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

Abstract

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-CO 2 blends to obtain pH values of 8.02, 7.64, and 7.41, corresponding to pCO 2 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.KEY WORDS: Calcification · Acidification · Size-dependent · Hard clam · Post-larval Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 417: [171][172][173][174][175][176][177][178][179][180][181][182] 2010 dation of reduced metabolites in sediments during bioirrigation and particle reworking processes (Green et al. 2004b). As a result, estuarine or coastal pH is far more variable than that of the open ocean and subject to multiple processes making it difficult to parameterize, measure, and predict (Blackford & Gilbert 2007, Soetaert et al. 2007, Borges & Gypens 2010. However, gradual shifting-baseline type decreases in carbonate saturation state of coastal sediment pore waters due to rising atmospheric CO 2 has been noted (Andersson et al. 2006). Determining the potential ecological and economic consequences of acidification on living resources in coastal areas requires additional empirical data of shell producti...

The Impact of Ocean Acidification on Reproduction, Early Development and Settlement of Marine Organisms

“…If we are to move forward we need chronic experiments which allow the potential for species to acclimate over long term perturbations a measure of variability in responses of organisms within and between populations and an assessment of adaptive capacity associated environmentally induced plasticity [117] and focus on identifying the underlying mechanisms [43,44,46,77]. Current models remain constrained by acute experiments where in a period of days there is a sudden drop in pH of 0.4 units which does not mimic well the longer time frame over which this will occur (0.0044 pH/yr [15]).…”

“…Recently, significant differences in sensitivities to ocean acidification have been found even within the same species [43,44]. Selectively bred lines of the Sydney Rock oyster Saccostrea glomerata, when reared at elevated pCO 2 , were more resilient with only a 25% reduction compared to a 64% reduction in shell growth of spat of wild populations, perhaps suggesting inherent genetic diversity among populations of species or environmental pre adaptive capacity which may ameliorate the impacts of ocean acidification on oyster populations [43].…”

“…Similarly, calcification rate differed between source populations of Mercenaria spp. signifying possible genotypic variation [44], while maternal provisioning may safe guard larvae from a high CO 2 world and lead to differences in evolutionary responses between species including molluscs and echinoderms [46,75].…”

“…Variations in responses within and between species populations and the role in resilience and adaptation remain virtually unknown [43,44], especially amongst geographically isolated populations. Also as oceans acidify it is anticipated that they will also warm (by 4 °C [1]) and that the dual stress of elevated CO 2 and temperature may either act in combination to exacerbate impacts or the positive effects of temperature may ameliorate any negative effects of elevated CO 2 [34,45].…”

Ocean acidification and temperature rise: effects on calcification during early development of the cuttlefish Sepia officinalis

“…Riebesell et al 2000;Zondervan et al 2001), bivalves (e.g. Gazeau et al 2010Gazeau et al , 2011Waldbusser et al 2010;, pteropods (e.g. Comeau et al 2011) or echinoderms (reviewed by Dupont et al 2010).…”