Archive for the 'Science' Category



Predictive model for gross community production rate of coral reefs using ensemble learning methodologies

Coral reefs play a vital role in maintaining the ecological balance of the marine ecosystem. Various marine organisms depend on coral reefs for their existence and their natural processes. Coral reefs provide the necessary habitat for reproduction and growth for various exotic species of the marine ecosystem. In this article, we discuss the most important parameters which influence the lifecycle of coral and coral reefs such as ocean acidification, deoxygenation and other physical parameters such as flow rate and surface area. Ocean acidification depends on the amount of dissolved Carbon dioxide (CO2). This is due to the release of H+ ions upon the reaction of the dissolved CO2 gases with the calcium carbonate compounds in the ocean. Deoxygenation is another problem that leads to hypoxia which is characterized by a lesser amount of dissolved oxygen in water than the required amount for the existence of marine organisms. In this article, we highlight the importance of physical parameters such as flow rate which influence gas exchange, heat dissipation, bleaching sensitivity, nutrient supply, feeding, waste and sediment removal, growth and reproduction. In this paper, we also bring out these important parameters and propose an ensemble machine learning-based model for analyzing these parameters and provide better rates that can help us to understand and suitably improve the ocean composition which in turn can eminently improve the sustainability of the marine ecosystem, mainly the coral reefs

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Risk-induced trait response in planktonic larvae is altered under an acidified scenario

Highlights

  • Conspecific and potential predator odours, but not all, induced tail flicking behavior
  • Low pH disrupted the risk-induced trait response to a potential predator
  • Chemosensation and the predator-prey interaction was affected by acidification

Abstract

Our changing climate is affecting predator-prey interactions in different ways. Increasing atmospheric CO2 is acidifying the ocean and disrupting the chemosensation of several species. Here, we evaluated a risk-induced trait response to a potential predator under an acidified scenario. Using planktonic crab larvae as a prey model, we first verified their swimming avoidance response to different potential fish predators and conspecific odours. Prey intensified their avoidance response to conspecific and predator odours, but not to all predators, with no maternal effect. Then, larvae were exposed to a responsive predator odour under a predicted acidified scenario. A similar response was observed for both saltwater and predator odour under low pH conditions. Thus, acidification seems to affect the chemosensation of planktonic larvae, leading them to not distinguish between a non-harmful stimulus and a potential predator.

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Stylophora under stress: a review of research trends and impacts of stressors on a model coral species

Highlights

  • Stylophora pistillata is model coral and is increasingly used in stress studies.
  • Though its range spans the Indo-Pacific, 61% of studies are from the northern Red Sea.
  • Most studies (76%) assess a single stressor, and field experiments are scarce.
  • Temperature is the most tested (51% of studies) and most detrimental stressor.
  • Some stressors (e.g., hypoxia) and responses (e.g., microbiome) are understudied.

Abstract

Sometimes called the “lab rat” of coral research, Stylophora pistillata (Esper, 1797) has been extensively used in coral biology in studies ranging from reef ecology to coral metabolic processes, and has been used as a model for investigations into molecular and cellular biology. Previously thought to be a common species spanning a wide distribution through the Indo-Pacific region, “S. pistillata” is in fact four genetically distinct lineages (clades) with different evolutionary histories and geographical distributions. Here, we review the studies of stress responses of S. pistillata sensus lato (clades 1–4) and highlight research trends and knowledge gaps. We identify 126 studies on stress responses including effects of temperature, acidification, eutrophication, pollutants, and other local impacts. We find that most studies have focused on the effect of single stressors, especially increased temperature, and have neglected the combined effects of multiple stressors. Roughly 61% of studies on S. pistillata come from the northern Red Sea (clade 4), at the extreme limit of its current distribution; clades 2 and 3 are virtually unstudied. The overwhelming majority of studies were conducted in laboratory or mesocosm conditions, with field experiments constituting only 2% of studies. We also note that a variety of experimental designs and treatment conditions makes it difficult to draw general conclusions about the effects of particular stressors on S. pistillata. Given those knowledge gaps and limitations in the published research, we suggest a more standardized approach to compare responses across geographically disparate populations and more accurately anticipate responses to predicted future climate conditions.

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The history, biological relevance, and potential applications for polyp bailout in corals

Corals have evolved a variety of stress responses to changing conditions, many of which have been the subject of scientific research. However, polyp bailout has not received widespread scientific attention, despite being described more than 80 years ago. Polyp bailout is a drastic response to acute stress in which coral colonies break down, with individual and patches of polyps detaching from the colony and the calcareous skeleton Polyps retain their symbiotic partners, have dispersal ability, and may undergo secondary settlement and calcification. Polyp bailout has been described worldwide in a variety of anthozoan species, especially in Scleractinia. It can be induced by multiple natural stressors, but also artificially. Little is known about the evolutionary and ecological potential and consequences of breaking down modularity, the dispersal ability, and reattachment of polyps resulting from polyp bailout. It has been shown that polyp bailout can be used as a model system, with promise for implementation in various research topics. To date, there has been no compilation of knowledge on polyp bailout, which prompted us to review this interesting stress response and provide a basis to discuss research topics and priorities for the future.

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Crustose coralline algae display sensitivity to near future global ocean change scenarios

Most research investigating how ocean warming and acidification will impact marine species has focused on visually dominant species, such as kelps and corals, while ignoring visually cryptic species such as crustose coralline algae (CCA). CCA are important keystone species that provide settlement cues for invertebrate larvae and can be highly sensitive to global ocean change. However, few studies have assessed how CCA respond to low emission scenarios or conditions. In a laboratory experiment, we examined the responses of temperate CCA assemblages to combined warming and acidification projected under low, medium, and high emissions. Net calcification and net photosynthesis significantly declined in all emissions scenarios, while significant reductions in relative growth rates and increases in percentage bleaching were observed in the highest emission scenario. The negative responses of CCA to both low and medium emissions suggest that they may be adversely impacted by combined warming and acidification by 2030 if current emissions are sustained. This will have far reaching consequences for commercially important invertebrates that rely on them to induce settlement of larvae. These findings highlight the need to take rapid action to preserve these critical keystone species and the valuable services they provide.

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Novel environmental conditions due to climate change in the world’s largest marine protected areas

Highlights

  • Up to 97% of very large marine protected areas will contain novel conditions
  • Very large marine protected areas in the tropics most exposed to novelty
  • Novel conditions for pH emerge as soon as 2030
  • 44.9% of the ocean will see novel conditions by 2060, up to 87% by 2100

Science for society

Oceans cover more than 70% of the Earth’s surface and provide us with goods and services ranging from food and energy to cultural resources and identity. However, climate change threatens the availability of these ocean-derived benefits. Climate change is turning once familiar and stable ocean conditions into unfamiliar and novel ones. These changes might even be significant enough to undermine much of the work done to protect the ocean.

This research investigates the timing and impact of climate change on the oceans and the largest MPAs. We show that a majority (up to 87%) of the ocean will have novel conditions, as will almost all of the MPAs we examined (97%). These novel conditions may cause culturally and economically important species to migrate or possibly go extinct. Understanding when, where, and how these changes occur can help inform ocean and climate policy that connects people across space and time.

Summary

Climate change is altering the biogeochemical conditions of the ocean, leading to the emergence of novel environmental conditions that may drastically affect the performance of very large marine protected areas (VLMPAs) (area > 100,000 km2). Given the prominent role that VLMPAs play in ocean conservation, determining when and where novel conditions will emerge within VLMPAs is vital for ensuring a healthy ocean in the future. Here, using a non-parametric approach to detect novelty, we show that 60%–87% of the ocean and 76%–97% of VLMPAs are expected to contain novel conditions across multiple biogeochemical variables by 2100, with novel conditions in pH emerging by 2030. With most VLMPAs expected to contain environmental conditions unlike those currently within their boundaries, and given the likelihood of any of these climate futures unfolding, present-day management will need to consider alterations to current and future VLMPA design and use.

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Insignificant response of bacterioplankton community to elevated pCO2 during a short-term microcosm experiment in a subtropical eutrophic coastal ecosystem

Ocean acidification, as one of the major consequences of global climate change, markedly affects multiple ecosystem functions in disparate marine environments from coastal habitats to the deep ocean. Evaluation of the responses of marine microbial community to the increasing partial pressure of CO2 (pCO2) is crucial to explore the microbe-driven biogeochemical processes in the future ocean. In this study, a microcosm incubation of eutrophic coastal water from Xiamen Bay under elevated pCO2 (about 1,000 μatm) and control (ambient air, about 380–410 μatm) conditions was conducted to investigate the effect of ocean acidification on the natural bacterioplankton community. During the 5-day incubation period, the chlorophyll a concentration and bacterioplankton abundance were not significantly affected by increased pCO2. Hierarchical clustering and non-metric multidimensional scaling analysis based on Bray-Curtis similarity among the bacterioplankton community derived from the 16S rRNA genes revealed an inconspicuous impact of elevated pCO2 on the bacterial community. During the incubation period, Proteobacteria, Bacteroidetes, Actinobacteria, Cyanobacteria, and Epsilonbacteraeota were predominant in all microcosms. Despite the distinct temporal variation in the composition of the bacterioplankton community during the experimental period, statistical analyses showed that no significant difference was found on bacterioplankton taxa between elevated pCO2 and control, indicating that the bacterioplankton at the population-level were also insensitive to elevated pCO2. Our results therefore suggest that the bacterioplankton communities in the fluctuating and eutrophic coastal ecosystems appear to be adaptable to the short-term elevated pCO2.

Continue reading ‘Insignificant response of bacterioplankton community to elevated pCO2 during a short-term microcosm experiment in a subtropical eutrophic coastal ecosystem’

A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: the enhancement of metabolic carbonate dissolution in a semienclosed lagoon

In contrast to other seagrass meadows where seawater carbonate chemistry generally shows strong diel variations with higher pH but lower partial pressure of CO2 (pCO2) during the daytime and lower pH but higher pCO2 during nighttime due to the alternation in photosynthesis and respiration, the seagrass meadows of the inner lagoon (IL) on Dongsha Island had a unique diel pattern with extremely high pH and low pCO2 across a diel cycle. We suggest that this distinct diel pattern in pH and pCO2 could be associated with the enhancement of total alkalinity (TA) production coupled to carbonate sediment dissolution in a semienclosed lagoon. The confinement of the IL may hamper water exchange and seagrass detritus export to the adjacent open ocean, which may result in higher organic matter loading to the sediments, and longer residence time of the water in the IL, accompanied by microbial respiration (both aerobic and anaerobic) that may reduce carbonate saturation level to drive carbonate dissolution and thus TA elevation, thereby forming such a unique diel pattern in carbonate chemistry. This finding further highlights the importance of considering TA production through metabolic carbonate dissolution when evaluating the potential of coastal blue carbon ecosystems to buffer ocean acidification and to absorb atmospheric CO2, in particular in a semienclosed setting.

Continue reading ‘A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: the enhancement of metabolic carbonate dissolution in a semienclosed lagoon’

Red tide events and seasonal variations in the partial pressure of CO2 and related parameters in shellfish-farming bays, Southeastern Coast of Korea

Mixed results have been reported on the evaluation of the coastal carbon cycle and its contribution to the global carbon cycle, mainly due to the shortage of observational data and the considerable spatiotemporal variability arising from complex biogeochemical factors. In this study, the partial pressure of carbon dioxide (pCO2) and related environmental factors were measured in the Jinhae–Geoje–Tongyeong bay region of the southeastern Korean Peninsula in February 2014, August 2014, April 2015, and October 2015. The mean pCO2 of surface seawater ranged from 215 to 471 μatm and exhibited a high correlation with the surface seawater temperature when data for August were excluded (R2 = 0.69), indicating that the seasonal variation in CO2 could be largely attributed to the variation in seawater temperature. However, a severe red tide event occurred in August 2014, when the lowest pCO2 value was observed despite a relatively high seawater temperature. It is considered that the active biological production of phytoplankton related to red tides counteracted the summer increase in pCO2. Based on the correlation between pCO2 and temperature, the estimated decrease in pCO2 caused by non-thermal factors was approximately 200 μatm. During the entire study period, the air–sea CO2 flux ranged from −14.2 to 3.7 mmol m–2 d–1, indicating that the study area served as an overall sink for atmospheric CO2, and only functioned as a weak source during October. The mean annual CO2 flux estimated from the correlation with temperature was −5.1 mmol m–2 d–1. However, because this estimate did not include reductions caused by sporadic events of biological production, such as red tides and phytoplankton blooms, the actual uptake flux is considered to be higher. The mean saturation state (ΩAr) value of carbonate aragonite was 2.61 for surface water and 2.04 for bottom water. However, the mean ΩAr of bottom water was <2 in August and October, and the ΩAr values measured at some of the bottom water stations in August were <1. Considering that the period from August to October corresponds to the reproduction and growth stages of shellfish, such low ΩAr values could be very damaging to shellfish production and the aquaculture industry.

Continue reading ‘Red tide events and seasonal variations in the partial pressure of CO2 and related parameters in shellfish-farming bays, Southeastern Coast of Korea’

Decadal acidification in a subtropical coastal area under chronic eutrophication

Highlights

  • Acidification rate was −0.0085 ± 0.0069 pH·unit·yr−1 in Hong Kong Coast from 1986 to 2017.
  • The coastal acidification was dominated by water discharges particularly after 2001.
  • Increasing DIN:DIP was highlighted in this region during this acidification intensification.

Abstract

Acidification in coastal water usually becomes more intense due to the coupling of anthropogenic activities and climate change. In order to better understand the relationship between long-term coastal acidification (CA) and coastal eutrophication (CE), in-situ monthly data over the past three decades (1986–2017) were analyzed from Hong Kong Coast (HKC). The coastwide annual mean pH change (ΔpHmean) was estimated at −0.0085 ± 0.0069 unit·yr−1 in last decades, which was over four times stronger than current estimation on open ocean acidification rate (∼−0.0019 unit·yr−1). According to the CA spatial pattern, greater pH decline (ΔpHmean = −0.017 ± 0.009 unit·yr−1) occurred in northwest, central south and central east HKC areas, much higher than the less acidified (ΔpHmean = −0.004 ± 0.002 unit·yr−1) southwest and northeast HKC areas. The spatiotemporal CA variations were associated with water discharges, atmospheric CO2 increase and respiration/production that was indicated by DIN:DIP structure changes. The annual mean DIN:DIP ratio increased progressively from initial ∼16 in 1986 to ∼37 in 2017, revealing excess nitrogen load from rapid urbanization in this region. Such discharge-induced acidification was estimated as the major contributor for the total CA in HKC over the last three decades. In addition, our simulation results indicated that a potential CA rate at ∼0.0035 unit·yr−1 could be reached if reducing mean DIN:DIP from discharged water to ∼23 from HKC. This study revealed a previously not recognized relationship between coastal acidification and changing coastal nutrient stoichiometry, and proposed possible management approaches.

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The promotion of stress tolerant Symbiodiniaceae dominance in juveniles of two coral species due to simulated future conditions of ocean warming and acidification

The symbiotic relationship between coral and its endosymbiotic algae, Symbiodiniaceae, greatly influences the hosts’ potential to withstand environmental stress. To date, the effects of climate change on this relationship has primarily focused on adult corals. Uncovering the effects of environmental stress on the establishment and development of this symbiosis in early life stages is critical for predicting how corals may respond to climate change. To determine the impacts of future climate projections on the establishment of symbionts in juvenile corals, ITS2 amplicon sequencing of single coral juveniles was applied to Goniastrea retiformis and Acropora millepora before and after exposure to three climate conditions of varying temperature and pCO2 levels (current and RCP8.5 in 2050 and 2100). Compared to ambient conditions, juvenile corals experienced shuffling in the relative abundance of Cladocopium (C1m, reduction) to Durusdinium (D1 and D1a, increase) over time. We calculated a novel risk metric incorporating functional redundancy and likelihood of impact on host physiology to identify the loss of D1a as a ‘low risk’ to the coral compared to the loss of “higher risk” taxa like D1 and C1m. Although the increase in stress tolerant Durusdinium under future warming was encouraging for A. millepora, by 2100, G. retiformis communities displayed signs of symbiosis de-regulation, suggesting this acclimatory mechanism may have species-specific thresholds. These results emphasize the need for understanding of long-term effects of climate change induced stress on coral juveniles and their potential for increased acclimation to heat tolerance through changes in symbiosis.

Originality Statement Here we assessed changes in the uptake and establishment of Symbiodiniaceae in the early lifehistory stages of two coral species under future climate scenarios. Our study represents the first such assessment of future climate change projections (increased temperature and pCO2) influencing Symbiodiniaceae acquisition and specifically shows a community structure dominated by the stress tolerant genus Durusdinium. We also develop a novel risk metric that includes taxonomic function and redundancy to estimate the impact of symbiont taxa changes on coral physiology. Through the risk metric, we relate the stress-induced changes in symbiont community structure to the likelihood of functional loss to better understand the extent to which these changes may lead to a decrease in coral health.

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Experimental evolution reveals the synergistic genomic mechanisms of adaptation to ocean warming and acidification in a marine copepod

Metazoan adaptation to global change will rely on selection of standing genetic variation. Determining the extent to which this variation exists in natural populations, particularly for responses to simultaneous stressors, is therefore essential to make accurate predictions for persistence in future conditions. Here, we identify the genetic variation enabling the copepod Acartia tonsa to adapt to experimental ocean warming, acidification, and combined ocean warming and acidification (OWA) conditions over 25 generations. Replicate populations showed a strong and consistent polygenic response to each condition, targeting an array of adaptive mechanisms including cellular homeostasis, development, and stress response. We used a genome-wide covariance approach to partition the genomic changes into selection, drift, and lab adaptation and found that the majority of allele frequency change in warming (56%) and OWA (63%) was driven by selection but acidification was dominated by drift (66%). OWA and warming shared 37% of their response to selection but OWA and acidification shared just 1%. Accounting for lab adaptation was essential for not inflating a shared response to selection between all treatments. Finally, the mechanisms of adaptation in the multiple-stressor OWA conditions were not an additive product of warming and acidification, but rather a synergistic response where 47% of the allelic responses to selection were unique. These results are among the first to disentangle how the genomic targets of selection differ between single and multiple stressors and to demonstrate the complexity that non-additive multiple stressors will contribute to attempts to predict adaptive responses to complex environments.

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Near-future levels of pCO2 impact skeletal weights of coral primary polyps (Acropora digitifera)

Ocean acidification poses a severe threat to corals; declines in carbonate ion concentrations caused by increasing atmospheric CO2 partial pressure (pCO2) can severely impact coral calcification. Thus, there is an urgent need to understand the impacts of near-future ocean acidification on corals. In this study, we compared the effects of seawater at present and near-future pCO2 (approximately +200 μatm) levels on skeletal weights of new coral recruits. Experiments were carried out using precisely pCO2-controlled aquaria supplying stable pCO2-controlled seawater in a flow-through system. Our results show that skeletal weights of new coral recruits decreased significantly at +200 μatm pCO2, which is expected to be reached within this century if ocean acidification continues at the present pace.

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Marine macrophytes as carbon sinks: comparison between seagrasses and the non-native alga Halimeda incrassata in the Western Mediterranean (Mallorca)

Seagrass species play a critical role in the mitigation of climate change by acting as valuable carbon sinks and storage sites. Another important ecosystem service of this coastal vegetation is nutrient removal. However, coastal ecosystems are under increasing pressure of global warming and associated establishment of invasive species. To elucidate the respective contributions of seagrass species Posidonia oceanica and Cymodocea nodosa and the non-native macroalga Halimeda incrassata as primary producers and nutrient sinks in coastal habitats we conducted in-situ incubations in the North-western Mediterranean Sea. Measured metabolic activity and nutrient removal as well as calcification rates in these habitats over a 24 h period in spring and summer confirmed that the endemic seagrass P. oceanica represents a valuable ecosystem with high O2 production and considerable carbon capture. The documented regression of P. oceanica meadows with higher temperatures and decline in autotrophy as measured here causes concern for the continuity of ecosystem services rendered by this habitat throughout the Mediterranean Sea with progressing climate warming. In contrast, the enhanced performance of C. nodosa and the calcifying alga H. incrassata with increasing temperatures, under expected rates of future warming is uncertain to mitigate loss of productivity in case of a potential shift in marine vegetation. This could ultimately lead to a decline in ecosystem services, decreased carbon storage and mitigation of climate change. Furthermore, this study provides a first estimate for the growth rate of H. incrassata in the Mediterranean Sea, supporting evidence for the mechanism of its rapid extension.

Continue reading ‘Marine macrophytes as carbon sinks: comparison between seagrasses and the non-native alga Halimeda incrassata in the Western Mediterranean (Mallorca)’

Development of ocean acidification endpoint characterization model for life cycle assessment

Ocean acidification, also referred to as the evil twin of global warming, occurs due to the CO2 absorption of the oceans from the atmosphere. Both the pH and carbonate saturations are altered with this absorption process. The optimal operating conditions of the biological systems in the marine environment are therefore no longer maintained. The marine species are reacting in various ways to this change, eventually leading to a loss in biodiversity. With the current trend in emissions, the pH levels of the oceans are expected to decrease from 8.1 to 7.8 by the end of the century. In combination with the other stressors, it is projected that OA will have a wide range of impacts on marine life and its services to humanity. The representation of these implications is limited in environmental assessment tools such as Life Cycle Assessment.

This research explores the relationship between the changing acidity of the oceans and marine biodiversity loss. This relation is quantified through utilizing the ecotoxicology impact assessment approach for LCA. Following this approach, an endpoint characterization model is developed for ocean acidification. The approach consists of the development and integration of fate, exposure, effect and damage models. The fate model, expressing the relation between the GHG emissions (CO2, CO, CH4) and change in acidity of the ocean is based on the work of Bach et al. (2016). The effect model has been developed by constructing species sensitivity distributions utilizing species response data from 5 taxonomic groups (mollusca, echinodermata, fish, cnidaria, crustacea) to obtain the potentially affected fraction of species with changing pH. Furthermore, 3 different categorizations (climate zones, calcification, exposure duration) were made to assess their effects on species responses. The results revealed that there is no significant difference in responses based on different exposure durations or climate zones. Calcifying species on the other hand is found to have a higher sensitivity to ocean acidification as the change in carbonate chemistry directly influences the shell and skeleton formation of these organisms. Lastly, these models were integrated into an endpoint characterization model for ocean acidification. From the 3 GHG emissions included within the scope of this research, CO2 has the highest (CFCO2 = 4.883 × 104 (𝑃𝐷𝐹)𝑚3/𝑘𝑔𝐺𝐻𝐺) and CH4 has the lowest (CFCH4 = 4.072 × 104 𝑃𝐷𝐹)𝑚3/𝑘𝑔𝐺𝐻𝐺) impact on marine biodiversity loss due to OA. These ecosystem damage indicators can be utilized in the impact assessment phase of the Life Cycle Assessment to translate the inventory results into impact on marine biodiversity.

Through the quantification of the impacts of ocean acidification, the effects of this major stressor on marine life can be better understood and targeted strategies can be developed. However, more research is required to increase the robustness of these models through expanding the species scope and incorporating temporal and geographical aspects into the models. Furthermore, the cascading effects of the changing ocean pH are still unknown and its consequences on ecosystems and socio-economic structures are unprecedented. To establish science-based targets and strategies to conserve the species richness in marine life, the extent of our understanding of the damage caused by anthropogenic actions needs to be further explored and estimated for the future.

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A low-cost, accessible, and high-performing Arduino-based seawater pH control system for biological applications

Highlights

  • Seawater pH control system for marine biological experiments.
  • Low-cost aquarium pH control alternative to more expensive options.
  • Accessible to researchers with little instrument development or coding experience.
  • Adaptable system to fit a variety of marine species and experimental designs.

Abstract

In the last two decades, the need for seawater pH control methodologies paralleled the rise in attention to the biological impacts of ocean acidification. Many effective and high-performing systems have been created, but they are often expensive, complex, and difficult to establish. We developed a system that is similarly high performing, but at a low cost and with a simple and accessible design. This system is controlled by an Arduino Nano, an open-source electronics platform, which regulates the flow of CO2 gas through electric solenoid valves. The Arduino and other inexpensive materials total ∼$150 (plus CO2 gas and regulator), and a new treatment can be added for less than $35. Easy-to-learn code and simple wire-to-connect hardware make the design extremely accessible, requiring little time and expertise to establish. The system functions with a variety of pH probes and can be adapted to fit a variety of experimental designs and organisms. Using this set up, we were able to constrain seawater pH within a range of 0.07 pH units. Our system thus maintains the performance and adaptability of existing systems but expands their accessibility by reducing cost and complexity.

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Climate change alters shellfish reef communities: a temperate mesocosm experiment

Highlights

  • Climate change will cause significant changes to rocky shore diversity.
  • Outdoor mesocosms were used to test predictions of warming and ocean acidification.
  • Elevated carbon dioxide in the atmosphere reduced the growth of the native mussels.
  • Warming and carbon dioxide influenced the species that colonised the mussels.

Abstract

Climate change is expected to cause significant changes to rocky shore diversity. This study used outdoor mesocosms to test the predictions that warming and ocean acidification will alter the responses of native Trichomya hirsuta and introduced Mytilus galloprovincialis mussels, and their associated communities of infauna. Experiments consisted of orthogonal combinations of temperature (ambient 22 °C or elevated 25 °C), pCO2 (ambient 400 μatm or elevated 1000 μatm), mussel species (T. hirsuta or M. galloprovincialis), and mussel configuration (native, introduced, or both), with n = 3 replicates. Elevated pCO2 reduced the growth of T. hirsuta but not that of M. galloprovincialis, and warming and pCO2 influenced the infauna that colonised both species of mussels. There was a reduction in infaunal molluscs and an increase in polychaetes; there was, however, no effect on crustaceans. Results from this study suggest that climate-driven changes from one mussel species to another can significantly influence infaunal communities.

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Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems

Highlights

  • Ocean acidification (OA) and ocean cooling (OC) will influence upwelling systems.
  • The snail Acanthina monodon growth, feeding and calcification rates increased with OC.
  • Metabolic rates also increased with OA but only under OC conditions.
  • Self-righting was unaltered, suggesting a complex repertoire of responses to OA and OC.

Abstract

Ocean acidification (OA) is expected to rise towards the end of the 21st century altering the life history traits in marine organisms. Upwelling systems will not escape OA, but unlike other areas of the ocean, cooling effects are expected to intensify in these systems. Regardless, studies evaluating the combined effects of OA and cooling remain scarce. We addressed this gap using a mesocosm system, where we exposed juveniles of the intertidal muricid snail Acanthina monodon to current and projected pCO2 (500 vs. 1500 ppm) and temperature (15 vs. 10 °C) from the southeast Pacific upwelling system. After 9 weeks of experimental exposure to those conditions, we conducted three estimations of growth (wet weight, shell length and shell peristomal length), in addition to measuring calcification, metabolic and feeding rates and the ability of these organisms to return to the normal upright position after being overturned (self-righting). Growth, feeding and calcification rates increased in projected cooling conditions (10 °C) but were unaffected by pCO2 or the interaction between pCO2 and temperature. Instead, metabolic rates were driven by pCO2, but a significant interaction with temperature suggests that in cooler conditions, metabolic rates will increase when associated with high pCO2 levels. Snail self-righting times were not affected across treatments. These results suggest that colder temperatures projected for this area would drive this species growth, feeding and calcification, and consequently, some of its population biology and productivity. However, the snails may need to compensate for the increase in metabolic rates under the effects of ocean acidification. Although A. monodon ability to adjust to individual or combined stressors will likely account for some of the changes described here, our results point to a complex dynamic to take place in intertidal habitats associated with upwelling systems.

Continue reading ‘Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems’

Reagentless acid–base titration for alkalinity detection in seawater

Herein, we report on a reagentless electroanalytical methodology for automatized acid–base titrations of water samples that are confined into very thin spatial domains. The concept is based on the recent discovery from our group (Wiorek, A. Anal. Chem. 2019, 91, 14951−14959), in which polyaniline (PANI) films were found to be an excellent material to release a massive charge of protons in a short time, achieving hence the efficient (and controlled) acidification of a sample. We now demonstrate and validate the analytical usefulness of this approach with samples collected from the Baltic Sea: the titration protocol indeed acts as an alkalinity sensor via the calculation of the proton charge needed to reach pH 4.0 in the sample, as per the formal definition of the alkalinity parameter. In essence, the alkalinity sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement with the values obtained by manual (classical) acid–base titrations (discrepancies <10%). Some crucial advantages of the new methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2 week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future digitalization of in situ acid–base titrations to obtain high-resolution data on alkalinity in water resources.

Abstract Image
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Experimental studies on the impact of the projected ocean acidification on fish survival, health, growth, and meat quality; Black Sea bream (Acanthopagrus schlegelii), physiological and histological studies

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This study’s data suggest that under the projected scenarios of ocean acidification by 2100 and beyond, significant negative impacts on growth, health, and meat quality are expected, particularly on black sea bream, and will be susceptible to the scientifically approved fish having a weaker resistance to diseases and environmental changes if CO2 emissions in the atmosphere are not curbed. Knowing the expected consequences, mitigation measures are urgently needed.

Abstract

Acidification (OA), a global threat to the world’s oceans, is projected to significantly grow if CO2 continues to be emitted into the atmosphere at high levels. This will result in a slight decrease in pH. Since the latter is a logarithmic scale of acidity, the higher acidic seawater is expected to have a tremendous impact on marine living resources in the long-term. An 8-week laboratory experiment was designed to assess the impact of the projected pH in 2100 and beyond on fish survival, health, growth, and fish meat quality. Two projected scenarios were simulated with the control treatment, in triplicates. The control treatment had a pH of 8.10, corresponding to a pCO2 of 321.37 ± 11.48 µatm. The two projected scenarios, named Predict_A and Predict_B, had pH values of 7.80-pCO2 = 749.12 ± 27.03 and 7.40-pCO2 = 321.37 ± 11.48 µatm, respectively. The experiment was preceded by 2 weeks of acclimation. After the acclimation, 20 juvenile black sea breams (Acanthopagrus schlegelii) of 2.72 ± 0.01 g were used per tank. This species has been selected mainly due to its very high resistance to diseases and environmental changes, assuming that a weaker fish resistance will also be susceptibly affected. In all tanks, the fish were fed with the same commercial diet. The seawater’s physicochemical parameters were measured daily. Fish samples were subjected to physiological, histological, and biochemical analyses. Fish growth, feeding efficiency, protein efficiency ratio, and crude protein content were significantly decreased with a lower pH. Scanning electron microscopy revealed multiple atrophies of microvilli throughout the small intestine’s brush border in samples from Predict_A and Predict_B. This significantly reduced nutrient absorption, resulting in significantly lower feed efficiency, lower fish growth, and lower meat quality. As a result of an elevated pCO2 in seawater, the fish eat more than normal but grow less than normal. Liver observation showed blood congestion, hemorrhage, necrosis, vacuolation of hepatocytes, and an increased number of Kupffer cells, which characterize liver damage. Transmission electron microscopy revealed an elongated and angular shape of the mitochondrion in the liver cell, with an abundance of peroxisomes, symptomatic of metabolic acidosis.

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