Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere

A new calibration database of census counts of organic-walled dinoflagellate cyst (dinocyst) assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the Northern Hemisphere after standardisation of taxonomy and laboratory procedures. The database comprises 940 reference data points from the North Atlantic, Arctic and North Pacific oceans and their adjacent seas, including the Mediterranean Sea, as well as epicontinental environments such as the Estuary and Gulf of St. Lawrence, the Bering Sea and the Hudson Bay. The relative abundance of taxa was analysed to describe the distribution of assemblages. The best analogue technique was used for the reconstruction of Last Glacial Maximum (LGM) sea-surface temperature and salinity during summer and winter, in addition to sea-ice cover extent, at sites from the North Atlantic (n=63), Mediterranean Sea (n=1) and eastern North Pacific (n=1). Three of the North Atlantic cores, from the continental margin of eastern Canada, revealed a barren LGM interval, probably because of quasi-permanent sea ice. Six other cores from the Greenland and Norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation. At the remaining sites (n= 54), relatively close modern analogues were found for most LGM samples, which allowed reconstructions. The new LGM results are consistent with previous reconstructions based on dinocyst data, which show much cooler conditions than at present along the continental margins of Canada and Europe, but sharp gradients of increasing temperature offshore. The results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea-ice cover, whereas relatively warm conditions may have prevailed offshore in summer. From these data, we hypothesise low thermal inertia in a shallow and low-density surface water layer.

Seawater carbonate chemistry and toxicity of Pseudo-nitzschia fraudulenta in a laboratory experiment

Anthropogenic CO2 is progressively acidifying the ocean, but the responses of harmful algal bloom species that produce toxins that can bioaccumulate remain virtually unknown. The neurotoxin domoic acid is produced by the globally-distributed diatom genus Pseudo-nitzschia. This toxin is responsible for amnesic shellfish poisoning, which can result in illness or death in humans and regularly causes mass mortalities of marine mammals and birds. Domoic acid production by Pseudo-nitzschia cells is known to be regulated by nutrient availability, but potential interactions with increasing seawater CO2 concentrations are poorly understood. Here we present experiments measuring domoic acid production by acclimatized cultures of Pseudo-nitzschia fraudulenta that demonstrate a strong synergism between projected future CO2 levels (765 ppm) and silicate-limited growth, which greatly increases cellular toxicity relative to growth under modern atmospheric (360 ppm) or pre-industrial (200 ppm) CO2 conditions. Cellular Si:C ratios decrease with increasing CO2, in a trend opposite to that seen for domoic acid production. The coastal California upwelling system where this species was isolated currently exhibits rapidly increasing levels of anthropogenic acidification, as well as widespread episodic silicate limitation of diatom growth. Our results suggest that the current ecosystem and human health impacts of toxic Pseudo-nitzschia blooms could be greatly exacerbated by future ocean acidification and 'carbon fertilization' of the coastal ocean.

Seawater carbonate chemistry, physiology, morphology of larval sea urchins, Strongylocentrotus purpuratus in a laboratory experiment

Ocean warming and ocean acidification, both consequences of anthropogenic production of CO2, will combine to influence the physiological performance of many species in the marine environment. In this study, we used an integrative approach to forecast the impact of future ocean conditions on larval purple sea urchins (Strongylocentrotus purpuratus) from the northeast Pacific Ocean. In laboratory experiments that simulated ocean warming and ocean acidification, we examined larval development, skeletal growth, metabolism and patterns of gene expression using an orthogonal comparison of two temperature (13°C and 18°C) and pCO2 (400 and 1100 µatm) conditions. Simultaneous exposure to increased temperature and pCO2 significantly reduced larval metabolism and triggered a widespread downregulation of histone encoding genes. pCO2 but not temperature impaired skeletal growth and reduced the expression of a major spicule matrix protein, suggesting that skeletal growth will not be further inhibited by ocean warming. Importantly, shifts in skeletal growth were not associated with developmental delay. Collectively, our results indicate that global change variables will have additive effects that exceed thresholds for optimized physiological performance in this keystone marine species.

Seawater carbonate chemistry and early development of the sea urchin Lytechinus variegatus in a laboratory experiment using artificial seawater

Land-based aquaculture facilities often utilize additional bicarbonate sources such as commercial sea salts that are designed to boost alkalinity in order to buffer seawater against reductions in pH. Despite these preventative measures, many facilities are likely to face occasional reductions in pH and corresponding reductions in carbonate saturation states due to the accumulation of metabolic waste products. We investigated the impact of reduced carbonate saturation states (Omega Ca, Omega Ar) on embryonic developmental rates, larval developmental rates, and echinoplutei skeletal morphometrics in the common edible sea urchin Lytechinus variegatus under high alkalinity conditions. Commercial artificial seawater was bubbled with a mixture of air and CO2 gas to reduce the carbonate saturation state. Rates of embryonic and larval development were significantly delayed in both the low and extreme low carbonate saturation state groups relative to the control at a given time. Although symmetry of overall skeletal body lengths was not affected, allometric relationships were significantly different between treatment groups. Larvae reared under ambient conditions had significantly greater postoral arm and overall body lengths relative to body lengths than larvae grown under extreme low carbonate saturation state conditions, indicating that extreme changes in the carbonate system affected not only developmental rates but also larval skeletal shape. Reduced rates of embryonic development and delayed and altered larval skeletal growth are likely to negatively impact larval culturing of L. variegatus in land-based, intensive culture situations where calcite and aragonite saturation states are lowered by the accumulation of metabolic waste products.

Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy. Wave-resistant algal rims, predominantly made up of the crustose coralline algae (CCA) Porolithon onkodes and P. pachydermum, are therefore critical structural elements for the survival of many shallow coral reefs. Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons. However, the recent discovery of dolomite (Mg0.5Ca0.5(CO3)), a stable carbonate, in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA. Here we show, using a dissolution experiment, that dried dolomite-rich CCA have 6-10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 (~ 700 ppm) and control (~ 380 ppm) environments, respectively. We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals. Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact. Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises.

Seawater carbonate chemistry and buffer capacity of the coelomic fluid in echinoderms in a laboratory experiment

The increase in atmospheric CO2 due to anthropogenic activity results in an acidification of the surface waters of the oceans. The impact of these chemical changes depends on the considered organisms. In particular, it depends on the ability of the organism to control the pH of its inner fluids. Among echinoderms, this ability seems to differ significantly according to species or taxa. In the present paper, we investigated the buffer capacity of the coelomic fluid in different echinoderm taxa as well as factors modifying this capacity. Euechinoidea (sea urchins except Cidaroidea) present a very high buffer capacity of the coelomic fluid (from 0.8 to 1.8 mmol/kg SW above that of seawater), while Cidaroidea (other sea urchins), starfish and holothurians have a significantly lower one (from -0.1 to 0.4 mmol/kg SW compared to seawater). We hypothesize that this is linked to the more efficient gas exchange structures present in the three last taxa, whereas Euechinoidea evolved specific buffer systems to compensate lower gas exchange abilities. The constituents of the buffer capacity and the factors influencing it were investigated in the sea urchin Paracentrotus lividus and the starfish Asterias rubens. Buffer capacity is primarily due to the bicarbonate buffer system of seawater (representing about 63% for sea urchins and 92% for starfish). It is also partly due to coelomocytes present in the coelomic fluid (around 8% for both) and, in P. lividus only, a compound of an apparent size larger than 3 kDa is involved (about 15%). Feeding increased the buffer capacity in P. lividus (to a difference with seawater of about 2.3 mmol/kg SW compared to unfed ones who showed a difference of about 0.5 mmol/kg SW) but not in A. rubens (difference with seawater of about 0.2 for both conditions). In P. lividus, decreased seawater pH induced an increase of the buffer capacity of individuals maintained at pH 7.7 to about twice that of the control individuals and, for those at pH 7.4, about three times. This allowed a partial compensation of the coelomic fluid pH for individuals maintained at pH 7.7 but not for those at pH 7.4.

Seawater carbonate chemistry and maximum growth rates of Skeletonema marinoi and Alexandrium ostenfeldii, toxin composition of Alexandrium ostenfeldii in a laboratory experiment

Phytoplankton populations can display high levels of genetic diversity that, when reflected by phenotypic variability, may stabilize a species response to environmental changes. We studied the effects of increased temperature and CO2 availability as predicted consequences of global change, on 16 genetically different isolates of the diatom Skeletonema marinoi from the Adriatic Sea and the Skagerrak (North Sea), and on eight strains of the PST (paralytic shellfish toxin)-producing dinoflagellate Alexandrium ostenfeldii from the Baltic Sea. Maximum growth rates were estimated in batch cultures of acclimated isolates grown for five to 10 generations in a factorial design at 20 and 24 °C, and present day and next century applied atmospheric pCO2, respectively. In both species, individual strains were affected in different ways by increased temperature and pCO2. The strongest response variability, buffering overall effects, was detected among Adriatic S. marinoi strains. Skagerrak strains showed a more uniform response, particularly to increased temperature, with an overall positive effect on growth. Increased temperature also caused a general growth stimulation in A. ostenfeldii, despite notable variability in strain-specific response patterns. Our data revealed a significant relationship between strain-specific growth rates and the impact of pCO2 on growth-slow growing cultures were generally positively affected, while fast growing cultures showed no or negative responses to increased pCO2. Toxin composition of A. ostenfeldii was consistently altered by elevated temperature and increased CO2 supply in the tested strains, resulting in overall promotion of saxitoxin production by both treatments. Our findings suggest that phenotypic variability within populations plays an important role in the adaptation of phytoplankton to changing environments, potentially attenuating short-term effects and forming the basis for selection. In particular, A. ostenfeldii blooms may expand and increase in toxicity under increased water temperature and atmospheric pCO2 conditions, with potentially severe consequences for the coastal ecosystem.

Experiment: Organic matter exudation by Emiliania huxleyi under simulated future ocean conditions

Emiliania huxleyi (strain B 92/11) was exposed to different nutrient supply, CO2 and temperature conditions in phosphorus controlled chemostats to investigate effects on organic carbon exudation and partitioning between the pools of particulate organic carbon (POC) and dissolved organic carbon (DOC). 14C incubation measurements for primary production (PP) and extracellular release (ER) were performed. Chemical analysis included the amount and composition of high molecular weight (>1 kDa) dissolved combined carbohydrates (HMW-dCCHO), particulate combined carbohydrates (pCCHO) and the carbon content of transparent exopolymer particles (TEP-C). Applied CO2 and temperature conditions were 300, 550 and 900 µatm pCO2 at 14 °C, and additionally 900 µatm pCO2 at 18 °C simulating a greenhouse ocean scenario. Enhanced nutrient stress by reducing the dilution rate (D) from D = 0.3 /d to D = 0.1 /d (D = µ) induced the strongest response in E. huxleyi. At µ = 0.3 /d, PP was significantly higher at elevated CO2 and temperature and DO14C production correlated to PO14C production in all treatments, resulting in similar percentages of extracellular release (PER; (DO14C production/PP) × 100) averaging 3.74 ± 0.94%. At µ = 0.1 /d, PO14C production decreased significantly, while exudation of DO14C increased. Thus, indicating a stronger partitioning from the particulate to the dissolved pool. Maximum PER of 16.3 ± 2.3% were observed at µ = 0.1 /d at elevated CO2 and temperature. While cell densities remained constant within each treatment and throughout the experiment, concentrations of HMW-dCCHO, pCCHO and TEP were generally higher under enhanced nutrient stress. At µ= 0.3 /d, pCCHO concentration increased significantly with elevated CO2 and temperature. At µ = 0.1 /d, the contribution (mol % C) of HMW-dCCHO to DOC was lower at elevated CO2 and temperature while pCCHO and TEP concentrations were higher. This was most pronounced under greenhouse conditions. Our findings suggest a stronger transformation of primary produced DOC into POC by coagulation of exudates under nutrient limitation. Our results further imply that elevated CO2 and temperature will increase exudation by E. huxleyi and may affect organic carbon partitioning in the ocean due to an enhanced transfer of HMW-dCCHO to TEP by aggregation processes.

Seawater carbonate chemistry and length, weight, survival rate, metabolic rate of coral reef fish Amphiprion melanopus in a laboratory experiment

Carbon dioxide concentrations in the surface ocean are increasing owing to rising CO2 concentrations in the atmosphere. Higher CO2 levels are predicted to affect essential physiological processes of many aquatic organisms, leading to widespread impacts on marine diversity and ecosystem function, especially when combined with the effects of global warming. Yet the ability for marine species to adjust to increasing CO2 levels over many generations is an unresolved issue. Here we show that ocean conditions projected for the end of the century (approximately 1,000 µatm CO2 and a temperature rise of 1.5-3.0 °C) cause an increase in metabolic rate and decreases in length, weight, condition and survival of juvenile fish. However, these effects are absent or reversed when parents also experience high CO2 concentrations. Our results show that non-genetic parental effects can dramatically alter the response of marine organisms to increasing CO2 and demonstrate that some species have more capacity to acclimate to ocean acidification than previously thought.

Seawater carbonate chemistry and swimming behaviors of the raphidophyte Heterosigma akashiwo in a laboratory experiment

We investigated the effects of pH on movement behaviors of the harmful algal bloom causing raphidophyte Heterosigma akashiwo. Motility parameters from >8000 swimming tracks of individual cells were quantified using 3D digital video analysis over a 6-h period in 3 pH treatments reflecting marine carbonate chemistry during the pre-industrial era, currently, and the year 2100. Movement behaviors were investigated in two different acclimation-to-target-pH conditions: instantaneous exposure and acclimation of cells for at least 11 generations. There was no negative impairment of cell motility when exposed to elevated PCO2 (i.e., low pH) conditions but there were significant behavioral responses. Irrespective of acclimation condition, lower pH significantly increased downward velocity and frequency of downward swimming cells (p < 0.001). Rapid exposure to lower pH resulted in 9% faster downward vertical velocity and up to 19% more cells swimming downwards (p < 0.001). Compared to pH-shock experiments, pre-acclimation of cells to target pH resulted in ~30% faster swimming speed and up to 46% faster downward velocities (all p < 0.001). The effect of year 2100 PCO2 levels on population diffusivity in pre-acclimated cultures was >2-fold greater than in pH-shock treatments (2.2 × 105 µm**2/s vs. 8.4 × 104 µm**2/s). Predictions from an advection-diffusion model, suggest that as PCO2 increased the fraction of the population aggregated at the surface declined, and moved deeper in the water column. Enhanced downward swimming of H. akashiwo at low pH suggests that these behavioral responses to elevated PCO2 could reduce the likelihood of dense surface slick formation of H. akashiwo through reductions in light exposure or growth independent surface aggregations. We hypothesize that the HAB alga's response to higher PCO2 may exploit the signaling function of high PCO2 as indicative of net heterotrophy in the system, thus indicative of high predation rates or depletion of nutrients.

Seawater carbonate chemistry, clearance rates, respiration rates, condition index and cellular turnover (RNA: DNA) of Juvenile King Scallop, Pecten maximus in a laboratory experiment

The decline in ocean water pH and changes in carbonate saturation states through anthropogenically mediated increases in atmospheric CO2 levels may pose a hazard to marine organisms. This may be particularly acute for those species reliant on calcareous structures like shells and exoskeletons. This is of particular concern in the case of valuable commercially exploited species such as the king scallop, Pecten maximus. In this study we investigated the effects on oxygen consumption, clearance rates and cellular turnover in juvenile P. maximus following 3 months laboratory exposure to four pCO2 treatments (290, 380, 750 and 1140 µatm). None of the exposure levels were found to have significant effect on the clearance rates, respiration rates, condition index or cellular turnover (RNA: DNA) of individuals. While it is clear that some life stages of marine bivalves appear susceptible to future levels of ocean acidification, particularly under food limiting conditions, the results from this study suggest that where food is in abundance, bivalves like juvenile P. maximus may display a tolerance to limited changes in seawater chemistry.

Seawater carbonate chemistry and sea urchin larval size in a laboratory experiment

Ocean acidification results from an increase in the concentrations of atmospheric carbon dioxide (CO2) impacts on marine calcifying species, which is predicted to become more pronounced in the future. By the end of this century, atmospheric pCO2 levels will have doubled relative to the pre-industrial levels of 280 ppm. However, the effects of pre-industrial pCO2 levels on marine organisms remain largely unknown. In this study, we investigated the effects of pre-industrial pCO2 conditions on the size of the pluteus larvae of sea urchins, which are known to be vulnerable to ocean acidification. The larval size of Hemicentrotus pulcherrimus significantly increased when reared at pre-industrial pCO2 level relative to the present one, and the size of Anthocidaris crassispina larvae decreased as the pCO2 levels increased from the pre-industrial level to the near future ones after 3 days' exposure. In this study, it is suggested that echinoid larvae responded to pre-industrial pCO2 levels. Ocean acidification may be affecting some sensitive marine calcifiers even at the present pCO2 level.

Wave height (regular and irregular waves) reduction in 2m water depth over a 40-m-long salt marsh test section in a large scale laboratory flume

Coastal communities around the world face increasing risk from flooding as a result of rising sea level, increasing storminess, and land subsidence. Salt marshes can act as natural buffer zones, providing protection from waves during storms. However, the effectiveness of marshes in protecting the coastline during extreme events when water levels and waves are highest is poorly understood. Here, we experimentally assess wave dissipation under storm surge conditions in a 300-m-long wave flume that contains a transplanted section of natural salt marsh. We find that the presence of marsh vegetation causes considerable wave attenuation, even when water levels and waves are high. From a comparison with experiments without vegetation, we estimate that up to 60% of observed wave reduction is attributed to vegetation. We also find that although waves progressively flatten and break vegetation stems and thereby reduce dissipation, the marsh substrate remained remarkably stable and resistant to surface erosion under all conditions.The effectiveness of storm wave dissipation and the resilience of tidal marshes even at extreme conditions suggest that salt marsh ecosystems can be a valuable component of coastal protection schemes.

Seawater carbonate chemistry, productivity and calcification of Marginopora vertebralis in a laboratory experiment

Changes in the seawater carbonate chemistry (ocean acidification) from increasing atmospheric carbon dioxide (CO2 ) concentrations negatively affect many marine calcifying organisms, but may benefit primary producers under dissolved inorganic carbon (DIC) limitation. To improve predictions of the ecological effects of ocean acidification, the net gains and losses between the processes of photosynthesis and calcification need to be studied jointly on physiological and population levels. We studied productivity, respiration, and abundances of the symbiont-bearing foraminifer species Marginopora vertebralis on natural CO2 seeps in Papua New Guinea and conducted additional studies on production and calcification on the Great Barrier Reef (GBR) using artificially enhanced pCO2 . Net oxygen production increased up to 90% with increasing pCO2 ; temperature, light, and pH together explaining 61% of the variance in production. Production increased with increasing light and increasing pCO2 and declined at higher temperatures. Respiration was also significantly elevated (~25%), whereas calcification was reduced (16-39%) at low pH/high pCO2 compared to present-day conditions. In the field, M. vertebralis was absent at three CO2 seep sites at pHTotal levels below ~7.9 (pCO2 ~700 µatm), but it was found in densities of over 1000 m(-2) at all three control sites. The study showed that endosymbiotic algae in foraminifera benefit from increased DIC availability and may be naturally carbon limited. The observed reduction in calcification may have been caused either by increased energy demands for proton pumping (measured as elevated rates of respiration) or by stronger competition for DIC from the more productive symbionts. The net outcome of these two competing processes is that M. vertebralis cannot maintain populations under pCO2 exceeding 700 µatm, thus are likely to be extinct in the next century.

Seawater carbonate chemistry and larval development and settlement of the sea urchin Arbacia lixula in a laboratory experiment

We studied the effects of temperature and pH on larval development, settlement and juvenile survival of a Mediterranean population of the sea urchin Arbacia lixula. Three temperatures (16, 17.5 and 19 °C) were tested at present pH conditions (pHT 8.1). At 19 °C, two pH levels were compared to reflect present average (pHT 8.1) and near-future average conditions (pHT 7.7, expected by 2100). Larvae were reared for 52-days to achieve the full larval development and complete the metamorphosis to the settler stage. We analyzed larval survival, growth, morphology and settlement success. We also tested the carry-over effect of acidification on juvenile survival after 3 days. Our results showed that larval survival and size significantly increased with temperature. Acidification resulted in higher survival rates and developmental delay. Larval morphology was significantly altered by low temperatures, which led to narrower larvae with relatively shorter skeletal rods, but larval morphology was only marginally affected by acidification. No carry-over effects between larvae and juveniles were detected in early settler survival, though settlers from larvae reared at pH 7.7 were significantly smaller than their counterparts developed at pH 8.1. These results suggest an overall positive effect of environmental parameters related to global change on the reproduction of A. lixula, and reinforce the concerns about the increasing negative impact on shallow Mediterranean ecosystems of this post-glacial colonizer.