Differential responses of growth and photosynthesis in the marine diatom Chaetoceros muelleri to CO2 and light availability

This study investigated the impact of photon flux and elevated CO₂ concentrations on growth and photosynthetic electron transport on the marine diatom Chaetoceros muelleri and looked for evidence for the presence of a CO₂-concentrating mechanism (CCM). pH drift experiments clearly showed that C. muelleri has the capacity to use bicarbonate to acquire inorganic carbon through one or multiple CCMs. The final pH achieved in unbuffered cultures was not changed by light intensity, even under very low photon flux, implying a low energy demand of bicarbonate use via a CCM. In short-term pH drift experiments, only treatment with the carbonic anhydrase inhibitor ethoxyzolamide (EZ) slowed down the rise in pH considerably. EZ was also the only inhibitor that altered the final pH attained, although marginally. In growth experiments, CO₂ availability was manipulated by changing the pH in closed flasks at a fixed dissolved inorganic carbon (DIC) concentration. Low-light-treated samples showed lower growth rates in elevated CO₂ conditions. No CO₂ effect was recorded under high light exposure. The maximal photosynthetic capacity, however, increased with CO₂ concentration in saturating, but not in subsaturating, light intensities. Growth and photosynthetic capacity therefore responded in opposite ways to increasing CO₂ availability. The capacity to photoacclimate to high and low photon flux appeared not to be affected by CO₂ treatments. However, photoacclimation was restricted to growth photon fluxes between 30 and 300 µmol photons m⁻² s⁻¹. The light saturation points for photosynthetic electron transport and for growth coincided at 100 µmol photons m⁻² s⁻¹. Below 100 µmol photons m⁻² s⁻¹ the light saturation point for photosynthesis was higher than the growth photon flux (i.e. photosynthesis was not light saturated under growth conditions), whereas at higher growth photon flux, photosynthesis was saturated below growth light levels.

Applications of in situ pH measurements for inorganic carbon calculations

This study examines the utility of combining pH measurements with other inorganic carbon parameters for autonomous mooring-based carbon cycle research. Determination of the full suite of inorganic carbon species in the oceans has previously been restricted to ship-based studies. Now with the availability of autonomous sensors for pH and the partial pressure of CO₂ (pCO₂), it is possible to characterize the inorganic carbon system on moorings and other unmanned platforms. The indicator-based pH instrument, SAMI-pH, was deployed with an autonomous equilibrator-infrared pCO₂ system in Monterey Bay, California USA from June to August 2007. The two-month time-series show a high degree of short-term variability, with pH and pCO₂ changing by as much as 0.32 pH units and 240 μatm, respectively, during upwelling periods. The pH and salinity-derived alkalinity (A_Tsalin) were used to calculate the other inorganic carbon parameters, including pCO₂, total dissolved inorganic carbon (DIC) and CaCO₃ saturation states. The calculated pCO₂ was within 2 μatm of the measured pCO₂ during the first day of the deployment and within 8 μatm over the first month. The DIC calculated from pH-A_Tsalin and pCO₂-A_Tsalin were within 5 μmol kg^-1 of each other during the first month. However, DIC calculated from pH-pCO₂ differed by ~ 50 μmol kg^-1 from the other estimates over the same period, reflecting the sensitivity of the pH-pCO₂ calculation to measurement error. The data continued to diverge during the final month and was likely driven by extensive biofouling. Because of the relative insensitivity of CO₃^2- concentration to these errors, aragonite saturation calculated from the pH-pCO₂ pair was within 0.150 ± 0.095 of the pH-A_Tsalin values over the entire deployment. These results show that in situ pH, when combined with other CO₂ parameters, can provide valuable insights into both data quality and inorganic carbon cycling.

A volcanically induced climate warming and floral change preceded the onset of OAE1a (Early Cretaceous)

The Aptian Oceanic Anoxic Event 1a (OAE1a) is preceded by a prominent negative C-isotope excursion (NCIE) attributed to major volcanism on the Ontong-Java plateau that is supposed to lead to a pCO₂ increase and a climate change. Lower Aptian sporomorph assemblages in two pelagic sections from the southern Tethys margin (N-Italy) were analysed in order to test if the postulated climate changes affected the terrestrial vegetation. At the base of the NCIE the sporomorph assemblages comprise abundant bisaccate pollen reflecting a warm-temperate climate. Several tens of kiloyears (ka) after the start of the NCIE decreasing bisaccate pollen and increasing Classopollis spp. and Araucariacites spp. suggest the beginning of a long-term temperature rise. Palynomorphs indicate that maximum temperatures were reached several tens of ka after the end of the NCIE and the onset of OAE1a. The highest temperatures coincide with arid conditions, which could reflect a northward shift of the hot-arid Northern Gondwana floral province as a result of an increasing pCO₂. Over 200 ka after the onset of OAE1a reduced volcanic activity and/or increased black shale deposition allowed for a drawdown of most of the excess CO₂ and a southward shift of floral belts.

Elevated seawater CO2 concentrations impair larval development and reduce larval survival in endangered northern abalone (Haliotis kamtschatkana)

Increasing levels of anthropogenic carbon dioxide in the world’s oceans are resulting in a decrease in the availability of carbonate ions and a drop in seawater pH. This process, known as ocean acidification, is a potential threat to marine populations via alterations in survival and development. To date, however, little research has examined the effects of ocean acidification on rare or endangered species. To begin to assess the impacts of acidification on endangered northern abalone (Haliotis kamtschatkana) populations, we exposed H. kamtschatkana larvae to various levels of CO₂ [400 ppm (ambient), 800 ppm, and 1800 ppm CO₂] and measured survival, settlement, shell size, and shell development. Larval survival decreased by ca. 40% in elevated CO₂ treatments relative to the 400 ppm control. However, CO₂ had no effect on the proportion of surviving larvae that metamorphosed at the end of the experiment. Larval shell abnormalities became apparent in approximately 40% of larvae reared at 800 ppm CO₂, and almost all larvae reared at 1800 ppm CO₂ either developed an abnormal shell or lacked a shell completely. Of the larvae that did not show shell abnormalities, shell size was reduced by 5% at 800 ppm compared to the control. Overall, larval development of H. kamtschatkana was found to be sensitive to ocean acidification. Near future levels of CO₂ will likely pose a significant additional threat to this species, which is already endangered with extinction due in part to limited reproductive output and larval recruitment.

The ocean acidification seascape and its relationship to the performance of calcifying marine invertebrates: Laboratory experiments on the development of urchin larvae framed by environmentally-relevant pCO2/pH

Variation in ocean pH is a dynamic process occurring naturally in the upwelling zone of the California Current Large Marine Ecosystem. The nearshore carbonate chemistry is under-characterized and the physiology of local organisms may be under constant challenge from cyclical changes in pH and carbonate ion concentration of unexpectedly high magnitude. We looked to environmental pH conditions of coastal upwelling and used those values to examine effects of low pH on 4-arm larvae of purple sea urchin Strongylocentrotus purpuratus. We deployed a pH sensor at a nearshore shallow benthic site for 3 weeks during summer 2010 to assess the changes in pH in the Santa Barbara Channel, a region considered to have relatively less intense upwelling along the US Pacific Coast. Large fluctuations in pH of up to 0.67 pH units were observed over short time scales of several days. Daily pH fluctuations on a tidal pattern followed temperature fluctuations over short time scales, but not over scales greater than a day. The lowest pH values recorded (~ 7.70) are lower than some of those pH values predicted to occur in surface oceans at the end of the century. In the context of this dynamic pH exposure, larvae were raised at elevated pCO₂ levels of 1000 ppm and 1450 ppm CO₂ (pH 7.7 and 7.5 respectively) and measured for total larval length (from the spicule tip of the postoral arm to the spicule tip of the aboral point) along the spicules, to assess effects of low pH upwelling water on morphology. Larvae in all treatments maintained normal development and developmental schedule to day 6, and did not exhibit significant differences in larval asymmetry between treatments. At day 3 and day 6, larvae in the 1450 ppm CO₂ treatment were significantly smaller (p < 0.001) than the control larvae by only 7–13%. The observation of smaller larvae raised under high pCO₂ has an as yet undetermined physiological mechanism, but has implications for locomotion and feeding. These effects of small magnitude in these urchin larvae are indicative of a potential resilience to near-future levels of ocean acidification. Using environmental monitoring of pH to inform experimental parameters provides a means to improve our understanding of acclimatization of organisms in a dynamic ecosystem.

Growth rates of Florida corals from 1937 to 1996 and their response to climate change

Ocean acidification causes declines in calcification rates of corals because of decreasing aragonite saturation states (Ωarag). Recent evidence also indicates that increasing sea surface temperatures may have already reduced growth and calcification rates because of the stenothermic threshold of localized coral populations. Density banding in coral skeletons provides a record of growth over the coral’s lifespan. Here we present coral extension, bulk density and calcification master chronologies from seven subtropical corals (Montastraea faveolata) located in the Florida Keys, USA with a 60-year common period, 1937–1996. Linear trends indicate that extension increased, density decreased and calcification remained stable while the most recent decade was not significantly different than decadal averages over the preceding 50 years for extension and calcification. The results suggest that growth rates in this species of subtropical coral have been tolerant to recent climatic changes up to the time of collection (1996).

Modeling economic impacts of climate change and ocean acidification to fisheries

Ocean acidification appears to have potential to be a significant problem. Past declines in ocean surface pH have been linked to mass extinction events (Guinotte and Fabry, 2008). While I am not an expert in the science, the issue starts with declines in pH (increased acidity) causing a reduction in carbonate ion concentration which in turn causes a reduction in calcium carbonate saturation. This has impacts on marine organisms that are calcifiers and essentially requires marine calcifying organisms to use more energy to form biogenic calcium carbonate (Guinotte and Fabry, 2008). The observable consequences are thought to be hampered reef formation of corals, algaes and hampered shell formation of oysters, clams and crabs (although there are varying consequences on species depending on studies as shown by Dr. Cooley).

Carbon in air leads to acid in oceans

Whether human activity is responsible for the spike in carbon dioxide in the atmosphere or not, one result that must be dealt with is ocean acidification.

That was the consensus of a panel that addressed those attending Clam Day at the Maine Fishermen’s Forum March 3 at the Samoset Resort.

Thursday’s session was moderated by Sherman Hoyt of the University of Maine Cooperative Extension and Sea Grant, and included presentations from Joseph Salisbury of the Ocean Processing Analysis Laboratory of the University of New Hampshire at Durham, N.H.; biologist Mark Green of Saint Joseph’s College in Standish; Bill Mook of Mook Sea Farm in Damariscotta; and Chad Coffin, president of Maine Clammers Association.

Salisbury, who lived in South Portland for most of his life and was a fisherman in his teens and 20s, said he worked in a lab to learn about ocean acidification.

He said increased CO2 in the atmosphere and water led to increased acid in the ocean.

Earth Systems: Past records of ocean acidification

9 March 2011
17:00 – 19:00 U.K. – England – London

Speaker details
Daniela Schmidt University of Bristol

Event contact
Elisa Lawson (e.lawson@soton.ac.uk) University of Southampton

Event resources
Daniela Schmidt (University of Bristol), ‘Past records of ocean acidification’. For more information please visit the series collaborators’ site (members only).

Estuaries, oysters, and ocean acidification

What can a bottle of smelly marsh water and an oyster superglued to a plate tell us about ocean acidification?

As part of ongoing ocean acidification research focused on estuaries and near shore environments, Whitman Miller, Trace Element Lab scientist Fritz Riedel, and I are trying to find out the answer to that very question. In the last two centuries, atmospheric concentrations of carbon dioxide (CO₂) have risen from 280 to 380 microatmospheres (µatm), a unit essentially equivalent to parts per million by volume. One third of this anthropogenic CO₂ is absorbed by the earth’s oceans, which significantly lowers the pH of the oceans and alters carbonate chemistry in their surface waters, a phenomenon called ocean acidification: as the partial pressure of CO₂ (pCO₂) increases, pH decreases. This shift in pH lowers the availability of carbonate ions in the water column, ions used by calcifying creatures like corals, pteropods, and oysters to build their shells, making it more difficult for them to maintain the integrity of their structures. Most acidification research has been focused on open oceans, with little attention paid to lower salinity estuaries and temperate near shore environments. But estuaries and coastal ecosystems are incredibly complex, both biologically productive and economically important; yet their shallow waters, and lower salinity and alkalinity make them more susceptible to pH changes than open ocean environments. How do we attempt to study the effects of ocean acidification on biota in such a complex and diverse environment? That’s where water chemistry and oysters on plates come into play.