Posts Tagged 'biological response'



Elucidating the acid-base mechanisms underlying otolith overgrowth in fish exposed to ocean acidification

Over a decade ago, ocean acidification (OA) exposure was reported to induce otolith overgrowth in teleost fish. This phenomenon was subsequently confirmed in multiple species; however, the underlying physiological causes remain unknown. Here, we report that splitnose rockfish (Sebastes diploproa) exposed to ~1,600 μatm pCO2 (pH ~7.5) were able to fully regulated the pH of both blood and endolymph (the fluid that surrounds the otolith within the inner ear). However, while blood was regulated around pH 7.80, the endolymph was regulated around pH ~8.30. These different pH setpoints result in increased pCO2 diffusion into the endolymph, which in turn leads to proportional increases in endolymph [HCO3] and [CO32−]. Endolymph pH regulation despite the increased pCO2 suggests enhanced H+ removal. However, a lack of differences in inner ear bulk and cell-specific Na+/K+-ATPase and vacuolar type H+-ATPase protein abundance localization pointed out to activation of preexisting ATPases, non-bicarbonate pH buffering, or both, as the mechanism for endolymph pH-regulation. These results provide the first direct evidence showcasing the acid-base chemistry of the endolymph of OA-exposed fish favors otolith overgrowth, and suggests that this phenomenon will be more pronounced in species that count with more robust blood and endolymph pH regulatory mechanisms.

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Growth, DMS and DMSP production in Emiliania huxleyi under elevated CO2 and UV radiation

Highlights

  • Elevated CO2 decreased dimethylsulfide by 20% in the semi-continuous culture.
  • Addition UVA to PAR increased growth and cell size of Emiliania huxleyi on day 4.
  • Addition UVA + UVB to PAR significantly decreased cellular dimethylsulfide.
  • Addition UVA or UVA + UVB to PAR increased particulate dimethylsulfoniopropionate.
  • pCO2 and UVR interacted with particulate dimethylsulfoniopropionate.

Abstract

The effects of ocean acidification and solar radiation on marine organisms have received increasing attention. Coccolithophores are a major producer of dimethylsulfoniopropionate (DMSP), which is a precursor of dimethylsulfide (DMS), a volatile biogenic active gas related to climate. Here, we investigated the individual and combined effects of elevated CO2 and ultraviolet radiation (UVR) on growth, DMS, and DMSP production of Emiliania huxleyi. Elevated CO2 (1000 μatm, HC) decreased the cell concentration, DMS, and particulate DMSP (DMSPp) concentrations by 17%, 20%, and 13%, respectively, compared with ambient CO2 (400 μatm, LC) in the semi-continuous culture. The addition of UVA to photosynthetically active radiation (PAR) increased cell concentration of E. huxleyi by 16% on day 4, which may be due to the photorepair effects induced by UVA, and the effect was time-dependent. PAR + UVA and PAR + UVA + UVB exposure decreased cellular DMS by 25%–56%, and increased cellular DMSPp by 60%–130% compared with PAR on days 3–4. Cellular DMSPp followed the order: PAR + UVA > PAR + UVA + UVB > PAR, and HC had no significant effects on cellular DMSPp compared with LC in the combined experiment. These results aid our understanding of the effects of ocean acidification and UV radiation on the production of methyl sulfur compounds in the ocean.

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Carbonate chemistry in the microenvironment within cyanobacterial aggregates under present-day and future pCO2 levels

Photosynthesis and respiration cause distinct chemical microenvironments within cyanobacterial aggregates. Here, we used microsensors and a diffusion–reaction model to characterize gradients in carbonate chemistry and investigate how these are affected by ocean acidification in Baltic vs. Pacific aggregates (Nodularia and Dolichospermum vs. Trichodesmium). Microsensor measurements of O2 and pH were performed under in situ and expected future pCO2 levels on Nodularia and Dolichospermum aggregates collected in the Baltic Sea. Under in situ conditions, O2 and pH levels within the aggregates covered ranges of 80–175% air saturation and 7.7–9.4 in dark and light, respectively. Carbon uptake in the light was predicted to reduce HCO3 by 100–150 μmol L−1 and CO2 by 3–6 μmol L−1 in the aggregate center compared to outside, inducing strong CO2 depletion (down to 0.5 μmol L−1 CO2 remaining in the center) even when assuming that HCO3 covered 80–90% of carbon uptake. Under ocean acidification conditions, enhanced CO2 availability allowed for significantly lower activity of carbon concentrating mechanisms, including a reduction of the contribution of HCO3 to carbon uptake by up to a factor of 10. The magnification of proton gradients under elevated pCO2 that was predicted based on a lower buffer capacity was observed in measurements despite a concurrent decrease in photosynthetic activity. In summary, we provide a quantitative image of the inorganic carbon environment in cyanobacterial aggregates under present-day and expected future conditions, considering both the individual and combined effects of the chemical and biological processes that shape these environments.

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Performance of a potentially invasive species of ornamental seaweed Caulerpa sertularioides in acidifying and warming oceans

Caulerpa, a (sub) tropical seaweed, is a notorious taxonomic group and an invasive seaweed worldwide. Similar to several species that have been introduced to benthic habitats through aquariums, Caulerpa sertularioides has also been introduced into Korean aquariums, although it is not native to the region. Thus, it is necessary to evaluate the potential of this species for invading domestic macroalgal habitats. Therefore, an indoor mesocosm experiment was conducted to examine the ecophysiological invasion risk of non-native seaweed C. sertularioides under various climate conditions and exposure to three future climate scenarios: acidification (doubled CO2), warming (5 °C increase from ambient temperature), and greenhouse (GR: combination of acidification and warming); additionally, we compared the invasion risk between future and present climates (control: 20 °C and 470 µatm CO2). High CO2 concentrations and increased temperatures positively affected the photosynthesis and growth of C. sertularioides. Photosynthesis and growth were more synergistically increased under GR conditions than under acidification and warming. Consequently, the performance of this potentially invasive species in the native macroalgal Korean habitat will be higher in the future in coastal environments. Therefore, proper management is required to prevent the geographic expansion of C. sertularioides in the Korean coastal ocean.

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Effects of variable daily light integrals and elevated CO2 on the adult and juvenile performance of two Acropora corals

Reef-building corals are subject to multi-day periods of reduced light and progressive ocean acidification. We experimentally assessed how adult and early post-settlement Acropora tenuis and A. hyacinthus corals responded to contrasting daily light integrals (DLI) and to multi-day variability in DLI, and whether contrasting DLIs altered the effects of ocean acidification. Four light treatments—three with stable DLIs (12.6, 7.6, 2.5 mol photons m−2 d−1) and one with variable DLI that averaged 7.6 mol photons m−2 d−1 were fully crossed with two levels of pCO2 (400 and 900 ppm) in a 63-day aquarium experiment. Adult coral growth and protein content declined as average DLI declined, regardless of whether DLI was stable or variable. In both species, photoacclimation was insufficient to compensate for low DLI, although both effective (φPSII) and maximum (Fv/Fm) quantum yields of photosystem two varied by < 5% between all stable DLI treatments. Under variable DLI, both species adjusted their φPSII on the day of change in DLI, whereas Fv/Fm remained relatively constant despite five-fold difference in DLI between days. Elevated CO2 increased protein content in adult A. tenuis at all DLIs, but otherwise had little effect on measured parameters. For juveniles, both species had reduced survival at low DLI due to overgrowth by Peyssonnelia algae, and A. tenuis growth was fastest at low DLI. Our study shows that the effects of multi-day periods of DLI reductions accumulate over time for corals, negatively affecting Acropora adult growth rates and juvenile survival, and hence slowing reef recovery after disturbance.

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Spatiotemporal variability in kelp forest and seagrass ecosystems: can local biogeochemical modification combat acidification stress?

Anthropogenic carbon dioxide (CO2) emissions have driven widespread ocean acidification (OA). OA has reduced surface ocean pH by at least 0.1 pH units since the beginning of the industrial era and global models forecast a further decrease of 0.3 to 0.4 pH units by the end of the century. Submerged aquatic vegetation, such as kelp forests and seagrass beds, has the potential to locally ameliorate OA by removing CO2 during photosynthesis and storing it as fixed carbon. Thus, understanding the contribution of these habitats to local biogeochemistry is essential to inform coastal management and policy, especially as the impacts of anthropogenic climate change become more prevalent. The following work describes high resolution spatiotemporal variability in seagrass and kelp forest biogeochemistry (Chapters 1 and 2) and in the surface canopy extent of a giant kelp forest (Chapter 3).

In order to understand the contributions of kelp forest and seagrass metabolism to their respective local biogeochemistry, we must determine the natural variability in these systems and disentangle the physical and biological drivers of local biogeochemical variability. In Chapter 1, I deployed an extensive instrument array in Monterey Bay, CA, inside and outside of a kelp forest to assess the degree to which kelp locally ameliorates present-day acidic conditions, which we expect to be further exacerbated by OA. Interactions between upwelling exposure, internal bores, and biological production shaped the local biogeochemistry inside and outside of the kelp forest. Significantly elevated pH, attributed to kelp canopy productivity, was observed at the surface inside the kelp forest. This modification was largely limited to a narrow band of surface water, implying that while kelp forests have the potential to locally ameliorate ocean acidification stress, this benefit may largely be limited to organisms living in the upper part of the canopy. In Chapter 2, I quantified net community production (NCP) over a mixed seagrass-coral community on Ngeseksau Reef, Ngermid Bay, Republic of Palau. We observed a net heterotrophic diel signal over the deployment, but dissolved oxygen (O2) fluxes during the day were largely positive, illustrating daytime autotrophy. pH, O2, and temperature followed a clear diel pattern with maxima typically occurring in the afternoon. The relationship between tidal regime and time of day drove the magnitude of the signals observed. The case studies described in Chapters 1 and 2 emphasize the importance of high-resolution measurements (high temporal frequency as well as high horizontal and vertical spatial resolution) and consideration of the multiple drivers responsible for shaping the observed biogeochemical variability. In addition to the photosynthetic biomass (kelp and seagrass) at the center of these studies, the physical environment played an important role in dictating the signals observed, in particular water circulation and residence time.

Biogeochemical studies rarely look beyond a few deployment sites, but the ecosystem contributing to the local biogeochemical variability includes influences from beyond those discrete points. Describing the area around these discrete points is important for accurate assessment of factors driving the signals observed at those points. Remote sensing can help us capture and describe the spatial patterns of biomass contributing to changes observed in our chemical records. In Chapter 3, I established a low altitude unmanned aerial vehicle (UAV) record of giant kelp surface areal extent over 18 months on the wave-protected side of Cabrillo Point (Hopkins Marine Station) in Monterey Bay, CA. This was the same canopy responsible for elevating pH in Chapter 1; however, in this case, the kelp canopy mapping did not overlap in time with biogeochemical measurements in the kelp forest. I compared the UAV kelp classification to canopy cover determined from Landsat satellite images obtained over the same period. There was a linear relationship between the drone kelp ratio and Landsat kelp canopy fraction for spatially-matched pixels; a Landsat kelp fraction of 0.64 was equivalent to 100% kelp cover in the drone data. The level of resolution provided by UAV, compared with Landsat images, could allow more detailed mapping of kelp responses to environmental change. Future studies should pair mapping flights with biogeochemical measurements to quantify the relationship between changes in canopy area and the relative surface canopy modification of pH.

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Tolerance to a highly variable environment does not infer resilience to future ocean warming and acidification in a branching coral

Coral populations from reef habitats that experience extreme daily abiotic fluctuations have been suggested as candidates to survive and proliferate under future climate change. Few studies, however, have exposed corals from dynamic environments to the synergistic effects of ocean warming and acidification to investigate whether tolerance of present-day environmental variability is maintained under future climate stress. This study assessed the impact of RCP2.6 (+0.8°C and +25 ppm) and RCP4.5 (+1.3°C and +66 ppm) ocean warming and acidification on the survivorship, primary calcification (i.e., extension), secondary calcification (i.e., densification), and protein densities of Isopora palifera originating from two distinct reef habitats (abiotically variable reef flat vs. stable reef slope) over 9 weeks. Temperature and pCO2 were offset from a reef slope baseline temperature of 26.0°C ± 0.6°C and pCO2 concentration of 559 ± 56 ppm, incorporating natural diurnal variability. A trade-off was observed in I. palifera originating from the reef flat, which significantly increased tissue protein densities but reduced densification relative to corals from the reef slope. Survivorship nor extension rates differed between corals originating from the variable or stable reef habitats. Mortality increased under RCP4.5 as extension rates increased, indicating that energetic investment in skeletal expansion becomes unsustainable under future climate stress. Increasing temperature and CO2 reduced calcification rates irrespective of the corals originating reef habitat suggesting with future climate change, exposure to greater environmental variability may not benefit coral calcification. These results demonstrate that tolerance to present-day abiotic variability does not necessarily infer resilience to moderate future ocean warming and acidification conditions.

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Response of microbial communities on culturing plates of post-settlement sea cucumbers to seawater acidification and warming

Seawater acidification and warming have been found to affect the early life of many marine organisms, but their effects on the microbial community in the environment related to the early development stage of aquaculture species have been rarely investigated. To understand how seawater acidification and warming impact the microbial community in aquaculture systems, we designed four microcosms to monitor and characterize the microbial composition on the corrugated plates in the Apostichopus japonicus culture tanks during its post-settlement stage. High-throughput 16S rRNA sequencing revealed that the bacterial community composition varied significantly in different periods of incubation. The bacterial diversity and community composition were obviously changed by seawater acidification and warming in the early period and then tended to revert to the level of the control group. Acidification significantly increased the relative abundance of dominant families Rhodobacteraceae and Flavobacteriaceae in the early period, suggesting that microbiota could increase the abundance of predominant taxa to adapt to increased CO2 concentration and reconstruct a stable community structure. No interaction effect of both factors was observed in the combined group. Results reveal that the microbial communities on the corrugated plates in A. japonicus culture tank were affected in the early period of incubation, and could then acclimatize to the increased CO2 and temperature. This study provides new insights into the variation and adaptation responses of the microbiota in aquaculture systems to seawater acidification and warming.

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Responses of biogenic sulfur compounds concentrations to dust aerosol enrichment and ocean acidification in the western Pacific Ocean

Abstract

Deck incubation experiments were conducted to investigate how the addition of atmospheric dust aerosols and ocean acidification (OA) affect phytoplankton growth and the production of dimethylsulfide (DMS), its precursor dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) in the oligotrophic western Pacific Ocean. The incubation experiment showed that the deposition of simulated dust aerosols greatly influenced phytoplankton growth and the release of biogenic sulfur compounds (BSCs). Furthermore, it altered the N:P ratios in seawater and phytoplankton community composition, elevating the proportions of strong DMSP and DMSO producers (mainly haptophytes). The average Chl-a and DMS/P/O concentrations in the acidified treatment (pH 7.9) were 86.76%, 82.53%, 84.17%, and 231.06% higher, respectively, than in the control. The results indicated that lower pH promoted the growth of diatoms and, to a certain extent, the release of the three BSCs.

Plain Language Summary

About 500 Mt of dust are deposited in the ocean each year. Atmospheric dust deposition can supply enough nutrients to the ocean to enhance marine primary productivity and affect the subsequent concentrations of the climate-gas dimethylsulfide (DMS) and related biogenic sulfur compounds (BSCs). Besides, ocean acidification is increasingly severe and low pH can affect the growth of phytoplankton. Therefore, we carried out deck incubation experiments to determine how the deposition of atmospheric dust aerosols and ocean acidification (OA) alter the production of BSCs. We found that the addition of dust aerosols elevated the abundance of strong DMSP and DMSO producers (Phaeocystis sp. and Gephyrocapsa oceanica) and increased the concentrations of sulfur compounds. The lower pH accelerated the growth of diatoms in the early and mid-late stages of treatments and promoted the production of BSCs.

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Behavioural stress propagation in benthic invertebrates caused by acute pH drop-induced metabolites

Studies on pH stress in marine animals typically focus on direct or species-specific aspects. We here test the hypothesis that a drop to pH = 7.6 indirectly affects the intra- and interspecific interactions of benthic invertebrates by means of chemical communication. We recorded fitness-relevant behaviours of small hermit crabs Diogenes pugilator, green shore crabs Carcinus maenas, and harbour ragworms Hediste diversicolor in response to short-term pH drop, and to putative stress metabolites released by conspecifics or gilt-head sea bream Sparus aurata during 30 min of acute pH drop. Not only did acute pH drop itself impair time to find a food cue in small hermit crabs and burrowing in harbour ragworms, but similar effects were observed under exposure to pH drop-induced stress metabolites. Stress metabolites from S. aurata, but not its regular control metabolites, also induced avoidance responses in all recipient species. Here, we confirm that a short-term abrupt pH drop, an abiotic stressor, has the capacity to trigger the release of metabolites which induce behavioural responses in conspecific and heterospecific individuals, which can be interpreted as a behavioural cost. Our findings that stress responses can be indirectly propagated through means of chemical communication warrant further research to confirm the effect size of the behavioural impairments caused by stress metabolites and to characterise their chemical nature.

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Inducible defenses in an estuarine bivalve do not alter predator handling times and are not affected by climate change

Mussels use their shells for protection which they can thicken or grow in response to predator cues, commonly referred to as an inducible defense. Oceans are experiencing elevated pCO2 due to climate change. Elevated pCO2 can have negative effects on bivalve morphology and physiology, but we are still learning about the consequences of these effects on predator-prey interactions, a key motivation of this study. Using a 4 wk (short-term) laboratory experiment, we orthogonally manipulated 2 levels of pCO2 (ambient or elevated to predicted future conditions that mimicked diel variability) and 2 levels of predator presence (absent or present) of blue crabs Callinectes sapidus to determine their effects on the morphology and predator handling times on southern ribbed mussels Geukensia granosissima. Experimental results indicated that shell length and width increased in mussels in response to the predator cues, and these inducible defenses were not affected by elevated pCO2. Unexpectedly, mussels exposed to elevated pCO2 exhibited greater growth in shell depth independent of the predator treatment, resulting in shells with rounder shapes. These effects on mussel morphometrics did not affect average crab handling times, but mussels exposed to the presence of a predator under elevated pCO2 conditions had highly variable handling times. This work highlights the complexity of animal physiology, morphology, and interspecific interactions on predator-prey relationships in a changing ocean.

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The effectiveness of Laminaria Digitata on mitigating ocean acidification through pH analysis

In recent years CO2 levels have been rising worldwide, causing increased acidification of ocean water. Currently the average oceanic pH is 8, and while it is known that ocean water is naturally slightly alkaline, CO2 emissions continue to rise and the ocean continues to absorb these emissions. This leads to a decrease in oceanic pH as it continues to become more acidic. The pH levels of the ocean have already fallen by 0.1 in the last 200 years. A 0.1 decrease may not seem drastic but consider the fact that the human body has a natural pH of around 7.4, and if it drops to 7.2 (just a 0.2 decrease) it may lead to death. A seemingly insignificant difference in pH level can have drastic effects on the human body, thus, the same can be considered when it comes to the ocean. Ocean acidification has already impacted many different forms of marine life and will continue to do so if no method is found to prevent the further acidification of ocean water. In the following experiment, Laminaria (kelp) was tested for capabilities of neutralizing the pH of ocean water. To combat the current ocean acidification conflict, recently, macroalgaes have been in the spotlight for its capabilities of absorbing CO2 from ocean water with remarkable results. Laminarias have proven to be particularly effective at absorbing CO2 and restoring pH levels of ocean waters, justifying its use in this experiment. Through pH analysis, the effectiveness of the Laminaria was measured over a 21 day time frame, and data was collected.

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Study the effect of low pH on Ruditapes decussatus (Mollusca: Bivalvia)

The grooved carpet shell clam (Ruditapes decussatus) is one of the most economically essential mollusks in Mediterranean lagoons and sandy beaches, with fisheries and aquaculture both contributing to its abundance. The goal of this research is to see how varying amounts of acidity affect this calcifying organism. 420 ppm (ambient control), 550 ppm, 750 ppm, and 1050 ppm were used to incubate juvenile clams in CO2  enriched saltwater. With increasing pCO2 , the biological parameters evaluated revealed a small decline. Differences, however, were not substantial. In terms of overall weight, the reduction was greatest at 550 and 1050 ppm. Furthermore, clams kept at 550 parts per million had the lowest condition index and the greatest mortality rate of 8%. Both the 550 ppm and the control 420 ppm groups demonstrated an increase in metabolic rate and ammonia excretion in the physiological response testing. With increasing acidification, the algal feed clearance rate declined, with the highest average value in the control (420 ppm) group and the lowest average value in the extremely high pCO2 (1050 ppm) group. Ocean acidification may put further strain on R. decussatus’ health and economic value by the end of the century.

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Modelling ocean acidification effects with life stage-specific responses alters spatiotemporal patterns of catch and revenues of American lobster, Homarus americanus

Ocean acidification (OA) affects marine organisms through various physiological and biological processes, yet our understanding of how these translate to large-scale population effects remains limited. Here, we integrated laboratory-based experimental results on the life history and physiological responses to OA of the American lobster, Homarus americanus, into a dynamic bioclimatic envelope model to project future climate change effects on species distribution, abundance, and fisheries catch potential. Ocean acidification effects on juvenile stages had the largest stage-specific impacts on the population, while cumulative effects across life stages significantly exerted the greatest impacts, albeit quite minimal. Reducing fishing pressure leads to overall increases in population abundance while setting minimum size limits also results in more higher-priced market-sized lobsters (> 1 lb), and could help mitigate the negative impacts of OA and concurrent stressors (warming, deoxygenation). However, the magnitude of increased effects of climate change overweighs any moderate population gains made by changes in fishing pressure and size limits, reinforcing that reducing greenhouse gas emissions is most pressing and that climate-adaptive fisheries management is necessary as a secondary role to ensure population resiliency. We suggest possible strategies to mitigate impacts by preserving important population demographics.

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Combined effects of ocean warming and acidification on the larval stages of the European abalone Haliotis tuberculata

Highlights

  • Combined impacts of ocean acidification and warming on the larvae of the European abalone were investigated.
  • No interactive impact of temperature and pH was recorded.
  • Tissue organogenesis, shell formation, and shell length significantly declined due to low pH.
  • High temperature significantly increased the proportion of fully shelled larvae at 24 hpf, but increased the proportion of unshelled larvae at 72 hpf.
  • High temperature increased the settlement rate of the larvae.

Abstract

This study examined the physiological responses of the larval stages of Haliotis tuberculata, an economically important abalone, to combined temperature (17 °C and 19 °C) and pH (ambient pH and −0.3 units, i.e., +200% increase in seawater acidity) in a full factorial experiment. Tissue organogenesis, shell formation, and shell length significantly declined due to low pH. High temperature significantly increased the proportion of fully shelled larvae at 24 h post-fertilization (hpf), but increased the proportion of unshelled larvae at 72 hpf. Percentage of swimming larvae at 24 hpf, 72 hpf and 96 hpf significantly declined due to high temperature, but not because of low pH. Larval settlement increased under high temperature, but was not affected by low pH. Despite the fact that no interaction between temperature and pH was observed, the results provide additional evidence on the sensitivity of abalone larvae to both low pH and high temperature. This may have negative consequences for the persistence of abalone populations in natural and aquaculture environments in the near future.

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Differences in organic carbon release between conchocelis and thalli of Pyropia haitanensis and responses to changes in light intensity and pH

Highlights

  • DOC production rate of thallus was much higher than that of conchocelis.
  • DOC production rate of thallus tends to increase with light intensity.
  • Ocean acidification did not significantly change the DOC production rate of thallus.

Abstract

The large-scale cultivation of macroalgae has the potential to act as a carbon sink because macroalgae can release a large amount of organic carbon into the surrounding seawater. However, this needs to be evaluated on the basis of the entire life cycle under a background of changes in pH and light intensity. The present study investigated the difference in organic carbon release between conchocelis and thallus stages of the economically important red alga Pyropia haitanensis in response to three light intensities (10, 50, and 500 μmol m−2 s−1) and two pH conditions (current pH: 8.1, projected future pH: 7.5). The study found that regardless of the light intensity and pH values, the growth rates, production rates of tissue carbon, and dissolved organic carbon (DOC) of thalli tended to be higher than those of conchocelis, by more than 170%, 85%, and 106%, respectively. The DOC production rate was higher than the production rate of particulate organic carbon (POC) by at least two orders of magnitude. Positive correlations were found between growth rate and production rates of tissue carbon and growth rate and DOC production rate, but no clear relationship was found between growth and POC production. The DOC production rate of thallus tended to increase with light intensity but was not significantly influenced by ocean acidification. However, decay of tissue caused by exposure of the conchocelis to high light intensity resulted in increased POC and DOC production rates, indicating the complexity of organic carbon release by Phaitanensis. This study provides insights into the release of organic carbon during the complete life cycle of Phaitanensis, and the results can further our understanding of the carbon metabolism of this cultivated macroalgal species.

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The short and long-term implications of warming and increased sea water pCO2 on the physiological response of a temperate neogastropod species

Global average temperatures and seawater pCO2 have rapidly increased due to the oceanic uptake of atmospheric carbon dioxide producing severe consequences for a broad range of species. The impacts on marine ectotherms have been largely reported at short-term scales (i.e. from days to weeks); however, the prolonged effects on long-term processes such as reproduction have received little attention. The gastropod Ocenebra erinaceus is a key predator structuring communities on rocky shores of the French and UK coasts. Even though rocky shore species are regarded as being very tolerant to changes in temperature and pH, many of them are living near their upper tolerance limits, making them susceptible to rapid environmental changes. Here, we report that future mean seawater conditions (RCP8.5, + 3 °C and ~ 900 μatm CO2) do not significantly affect the physiology and molecular response of O. erinaceus adults after 132 days. During the first 50 days, there was a slight impact on oxygen consumption rates and body weight; however, after 95 days of exposure, gastropods fully acclimated to the experimental condition. Despite this, reproduction in females exposed to these future seawater conditions ceased after long-term exposure (~ 10 months). Therefore, in the short-term, O. erinaceus appear to be capable of full compensation; however, in the long-term, they fail to invest in reproduction. We conclude studies should be based on combined results from both short- and long-term effects, to present realistic projections of the ecological consequences of climate warming.

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Effects of ocean acidification on the performance and interaction of fleshy macroalgae and a grazing sea urchin

Highlights

  • We investigated the direct and indirect effects of CO2 on an urchin and macroalgae.
  • Elevated CO2 increased production of fleshy macroalgae biomass but not photosynthesis.
  • Urchin respiration, biomass, righting time, and consumption rate were unaffected.
  • Reduced algal nutrition interacted with impaired chemosensing to preserve foraging.
  • Foraging and consumption suggest sustained trophic interactions under acidification.

Abstract

When predicting the response of marine ecosystems to climate change, it is increasingly recognized that understanding the indirect effects of ocean acidification on trophic interactions is as important as studying direct effects on organism physiology. Furthermore, comprehensive studies that examine these effects simultaneously are needed to identify and link the underlying mechanisms driving changes in species interactions. Using an onshore ocean acidification simulator system, we investigated the direct and indirect effects of elevated seawater pCO2 on the physiology and trophic interaction of fleshy macroalgae and the grazing sea urchin Lytechinus variegatus. Macroalgal (Dictyota spp.) biomass increased despite decreased photosynthetic rates after two-week exposure to elevated pCO2. Algal tissue carbon content remained constant, suggesting the use of alternative carbon acquisition pathways beneficial to growth under acidification. Higher C:N ratios driven by a slight reduction in N content in algae exposed to elevated pCO2 suggest a decrease in nutritional content under acidification. Urchin (L. variegatus) respiration, biomass, and righting time did not change significantly after six-week exposure to elevated pCO2, indicating that physiological stress and changes in metabolism are not mechanisms through which the trophic interaction was impacted. Correspondingly, urchin consumption rates of untreated macroalgae (Caulerpa racemosa) were not significantly affected by pCO2. In contrast, exposure of urchins to elevated pCO2 significantly reduced the number of correct foraging choices for ambient macroalgae (Dictyota spp.), indicating impairment of urchin chemical sensing under acidification. However, exposure of algae to elevated pCO2 returned the number of correct foraging choices in similarly exposed urchins to ambient levels, suggesting alongside higher C:N ratios that algal nutritional content was altered in a way detectable by the urchins under acidification. These results highlight the importance of studying the indirect effects of acidification on trophic interactions simultaneously with direct effects on physiology. Together, these results suggest that changes to urchin chemical sensing and algal nutritional quality are the driving mechanisms behind surprisingly unaltered urchin foraging behavior for fleshy macroalgae under joint exposure to ocean acidification. Consistent foraging behavior and consumption rates suggest that the trophic interaction between L. variegatus and fleshy macroalgae may be sustained under future acidification. However, increases in fleshy macroalgal biomass driven by opportunistic carbon acquisition strategies have the potential to cause ecological change, depending on how grazer populations respond. Additional field research is needed to determine the outcome of these results over time and under a wider range of environmental conditions.

Continue reading ‘Effects of ocean acidification on the performance and interaction of fleshy macroalgae and a grazing sea urchin’

Who wins or loses matters: strongly interacting consumers drive seagrass resistance under ocean acidification

Highlights

  • Ocean acidification (OA) directly facilitated algal epiphyte and seagrass.
  • Co-occurring grazers variably controlled algal overgrowth on seagrass.
  • pH-tolerant, strongly interacting grazers maintained overall grazing pressure.
  • Grazing and OA additively increased seagrass productivity.

Abstract

Global stressors are increasingly altering ecosystem resistance, resilience, and functioning by reorganizing vital species interactions. However, our predictive understanding of these changes is hindered by failures to consider species-specific functional roles and stress responses within communities. Stressor-driven loss or reduced performance of strongly interacting species may generate abrupt shifts in ecosystem states and functions. Yet, empirical support for this prediction is scarce, especially in marine climate change research. Using a marine assemblage comprising a habitat-forming seagrass (Phyllospadix torreyi), its algal competitor, and three consumer species (algal grazers) with potentially different functional roles and pH tolerance, we investigated how ocean acidification (OA) may, directly and indirectly, alter community resistance. In the field and laboratory, hermit crabs (Pagurus granosimanus and P. hirsutiusculus) and snails (Tegula funebralis) displayed distinct microhabitat use, with hermit crabs more frequently grazing in the area of high algal colonization (i.e., surfgrass canopy). In mesocosms, this behavioral difference led to hermit crabs exerting ~2 times greater per capita impact on algal epiphyte biomass than snails. Exposure to OA variably affected the grazers: snails showed reduced feeding and growth under extreme pH (7.3 and 7.5), whereas hermit crabs (P. granosimanus) maintained a similar grazing rate under all pH levels (pH 7.3, 7.5, 7.7, and 7.95). Epiphyte biomass increased more rapidly under extreme OA (pH 7.3 and 7.5), but natural densities of snails and hermit crabs prevented algal overgrowth irrespective of pH treatments. Finally, grazers and acidification additively increased surfgrass productivity and delayed the shoot senescence. Hence, although OA impaired the function of the most abundant consumers (snails), strongly interacting and pH-tolerant species (hermit crabs) largely maintained the top-down pressure to facilitate seagrass dominance. Our study highlights significant within-community variation in species functional and response traits and shows that this variation has important ecosystem consequences under anthropogenic stressors.

Continue reading ‘Who wins or loses matters: strongly interacting consumers drive seagrass resistance under ocean acidification’

Effects of ocean acidification on resident and active microbial communities of Stylophora pistillata

Ocean warming and ocean acidification (OA) are direct consequences of climate change and affect coral reefs worldwide. While the effect of ocean warming manifests itself in increased frequency and severity of coral bleaching, the effects of ocean acidification on corals are less clear. In particular, long-term effects of OA on the bacterial communities associated with corals are largely unknown. In this study, we investigated the effects of ocean acidification on the resident and active microbiome of long-term aquaria-maintained Stylophora pistillata colonies by assessing 16S rRNA gene diversity on the DNA (resident community) and RNA level (active community). Coral colony fragments of S. pistillata were kept in aquaria for 2 years at four different pCO2 levels ranging from current pH conditions to increased acidification scenarios (i.e., pH 7.2, 7.4, 7.8, and 8). We identified 154 bacterial families encompassing 2,047 taxa (OTUs) in the resident and 89 bacterial families including 1,659 OTUs in the active communities. Resident communities were dominated by members of Alteromonadaceae, Flavobacteriaceae, and Colwelliaceae, while active communities were dominated by families Cyclobacteriacea and Amoebophilaceae. Besides the overall differences between resident and active community composition, significant differences were seen between the control (pH 8) and the two lower pH treatments (7.2 and 7.4) in the active community, but only between pH 8 and 7.2 in the resident community. Our analyses revealed profound differences between the resident and active microbial communities, and we found that OA exerted stronger effects on the active community. Further, our results suggest that rDNA- and rRNA-based sequencing should be considered complementary tools to investigate the effects of environmental change on microbial assemblage structure and activity.

Continue reading ‘Effects of ocean acidification on resident and active microbial communities of Stylophora pistillata’

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