Risposte biologiche delle Corallinales ai cambiamenti climatici globali: proposta di un percorso didattico per imparare a pensare la complessità dell’ecosistema (in Italian)

La riduzione del pH dell’acqua marina (ocean acidification) causata del progressivo aumento della CO2 atmosferica sembra essere un fenomeno poco noto. Con l’obiettivo di creare un canale diretto fra la ricerca ed il sistema scolastico, l’Università di Trieste ha instaurato un rapporto di collaborazione con una scuola media, offrendo un corso sperimentale per gli studenti sul tema dei cambiamenti climatici globali e acidificazione del mare. Durante il corso sono state evidenziate le reazioni all’acidificazione di alghe rosse calcaree durante la fase riproduttiva. Gli studenti hanno imparato a usare strumenti, a raccogliere dati quantitativi e qualitativi, a rappresentarli, elaborarli e trarre conclusioni dai risultati. Il corso è stato un’opportunità per trasferire ai giovani conoscenze sui cambiamenti climatici globali e per utilizzare un metodo didattico innovativo con lo scopo di implementare abilità e competenze scientifiche a livello scolastico.

Structural and geochemical alterations in the Mg calcite bryozoan Myriapora truncata under elevated seawater pCO2 simulating ocean acidification

The possible effects of ocean acidification on the calcareous skeleton of the Mediterranean bryozoan Myriapora truncata (Pallas, 1766) were studied by transplanting live and dead colonies into an area of natural volcanic CO2 vents at Ischia (Gulf of Naples, Tyrrhenian Sea), Italy. Morphology and geochemistry were compared between colonies from normal (mean pH = 8.07, min. pH 7.95), below-normal (mean pH 7.66, min. pH 7.32) and acidic (mean pH 7.43, min. pH 6.83) conditions after colonies had been exposed in situ for 45 and 128 days. Both distal (juvenile) and proximal (adult) parts of the branches were investigated. Skeletons of live colonies in acidic pH site after 45 days of exposure were less corroded than those of dead colonies, suggesting that the organic tissues enveloping the skeleton play a protective role. Colonies remained alive at the below-normal and acidic pH sites during the 45-day experiment but corrosion was very striking after 128 days, with colonies from the acidic site showing significant loss of skeleton. Compared to the control, these colonies also had lower levels of Mg (mean 8 versus 9.5 wt% Mg) within their skeletons. Electron microprobe mapping showed Mg to be higher in the outer layers of the skeletal walls in colonies from the normal pH site. Corrosion of outer layers of the walls probably explains the lower Mg level found in colonies exposed to acidic conditions. As solubility of calcite increases with Mg content, the enrichment of Mg in outer layers of the skeleton should enhance the vulnerability of Myriapora truncata to dissolution. These findings raise concerns over the survival of bryozoans with Mg calcite skeletons in the face of predicted decreases in oceanic pH levels.

Moore Foundation Grant Summary

University of California, San Diego Scripps Institution of Oceanography

Linking West Coast ocean acidification research and shellfish industry adaptation needs

Term
16 months

Amount
$261,847

Date Approved
Nov. 2010

Purpose
This grant will support enhancing communication and collaboration between managers, shellfish industry representatives, and scientists to respond to the evolving threats posed by ocean acidification along the U.S. West Coast. Funding will be used to design an effective and sustainable ocean acidification monitoring system that builds upon current efforts and addresses pressing needs of the shellfish industry and the scientific community.

Projected ocean acidification by 2100

The maps show projected ocean acidification and related impacts on corals by 2020, 2060 and 2100: from better (blue) to worse (orange) conditions for coral skeletal growth.

The effects of climate change on aquaculture

Climate change is an additional pressure on top of the many (fishing pressure, loss of habitat, pollution, disturbance, introduced species) which fish stocks already experience. The impact of climate change must be evaluated in the context of other anthropogenic pressures, which often have much greater and more immediate effect. Factors that can shape climate are climate changes. These include such processes as variations in solar radiation, deviations in the Earth’s orbit, mountain-building and continental drift, and changes in greenhouse gas concentrations. Some parts of the climate system, such as the oceans and ice caps, respond slowly in reaction to climate changes because of their large mass. Therefore, the climate system can take centuries or longer to fully respond to new external changes. Many of the studies made assumptions about changes in baseline socioeconomic conditions, adaptation, and biophysical processes. Almost all of the studies we examined estimated that there will be increasing adverse impacts beyond an approximate 3 to 4°C increase in global mean temperature. The studies do not show a consistent relationship between impacts and global mean temperatures between 0 and 3 to 4°C. In coastal resources it is clear that impacts will be adverse with low levels of temperature change.

The effects of exposure to near-future levels of ocean acidification on shell characteristics of Pinctada fucata (Bivalvia: Pteriidae)

Atmospheric carbon dioxide concentrations have greatly increased since the beginning of the industrial age. This has led to a decline in global ocean pH by 0.1 units, and continued decline of 0.3–0.5 units is predicted by the end of 2100. Acidification of the ocean has led to decreased calcification rates and dissolution of calcareous structures in a range of marine species. Shells of the pearl oyster Pinctada fucata exposed to acidified seawater (pH 7.8 and pH 7.6) for 28 days were 25.9% and 26.8% weaker than controls (pH 8.1–8.2), respectively, but there was no reduction in the organic content of shells exposed to acidified conditions. Scanning electron microscopy analysis of the growing edge of nacre lining the shells of P. fucata showed that shells exposed to acidified conditions (pH 7.6) showed signs of malformation and/or dissolution, when compared to controls. The reduction in shell strength and the possible nacre malformation could have broad impacts on the ecology of pearl oysters and consequences for the cultured pearl industry that relies on them.

Size-dependent pH effect on calcification in post-larval hard clam Mercenaria spp.

Increasing atmospheric carbon dioxide threatens to decrease pH in the world’s oceans. Coastal and estuarine calcifying organisms of significant ecological and economical importance are at risk; however, several biogeochemical processes drive pH in these habitats. In particular, coastal and estuarine sediments are frequently undersaturated with respect to calcium carbonate due to high rates of organic matter remineralization, even when overlying waters are saturated. As a result, the post-larval stages of infaunal marine bivalves must be able to deposit new shell material in conditions that are corrosive to shell. We measured calcification rates on the hard clam, Mercenaria spp., in 5 post-larval size classes (0.39, 0.56, 0.78, 0.98, and 2.90 mm shell height) using the alkalinity anomaly method. Acidity of experimental water was controlled by bubbling with air–CO2 blends to obtain pH values of 8.02, 7.64, and 7.41, corresponding to pCO2 values of 424, 1120, and 1950 µatm. These pH values are typical of those found in many near-shore terrigenous marine sediments. Our results show that calcification rate decreased with lower pH in all 5 size classes measured. We also found a significant effect of size on calcification rate, with the smaller post-larval sizes unable to overcome dissolution pressure. Increased calcification rate with size allowed the larger sizes to overcome dissolution pressure and deposit new shell material under corrosive conditions. Size dependency of pH effects on calcification is likely due to organogenesis and developmental shifts in shell mineralogy occurring through the post-larval stage. Furthermore, we found significantly different calcification rates between the 2 sources of hard clams we used for these experiments, most likely due to genotypic differences. Our findings confirm the susceptibility of the early life stages of this important bivalve to decreasing pH and reveal mechanisms behind the increased mortality in post-larval juvenile hard clams related to dissolution pressure, that has been found in previous studies.

CO2 availability and phytoplankton trace metal requirements

Marine phytoplankton–single-celled photosynthesizing organisms that account for about half of global carbon fixation (Behrenfeld & Falkowski, 1997)–require a suite of nutrient elements including carbon (C), nitrogen (N), phosphorous (P), and, in the case of diatoms, silicon (Si). Of these elements, C is the highest molar constituent of phytoplankton and is utilized from the ocean in the form of carbon dioxide (CO2) and bicarbonate (HCO3-). Although HCO3- is present at relatively high concentrations, CO2 is the preferred substrate and comprises <1% of total dissolved inorganic C.

Over the next century, due to anthropogenic fossil fuel use, the partial pressure of atmospheric CO2 (pCO2) is predicted to rise from ~380 ppm (present day) to ~750 ppm (year 2100) (Solomon et al., 2007) resulting in a decrease in carbonate (CO32-) and seawater pH. The consequences of these changes on marine phytoplankton are currently not entirely understood but include potentially deleterious effects for calcifying organisms such as coccolithophores. On the other hand, higher CO2 availability has been shown to relieve CO2 limitation of nitrogen-fixing diazotrophs such as Trichodesmium (Hutchins et al., 2009).

Diurnal and seasonal variation of coastal carbonate system parameters in South Florida and the Caribbean

Assessing the impact of climate change and ocean acidification on coastal and marine ecosystems requires accurate characterization of its chemical and physical effects on the carbonate system in seawater. Very few data exist that characterize natural variations in coastal carbonate chemistry, limiting the development and validation of coastal climate change and ocean acidification models. We measured carbonate system parameters over diurnal cycles in shallow, coastal ecosystems of Florida Bay, Tampa Bay, Biscayne National Park, Puerto Rico, the U.S. Virgin Islands, Tobago, and the Bahamas. Salinity, temperature, and dissolved oxygen were measured continuously, and seawater samples were collected every 4 hours throughout multiple 24-hour time periods. Total alkalinity and pH were measured using spectrophotometric techniques, dissolved inorganic carbon was measured via carbon coulometry, and remaining carbonate system parameters were calculated using CO2SYS. Seasonal variability was either determined from existing data sets, or modeled using salinity and temperature data collected from CTDs deployed at study locations or long-term monitoring sites. Results indicate that all carbonate system parameters showed distinct variation over diurnal timescales primarily due to productivity, respiration, and precipitation and dissolution of calcium carbonate. The average range of diurnal variation was up to 102% of the seasonal range of variability in carbonate chemistry. Our data indicate that use of seasonal data sets without careful consideration of diurnal variability (or vice versa) may impart significant error in calculation of annual carbon budgets and modeling carbon cycling in coastal ecosystems. Implications for modeling long-term impacts of ocean acidification in coastal ecosystems will be discussed.

Inorganic carbon dynamics in the upwelling system off the Oregon coast and implications for commercial shellfish hatcheries

The increasing absorption of anthropogenic CO2 by the global ocean and concomitant decrease in pH will alter seawater carbonate chemistry in ways that may negatively impact calcifying organisms. In particular, the change in saturation state (Ω) of calcium carbonate minerals calcite and aragonite may be energetically unfavorable for shell formation while favoring shell dissolution. Eastern boundary upwelling systems may provide insights into how ecosystems respond to future conditions of ocean acidification when deep water with high dissolved inorganic carbon (DIC), low pH and low Ω is forced toward the surface. Mortality in commercial seed stock and reduced wild set of the oyster Crassostrea gigas in the northeast Pacific during 2005-2009 reinforced the need for understanding biological responses to acidified ocean water. In response, a long-term strategy to understand local carbonate chemistry dynamics, seasonal perturbations and the effects on development of calcifying bivalves was developed. At present, a time-series of pCO2 measurements was implemented in April 2010 in Netarts Bay, Oregon at Whiskey Creek Shellfish Hatchery (WCH). The intake sits at a depth of 0.5-8ft and water is pumped in at 100gpm. A line taken off the intake is run continuously through a thermosalinograph at approximately 1.5gpm into a showerhead style equilibrator in which the headspace is recirculated by aerating the water for enhanced gas exchange. CO2 in equilibrated air is analyzed by NDIR. Additionally two discrete samples of intake seawater were taken across tidal cycles weekly and analyzed for total CO2 (TCO2) according to the methods of Hales et al. (2004) and pCO2 for quality control. The pCO2 in the bay exhibits a diurnal cycle representative of daytime photosynthesis and nighttime respiration. However, the phasing and profiles of these cycles are dominated by tidal mixing and are affected by the introduction of high pCO2 water during upwelling events. Diurnal pCO2 during periods of low wind stress ranges from 100-700µatm. When strong equatorward winds induce upwelling, pCO2 levels exhibit a higher daily range of 300-2000µatm. The saturation state was calculated from the pCO2/TCO2 measurements of the discrete samples. The Ω for calcite and aragonite ranged from 2.07 and 1.15 to 8.58 and 4.69 respectively from April through August. Increased pCO2 and decreased pH have been shown to negatively impact larval development in C. gigas (Kurihara, 2007). Periods of elevated pCO2 in May and June 2010 correlated with commercial losses at WCH. The use of precise pCO2 measurements in real time has proven to be a valuable tool for use in aquaculture. As a commercial practice WCH has elected to only use source water that is below empirical pCO2 thresholds for spawning and culturing larvae. This has resulted in continued production and cost saving in an industry crucial to coast economies. A continuous TCO2/pCO2 monitoring system will be integrated into this long time-series to constrain inorganic carbon providing insight into carbonate chemistry dynamics in Netarts Bay, effects of ocean acidification on bivalve development and possible water treatment approaches for commercial aquaculture.