly reduced. In comparison, warming up to 4°C stimulated the growth of the cryptophyte and even alleviated the previously observed negative effects of HL at 2°C. When grown, however, at temperatures above 4°C, the cryptophyte already reached its maximal thermal limit at 8°C, pointing out its vulnerability toward even higher temperatures. Hence, our results clearly indicate that warming and high light and not pCO2 control the growth of G. cryophila.
Continue reading ‘Physiological response of an Antarctic cryptophyte to increasing temperature, CO2, and irradiance’The impact of ocean acidification on the physiology of the blue mussel Mytilus edulis
Published 10 July 2023 Science ClosedTags: biological response, growth, laboratory, mollusks, morphology, mortality, North Atlantic
Bivalve aquaculture garners global ecological and economic benefits, which makes the continued health of bivalve populations paramount. Ocean acidification presents a novel pressure on bivalves. Decreased pH due to acidification limits the carbonate available for bivalves to takeup, thus inhibiting the formation and growth of their calcium carbonate-based shells. The aragonite saturation (Ω) of seawater serves a useful biologic contextualization for pH in studies of acidification and bivalves, as an Ω of 1 indicates that calcium and carbonate ions can bond to form calcium carbonate. Shell health is a central aspect of bivalve fitness as it is the main defense of these organisms against predation and exposure to disease or other unfavorable environmental conditions. Resistance of the shell against crushing force is highly relevant as aquaculture bivalves are reportedly becoming increasingly predated upon by crustaceans in the Gulf of Maine as more invasive crab species become established in the region. Juvenile bivalves seem exceptionally susceptible based on reports from the Gulf of Maine shellfish industry that has recently been losing large portions of their juvenile stock to crab predation.
The blue mussel Mytilus edulis was selected for this study as it is a model species in bivalve research and has commercial relevance in the Gulf of Maine. Three cohorts of M. edulis were housed for this study. One cohort was housed in aquaria to simulate ambient pH Gulf of Maine seawater, whereas two were exposed to moderately and highly acidified conditions (0.25 pH and 0.5 pH below ambient) in aquaria. Exposure was conducted for three months and enabled examination of the significance of pH, Ω, and the length of exposure time to the physical conditions of resistance to crushing force, lengthwise growth, and mortality.
Mussels with greater shell length had more resistance to crushing force than smaller mussels, and the force required to crush mussels of all length classes increased at a consistent rate of 1.25 lbf per millimeter of shell length within each length class. The average force required to crush mussels between 40 and 45 mm long was significantly greater than for mussels between 35 and 39.99 mm long. The average force required to crush mussels greater than 45 mm long was also significantly greater than for mussels between 40 and 45 mm long. Exposure time did not have a significant effect on the force required to crush the shells of M. edulis housed for the acidification treatment, but resistance to crushing force increased linearly with increased Ω. Crushing force resistance, standardized against length, was expected to increase by 0.609 lbf/mm per one unit increase of Ω.
Lengthwise growth rates were unaffected by the amount of time that mussels were exposed to treatment, but lower Ω decreased lengthwise growth rates. For every one unit increase of Ω, lengthwise growth was expected to increase by 176%. Mussels housed at ambient pH levels had the highest average lengthwise growth rate, whereas the average lengthwise growth was lowest in the -0.5 pH treatment. One additional mortality out of one-thousand mussels per day was estimated by the end of the study period, but Ω did not significantly affect mussel mortality. The number of mussel mortalities in the aquaria increased over the course of the study period, but percent mortality never exceeded 5% of the total cohort in any of the treatment aquaria, and biweekly percent mortality ranged between 0.18% to 4.92%. Acidification may lower blue mussel shell resistance to crushing force and may increase the timeframe when mussels are more actively susceptible to predation by crabs and other damage through the paired effects of acidification on force resistance and lengthwise growth.
Continue reading ‘The impact of ocean acidification on the physiology of the blue mussel Mytilus edulis’Potential for acclimation of banded-dye murex, Hexaplex trunculus (Linnaeus, 1758) aft er long-term exposure to low pH
Published 5 July 2023 Science ClosedTags: adaptation, biological response, growth, laboratory, Mediterranean, mollusks, multiple factors, otherprocess, temperature
Previous work on ocean acidification highlighted contrasting response between marine species and population. This so-called species-specific response was hypothesized to be partly a consequence of local adaptation to the present range of natural variability in the carbonate chemistry. Under that hypothesis, species tolerance threshold should be correlated to its environmental pH niche. This paper aims to evaluate shell growth rate of Hexaplex trunculus, an important predatory gastropod in benthic communities of Mali Ston Bay. A long-term experiment (310 days) was designed to test a range of pH treatments covering present and future pH levels relevant in the context of future ocean acidification (7.95-7.22 pHT) at the sampling site. Sex had an effect on the shell growth rate irrespective of pH, and was only significant after 236 days. As growth rate in all pH treatments followed seasonal patterns correlating to changes in seawater temperature, the data were divided into 3 time periods. A positive relationship between shell growth rate (SGR, mm day-1) and pH was observed for the period 1-59 days (temperature ranging between 26.5 & 18.8 °C), whereas SGR decreased significantly with pH for the following period (60-236 days, temperature ranging between 20.6 & 8.5 °C). After 236 days (temperature ranging between 27.5 & 14.1 °C), there was no significant difference in SGR among pH. Similar temperature was experienced between the first and third period and the difference in response could be explained as a consequence of an acute negative response versus a longer exposure indicating possible potential for acclimation. Our results highlight the modulating eff ect of temperature and the importance of long-term experiments to better assess impacts of ocean acidifi cation on marine organisms.
Continue reading ‘Potential for acclimation of banded-dye murex, Hexaplex trunculus (Linnaeus, 1758) aft er long-term exposure to low pH’Elevated pCO2 alleviates the toxic effects of polystyrene nanoparticles on the marine microalga Nannochloropsis oceanica
Published 4 July 2023 Science ClosedTags: biological response, growth, laboratory, molecular biology, multiple factors, North Pacific, physiology, phytoplankton, toxicants
Highlights
- Inhibition of marine microalgae by polystyrene nanoparticles (100 nm) was evaluated.
- Increased pCO2 mitigated growth inhibition of algal cells caused by polystyrene nanoparticles.
- Polystyrene nanoparticles achieve inhibition effect by down-regulating key enzymes of TCA cycle.
- Increased pCO2 mitigated the toxicity of polystyrene nanoparticles by upregulating ribosomes and corresponding synthesis processes.
- Aggregation of polystyrene nanoparticles was detected in acidizing experimental medium.
Abstract
Concerns about the environmental effects of nanoplastics on marine ecosystems are increasing. Ocean acidification (OA) has also become a global environmental problem. Plastic pollution occurs concomitantly with anthropogenic climate stressors such as OA. However, the combined effects of NP and OA on marine phytoplankton are still not well understood. Therefore, we have investigated the behavior of ammonia (NH2) polystyrene nanoparticles (PS NP) in f/2 medium under 1000 μatm pCO2 and discussed the toxicity of PS NP (100 nm; 0.5 and 1.5 mg/L) on Nannochloropsis oceanica under long and short-term acidification (LA and SA; pCO2 ~ 1000 μatm). We observed PS NP suspended in pCO2 1000 μatm f/2 medium aggregated to a size greater than nanoscale (1339.00 ± 76.10 nm). In addition, we found that PS NP significantly inhibited the growth of N. oceanica at two concentrations, which also produced oxidative stress. Whereas, the growth of algal cells under the coupling of acidification and PS NP was significantly better than that of single PS NP exposure. This indicated that acidification significantly alleviated the toxic effects of PS NP on N. oceanica, and long-term acidification can even promote the growth of N. oceanica under low-density NP. To further understand the mechanism, we analyzed a comparative transcriptome. The results showed that PS NP exposure inhibited the expression of genes involved in the TCA cycle. The acidification was possibly reflected in ribosomes and corresponding processes, which alleviated the negative effects of PS NP on N. oceanica by promoting the synthesis of related enzymes and proteins. This study provided a theoretical basis for assessing the damage of NP to marine phytoplankton under OA. We propose that future studies evaluating the toxicology of NP to marine ecology should consider the changing ocean climate.
Continue reading ‘Elevated pCO2 alleviates the toxic effects of polystyrene nanoparticles on the marine microalga Nannochloropsis oceanica’Combined effects of ocean deoxygenation, acidification, and phosphorus limitation on green tide macroalga, Ulva prolifera
Published 29 June 2023 Science ClosedTags: algae, biogeochemistry, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, oxygen, photosynthesis, physiology
Highlights
- Additive and antagonistic interactions between the three stressors were mainly observed.
- Ocean deoxygenation, acidification, and P limitation can dysregulate the Ulva prolifera of photosynthetic efficiency.
- Green tide macroalgal Ulva prolifera has a strong acclimation capacity to elevated CO2, low O2, and high N/P.
- Ulva prolifera could use organic P to support its growth under low inorganic phosphorus conditions.
- Increased CO2 levels can decrease the energy costs associated with CCM, and can support the growth of macroalgal cells.
Abstract
Ocean deoxygenation, acidification, and decreased phosphorus availability are predicted to increase in coastal ecosystems under future climate change. However, little is known regarding the combined effects of such environmental variables on the green tide macroalga Ulva prolifera. Here, we provide quantitative and mechanistic understanding of the acclimation mechanisms of U. prolifera to ocean deoxygenation, acidification, and phosphorus limitation under both laboratory and semi-natural (mesocosms) conditions. We found that there were significant interactions between these global environmental conditions on algal physiological performance. Although algal growth rate and photosynthesis reduced when the nitrogen-to‑phosphorus (N/P) ratio increased from 16:1 to 35:1 under ambient CO2 and O2 condition, they remained constant with further increasing N/P ratios of 105:1, 350:1, and 1050:1. However, the increasing alkaline phosphatase activities at high N/P ratios suggests that U. prolifera could use organic P to support its growth under phosphorus limitation. Deoxygenation had no effect on specific growth rate (SGR) but decreased photosynthesis under low N/P ratios of 16:1, 35:1, and 105:1, with reduced activities of several enzymes involved in N assimilation pathway being observed. Elevated CO2 promoted algal growth and alleviated the negative effect of deoxygenation on algal photosynthesis. The patterns of responses to high CO2 and low O2 treatments in in situ experiments were generally consistent with those observed in laboratory experiments. Our results generally found that the strong physiological acclimation capacity to elevated CO2, low O2, and high N/P could contribute to its large-scale blooming in coastal ecosystem.
Continue reading ‘Combined effects of ocean deoxygenation, acidification, and phosphorus limitation on green tide macroalga, Ulva prolifera’Organismal responses to coastal acidification informed by interrelating erosion, roundness and growth of gastropod shells
Published 28 June 2023 Science ClosedTags: biological response, dissolution, field, growth, mollusks, morphology, North Pacific
Current understanding of how calcifying organisms respond to externally forced oceanic and coastal acidification (OCA) is largely based on short-term, controlled laboratory or mesocosm experiments. Studies on organismal responses to acidification (reduced carbonate saturation and pH) in the wild, where animals simultaneously interact with a range of biotic and abiotic circumstances, are limited in scope and interpretation. The present study aimed to better understand the value of gastropod shell attributes and their interrelations in informing about responses to coastal acidification. We investigated shell chemical erosion, shell roundness, and growth rate of Planaxis sulcatus snails, which are locally exposed to acidified or non-acidified rocky intertidal water. We trialed a new approach to quantifying shell erosion based on the spiral suture length (EI, erosion index), and found that shell erosion mirrored field acidification conditions. Acidification caused shells to become rounder (width/length) compared to those of snails from a non-acidified shore. Field growth rate, determined from apertural margin extension of marked and later recaptured snails, was strongly negatively related to both shell erosion and shell roundness. Because the different shell attributes inform about different associations – shell erosion represents an extrinsic passive marker of acidification, and shell roundness and growth rate are intrinsic performance responders – their interrelations imply causation, infer predictive power and improve interpretation confidence. This study contributes to the methodology and interpretation of findings of trait-based field investigations to understand organismal responses to coastal acidification.
Continue reading ‘Organismal responses to coastal acidification informed by interrelating erosion, roundness and growth of gastropod shells’Growth performance, antioxidant indexes, and the expression of genes were considerably promoted by dietary supplementation of alanyl-glutamine and vitamin E in juvenile marine medaka in seawater acidification by carbon dioxide
Published 26 June 2023 Science ClosedTags: biological response, fish, growth, laboratory, molecular biology, morphology, mortality, multiple factors, North Pacific, nutrients, physiology
The experiment was conducted to study the effect of different dietary supplementation of alanyl-glutamine dipeptide (AGD) and/or vitamin E (VE) on the growth performance, antioxidant indexes, and the expression of glutathione peroxidase (GPx) and peroxisome proliferator-activated receptor α (PPARⱭ) genes in juvenile marine medaka (Oryzias melastigma) in seawater acidification. Seven groups of juvenile marine medaka in triplicate were studied in an ecosystem. One of them was in normal seawater (pH 8.1, pH control), and the others were in seawater acidification (pH 7.7) regulated by carbon dioxide (CO2). The juveniles were separately fed for 10 weeks using one of six different diets. The six diets were one control diet (basic feed) without supplements and the other diets with different amounts of additional AGD and/or VE. The juveniles were sampled randomly for analysis of a whole fish in week 0 and week 10. The results showed that different dietary supplementation of AGD and/or VE could considerably promote the growth performance, antioxidant indexes, and the expression of GPx and PPARα genes of juvenile marine medaka in seawater acidification. The optimal diet was D4, with additional AGD 5 g and VE 50 IU per kg of dried feed.
Continue reading ‘Growth performance, antioxidant indexes, and the expression of genes were considerably promoted by dietary supplementation of alanyl-glutamine and vitamin E in juvenile marine medaka in seawater acidification by carbon dioxide’
