Seawater carbonate chemistry, thickness and carbonate elemental composition of the test of juvenile sea urchins in a laboratory experiment

Ocean surface CO2 levels are increasing in line with rising atmospheric CO2 and could exceed 900 µatm by year 2100, with extremes above 2000 µatm in some coastal habitats. The imminent increase in ocean pCO2 is predicted to have negative consequences for marine fishes, including reduced aerobic performance, but variability among species could be expected. Understanding interspecific responses to ocean acidification is important for predicting the consequences of ocean acidification on communities and ecosystems. In the present study, the effects of exposure to near-future seawater CO2 (860 µatm) on resting (M O2rest) and maximum (M O2max) oxygen consumption rates were determined for three tropical coral reef fish species interlinked through predator-prey relationships: juvenile Pomacentrus moluccensis and Pomacentrus amboinensis, and one of their predators: adult Pseudochromis fuscus. Contrary to predictions, one of the prey species, P. amboinensis, displayed a 28-39% increase in M O2max after both an acute and four-day exposure to near-future CO2 seawater, while maintaining M O2rest. By contrast, the same treatment had no significant effects on M O2rest or M O2max of the other two species. However, acute exposure of P. amboinensis to 1400 and 2400 µatm CO2 resulted in M O2max returning to control values. Overall, the findings suggest that: (1) the metabolic costs of living in a near-future CO2 seawater environment were insignificant for the species examined at rest; (2) the M O2max response of tropical reef species to near-future CO2 seawater can be dependent on the severity of external hypercapnia; and (3) near-future ocean pCO2 may not be detrimental to aerobic scope of all fish species and it may even augment aerobic scope of some species. The present results also highlight that close phylogenetic relatedness and living in the same environment, does not necessarily imply similar physiological responses to near-future CO2.

Seawater carbonate chemistry, pigments and proteins during experiments with phytoplankton, 2010

In the high-nutrient, low-chlorophyll waters of the Gulf of Alaska, microcosm manipulation experiments were used to assess the effect of CO2 on growth and primary production under iron-limited and iron-replete conditions. As expected, iron had a strong effect on growth and photosynthesis. A modest and variable stimulation of growth and biomass production by CO2 (high CO2: 77-122 Pa; low CO2: 11-17 Pa) was observed under both iron-replete and iron-limited conditions, though near the limit of precision of our measurements in slow-growing low-iron experiments. Physiological acclimations responsible for the changes in growth were assessed. Under iron-limited conditions, growth stimulation at high CO2 appeared to result from an increase in photosynthetic efficiency, which we attribute to energy savings from down-regulation of the carbon concentrating mechanisms. In some cases, iron-rich photosynthetic proteins (PsbA, PsaC, and cytochrome b6) were down-regulated at elevated CO2in iron-limited controls. Under iron-replete conditions, there was an increase in growth rate and biomass at high CO2 in some experiments. This increase was unexpectedly supported by reductions in cellular carbon loss, most likely decreased respiration. We speculate that this effect may be due to acclimation to decreased pH rather than high CO2. The variability in responses to CO2 among experiments did not appear to be caused by differences in phytoplankton community structure and may reflect the sensitivity of the net response of phytoplankton to antagonistic effects of the several parameters that co-vary with CO2.

Seawater carbonate chemistry, biomass and calcification of Porites spp. corals during experiments, 2011

I tested the hypothesis that the effects of high pCO2 and temperature on massive Porites spp. (Scleractinia) are modified by heterotrophic feeding (zooplanktivory). Small colonies of massive Porites spp. from the back reef of Moorea, French Polynesia, were incubated for 1 month under combinations of temperature (29.3°C vs. 25.6°C), pCO2 (41.6 vs. 81.5 Pa), and feeding regimes (none vs. ad libitum access to live Artemia spp.), with the response assessed using calcification and biomass. Area-normalized calcification was unaffected by pCO2, temperature, and the interaction between the two, although it increased 40% with feeding. Biomass increased 35% with feeding and tended to be higher at 25.6°C compared to 29.3°C, and as a result, biomass-normalized calcification statistically was unaffected by feeding, but was depressed 12-17% by high pCO2, with the effect accentuated at 25.6°C. These results show that massive Porites spp. has the capacity to resist the effects on calcification of 1 month exposure to 81.5 Pa pCO2 through heterotrophy and changes in biomass. Area-normalized calcification is sustained at high pCO2 by a greater biomass with a reduced biomass-normalized rate of calcification. This mechanism may play a role in determining the extent to which corals can resist the long-term effects of ocean acidification.

Seawater carbonate chemistry, nutrients and growth rate of coral (Acropora intermedia) and coral-reef seaweed (Lobophora papenfussii) during experiments, 2011

Space competition between corals and seaweeds is an important ecological process underlying coral-reef dynamics. Processes promoting seaweed growth and survival, such as herbivore overfishing and eutrophication, can lead to local reef degradation. Here, we present the case that increasing concentrations of atmospheric CO2 may be an additional process driving a shift from corals to seaweeds on reefs. Coral (Acropora intermedia) mortality in contact with a common coral-reef seaweed (Lobophora papenfussii) increased two- to threefold between background CO2 (400 ppm) and highest level projected for late 21st century (1140 ppm). The strong interaction between CO2 and seaweeds on coral mortality was most likely attributable to a chemical competitive mechanism, as control corals with algal mimics showed no mortality. Our results suggest that coral (Acropora) reefs may become increasingly susceptible to seaweed proliferation under ocean acidification, and processes regulating algal abundance (e.g. herbivory) will play an increasingly important role in maintaining coral abundance.

Seawater carbonate chemistry, biomass and metabolic rates (leucine incorporation, CO2 fixation and respiration) of Rhodobacteraceae (strain MED165) and Flavobacteriaceae (strain MED217) in a laboratory experiment

Experimental results related to the effects of ocean acidification on planktonic marine microbes are still rather inconsistent and occasionally contradictory. Moreover, laboratory or field experiments that address the effects of changes in CO2 concentrations on heterotrophic microbes are very scarce, despite the major role of these organisms in the marine carbon cycle. We tested the direct effect of an elevated CO2 concentration (1000 ppmv) on the biomass and metabolic rates (leucine incorporation, CO2 fixation and respiration) of 2 isolates belonging to 2 relevant marine bacterial families, Rhodobacteraceae (strain MED165) and Flavobacteriaceae (strain MED217). Our results demonstrate that, contrary to some expectations, high pCO2 did not negatively affect bacterial growth but increased growth efficiency in the case of MED217. The elevated partial pressure of CO2 (pCO2) caused, in both cases, higher rates of CO2 fixation in the dissolved fraction and, in the case of MED217, lower respiration rates. Both responses would tend to increase the pH of seawater acting as a negative feedback between elevated atmospheric CO2 concentrations and ocean acidification.

Seawater carbonate chemistry, length and survival of Inland silverside, Menidia beryllina, during experiments, 2012

Absorption of anthropogenic carbon dioxide by the world's oceans is causing mankind's 'other CO2 problem', ocean acidification. Although this process will challenge marine organisms that synthesize calcareous exoskeletons or shells, it is unclear how it will affect internally calcifying organisms, such as marine fish. Adult fish tolerate short-term exposures to CO2 levels that exceed those predicted for the next 300 years (~2,000 ppm), but potential effects of increased CO2 on growth and survival during the early life stages of fish remain poorly understood. Here we show that the exposure of early life stages of a common estuarine fish (Menidia beryllina) to CO2 concentrations expected in the world's oceans later this century caused severely reduced survival and growth rates. When compared with present-day CO2 levels (~400 ppm), exposure of M. beryllina embryos to ~1,000 ppm until one week post-hatch reduced average survival and length by 74% and 18%, respectively. The egg stage was significantly more vulnerable to high CO2-induced mortality than the post-hatch larval stage. These findings challenge the belief that ocean acidification will not affect fish populations, because even small changes in early life survival can generate large fluctuations in adult-fish abundance.

Seawater carbonate chemistry, mortality and hatching rate, size and mass of Clupea harengus during experiments, 2011

Due to atmospheric accumulation of anthropogenic CO2 the partial pressure of carbon dioxide (pCO2) in surface seawater increases and the pH decreases. This process known as ocean acidification might have severe effects on marine organisms and ecosystems. The present study addresses the effect of ocean acidification on early developmental stages, the most sensitive stages in life history, of the Atlantic herring (Clupea harengus L.). Eggs of the Atlantic herring were fertilized and incubated in artificially acidified seawater (pCO2 1260, 1859, 2626, 2903, 4635 µatm) and a control treatment (pCO2 480 µatm) until the main hatch of herring larvae occurred. The development of the embryos was monitored daily and newly hatched larvae were sampled to analyze their morphometrics, and their condition by measuring the RNA/DNA ratios. Elevated pCO2 neither affected the embryogenesis nor the hatch rate. Furthermore the results showed no linear relationship betweenpCO2 and total length, dry weight, yolk sac area and otolith area of the newly hatched larvae. For pCO2 and RNA/DNA ratio, however, a significant negative linear relationship was found. The RNA concentration at hatching was reduced at higher pCO2 levels, which could lead to a decreased protein biosynthesis. The results indicate that an increased pCO2 can affect the metabolism of herring embryos negatively. Accordingly, further somatic growth of the larvae could be reduced. This can have consequences for the larval fish, since smaller and slow growing individuals have a lower survival potential due to lower feeding success and increased predation mortality. The regulatory mechanisms necessary to compensate for effects of hypercapnia could therefore lead to lower larval survival. Since the recruitment of fish seems to be determined during the early life stages, future research on the factors influencing these stages are of great importance in fisheries science.

Seawater carbonate chemistry, nutrients and growth rate during experiments with coral Astrangia poculata and field observations, 2010

Zooxanthellate colonies of the scleractinian coral Astrangia poculata were grown under combinations of ambient and elevated nutrients (5 µM NO, 0.3 µM PO4, and 2nM Fe) and CO2 (780 ppmv) treatments for a period of 6 months. Coral calcification rates, estimated from buoyant weights, were not significantly affected by moderately elevated nutrients at ambient CO2 and were negatively affected by elevated CO2 at ambient nutrient levels. However, calcification by corals reared under elevated nutrients combined with elevated CO2 was not significantly different from that of corals reared under ambient conditions, suggesting that CO2 enrichment can lead to nutrient limitation in zooxanthellate corals. A conceptual model is proposed to explain how nutrients and CO2 interact to control zooxanthellate coral calcification. Nutrient limited corals are unable to utilize an increase in dissolved inorganic carbon (DIC) as nutrients are already limiting growth, thus the effect of elevated CO2 on saturation state drives the calcification response. Under nutrient replete conditions, corals may have the ability to utilize more DIC, thus the calcification response to CO2 becomes the product of a negative effect on saturation state and a positive effect on gross carbon fixation, depending upon which dominates, the calcification response can be either positive or negative. This may help explain how the range of coral responses found in different studies of ocean acidification can be obtained.

Seawater carbonate chemistry, processes and elements during experiments with planktonic foraminifera Orbulina universa, 2004

We investigate the sensitivity of U/Ca, Mg/Ca, and Sr/Ca to changes in seawater [CO3[2-]] and temperature in calcite produced by the two planktonic foraminifera species, Orbulina universa and Globigerina bulloides, in laboratory culture experiments. Our results demonstrate that at constant temperature, U/Ca in O. universa decreases by 25 +/- 7% per 100 µmol [CO3[2-]] kg**-1, as seawater [CO3[2-]] increases from 110 to 470 µmol kg**-1. Results from G. bulloides suggest a similar relationship, but U/Ca is consistently offset by ~+40% at the same environmental [CO3[2-]]. In O. universa, U/Ca is insensitive to temperature between 15°C and 25°C. Applying the O. universa relationship to three U/Ca records from a related species, Globigerinoides sacculifer, we estimate that Caribbean and tropical Atlantic [CO3[2-]] was 110 +/- 70 µmol kg**-1 and 80 +/- 40 µmol kg**-1 higher, respectively, during the last glacial period relative to the Holocene. This result is consistent with estimates of the glacial-interglacial change in surface water [CO3[2-]] based on both modeling and on boron isotope pH estimates. In settings where the addition of U by diagenetic processes is not a factor, down-core records of foraminiferal U/Ca have potential to provide information about changes in the ocean's carbonate concentration.

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.