Seawater carbonate chemistry and copepod Centropages tenuiremis feeding, filtering and respiration rate during experiments, 2012

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.

Seawater carbonate chemistry, respiration, maximum photochemical efficiency and mortality of brooded larvae of Pocillopora//damicornis in a laboratory experiment

To evaluate the effects of temperature and pCO2 on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21°56.179' N, 120°44.85' E), were exposed to ambient (419-470 µatm) and high (604-742 µatm) pCO2 at ~25 and ~29 °C in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (F v/F m), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD × temperature interaction in 2010 and 2012, as well as an LD × pCO2 × temperature interaction in 2012; F v/F m was affected by LD in 2010 (but not 2012); and mortality was affected by an LD × pCO2 interaction in 2010, and an LD × temperature interaction in 2012. There were no main effects of pCO2 in 2010, but in 2012, high pCO2 depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.