Seawater carbonate chemistry, mass, size and regenerative capacity of Luidia clathrata during experiments, 2011

The present study examines sublethal effects of near-future (year 2100) ocean acidification (OA) on regenerative capacity, biochemical composition, and behavior of the sea star Luidia clathrata, a predominant predator in sub-tropical soft-bottom habitats. Two groups of sea stars, each with two arms excised, were maintained on a formulated diet in seawater bubbled with air alone (pH 8.2, approximating a pCO2 of 380 µatm) or with a controlled mixture of air/C02 (pH 7.8, approximating a pCO2 of 780 µatm). Arm length, total body wet weight, and righting responses were measured weekly. After 97 days, a period of time sufficient for 80% arm regeneration, pyloric caecal indices, and protein, carbohydrate, lipid, and ash levels were determined for body wall and pyloric caecal tissues of intact and regenerating arms of individuals held in both seawater pH treatments. The present study indicates that predicted near-term levels of ocean acidification (seawater pH 7.8) do not significantly impact whole animal growth, arm regeneration rates, biochemical composition, or righting behavior in this common soft bottom sea star.

Seawater carbonate chemistry and dark respiration and photosynthetic capacity during experiments with coral Acropora formosa, 2010

Ocean acidification is expected to lower the net accretion of coral reefs yet little is known about its effect on coral photophysiology. This study investigated the effect of increasing CO2 on photosynthetic capacity and photoprotection in Acropora formosa. The photoprotective role of photorespiration within dinoflagellates (genus Symbiodinium) has largely been overlooked due to focus on the presence of a carbon-concentrating mechanism despite the evolutionary persistence of a Form II Rubisco. The photorespiratory fixation of oxygen produces phosphoglycolate that would otherwise inhibit carbon fixation though the Calvin cycle if it were not converted to glycolate by phosphoglycolate phosphatase (PGPase). Glycolate is then either excreted or dealt with by enzymes in the photorespiratory glycolate and/or glycerate pathways adding to the pool of carbon fixed in photosynthesis. We found that CO2 enrichment led to enhanced photoacclimation (increased chlorophyll a per cell) to the subsaturating light levels. Light-enhanced dark respiration per cell and xanthophyll de-epoxidation increased, with resultant decreases in photosynthetic capacity (Pnmax) per chlorophyll. The conservative CO2 emission scenario (A1B; 600-790 ppm) led to a 38% increase in the Pnmax per cell whereas the 'business-as-usual' scenario (A1F1; 1160-1500 ppm) led to a 45% reduction in PGPase expression and no change in Pnmax per cell. These findings support an important functional role for PGPase in dinoflagellates that is potentially compromised under CO2 enrichment.

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.

The effects of water acidification, temperature and salinity on the regenerative capacity of the polychaete Diopatra neapolitana

Changes in seawater pH, temperature and salinity are expected to occur in the near future, which can be a threat to aquatic systems, mainly for marine coastal areas, and their inhabiting species. Hence, the present study proposes to evaluate the effects of temperature shifts, pH decrease and salinity changes in the tissue's regenerative capacity of the polychaete Diopatra neapolitana. This study evidenced that D. neapolitana individuals exposed to lower pH exhibited a significantly lower capacity to regenerate their body, while with the increase of temperature individuals showed a higher capacity to regenerate their tissues. Furthermore, the present work demonstrated that individuals exposed to salinities 28 and 35 did not present significant differences between them, while salinities 21 and 42 negatively influenced the regenerative capacity of D. neapolitana. At the end of regeneration, comparing all conditions, high salinity (42) seemed to have a greater impact on the regenerative capacity of individuals than the other factors, since under this condition individuals took longer to completely regenerate. Overall, this study demonstrated that variations in abiotic factors can strongly affect D. neapolitana's performance.

Seawater acidification affects the physiological energetics and spawning capacity of the Manila clam Ruditapes philippinarum during gonadal maturation

Ocean acidification is predicted to have widespread implications for marine bivalve mollusks. While our understanding of its impact on their physiological and behavioral responses is increasing, little is known about their reproductive responses under future scenarios of anthropogenic climate change. In this study, we examined the physiological energetics of the Manila clam Ruditapes philippinarum exposed to CO2-induced seawater acidification during gonadal maturation. Three recirculating systems filled with 600 L of seawater were manipulated to three pH levels (8.0, 7.7, and 7.4) corresponding to control and projected pH levels for 2100 and 2300. In each system, temperature was gradually increased ca. 0.3 °C per day from 10 to 20 °C for 30 days and maintained at 20 °C for the following 40 days. Irrespective of seawater pH levels, clearance rate (CR), respiration rate (RR), ammonia excretion rate (ER), and scope for growth (SFG) increased after a 30-day stepwise warming protocol. When seawater pH was reduced, CR, ratio of oxygen to nitrogen, and SFG significantly decreased concurrently, whereas ammonia ER increased. RR was virtually unaffected under acidified conditions. Neither temperature nor acidification showed a significant effect on food absorption efficiency. Our findings indicate that energy is allocated away from reproduction under reduced seawater pH, potentially resulting in an impaired or suppressed reproductive function. This interpretation is based on the fact that spawning was induced in only 56% of the clams grown at pH 7.4. Seawater acidification can therefore potentially impair the physiological energetics and spawning capacity of R. philippinarum.