n the past decade, many studies have investigated the effects of low pH/high CO2 as a proxy for ocean acidification on olfactory-mediated behaviours of marine organisms. The effects of ocean acidification on the behaviour of fish vary from very large to none at all, and most of the maladaptive behaviours observed have been attributed to changes in acid–base regulation, leading to changes in ion distribution over neural membranes, and consequently affecting the functioning of gamma-aminobutyric acid-mediated (GABAergic) neurotransmission. Here, we highlight a possible additional mechanism by which ocean acidification might directly affect olfaction in marine fish and invertebrates. We propose that a decrease in pH can directly affect the protonation, and thereby, 3D conformation and charge distribution of odorants and/or their receptors in the olfactory organs of aquatic animals. This can sometimes enhance signalling, but most of the time the affinity of odorants for their receptors is reduced in high CO2/low pH; therefore, the activity of olfactory receptor neurons decreases as measured using electrophysiology. The reduced signal reception would translate into reduced activation of the olfactory bulb neurons, which are responsible for processing olfactory information in the brain. Over longer exposures of days to weeks, changes in gene expression in the olfactory receptors and olfactory bulb neurons cause these neurons to become less active, exacerbating the problem. A change in olfactory system functioning leads to inappropriate behavioural responses to odorants. We discuss gaps in the literature and suggest some changes to experimental design in order to improve our understanding of the underlying mechanisms and their effects on the associated behaviours to resolve some current controversy in the field regarding the extent of the effects of ocean acidification on marine fish.
Ocean acidification, a reduction in the pH of the oceans caused by increasing CO2, can have negative physiological effects on marine species. In this study, we examined how CO2-driven acidification affected the growth and survival of juvenile golden king crab (Lithodes aequispinus), an important fishery species in Alaska. Juveniles were reared from larvae in surface ambient pH seawater at the Kodiak Laboratory. Newly molted early benthic instar crabs were randomly assigned to one of three pH treatments: (1) surface ambient pH ~ 8.2, (2) likely in situ ambient pH 7.8, and (3) pH 7.5. Thirty crabs were held in individual cells in each treatment for 127 days and checked daily for molting or death. Molts and dead crabs were photographed under a microscope and measured using image analysis to assess growth and morphology. Mortality was primarily associated with molting in all treatments, differed among all treatments, and was highest at pH 7.5 and lowest at ambient pH. Crabs at pH 7.5 were smaller than crabs at ambient pH at the end of the experiment, both in terms of carapace length and wet mass; had a smaller growth increment after molting; had a longer intermolt period. Carapace morphology was not affected by pH treatment. Decreased growth and increased mortality in laboratory experiments suggest that lower pH could affect golden king crab stocks and fisheries. Future work should examine if larval rearing conditions affect the juvenile response to low pH.
Over the last 250 years, the intensive burning of fossil fuels along with industrial processes and land uses (e.g. clearing forests and agriculture) has contributed to an increase in atmospheric CO2 from approximately 280 to 410 ppm, with a further increase (from 730 to 1020 ppm) projected by the end of this century. About 30% of the anthropogenic CO2 has been absorbed by the ocean, with a consequent decrease of the ocean’s surface pH causing a phenomenon better known as Ocean Acidification (OA). The average pH of the surface ocean has declined from 8.2 by 0.1 units since pre-industrial times as a result of CO2 emissions and a further reduction of 0.3–0.5 pH units is expected to occur by the 2100.
This increased concentration of atmospheric CO2 has driven an increase in atmospheric and oceanic temperatures enhanced at a rate of ~ 0.2˚C per decade in the past 30 years. These rapid changing ocean conditions in pCO2 and temperature are considered two of the major threats to marine biodiversity, leading to changes in the distribution, physiology and behaviour of marine organisms, with potential consequences in community and ecosystem functioning and structure. Despite the increasing interest and amount of literature on this topic, the effects of OA and ocean warming (OW) on marine fauna is difficult to predict, especially because a wide range of impacts have been found across different life stages-and species suggesting that tolerance thresholds to such stressors can vary among life stages experienced by an organism or even between species. In this regard, an increased number of studies has been conducted to better understand the mechanisms by which species can cope with these rapid environmental changes.
The first response of animals to a changing environment is predominantly through modification of their behaviour. To date, only a few climate change biology studies have considered behavioural plasticity as a way that animals can adjust their performance under rapid climate change, especially for marine ectotherms.
The general objective of this thesis was to evaluate the effects of ocean warming and acidification on different aspects of behaviour in marine ectotherms. To achieve this aim I investigated the behavioural responses of two marine fish and one invertebrate, through field-based and laboratory experiments.
O aumento das emissões de gás carbônico atmosférico proveniente de atividades antrópicas desde a Revolução Industrial teve como consequência uma maior participação de águas superficiais no processo de sequestro de dióxido de carbono, a fim de amenizar o efeito estufa. A principal consequência do aumento de captura de gás carbônico pelos oceanos é um fenômeno denominado acidificação oceânica. Alguns poluentes presentes na água, como por exemplo fármacos e produtos de cuidados pessoais (FPCPs) podem sofrer alterações na sua mobilidade e biodisponibilidade por conta da diminuição do pH do meio. Atualmente a quantidade de dados sobre os efeitos e o risco ambiental de FPCPs em organismos marinhos ainda é escassa. Diante deste cenário o presente estudo teve como objetivo analisar a ocorrência, o comportamento e a biodisponibilidade do fármaco orfenadrina frente a diferentes cenários de acidificação oceânica. O fármaco orfenadrina, empregado como relaxante muscular e amplamente consumido foi observado em todos os pontos de amostragem das áreas de influência dos emissários submarinos de Santos e Guarujá – SP, com concentrações que variaram LOQ a 0,5 ng/g em sedimentos. Os resultados do ensaio de toxicidade com água empregando ouriços do mar (Echinometra lucunter) nos diferentes pHs 8,0; 7,6; 7,3 apresentaram valores de CEO de 0,05mg/L e o EpH50 foi estabelecido em 7,30. Quanto aos ensaios com mexilhões Perna perna foram observados efeitos em concentrações ambientalmente relevantes, com CEO de 200 ng/g. Os resultados dos ensaios feitos para a avaliação do desenvolvimento embriolarval em água indicaram que tanto o processo de acidificação quanto o aumento da concentração afetam o desenvolvimento dos embriões de ouriço do mar. Já nos ensaios com P. perna foi possível verificar ainda que a presença do fármaco de caráter básico reduziu os efeitos da acidificação oceânica. Os resultados da análise de bioacumulação detectaram a presença da orfenadrina em todos os tecidos analisados. A análise dos ensaios de citotoxicidade nesta ocasião refutou a hipótese inicial do estudo, visto que a presença do fármaco de caráter básico reduziu os efeitos da acidificação oceânica. Neste sentido, fica evidente necessidade de se aprofundar os estudos sobre toxicologia relacionada a fármacos sob cenários de acidificação em ambiente marinho.
The integrity of coral reefs worldwide is jeopardized by ocean acidification (OA). Most studies conducted so far have focused on the vulnerability to OA of corals inhabiting shallow reefs, while nothing is currently known about the response of mesophotic scleractinian corals. In this study we assessed the susceptibility to OA of corals, together with their algal partners, inhabiting a wide depth range. We exposed fragments of the depth generalist coral Stylophora pistillata collected from either 5 or 45 meters to simulated future OA conditions, and assessed key molecular, physiological and photosynthetic processes influenced by the lowered pH. Our comparative analysis reveals that mesophotic and shallow S. pistillata corals are genetically distinct and possess different symbiont types. Under the exposure to acidification conditions, we observed a 50% drop of metabolic rate in shallow corals, whereas mesophotic corals were able to maintain unaltered metabolic rates. Overall, our gene expression and physiological analyses show that mesophotic corals possess a greater capacity to cope with the effects of OA compared to their shallow counterparts. Such capability stems from physiological characteristics (i.e. biomass and lipids energetics), a greater capacity to regulate cellular acid-base parameters, and a higher baseline expression of cell-adhesion and extracellular matrix genes. Moreover, our gene expression analysis suggests that the enhanced symbiont photochemical efficiency under high pCO₂ levels could prevent acidosis of the host cells and it could support a greater translocation of photosynthates, increasing the energy pool available to the host. With this work, we provide new insights on the response to OA of corals living at mesophotic depths. Our investigation discloses key genetic and physiological traits underlying the potential for corals to cope with future OA conditions.
Marine sponges are becoming an increasing source of novel biomedical and antibacterial compounds. Many of these compounds are synthesized as secondary metabolites from symbiotic bacteria and have immense potential in the pharmaceutical industry. However, climate change may pose a threat to the viability of marine sponges and result in the loss of future medical discoveries. Therefore, this paper looks at the effect climate change may have on marine sponges by subjecting fragments of the marine sponge, Halichondria panicea, into aquaria representing different climate change scenarios to study the effect that global warming and ocean acidification may have on its symbiotic bacteria. To model climate change towards the end of the 21st century, conditions from the IPCC’s 2014 climate change report were simulated to determine specific growth conditions. The fragments were placed in the different RCP growth conditions for two weeks, then dissociated, filtered, and the extracts incubated on Hektoen enteric agar for 48 hours. The results showed that climate change has adverse effects on the marine sponge, Halichondria panicea, by decreasing their symbiotic bacterial population by around 18 %
Otopetrins comprise a family of proton channels that are required for the development of calcified structures including otoliths and statoconia in vertebrates. To date, it remains unknown how otopetrins contribute to the calcification process. Using the sea urchin larva, we could demonstrate that the otopetrin ortholog otop2l encodes a proton channel that is essential for the formation of the CaCO3 skeleton. otop2l is exclusively expressed by the calcifying primary mesenchyme cells, where it promotes the exit of protons liberated by the mineralization process. Given the deep phylogenetic origin of otopetrins in animals, our work identified a key mechanism in the mineralization process with relevance for many calcifying species and their responses to changes in environmental pH.
Otopetrins comprise a family of proton-selective channels that are critically important for the mineralization of otoliths and statoconia in vertebrates but whose underlying cellular mechanisms remain largely unknown. Here, we demonstrate that otopetrins are critically involved in the calcification process by providing an exit route for protons liberated by the formation of CaCO3. Using the sea urchin larva, we examined the otopetrin ortholog otop2l, which is exclusively expressed in the calcifying primary mesenchymal cells (PMCs) that generate the calcitic larval skeleton. otop2l expression is stimulated during skeletogenesis, and knockdown of otop2l impairs spicule formation. Intracellular pH measurements demonstrated Zn2+-sensitive H+ fluxes in PMCs that regulate intracellular pH in a Na+/HCO3−-independent manner, while Otop2l knockdown reduced membrane proton permeability. Furthermore, Otop2l displays unique features, including strong activation by high extracellular pH (>8.0) and check-valve–like outwardly rectifying H+ flux properties, making it into a cellular proton extrusion machine adapted to oceanic living conditions. Our results provide evidence that otopetrin family proton channels are a central component of the cellular pH regulatory machinery in biomineralizing cells. Their ubiquitous occurrence in calcifying systems across the animal kingdom suggest a conserved physiological function by mediating pH at the site of mineralization. This important role of otopetrin family proton channels has strong implications for our view on the cellular mechanisms of biomineralization and their response to changes in oceanic pH.
- We identified orthologous genes (ompa and ompb) in European sea bass
- Ompa and ompb genes differ in amino acid sequences and in their expression pattern
- Acidification induces intra- and intergenerational plasticity in omps expression
- Both ompa and ompb mRNA could be used as novel molecular markers of OSN in sea bass
Since sensory system allows organisms to perceive and interact with their external environment, any disruption in their functioning may have detrimental consequences on their survival. Ocean acidification has been shown to potentially impair olfactory system in fish and it is therefore essential to develop biological tools contributing to better characterize such effects. The olfactory marker protein (omp) gene is involved in the maturation and the activity of olfactory sensory neurons in vertebrates. In teleosts, two omp genes (ompa and ompb) originating from whole genome duplication have been identified. In this study, bioinformatic analysis allowed characterization of the ompa and ompb genes from the European seabass (Dicentrarchus labrax) genome. The European seabass ompa and ompb genes differ in deduced amino acid sequences and in their expression pattern throughout the tissues. While both ompa and ompb mRNA are strongly expressed in the olfactory epithelium, ompb expression was further observable in different brain areas while ompa expression was also detected in the eyes and in other peripheral tissues. Expression levels of ompa and ompb mRNA were investigated in adult seabass (4 years-old, F0) and in their offspring (F1) exposed to pH of 8 (control) or 7.6 (ocean acidification, OA). Under OA ompb mRNA was down-regulated while ompa mRNA was up-regulated in the olfactory epithelium of F0 adults, suggesting a long-term intragenerational OA-induced regulation of the olfactory sensory system. A shift in the expression profiles of both ompa and ompb mRNA was observed at early larval stages in F1 under OA, suggesting a disruption in the developmental process. Contrary to the F0, the expression of ompa and ompb mRNA was not anymore significantly regulated under OA in the olfactory epithelium of juvenile F1 fish. This work provides evidence for long-term impact of OA on sensorial system of European seabass as well as potential intergenerational acclimation of omp genes expression to OA in European seabass.
- Gene expression profiles of the sea pen Malacobelemnon daytoni revealed an important number of transcripts upregulated in response to short-term and long-term Low pH conditions.
- The biomineralization in this coral is not acclimated after two months in the Low pH condition, indicating that the pennatulid would be striving to produce its calcium carbonate structure.
- Malacobelemnon daytoni is working extra hard at the molecular level to maintain the same enzyme activity levels.
Benthic organisms of the Southern Ocean are particularly vulnerable to ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. OA most strongly affects animals with calcium carbonate skeletons or shells, such as corals and mollusks. We exposed the abundant cold-water coral Malacobelemnon daytoni from an Antarctic fjord to low pH seawater (LpH) (7.68 ± 0.17) to test its physiological responses to OA, at the level of gene expression (RT-PCR) and enzyme activity. Corals were exposed in short- (3 days) and long-term (54 days) experiments to two pCO2 conditions (ambient and elevated pCO2 equaling RCP 8.5, IPCC 2019, approximately 372.53 and 956.78 μatm, respectively).
Of the eleven genes studied through RT-PCR, six were significantly upregulated compared with control in the short-term in the LpH condition, including the antioxidant enzyme superoxide dismutase (SOD), Heat Shock Protein 70 (HSP70), Toll-like receptor (TLR), galaxin and ferritin. After long-term exposure to low pH conditions, RT-PCR analysis showed seven genes were upregulated. These include the mannose-binding C-Lectin and HSP90. Also, the expression of TLR and galaxin, among others, continued to be upregulated after long-term exposure to low pH. Expression of carbonic anhydrase (CA), a key enzyme involved in calcification, was also significantly upregulated after long-term exposure. Our results indicated that, after two months, M. daytoni is not acclimatized to this experimental LpH condition. Gene expression profiles revealed molecular impacts that were not evident at the enzyme activity level. Consequently, understanding the molecular mechanisms behind the physiological processes in the response of a coral to LpH is critical to understanding the ability of polar species to cope with future environmental changes. Approaches integrating molecular tools into Antarctic ecological and/or conservation research make an essential contribution given the current ongoing OA processes.
Nitrous oxide (N2O) is a powerful greenhouse gas that degrades ozone. Hypoxia and ocean acidification are becoming more intense as a result of climate change. The former stimulates N2O emissions, whereas the effects of the latter on N2O production vary by the ocean. Hypoxia and ocean acidification may play a critical role in the evolution of future oceanic N2O production. However, the interactive effects of hypoxia and ocean acidification on N2O production remain unclear. We conducted a research cruise in the Bohai Sea of China to assess the occurrence of ocean acidification in the seasonal oxygen minimum zone of the sea and further conducted laboratory incubation experiments to determine the effects of ocean acidification and hypoxia on N2O production. When pH decreased by 0.25, N2O production decreased by 50.77 and 72.38%, respectively. In contrast, hypoxia had a positive impact; when dissolved oxygen (DO) decreased to 3.7 and 2.4 mg L−1, N2O production increased by 49.72 and 278.68%, respectively. The incubation experiments demonstrated that the coupling of ocean acidification and hypoxia significantly increased N2O production, but, individually, there was an antagonistic relationship between the two. Structural equation modeling showed that the total effects of hypoxia treatment on N2O production changes weakened the effects of ocean acidification, with overall positive effects. Generally speaking, our results suggest that N2O production from the coastal waters of the Bohai Sea may increase under future climate change scenarios due to increasingly serious ocean acidification and hypoxia working in combination.
Seagrass ecosystem is one of the most productive ecosystems in coastal waters providing numerous ecological functions and supporting a large biodiversity. However, various anthropogenic stressors including climate change are impacting these vulnerable habitats. Here, we investigated the independent and combined effects of ocean warming and ocean acidification on plant–herbivore interactions in a tropical seagrass community. Direct and indirect effects of high temperature and high pCO2 on the physiology of the tropical seagrass Thalassia hemprichii and sea urchin Tripneustes gratilla were evaluated. Productivity of seagrass was found to increase under high pCO2, while sea urchin physiology including feeding rate decreased particularly under high temperature. The present study indicated that future climate change will affect the bottom-up and top-down balance, which potentially can modify the ecosystem functions and services of tropical seagrass ecosystems.
- The carbonate system and its controlling factors in a mariculture area were studied.
- Massive bay scallop farming was a potential factor for coastal acidification.
- Scallop calcification reduced 75.66 μmol kg−1 of total alkalinity in surface water.
- Biochemical and physical processes jointly controlled the other CO2 parameters.
Seven cruises were carried out in a bay scallop (Argopecten irradians) farming area and its surrounding waters, North Yellow Sea, from March to November 2017 to study the dynamics of the carbonate system and its controlling factors. Results indicated that the studied parameters were highly variability over a range of spatiotemporal scales, comprehensively forced by various physical and biochemical processes. Mixing effect and scallop calcification played the most important role in the seasonal variation of total alkalinity (TAlk). For dissolved inorganic carbon (DIC), in addition to mixing, air-sea exchange and microbial activity, e.g. photosynthesis and microbial respiration processes, had more important effects on its dynamics. Different from the former, the changes of water pHT, partial pressure of CO2 (pCO2) and aragonite saturation state (ΩA) were mainly controlled by the combining of the temperature, air-sea exchange, microbial activity and scallop metabolic activities. In addition, our results suggested that massive scallop farming can significantly increase the DIC/TAlk ratio by reducing the TAlk concentration in seawater, thereby reducing the buffering capacity of seawater to the carbonate system especially for ΩA. Preliminary calculated, ~75.7 μmol kg−1 and ~45.5 μmol kg−1 of TAlk was removed from the surface and bottom water in one scallop cultivating cycle. If these carbonates cannot be replenished in time, it is likely to accelerate the acidification process of coastal waters. This study highlighted the control mechanism of the carbonate system under the influence of bay scallop farming, and provided useful information for revealing the potential link between human activities (shelled-mollusc mariculture) and coastal acidification.
- Ocean acidification scenarios were assessed with mussel in presence of crack-cocaine.
- Lysosomal membrane stability, lipid peroxidation, and DNA strand breaks in Perna perna revealed toxicity increase.
- Adverse effects of acidification were detected for pH below 6.5.
- At pH 7.5–6.5 adverse effects are related to combined stressors (CO2 and cocaine).
The increasing CO2-concentrations in the atmosphere promote ocean acidification. Seawater chemistry changes interact with contaminants, such as illicit drugs in the coastal zones. This work evaluates impacts of pH decrease and crack-cocaine exposure on the commercial mussel Perna perna through biomarker responses (lysosomal membrane stability, lipid peroxidation, and DNA strand breaks). The organisms were exposed to different crack-cocaine concentrations (0.5, 5.0, and 50 μg L−1) combined with different pH values (8.3, 8.0, 7.5, 7.0, 6.5, and 6.0) for 96 h. Crack-cocaine in the different acidification scenarios triggered cyto-genotoxicity, which affected the overall health of mussels exposed to cocaine environmentally relevant concentration. This study produced the first data on biomarker responses associated with CO2-induced acidification and illicit drugs (crack-cocaine) in marine organisms.
We present a dipping probe total dissolved inorganic carbon (DIC) microsensor based on a localized acidic microenvironment in front of an amperometric CO2 microsensor. The acidic milieu facilitates conversion of bicarbonate and carbonate to CO2, which in turn is reduced at a silver cathode. Interfering oxygen is removed by an acidic CrCl2 oxygen trap. Theoretical simulations of microsensor functioning were performed to find a suitable compromise between response time and near-complete conversion of bicarbonate to CO2. The sensor exhibited a linear response over a wide range of 0–8 mM DIC, with a calculated LOD of 5 μM and a 90% response time of 150 s. The sensor was successfully tested in measuring DIC in bottled mineral water and seawater. This DIC microsensor holds the potential to become an important tool in environmental sensing and beyond for measurements of DIC at high spatial and temporal resolution.
Calcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO2 conditions. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition; it is less diverse today and was the most sensitive to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO2; it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO2 highlighted their lower fitness in response to ocean acidification. Reductions in CO2 emissions are needed to limit the risk of losing coralline algal diversity.
Pseudo-nitzschia australis (Frenguelli), a toxigenic pennate diatom capable of producing the neurotoxin domoic acid (DA), was examined in unialgal laboratory cultures to quantify its physiological response to ocean acidification (OA) – the decline in pH resulting from increasing partial pressure of CO2 (pCO2) in the oceans. Toxic blooms of P. australis are common in the coastal waters of eastern boundary upwelling systems (EBUS), including those of the California Current System (CCS) off the west coast of the United States where increased pCO2 and decreased seawater pH are well-known. This study determined the production of dissolved (dDA) and particulate DA (pDA), the rates of growth and nutrient (nitrate, silicate and phosphate) utilization, cellular elemental ratios of carbon and nitrogen, and the photosynthetic response to declining pH during the exponential and stationary growth phases of a strain of P. australis isolated during a massive toxic bloom that persisted for months along much of the U.S. west coast during 2015. Our controlled lab studies showed that DA production significantly increased as pCO2 increased, and total DA (pDA + dDA) normalized to cell density was 2.7 fold greater at pH 7.8 compared to pH 8.1 (control) during nutrient-limited stationary growth. However, exponential growth rates did not increase with declining pH, but remained constant until pH of 7.8 was reached, and then specific growth rates declined by ca. 30%. The toxin results demonstrate that despite minimal effects of OA observed during the nutrient-replete exponential growth phase, the enhancement of DA production, notably the 3-fold increase in particulate DA per cell, with declining pH from 8.1 to 7.8 during the nutrient-depleted stationary phase, supports the hypothesis that increasing pCO2 will result in greater toxic risk to coastal ecosystems from elevated ambient concentrations of particulate DA. The ecological consequences of decreasing silicate uptake rates and increasing cellular carbon quotas with declining pH may potentially ameliorate some negative impacts of OA on Pseudo-nitzschia growth in natural systems.
Coralline algae play foundational roles in coastal ecosystems and are globally significant components of benthic habitats down to the limits of the photic zone. Despite their vulnerability to ocean acidification (OA) and importance in low light environments, there is a limited understanding of how the interplay between irradiance and OA influences coralline reproduction and recruitment. To better understand this interaction, a 212-day experiment was run exposing coralline communities to two pH(T) levels (present-day pH(T) 8.07/ OA pH(T) 7.65) and a gradient of daily light dose (0.35, 0.17 and 0.1 mol m-2 d-1), based on in situ measurements. In the highest light dose treatment, lowered seawater pH projected for 2100 (pH(T) 7.65) reduced recruitment by 56%. This OA-driven reduction in recruitment was amplified under reduced light, with recruitment near zero in the lowest light treatment. This study shows, for the first time, the increased vulnerability of coralline community recruitment to OA under low light. Coralline algae are known to be the deepest growing macroalgae and thus, in these low light zones, OA many have the potential to reduce coralline depth distribution.
In this study, the variations of the seawater carbonate system parameters and air-sea CO2 flux (FCO2) of Shen’ao Bay, a typical subtropical aquaculture bay located in China, were investigated in spring 2016 (March to May). Parameters related to the seawater carbonate system and FCO2 were measured monthly in 3 different aquaculture areas (fish, oyster and seaweed) and in a non-culture area near the bay mouth. The results showed that the seawater carbonate system was markedly influenced by the biological processes of the culture species. Total alkalinity was significantly lower in the oyster area compared with the fish and seaweed areas, mainly because of the calcification process of oysters. Dissolved inorganic carbon (DIC) and CO2 partial pressure ( pCO2) were highest in the fish area, followed by the oyster and non-culture areas, and lowest in the seaweed area. Oysters and fish can have indirect influences on DIC and pCO2by releasing nutrients, which facilitate the growth of seaweed and phytoplankton and therefore promote photosynthetic CO2 fixation. For these reasons, Shen’ao Bay acts as a potential CO2 sink in spring, with an average FCO2 ranging from -1.2 to -4.8 mmol m-2 d-1. CO2 fixation in the seaweed area was the largest contributor to CO2 flux, accounting for ca. 58% of the total CO2 sink capacity of the entire bay. These results suggest that the carbonate system and FCO2 of Shen’ao Bay were significantly affected by large-scale mariculture activities. A higher CO2 sink capacity could be acquired by extending the culture area of seaweed.
In light of the chronic stress and mass mortality reef-building corals face under climate change, it is critical to understand the processes essential to reef persistence and replenishment, including coral reproduction and development. Here we quantify gene expression and size sensitivity to ocean acidification across a set of developmental stages in the rice coral, Montipora capitata. Gametes and then embryos and swimming larvae were exposed to three pH treatments ranging from 7.8 (Ambient), 7.6 (Low) and 7.3 (Xlow) from fertilization to 9 days post-fertilization. Embryo development and size, planula volume, and stage-specific gene expression were compared between treatments at each stage to determine the effects of acidified seawater on early development. While there was no measurable size differentiation between fertilized eggs and embryos at the prawn chip stage exposed to ambient, low, and extreme low pH, early gastrula and planula raised in reduced pH treatments were significantly smaller than those raised in ambient seawater, suggesting an energetic cost to developing under low pH. However, no differentially expressed genes emerged between treatments at any time point, except swimming larvae. Larvae from pH 7.6 showed upregulation of genes involved in cell division, regulation of transcription, lipid metabolism, and oxidative stress in comparison to the other two treatments, and smallest sizes in this treatment. While low pH appears to increase energetic demands and trigger oxidative stress, the developmental process is robust to this at a molecular level, with swimming larval stage reached in all pH treatments.
- High CO2 conditions profoundly affected biofilm community composition
- Species turnover explained differences in community composition
- Biofilm communities were more homogeneous under high CO2 conditions
- Toxin producing and turf-forming algae were enriched under high CO2 conditions
Biofilms harbour a wealth of microbial diversity and fulfil key functions in coastal marine ecosystems. Elevated carbon dioxide (CO2) conditions affect the structure and function of biofilm communities, yet the ecological patterns that underpin these effects remain unknown. We used high-throughput sequencing of the 16S and 18S rRNA genes to investigate the effect of elevated CO2 on the early successional stages of prokaryotic and eukaryotic biofilms at a CO2 seep system off Shikine Island, Japan. Elevated CO2 profoundly affected biofilm community composition throughout the early stages of succession, leading to greater compositional homogeneity between replicates and the proliferation of the potentially harmful algae Prymnesium sp. and Biddulphia biddulphiana. Species turnover was the main driver of differences between communities in reference and high CO2 conditions, rather than differences in richness or evenness. Our study indicates that species turnover is the primary ecological pattern that underpins the effect of elevated CO2 on both prokaryotic and eukaryotic components of biofilm communities, indicating that elevated CO2 conditions represent a distinct niche selecting for a distinct cohort of organisms without the loss of species richness.