Ocean acidification alters skeletogenesis and gene expression in larval sea urchins

Abstract

Ocean acidification, the reduction of ocean pH due to the absorption of anthropogenic atmospheric CO 2 , is expected to influence marine ecosystems through effects on marine calcifying organisms. These effects are not well understood at the community and ecosystem levels, although the consequences are likely to involve range shifts and population declines. A current focus in ocean acidification research is to understand the resilience that organisms possess to withstand such changes, and to extend these investigations beyond calcification, addressing impacts on other vulnerable physiological processes. Using morphometric methods and gene expression profiling with a DNA microarray, we explore the effects of elevated CO 2 conditions on Lytechinus pictus echinoplutei, which form a calcium carbonate endoskeleton during pelagic development. Larvae were raised from fertilization to pluteus stage in seawater with elevated CO 2 . Morphometric analysis showed significant effects of enhanced CO 2 on both size and shape of larvae; those grown in a high CO 2 environment were smaller and had a more triangular body than those raised in normal CO 2 conditions. Gene expression profiling showed that genes central to energy metabolism and biomineralization were down-regulated in the larvae in response to elevated CO 2 , whereas only a few genes involved in ion regulation and acid-base balance pathways were up-regulated. Taken together, these results suggest that, although larvae are able to form an endoskeleton, development at elevated CO 2 levels has consequences for larval physiology as shown by changes in the larval transcriptome.

Evolutionary change during experimental ocean acidification

“…Previous ocean-acidification experiments on purple sea urchin and other echinoderm larvae have often found stronger negative effects of CO 2 on growth and development than those documented here (23,24,33,34). The primary difference between our experimental design and previous studies is that our larval cultures were >10 times less dense, reflecting a more ecologically relevant condition (35), with perhaps less laboratory-generated stress.…”

“…3). Specifically, based on previous studies of physiological response to CO 2 , we hypothesized that genes related to biomineralization, ion homeostasis, and metabolism would show excess genetic change in response to high CO 2 (21)(22)(23)(24). In contrast, at ambient CO 2 , we expected changes to be random with respect to protein function.…”

“…Because we estimate allele frequency from mRNA from pools of larvae, it is conceivable that a change in allele frequency at a given locus is due to a change in allelespecific expression of one haplotype over another. To reduce this potential confounding effect, we excluded the SNPs in the few (23) genes that showed differential expression in response to CO 2 treatment. However, there could also be differences in allelespecific expression in genes with constant transcript abundances.…”

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

“…There was also down regulation of biomineralization, skeletogenesis and energy metabolism genes, whilst some acid-base and ion regulation genes were up-regulated in larvae of the sea urchin Lytechinus pictus which were significantly smaller and had more triangular skeletons and shorter arms than controls [80]. In contrast, decreased pH also had no effect on expression of two shell mineralisation genes ap24 or engrailed at any developmental stage in the abalone Haliotis rufescens [74], but up and down regulation of proteins was found in Saccostrea glomerata, although these are yet to be identified [46].…”

Adverse Effect of Ocean Acidification on Marine Organisms

“…Other studies, performed in mesocosms and natural waters around volcanic vents areas, did show a clear reduction of calcareous epibionts that in turn impacted the diversity of seagrass species [5]. Conversely, it was observed that sea urchin, corals and mussels are able to survive to a decreased calcification but suffer for a reduced mechanical performance affecting in turn key biotic and abiotic interactions [6]. The structural integrity of components such as shells in bivalve mussels is fundamentals to deter predator's actions as well as is important biomaterials aimed to ensure the attachment of animals to the rocks such as proteinaceous byssal threads that anchor mytilid mussels to hard substrates.…”