Seawater carbonate chemistry and energy status in the periwinkle Littorina littorea during experiments, 2011

In the future, marine organisms will face the challenge of coping with multiple environmental changes associated with increased levels of atmospheric Pco2, such as ocean warming and acidification. To predict how organisms may or may not meet these challenges, an in-depth understanding of the physiological and biochemical mechanisms underpinning organismal responses to climate change is needed. Here, we investigate the effects of elevated Pco2 and temperature on the whole-organism and cellular physiology of the periwinkle Littorina littorea. Metabolic rates (measured as respiration rates), adenylate energy nucleotide concentrations and indexes, and end-product metabolite concentrations were measured. Compared with values for control conditions, snails decreased their respiration rate by 31% in response to elevated Pco2 and by 15% in response to a combination of increased Pco2 and temperature. Decreased respiration rates were associated with metabolic reduction and an increase in end-product metabolites in acidified treatments, indicating an increased reliance on anaerobic metabolism. There was also an interactive effect of elevated Pco2 and temperature on total adenylate nucleotides, which was apparently compensated for by the maintenance of adenylate energy charge via AMP deaminase activity. Our findings suggest that marine intertidal organisms are likely to exhibit complex physiological responses to future environmental drivers, with likely negative effects on growth, population dynamics, and, ultimately, ecosystem processes.

Seawater carbonate chemistry, nutrient uptake and biological processes of coral Stylophora pistillata during experiments, 2011

The effects of ocean acidification and elevated seawater temperature on coral calcification and photosynthesis have been extensively investigated over the last two decades, whereas they are still unknown on nutrient uptake, despite their importance for coral energetics. We therefore studied the separate and combined impacts of increases in temperature and pCO2 on phosphate, ammonium, and nitrate uptake rates by the scleractinian coral S. pistillata. Three experiments were performed, during 10 days i) at three pHT conditions (8.1, 7.8, and 7.5) and normal temperature (26°C), ii) at three temperature conditions (26°, 29°C, and 33°C) and normal pHT(8.1), and iii) at three pHT conditions (8.1, 7.8, and 7.5) and elevated temperature (33°C). After 10 days of incubation, corals had not bleached, as protein, chlorophyll, and zooxanthellae contents were the same in all treatments. However, photosynthetic rates significantly decreased at 33°C, and were further reduced for the pHT 7.5. The photosynthetic efficiency of PSII was only decreased by elevated temperature. Nutrient uptake rates were not affected by a change in pH alone. Conversely, elevated temperature (33°C) alone induced an increase in phosphate uptake but a severe decrease in nitrate and ammonium uptake rates, even leading to a release of nitrogen into seawater. Combination of high temperature (33°C) and low pHT(7.5) resulted in a significant decrease in phosphate and nitrate uptake rates compared to control corals (26°C, pHT = 8.1). These results indicate that both inorganic nitrogen and phosphorus metabolism may be negatively affected by the cumulative effects of ocean warming and acidification.

Seawater carbonate chemistry and biological parameters of Sepia officinalis during experiments, 2009

Low pO2 values have been measured in the perivitelline fluids (PVF) of marine animal eggs on several occasions, especially towards the end of development, when embryonic oxygen consumption is at its peak and the egg case acts as a massive barrier to diffusion. Several authors have therefore suggested that oxygen availability is the key factor leading to hatching. However, there have been no measurements of PVF pCO2 so far. This is surprising, as elevated pCO2 could also constitute a major abiotic stressor for the developing embryo. As a first attempt to fill this gap in knowledge, we measured pO2, pCO2 and pH in the PVF of late cephalopod (Sepia officinalis) eggs. We found linear relationships between embryo wet mass and pO2, pCO2 and pH. pO2 declined from >12 kPa to less than 5 kPa, while pCO2 increased from 0.13 to 0.41 kPa. In the absence of active accumulation of bicarbonate in the PVF, pH decreased from 7.7 to 7.2. Our study supports the idea that oxygen becomes limiting in cephalopod eggs towards the end of development; however, pCO2 and pH shift to levels that have caused significant physiological disturbances in other marine ectothermic animals. Future research needs to address the physiological adaptations that enable the embryo to cope with the adverse abiotic conditions in their egg environment.

Seawater carbonate chemistry and calcification during experiments with coral communities, 2002

The effect of increased CO2 partial pressure (pCO2) on the community metabolism (primary production, respiration, and calcification) of a coral community was investigated over periods ranging from 9 to 30 d. The community was set up in an open-top mesocosm within which pCO2 was manipulated (411, 647, and 918 µatm). The effect of increased pCO2 on the rate of calcification of the sand area of the mesocosm was also investigated. The net community primary production (NCP) did not change significantly with respect to pCO2 and was 5.1 ± 0.9 mmol O2 m-2 h-1, Dark respiration (R) increased slightly during the experiment at high pCO2, but this did not affect significantly the NCP:R ratio (1.0 ± 0.2). The rate of calcification exhibited the trend previously reported; it decreased as a function of increasing pCO2 and decreasing aragonite saturation state. This re-emphasizes the predictions that reef calcification is likely to decrease during the next century. The dissolution process of calcareous sand does not seem to be affected by open seawater carbonate chemistry; rather, it seems to be controlled by the biogeochemistry of sediment pore water.

Seawater carbonate chemistry and Emiliania huxleyi biological processes during experiments, 2010

The calcifying phytoplankton species, coccolithophores, have their calcified coccoliths around the cells, however, their physiological roles are still unknown. Here, we hypothesized that the coccoliths may play a certain role in reducing solar UV radiation (UVR, 280-400 nm) and protect the cells from being harmed. Cells of Emiliania huxleyi with different thicknesses of the coccoliths were obtained by culturing them at different levels of dissolved inorganic carbon and their photophysiological responses to UVR were investigated. Although increased dissolved inorganic carbon decreased the specific growth rate, the increased coccolith thickness significantly ameliorated the photoinhibition of PSII photochemical efficiency caused by UVR. Increase by 91% in the coccolith thickness led to 35% increase of the PSII yield and 22% decrease of the photoinhibition of the effective quantum yield by UVR. The coccolith cover reduced more UVA (320-400 nm) than UVB (280-315 nm), leading to less inhibition per energy at the UV-A band.

Seawater carbonate chemistry and growth rate during experiments with phylotypes of Symbiodinium (Dinophyceae), 2011

We investigated the effect of elevated partial pressure of CO2 (pCO2) on the photosynthesis and growth of four phylotypes (ITS2 types A1, A13, A2, and B1) from the genus Symbiodinium, a diverse dinoflagellate group that is important, both free-living and in symbiosis, for the viability of cnidarians and is thus a potentially important model dinoflagellate group. The response of Symbiodinium to an elevated pCO2 was phylotype-specific. Phylotypes A1 and B1 were largely unaffected by a doubling in pCO2 in contrast, the growth rate of A13 and the photosynthetic capacity of A2 both increased by ~ 60%. In no case was there an effect of ocean acidification (OA) upon respiration (dark- or light-dependent) for any of the phylotypes examined. Our observations suggest that OA might preferentially select among free-living populations of Symbiodinium, with implications for future symbioses that rely on algal acquisition from the environment (i.e., horizontal transmission). Furthermore, the carbon environment within the host could differentially affect the physiology of different Symbiodinium phylotypes. The range of responses we observed also highlights that the choice of species is an important consideration in OA research and that further investigation across phylogenetic diversity, for both the direction of effect and the underlying mechanism(s) involved, is warranted.

Seawater carbonate chemistry and survival of mollusks: Mercenaria mercenaria, Argopecten irradians, and Crassostrea virginica during experiments, 2009

We present experiments that examined the metamorphosis, growth, and survivorship of larvae from three species of commercially and ecologically valuable shellfish (Mercenaria mercenaria, Argopecten irradians, and Crassostrea virginica) at the levels of CO2 projected to occur during the 21st century and beyond. Under CO2 concentrations estimated to occur later this century (~66 Pa, 650 ppm), M. mercenaria and A. irradians larvae exhibited dramatic declines (>50%) in survivorship as well as significantly delayed metamorphosis and significantly smaller sizes. Although C. virginica larvae also experienced lowered growth and delayed metamorphosis at ~66 Pa CO2, their survival was only diminished at ~152 Pa CO2. The extreme sensitivity of larval stages of shellfish to enhanced levels of CO2 indicates that current and future increases in pelagic CO2 concentrations may deplete or alter the composition of shellfish populations in coastal ecosystems.

Seawater carbonate chemistry, nutrients, and Calcidiscus leptoporus (strain RCC1135) growth rate and calcification rate during experiments, 2012

The coccolithophore Calcidiscus leptoporus was grown in batch culture under nitrogen (N) as well as phosphorus (P) limitation. Growth rate, particulate inorganic carbon (PIC), particulate organic carbon (POC), particulate organic nitrogen (PON), and particulate organic phosphorus (POP) production were determined and coccolith morphology was analysed. While PON production decreased by 70% under N-limitation and POP production decreased by 65% under P-limitation, growth rate decreased by 33% under N- as well as P-limitation. POC as well as PIC production (calcification rate) increased by 27% relative to the control under P-limitation, and did not change under N-limitation. Coccolith morphology did not change in response to either P or N limitation. While these findings, supported by a literature survey, suggest that coccolith morphogenesis is not hampered by either P or N limitation, calcification rate might be. The latter conclusion is in apparent contradiction to our data. We discuss the reasons for this inference.

Seawater carbonate chemistry and effects of CO2 and their modulation by light in the life-cycle stages of the coccolithophore Emiliania huxleyi strains RCC 1216 and 1217 during experiments, 2012

The effects of ocean acidification on the life-cycle stages of the coccolithophore Emiliania huxleyi and their by light were examined. Calcifying diploid and noncalcifying haploid cells (Roscoff culture collection 1216 and 1217) were acclimated to present-day and elevated CO2 partial pressures (PCO2; 38.5 vs. 101.3 Pa, ., 380 vs. 1000 matm) under low and high light (50 vs. 300 mmol photons m-2 s-1). Growth rates as well as quotas and production rates of C and N were measured. Sources of inorganic C for biomass buildup were using a 14C disequilibrium assay. Photosynthetic O2 evolution was measured as a function of dissolved inorganic C and light by means of membrane-inlet mass spectrometry. The diploid stage responded to elevated PCO2 by shunting resources from the production of particulate inorganic C toward organic C yet keeping the production of total particulate C constant. As the effect of ocean acidification was stronger under low light, the diploid stage might be less affected by increased acidity when energy availability is high. The haploid stage maintained elemental composition and production rates under elevated PCO2. Although both life-cycle stages involve different ways of dealing with elevated PCO2, the responses were generally modulated by energy availability, being typically most pronounced under low light. Additionally, PCO2 responses resembled those induced by high irradiances, indicating that ocean acidification affects the interplay between energy-generating processes (photosynthetic light reactions) and processes competing for energy (biomass buildup and calcification). A conceptual model is put forward explaining why the magnitude of single responses is determined by energy availability.

Seawater carbonate chemistry and biological processes of Emiliania huxleyi (strains RCC1256 and NZEH) during experiments, 2011

With respect to their sensitivity to ocean acidification, calcifiers such as the coccolithophore Emiliania huxleyi have received special attention, as the process of calcification seems to be particularly sensitive to changes in the marine carbonate system. For E. huxleyi, apparently conflicting results regarding its sensitivity to ocean acidification have been published (Iglesias-Rodriguez et al., 2008a; Riebesell et al., 2000). As possible causes for discrepancies, intra-specific variability and different effects of CO2 manipulation methods, i.e. the manipulation of total alkalinity (TA) or total dissolved inorganic carbon (DIC), have been discussed. While Langer et al. (2009) demonstrate a high degree of intra-specific variability between strains of E. huxleyi, the question whether different CO2 manipulation methods influence the cellular responses has not been resolved yet. In this study, closed TA as well as open and closed DIC manipulation methods were compared with respect to E. huxleyi's CO2-dependence in growth rate, POC- and PIC-production. The differences in the carbonate chemistry between TA and DIC manipulations were shown not to cause any differences in response patterns, while the latter differed between open and closed DIC manipulation. The two strains investigated showed different sensitivities to acidification of seawater, RCC1256 being more negatively affected in growth rates and PIC production than NZEH.

Seawater carbonate chemistry and growth rate during experiments with coral Acropora cervicornis, 2005

The growth rate of Acropora cervicornis branch tips maintained in the laboratory was measured before, during, and after exposure to elevated nitrate (5 and 10 µM NO3-), phosphate (2 and 4 µM P-PO43) and/or pCO2 (CO2 ~700 to 800 µatm). The effect of increased pCO2 was greater than that of nutrient enrichment alone. High concentrations of nitrate or phosphate resulted in significant decreases in growth rate, in both the presence and absence of increased pCO2. The effect of nitrate and phosphate enrichment combined was additive or antagonistic relative to nutrient concentration and pCO2 level. Growth rate recovery was greater after exposure to increased nutrients or CO2 compared to increased nutrients and CO2. If these results accurately predict coral response in the natural environment, it is reasonable to speculate that the survival and reef-building potential of this species will be significantly negatively impacted by continued coastal nutrification and projected pCO2 increases.

Seawater carbonate chemistry, calcification and survival of coral recruits in a laboratory experiment

Manipulative studies have demonstrated that ocean acidification (OA) is a threat to coral reefs, yet no experiments have employed diurnal variations in pCO2 that are ecologically relevant to many shallow reefs. Two experiments were conducted to test the response of coral recruits (less than 6 days old) to diurnally oscillating pCO2; one exposing recruits for 3 days to ambient (440 µatm), high (663 µatm) and diurnally oscillating pCO2 on a natural phase (420-596 µatm), and another exposing recruits for 6 days to ambient (456 µatm), high (837 µatm) and diurnally oscillating pCO2 on either a natural or a reverse phase (448-845 µatm). In experiment I, recruits exposed to natural-phased diurnally oscillating pCO2 grew 6-19% larger than those in ambient or high pCO2. In experiment II, recruits in both high and natural-phased diurnally oscillating pCO2 grew 16 per cent larger than those at ambient pCO2, and this was accompanied by 13-18% higher survivorship; the stimulatory effect on growth of oscillatory pCO2 was diminished by administering high pCO2 during the day (i.e. reverse-phased). These results demonstrate that coral recruits can benefit from ecologically relevant fluctuations in pCO2 and we hypothesize that the mechanism underlying this response is highly pCO2-mediated, night-time storage of dissolved inorganic carbon that fuels daytime calcification.

Seawater carbonate chemistry and biological processes of sand dollars Dendraster excentricus during experiments, 2011

Reduction in global ocean pH due to the uptake of increased atmospheric CO2 is expected to negatively affect calcifying organisms, including the planktonic larval stages of many marine invertebrates. Planktonic larvae play crucial roles in the benthic-pelagic life cycle of marine organisms by connecting and sustaining existing populations and colonizing new habitats. Calcified larvae are typically denser than seawater and rely on swimming to navigate vertically structured water columns. Larval sand dollars Dendraster excentricus have calcified skeletal rods supporting their bodies, and propel themselves with ciliated bands looped around projections called arms. Ciliated bands are also used in food capture, and filtration rate is correlated with band length. As a result, swimming and feeding performance are highly sensitive to morphological changes. When reared at an elevated PCO2 level (1000 ppm), larval sand dollars developed significantly narrower bodies at four and six-arm stages. Morphological changes also varied between four observed maternal lineages, suggesting within-population variation in sensitivity to changes in PCO2 level. Despite these morphological changes, PCO2 concentration alone had no significant effect on swimming speeds. However, acidified larvae had significantly smaller larval stomachs and bodies, suggesting reduced feeding performance. Adjustments to larval morphologies in response to ocean acidification may prioritize swimming over feeding, implying that negative consequences of ocean acidification are carried over to later developmental stages.

Seawater carbonate chemistry and benthic foraminifera Ammonia sp. mass, size, and growth rate during experiments, 2013

About 30% of the anthropogenically released CO2 is taken up by the oceans; such uptake causes surface ocean pH to decrease and is commonly referred to as ocean acidification (OA). Foraminifera are one of the most abundant groups of marine calcifiers, estimated to precipitate ca. 50 % of biogenic calcium carbonate in the open oceans. We have compiled the state of the art literature on OA effects on foraminifera, because the majority of OA research on this group was published within the last three years. Disparate responses of this important group of marine calcifiers to OA were reported, highlighting the importance of a process-based understanding of OA effects on foraminifera. We cultured the benthic foraminifer Ammonia sp. under a range of carbonate chemistry manipulation treatments to identify the parameter of the carbonate system causing the observed effects. This parameter identification is the first step towards a process-based understanding. We argue that CO3 is the parameter affecting foraminiferal size-normalized weights (SNWs) and growth rates. Based on the presented data, we can confirm the strong potential of Ammonia sp. foraminiferal SNW as a CO3 proxy.

Seawater carbonate chemistry and egg production, hatching and metabolic rates of a Mediterranean copepod species (Acartia clausi) in a laboratory experiment

This study includes the first information on the combined effect of low pH and raised temperature on egg production rate (EP), hatching success (HS), excretion and respiration of the Mediterranean copepod Acartia clausi. Adult individuals of A. clausi and fresh surface seawater were collected at a coastal station in Saronikos Gulf during April 2012. Four different conditions were applied: two different pH levels (present: 8.09 and future: 7.83) at two temperature values (present: 16°C and present+4 °C= 20°C). EP and HS success decreased significantly over the duration of exposure at future pH at both temperature conditions. However, the analysis of the combined effect of pH, T, chlorophyll a and the duration of the experiments on EP and HS revealed that ocean acidification had no discernible effect, whereas warming; food and the duration of exposure were more significant for the reproductive output of A. clausi. Temperature appeared to have a positive effect on respiration and excretion. Acidification had no clear effect on respiration, but a negative effect on the A. clausi excretion was observed. Acidification and warming resulted in the increase of the excretion rate and the increase was higher than that observed by warming only. Our findings showed that a direct effect of ocean acidification on copepod's vital rates was not obvious, except maybe in the case of excretion. Therefore, the combination of acidification with the ambient oligotrophic conditions and the warming could result in species being less able to allocate resources for coping with multiple stressors.