Climate change mediates marine chemical and physical environments and therefore influences marine organisms. While increasing atmospheric CO2 level and associated ocean acidification has been predicted to stimulate marine primary productivity and may affect community structure, the processes that impact food chain and biological CO2 pump are less documented. We hypothesized that copepods, as the secondary marine producer, may respond to future changes in seawater carbonate chemistry associated with ocean acidification due to increasing atmospheric CO2 concentration. Here, we show that the copepod, Centropages tenuiremis, was able to perceive the chemical changes in seawater induced under elevated CO2 concentration (>1700 µatm, pH < 7.60) with avoidance strategy. The copepod's respiration increased at the elevated CO2 (1000 µatm), associated acidity (pH 7.83) and its feeding rates also increased correspondingly, except for the initial acclimating period, when it fed less. Our results imply that marine secondary producers increase their respiration and feeding rate in response to ocean acidification to balance the energy cost against increased acidity and CO2 concentration.

The tolerance and physiological responses of the larvae of two congeneric gastropods, the intertidal Nassarius festivus and subtidal Nassarius conoidalis, to the combined effects of ocean acidification (PCO2 at 380, 950, 1250 ppm), temperature (15, 30 degrees C) and salinity (10, 30 psu) were compared. Results of three-way ANOVA on cumulative mortality after 72-h exposure showed significant interactive effects in which mortality increased with pCO(2) and temperature, but reduced at higher salinity for both species, with higher mortality being obtained for N. conoidalis. Similarly, respiration rate of the larvae increased with temperature and pCO(2) level for both species, with a larger percentage increase for N. conoidalis. Larval swimming speed increased with temperature and salinity for both species whereas higher pCO(2) reduced swimming speed in N. conoidalis but not N. festivus. The present findings indicated that subtidal congeneric species are more sensitive than their intertidal counterparts to the combined effects of these stressors. (c) 2014 Elsevier Ltd. All rights reserved.

Sea cucumbers are dominant invertebrates in several ecosystems such as coral reefs, seagrass meadows and mangroves. As bioturbators, they have an important ecological role in making available calcium carbonate and nutrients to the rest of the community. However, due to their commercial value, they face overexploitation in the natural environment. On top of that, occurring ocean acidification could impact these organisms, considered sensitive as echinoderms are osmoconformers, high-magnesium calcite producers and have a low metabolism. As a first investigation of the impact of ocean acidification on sea cucumbers, we tested the impact of short-term (6 to 12 days) exposure to ocean acidification (seawater pH 7.7 and 7.4) on two sea cucumbers collected in SW Madagascar, Holothuria scabra, a high commercial value species living in the seagrass meadows, and H. parva, inhabiting the mangroves. The former lives in a habitat with moderate fluctuations of seawater chemistry (driven by day-night differences) while the second lives in a highly variable intertidal environment. In both species, pH of the coelomic fluid was significantly negatively affected by reduced seawater pH, with a pronounced extracellular acidosis in individuals maintained at pH 7.7 and 7.4. This acidosis was due to an increased dissolved inorganic carbon content and pCO2 of the coelomic fluid, indicating a limited diffusion of the CO2 towards the external medium. However, respiration and ammonium excretion rates were not affected. No evidence of accumulation of bicarbonate was observed to buffer the coelomic fluid pH. If this acidosis stays uncompensated for when facing long-term exposure, other processes could be affected in both species, eventually leading to impacts on their ecological role.

We conducted shipboard microcosm experiments at both off-shore (SEATS) and near-shore (D001) stations in the northern South China Sea (NSCS) under three treatments, low temperature and low pCO2 (LTLC), high temperature and low pCO2 (HTLC), and high temperature and high pCO2 (HTHC). Biomass of phytoplankton at both stations were enhanced by HT. HTHC did not affect phytoplankton biomass at station D001 but decreased it at station SEATS. HT alone increased net primary productivity by 234% at station SEATS and by 67% at station D001 but the stimulating effect disappeared when HC was combined. HT also increased respiration rate by 236% at station SEATS and by 87% at station D001 whereas HTHC reduced it by 61% at station SEATS and did not affect it at station D001. Overall, our findings indicate that the positive effect of ocean warming on phytoplankton assemblages in NSCS could be damped or offset by ocean acidification.