Posts Tagged 'biological response'

Predicting effects of multiple interacting global change drivers across trophic levels

Global change encompasses many co-occurring anthropogenic drivers, which can act synergistically or antagonistically on ecological systems. Predicting how different global change drivers simultaneously contribute to observed biodiversity change is a key challenge for ecology and conservation. However, we lack the mechanistic understanding of how multiple global change drivers influence the vital rates of multiple interacting species. We propose that reaction norms, the relationships between a driver and vital rates like growth, mortality, and consumption, provide insights to the underlying mechanisms of community responses to multiple drivers. Understanding how multiple drivers interact to affect demographic rates using a reaction-norm perspective can improve our ability to make predictions of interactions at higher levels of organization—that is, community and food web. Building on the framework of consumer–resource interactions and widely studied thermal performance curves, we illustrate how joint driver impacts can be scaled up from the population to the community level. A simple proof-of-concept model demonstrates how reaction norms of vital rates predict the prevalence of driver interactions at the community level. A literature search suggests that our proposed approach is not yet used in multiple driver research. We outline how realistic response surfaces (i.e., multidimensional reaction norms) can be inferred by parametric and nonparametric approaches. Response surfaces have the potential to strengthen our understanding of how multiple drivers affect communities as well as improve our ability to predict when interactive effects emerge, two of the major challenges of ecology today.

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Oceans and the changing climate

Increasing levels of atmospheric greenhouse gases are producing changes in the world’s oceans and coastal environments, such as increasing sea surface temperatures, ocean acidification, and rising sea levels. This chapter explores the human dimensions of three climate change impacts: (1) rising sea levels, measures to adapt, and the potential displacement of persons from eroding, low-lying coastal areas; (2) the migration of fish stocks to new habitats resulting from increasing seawater temperatures; and (3) the degradation of coral reefs and impacts to shellfish resulting from ocean acidification. With sea level rise, millions of people in low-lying coastal cities and small island developing states must adapt or be displaced, and some will become climate refugees. In the case of fisheries, distributions of some fish stocks are already changing because of increasing ocean temperatures. These shifts have great implications for both fishers and managers of marine resources. Finally, rising atmospheric concentrations of CO2 that lower the ocean’s pH make it more difficult for corals and shellfish to precipitate the calcium carbonate that forms their exoskeletons and shells, affecting users of tropical coral reef ecosystems as well as the shellfish aquaculture industry.

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Wanted dead or alive: skeletal structure alteration of cold-water coral Desmophyllum pertusum (Lophelia pertusa) from anthropogenic stressors

Ocean acidification (OA) has provoked changes in the carbonate saturation state that may alter the formation and structural biomineralisation of calcium carbonate exoskeletons for marine organisms. Biomineral production in organisms such as cold-water corals (CWC) rely on available carbonate in the water column and the ability of the organism to sequester ions from seawater or nutrients for the formation and growth of a skeletal structure. As an important habitat structuring species, it is essential to examine the impact that anthropogenic stressors (i.e., OA and rising seawater temperatures) have on living corals and the structural properties of dead coral skeletons; these are important contributors to the entire reef structure and the stability of CWC mounds. In this study, dead coral skeletons in seawater were exposed to various levels of pCO2 and different temperatures over a 12-month period. Nanoindentation was subsequently conducted to assess the structural properties of coral samples’ elasticity (E) and hardness (H), whereas the amount of dissolution was assessed through scanning electron microscopy. Overall, CWC samples exposed to elevated pCO2 and temperature show changes in properties which leave them more susceptible to breakage and may in turn negatively impact the formation and stability of CWC mound development.

Continue reading ‘Wanted dead or alive: skeletal structure alteration of cold-water coral Desmophyllum pertusum (Lophelia pertusa) from anthropogenic stressors’

Ocean acidification-mediated food chain transfer of polonium between primary producers and consumers

Phytoplankton and zooplankton are key marine components that play an important role in metal distribution through a food web transfer. An increased phytoplankton concentration as a result of ocean acidification and warming are well-established, along with the fact that phytoplankton biomagnify 210Po by 3–4 orders of magnitude compared to the seawater concentration. This experimental study is carried out to better understand the transfer of polonium between primary producers and consumers. The experimental produced data highlight the complex interaction between the polonium concentration in zooplankton food, i.e. phytoplankton, its excretion via defecated fecal pellets, and its bioaccumulation at ambient seawater pH and a lower pH of 7.7, typical of ocean acidification scenarios in the open ocean. The mass of copepods recovered was 11% less: 7.7 pH compared to 8.2. The effects of copepod species (n = 3), microalgae species (n = 3), pH (n = 2), and time (n = 4) on the polonium activity in the fecal pellets (expressed as % of the total activity introduced through feeding) was tested using an ANOVA 4. With the exception of time (model: F20, 215 = 176.84, p < 0.001; time: F3 = 1.76, p = 0.16), all tested parameters had an impact on the polonium activity (copepod species: F2 = 169.15, p < 0.0001; algae species: F2 = 10.21, p < 0.0001; pH: F1 = 9.85, p = 0.002) with complex interactions (copepod x algae: F2 = 19.48, p < 0.0001; copepod x pH: F2 = 10.54, p < 0.0001; algae x pH: F2 = 4.87, p = 0.009). The experimental data underpin the hypothesis that metal bioavailability and bioaccumulation will be enhanced in secondary consumers such as crustacean zooplankton due to ocean acidification.

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Enormously enhanced particulate organic carbon and nitrogen production by elevated CO2 and moderate aluminum enrichment in the coccolithophore Emiliania huxleyi

Aluminum (Al) is abundant and ubiquitous in the environment. However, little information is available on its effects on photosynthetic microbes in alkaline seawater. Thus, we investigated the physiological performance in the most cosmopolitan coccolithophorid, viz., Emiliania huxleyi, grown under low (410 µatm) and high (1000 µatm) CO2 levels in seawater having none (0 nM, NAl), low (0.2 µM, LAl) and high (2 µM, HAl) Al concentrations. Under low CO2 conditions, the specific growth rate showed no significant difference between the NAl and LAl treatments, which was higher than the HAL treatment. Elevated CO2 inhibited the growth rate in the NAl and LAl cultures but did not affect the HAl cultures. The addition of Al had no effects on (LAl) or slightly elevated (HAl) the particulate organic carbon (POC) production rate under low CO2 conditions. With increasing CO2 concentration, the production rate of POC was enhanced by 55.3 % during the NAl treatment and further increased by 22.3 % by adding 0.2 µM Al. The responses of particulate organic nitrogen (PON) production rate, cellular POC, and PON contents to the different treatments revealed the same pattern as those of the POC production rate. The particulate inorganic carbon (PIC) production rate and PIC/POC ratio were not affected by Al under low CO2 conditions. They were significantly decreased by elevated CO2 in the LAl and HAl cultures. Our results indicate that high CO2 could increase carbon export to ocean depths by elevating the efficiency of the biological pump at low Al levels occurring in natural seawater (0.2 μM), with potentially significant implications for the carbon cycle of the ocean under accelerating anthropogenic influences.

Continue reading ‘Enormously enhanced particulate organic carbon and nitrogen production by elevated CO2 and moderate aluminum enrichment in the coccolithophore Emiliania huxleyi’

Effects of elevated CO2 on metabolic rate and nitrogenous waste handling in the early life stages of yellowfin tuna (Thunnus albacares)

Graphical abstract


  • Little is known about how tuna species will respond to ocean acidification (OA).
  • CO2 altered nitrogenous waste excretion and metabolic rate in yolk sac larvae.
  • CO2 did not change yolk sac depletion in embryos.
  • CO2 did not alter nitrogen accumulation in yellowfin tuna.
  • Yellowfin tuna were more robust to CO2 than predicted.


Ocean acidification is predicted to have a wide range of impacts on fish, but there has been little focus on broad-ranging pelagic fish species. Early life stages of fish are thought to be particularly susceptible to CO2 exposure, since acid-base regulatory faculties may not be fully developed. We obtained yellowfin tuna (Thunnus albacares) from a captive spawning broodstock population and exposed them to control or 1900 μatm CO2 through the first three days of development as embryos transitioned into yolk sac larvae. Metabolic rate, yolk sac depletion, and oil globule depletion were measured to assess overall energy usage. To determine if CO2 altered protein catabolism, tissue nitrogen content and nitrogenous waste excretion were quantified. CO2 exposure did not significantly impact embryonic metabolic rate, yolk sac depletion, or oil globule depletion, however, there was a significant decrease in metabolic rate at the latest measured yolk sac larval stage (36 h post fertilization). CO2-exposure led to a significant increase in nitrogenous waste excretion in larvae, but there were no differences in nitrogen tissue accumulation. Nitrogenous waste accumulated in embryos as they developed but decreased after hatch, coinciding with a large increase in nitrogenous waste excretion and increased metabolic rate in newly hatched larvae. Our results provide insight into how yellowfin tuna are impacted by increases in CO2 in early development, but more research with higher levels of replication is needed to better understand long-term impacts and acid-base regulatory mechanisms in this important pelagic fish.

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Effects of climate change on the Kenyan coral reef eco-system

The coral reef ecosystem is a natural habitat for many marine organisms that has high economic and tourist significance. Nonetheless, this ecosystem has very low tolerance to the effects of changes brought about by increasing sea surface temperatures and ocean acidification. This study sought to investigate the combined effect of rising sea surface temperatures and ocean acidification on the Kenyan coral reef ecosystem. This was achieved by determining the spatial-temporal variability of ocean acidification over the Kenyan coastline; and simulating the combined effect of sea surface temperature increases and ocean acidification on the coral reef ecosystem.

Historical (2000-2021) data on sea surface temperature (SSTs) was obtained from the National Oceanic and Atmospheric Administration (NOAA) and data on dissolved total carbon dioxide (TCO2) and pH from Global Ocean Data Analysis Project (GLODAP). Future (2022-2081) sea surface temperature and dissolved carbon dioxide data was downloaded from Coupled Model Intercomparison Project (CMIP6) experiment for two Shared Socioeconomic Pathways (SSPs) namely SSP2-4.5 and SSP5-8.5. Statistical, graphical and model simulations analyses were applied in the study to investigate the combined effect of increasing SST and ocean acidification on coral reef ecosystem over the Kenyan coastline.

Results indicate that mean sea surface temperature and dissolved carbon dioxide along the Kenyan coastline varied with seasons and had increased between the years 2000-2021. Trend tests of SSTs and TCO2 revealed a significant upward trend at 5% level of significance. Rising SSTs led to bleaching in coral reefs along this coastline whereas TCO2 led to reduced amount of carbonate ion concentration and reduced pH in the sea surface waters which affected the rates of calcification and survival of the coral reefs. The results of the Combined Mortality and Bleaching Output model simulation revealed that bleaching and ocean acidification had negatively affected the coral reef cover resulting in a decline of more than 30% of cover between 2000 and 2021. The results of the simulation also projected that the coral reef cover will continue to decline in the long-term by 52% under SSP2-4.5 and 63% under SSP5-8.5 if the trends in SSTs and TCO2 are maintained.

This study recommends collaborative implementation of climate change policies and practices by national and regional governments, communities and policy makers; enhanced efforts by coastal county governments in Kenya and research organisations to expound on scientific knowledge base while simultaneously implementing sustainable targeted solutions to ensure that the socio-economic benefits of the coral reef ecosystem are sustained.

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Juvenile Atlantic sea scallop, Placopecten magellanicus, energetic response to increased carbon dioxide and temperature changes

This study assessed the energy budget for juvenile Atlantic Sea Scallop, Placopecten magellanicus, during a natural drop in temperature (15.6°C to 5.8°C) over an 8-week time period during the fall at three different enrichment levels of carbon dioxide (CO2). Every 2 weeks, individuals were sampled for ecophysiological measurements of feeding activity, respiration rate (RR) and excretion rate (ER) to enable the calculation of scope for growth (SFG) and atomic oxygen:nitrogen ratios (O:N). In addition, 36 individuals per treatment were removed for shell height, dry tissue weight (DTW) and dry shell weight (DSW). We found a significant decrease in feeding rates as CO2 increased. Those rates also were significantly affected by temperature, with highest feeding at 9.4°C. No significant CO2 effect was observed for catabolic energy processes (RR and ER); however, these rates did increase significantly with temperature. The O:N ratio was not significantly affected by CO2, but was significantly affected by temperature. There was a significant interaction between CO2 and temperature for ER and the O:N ratio, with low CO2 levels resulting in a U-shaped response that was not sustained as CO2 levels increased. This suggests that the independent effects of CO2 and temperature observed at low levels are different once a CO2 threshold is reached. Additionally, there were significant differences in growth estimators (shell height and DSW), with the best growth occurring at the lowest CO2 level. In contrast to temperature variations that induced a trade-off response in energy acquisition and expenditure, results from this research support the hypothesis that sea scallops have a limited ability to alter physiological processes to compensate for increasing CO2.

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Thanks mum. Maternal effects in response to ocean acidification of sea urchin larvae at different ecologically relevant temperatures

Graphical abstract


  • Ocean acidification and temperature differently influence larval development of Arbacia lixula and Paracentrotus lividus.
  • Larvae of the two A. lixula populations (ambient-pH vs vent sites) respond differently to ocean acidification and temperature.
  • Maternal buffer effect was observed in response to ocean acidification and temperature in both species.
  • A. lixula seems to be more tolerant to changes in temperature than P. lividus.


Juvenile stages of marine species might be more vulnerable than adults to climate change, however larval vulnerability to predictable environmental changes can be mitigated by parental anticipatory buffer effects occurring during gametogenesis. In this study, ocean acidification effect were investigated on larval growth of two sea urchins, Arbacia lixula and Paracentrotus lividus, at different temperature levels. Results showed that altered pH and temperature affected larval development in both species, with significant length reductions of spicules and significant increases in abnormal larvae. Detrimental effects of reduced pH and high temperature were however dependent on the mother. Furthermore, the responses of A. lixula larvae from the ambient site (pH ∼ 8.0) were compared with those of larvae obtained from mothers collected from a natural CO2 vent (pH ∼ 7.7) in Ischia. Comparisons highlighted a transgenerational response, as the CO2 vent larvae proved to be more resilient to reduced pH, although more sensitive to increased temperature.

Continue reading ‘Thanks mum. Maternal effects in response to ocean acidification of sea urchin larvae at different ecologically relevant temperatures’

Effects of elevated pCO2 on the response of coccolithophore Emiliania huxleyi to prolonged darkness

Although numerous studies have examined the responses of coccolithophores to ocean acidification, less is known on the fate of those calcifying organisms when they sink to the ocean’s aphotic regions. In this study, the coccolithophore Emiliania huxleyi was first grown under a regular 12/12 light/dark cycle at 20°C, exposed to both high (1000 μatm) and ambient CO2 (410 μatm) levels. The cultures were then transferred to continuous darkness for 96 h at 20°C or 16°C. We found that elevated CO2 decreased the specific growth rate while increasing the cellular particulate organic carbon (POC) and nitrogen (PON) contents and the POC/PON ratio of E. huxleyi in the light/dark period. After 96 h of dark acclimation, the cell abundance decreased more obviously at 20°C than at 16°C but showed no significant difference between the two CO2 treatments. The decrease in volumetric POC concentration was most prominent in the high CO2/20°C treatment and least in the ambient CO2/16°C treatment. At 16°C, the PON concentration increased in the high CO2 cultures and exhibited no change in the ambient CO2 cultures. While at 20°C, the PON concentration decreased significantly both under high and ambient CO2 conditions. The final POC/PON ratio showed no significant differences among the different temperature and CO2 treatments. Overall, a higher percentage of POC relative to that of PON was lost in darkness with increasing CO2 concentration, with potential implications for the ocean’s nutrient cycle.

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Dynamics of an aquatic diffusive predator–prey model with double Allee effect and pH-dependent capture rate

To investigate ocean acidification and Allee effects on the dynamics of a marine predator–prey system, an aquatic diffusive predator–prey model with double Allee effect on prey and pH-dependent capture rate is considered. First, we study the stability of constant steady state solutions using linearized theory. Second, the nonexistence of nonconstant positive steady state solutions is shown for appropriate ranges of parameters. Furthermore, we show the existence of a Hopf bifurcation and derive the direction and stability of the bifurcating periodic solutions. Both theoretical analysis and numerical simulation show that changing predator–prey interaction strengths, due to changing environmental conditions, can fundamentally change the system dynamics, even for apparently small changes in interaction strength. As the interaction strength decreases due to decreasing ocean pH, the system dynamics transition from persistent fluctuations in species abundances (periodic solutions), to stable coexistence, to predator extinct (with stable non-zero prey abundance), suggesting the potential for ocean acidification to decrease the abundance and diversity of marine species by weakening predation rates. Moreover, double Allee effect parameters together determine the stability of periodic solutions when the spatially homogeneous bifurcating periodic solutions exist, and the wavelength becomes longer as the Allee effect increases.

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The involvement of a novel calmodulin-like protein isoform from oyster Crassostrea gigas in transcription factor regulation provides new insight into acclimation to ocean acidification

Marine organisms need to adapt to improve organismal fitness under ocean acidification (OA). Recent studies have shown that marine calcifiers can achieve acclimation by stimulating calcium binding/signaling pathways. Here, a CaM-like gene (CgCaLP-2) from oyster Crassostrea gigas which typically responded to long-term CO2 exposure (two months) rather than short-term exposure (one week) was characterized. The cloned cDNA was 678 bp and was shorter than the retrieved sequence from NCBI (1125 bp). The two sequences, designated as CgCaLP-2-v1 and CgCaLP-2-v2, were demonstrated to be different splice variants by the genome sequence analysis. Western blotting analysis revealed two bands of 23 kD and 43 kD in mantle and hemocytes, corresponding to predicted molecular weight of CgCaLP-2-v1 and CgCaLP-2-v2, respectively. The isoform CgCaLP-2-v1 (the 23 kD band) was highly stimulated in response to long-term CO2 exposure (42-day and 56-day treatment) in hemocytes and mantle tissue. The fluorescence signal of CgCaLP-2 in mantle and hemocytes became more intensive after long-term CO2 exposure. Besides, in hemocytes, CgCaLP-2 presented a higher localization on the nuclear membrane after long-term CO2 exposure (56 d). The target gene network of CgCaLP-2 was predicted, and a transcription factor (TF) gene annotated as Homeobox protein SIX4 (CgSIX4) showed a similar expressive trend to CgCaLP-2 during CO2 exposure. Suppression of CgCaLP-2 via RNA interference significantly reduced the mRNA expression of CgSIX4. The results suggested that CgCaLP-2 might mediate the Ca2+-CaLP-TF signal transduction pathway under long-term CO2 exposure. This study serves as an example to reveal that alternative splicing is an important mechanism for generation multiple protein isoforms and thus shape the plastic responses under CO2 exposure, providing new insight into the potential acclimation ability of marine calcifiers to future OA.

Continue reading ‘The involvement of a novel calmodulin-like protein isoform from oyster Crassostrea gigas in transcription factor regulation provides new insight into acclimation to ocean acidification’

Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors

Common sea stars (Asterias rubens) are at risk of physiological stress and decline with projected shifts in oceanic conditions. This study assessed changes in coelomic fluid (CF) blood gases, electrolytes, osmolality, and coelomocyte counts in adult common sea stars after exposure to stressors mimicking effects from climate change for 14 days, including decreased pH (−0.4 units, mean: 7.37), hypoxia (target dissolved oxygen ~1.75 mg O2/L, mean: 1.80 mg O2/L), or increased temperature (+10 °C, mean: 17.2 °C) and compared sea star CF electrolytes and osmolality to tank water. Changes in CF blood gases, electrolytes, and/or coelomocyte counts occurred in all treatment groups after stressor exposures, indicating adverse systemic effects with evidence of increased energy expenditure, respiratory or metabolic derangements, and immunosuppression or inflammation. At baseline, CF potassium and osmolality of all groups combined were significantly higher than tank water, and, after exposures, CF potassium was significantly higher in the hypoxia group as compared to tank water. These findings indicate physiological challenges for A. rubens after stressor exposures and, given increased observations of sea star wasting events globally, this provides evidence that sea stars as a broad group are particularly vulnerable to changing oceans.

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The effects of ocean acidification on fishes – history and future outlook

The effects of increased levels of carbon dioxide (CO2) on the Earth’s temperature have been known since the end of the 19th century. It was long believed that the oceans’ buffering capacity would counteract any effects of dissolved CO2 in marine environments, but during recent decades, many studies have reported detrimental effects of ocean acidification on aquatic organisms. The most prominent effects can be found within the field of behavioural ecology, e.g., complete reversal of predator avoidance behaviour in CO2-exposed coral reef fish. Some of the studies have been very influential, receiving hundreds of citations over recent years. The results have also been conveyed to policymakers and publicized in prominent media outlets for the general public. Those extreme effects of ocean acidification on fish behaviour have, however, spurred controversy, given that more than a century of research suggests that there are few or no negative effects of elevated CO2 on fish physiology. This is due to sophisticated acid–base regulatory mechanisms that should enable their resilience to near-future increases in CO2. In addition, an extreme “decline effect” has recently been shown in the literature regarding ocean acidification and fish behaviour, and independent research groups have been unable to replicate some of the most profound effects. Here, the author presents a brief historical overview on the effects of elevated CO2 and ocean acidification on fishes. This historical recap is warranted because earlier work, prior to a recent (c. 10 year) explosion in interest, is often overlooked in today’s ocean acidification studies, despite its value to the field. Based on the historical data and the current knowledge status, the author suggests future strategies with the aim to improve research rigour and clarify the understanding of the effects of ocean acidification on fishes.

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Malformation in coccolithophores in low pH waters: evidences from the eastern Arabian Sea

Oceanic calcifying plankton such as coccolithophores is expected to exhibit sensitivity to climate change stressors such as warming and acidification. Observational studies on coccolithophore communities along with carbonate chemistry provide important perceptions of possible adaptations of these organisms to ocean acidification. However, this phytoplankton group remains one of the least studied in the northern Indian Ocean. In 2017, the biogeochemistry group at the Council for Scientific and Industrial Research-National Institute of Oceanography (CSIR-NIO) initiated a coccolithophore monitoring study in the eastern Arabian Sea (EAS). Here, we document for the first time a detailed spatial and seasonal distribution of coccolithophores and their controlling factors from the EAS, which is a well-known source of CO2 to the atmosphere. To infer the seasonality, data collected at three transects (Goa, Mangalore, and Kochi) during the Southwest Monsoon (SWM) of 2018 was compared with that of the late SWM of 2017. Apart from this, the abundance of coccolithophores was studied at the Candolim Time Series (CaTS) transect, off Goa during the Northeast Monsoon (NEM). The most abundant coccolithophore species found in the study region was Gephyrocapsa oceanica. A high abundance of G. oceanica (1800 × 103cells L−1) was observed at the Mangalore transect during the late SWM despite experiencing low pH and can be linked to nitrogen availability. The high abundance of G. oceanica at Mangalore was associated with high dimethylsulphide (DMS). Particulate inorganic carbon (PIC) and scattering coefficient retrieved from satellites also indicated a high abundance of coccolithophores off Mangalore during the late SWM of 2017. Interestingly, G. oceanica showed malformation during the late SWM in low pH waters. Malformation in coccolithophores could have a far-reaching impact on the settling fluxes of organic matter and also on the emissions of climatically important gases such as DMS and CO2, thus influencing atmospheric chemistry. The satellite data for PIC in the EAS indicates a high abundance of coccolithophore in recent years, especially during the warm El Nino years (2015 and 2018). This warrants the need for a better assessment of the fate of coccolithophores in high-CO2 and warmer oceans.

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A novel approach effect of ocean acidification on oysters

We are pacing to a GHG free world to live in. Due to the escalated levels of carbon dioxide in the atmosphere, several living organisms are being affected. This is more intense for life under water. Carbon dioxide in the atmosphere gets dissolved in the ocean, leading to OCEAN ACIDIFICATION, reducing the pH of the ocean. This in return affects the ocean habitat. It makes calcium carbonate ions less available, which is a major building block for different species to build shells and skeletons. Due to the reduction of calcium carbonate ions in the ocean, the shells tend to dissolve. Oysters act as natural filters for the ocean, buffers for tides and their reefs serve as barriers to storms and tides, preventing erosion. Climate change and Ocean acidification has contributed to reduction of the species. This study aims to find out the optimum carbon dioxide, oysters’ metabolism to varying levels of carbon dioxide and alleviating the excess dissolved carbon dioxide.

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Interaction of CO2 and light availability on photophysiology of tropical coccolithophorids (Emiliania huxleyi, Gephyrocapsa oceanica, and Ochosphaera sp.)

The study to examine the calcification rate, adaptation, and the biotic response of three tropical coccolithophorids (Emiliania huxleyi, Gephyrocapsa oceanica, and Ochosphaera sp) to changes in CO2 concentration. Three selected calcifying coccolitophorids were grown at batch culture with CO2 system at two levels of CO2 (385 and 1000 ppm) and two light dark periods. The parameters measured and calculation including growth rate, particulate organic carbon content, particulate inorganic carbon content, chlorophyll a, cell size, photosynthetic, organic, inorganic carbon production, photosynthesis, and calcification rate.  The results showed that there was a different response to carbonate chemistry changes and dark and light periods in any of the analyzed parameters.  The growth rate of three selected calcifying microalgae tested was decreasing significantly at high concentrations of CO2 (1000 ppm) treatment on 14:10 hour light: dark periods. However, there was no significant difference between the two CO2 concentrations where they were illuminated by 24 hours light in growth rate.  The increasing CO2 concentration and light-dark periods were species-specific responses to photosynthesis and calcification rate for three selected calcifying microalgae.

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The effect of pH on the larvae of two sea urchin species using different pH manipulation methods

Climate change alters ocean pH, temperature, and salinity, which presents challenges for oceanic organisms, especially those with calcium carbonate skeletons. Our research examines how decreasing pH impacts larval survivorship and calcium carbonate skeletal development of two sea urchin species, Lytechinus variegatus and Arbacia punctulata. Based on previous work in various sea urchin species, it is expected that as pH decreases, survivorship decreases and skeletal malformations increase. Both L. variegatus and A. punctulata have been used in prior studies to explore pH change on survivorship and development, but these studies incorporated various outcomes and pH manipulation methods, limiting how comparable they are. Therefore, we wanted to measure the same outcomes between species and compare the effect of different pH manipulation within species. We altered pH by either HCL addition or CO2 bubbling through seawater. Larvae, at a concentration of 3 larvae/ml, were exposed to seawater of pH 8.4, 8.0, or 7.6. For each treatment, survivorship of 30-40 larvae was measured daily for 10-14 days depending on the trial. Larval malformations were quantified for about 10 larvae from daily fixed samples. Larval arm length, body length, and body width were measured using Image J. For both methods of pH manipulation and both species, there was a statistically significant (p<0.001) decrease in survivorship as pH decreases consistent with the prediction. Preliminary analysis of skeletal deformities suggests malformations increase as pH decreases, but data are still being collected. Similar abnormalities observed between species regardless of pH manipulations include uneven or missing arms and misshapen aboral sides. The effect of pH on larval survivorship and development in L. variegatus and A. punctulata are comparable to observations in other species suggesting effects are consistent across manipulation methods and species. With this research, we can continue to fine-tune methodology and build on our understanding of how climate change-driven ocean acidification can impact species.

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Deciphering pH-dependent microbial taxa and functional gene co-occurrence in the coral Galaxea fascicularis

How the coral microbiome responds to oceanic pH changes due to anthropogenic climate change, including ocean acidification and deliberate artificial alkalization, remains an open question. Here, we applied a 16S profile and GeoChip approach to microbial taxonomic and gene functional landscapes in the coral Galaxea fascicularis under three pH levels (7.85, 8.15, and 8.45) and tested the influence of pH changes on the cell growth of several coral-associated strains and bacterial populations. Statistical analysis of GeoChip-based data suggested that both ocean acidification and alkalization destabilized functional cores related to aromatic degradation, carbon degradation, carbon fixation, stress response, and antibiotic biosynthesis in the microbiome, which are related to holobiont carbon cycling and health. The taxonomic analysis revealed that bacterial species richness was not significantly different among the three pH treatments, but the community compositions were significantly distinct. Acute seawater alkalization leads to an increase in pathogens as well as a stronger taxonomic shift than acidification, which is worth considering when using artificial ocean alkalization to protect coral ecosystems from ocean acidification. In addition, our co-occurrence network analysis reflected microbial community and functional shifts in response to pH change cues, which will further help to understand the functional ecological role of the microbiome in coral resilience.

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Transitional traits determine the acclimation characteristics of the coccolithophore Chrysotila dentata to ocean warming and acidification

Ocean warming and acidification interactively affect the coccolithophore physiology and drives major biogeochemical changes. While numerous studies investigated coccolithophore under short-term conditions, knowledge on how different transitional periods over long-exposure could influence the element, macromolecular and metabolic changes for its acclimation are largely unknown. We cultured the coccolithophore Chrysotila dentata, (culture generations of 1st, 10th, and 20th) under present (low-temperature low-carbon-dioxide [LTLC]) and projected (high-temperature high-carbon-dioxide [HTHC]) ocean conditions. We examined elemental and macromolecular component changes and sequenced a transcriptome. We found that with long-exposure, most physiological responses in HTHC cells decreased when compared with those in LTLC, however, HTHC cell physiology showed constant elevation between each generation. Specifically, compared to 1st generation, the 20th generation HTHC cells showed increases in quota carbon (Qc:29%), nitrogen (QN:101%), and subsequent changes in C:N-ratio (68%). We observed higher lipid accumulation than carbohydrates within HTHC cells under long-exposure, suggesting that lipids were used as an alternative energy source for cellular acclimation. Protein biosynthesis pathways increased their efficiency during long-term HTHC condition, indicating that cells produced more proteins than required to initiate acclimation. Our findings suggest that the coccolithophore resilience increased between the 1st–10th generation to initiate the acclimation process under ocean warming and acidifying conditions.

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