Metabolic cost of calcification in bivalve larvae under experimental ocean acidification

Published OA 13 December 2016
Abstract: Physiological increases in energy expenditure frequently occur in response to environmental stress. Although energy limitation is often invoked as a basis for decreased calcification under ocean acidification, energy-relevant measurements related to this process are scant. In this study we focus on first-shell (prodissoconch I) formation in larvae of the Pacific oyster, Crassostrea gigas. The energy cost of calcification was empirically derived to be ≤ 1.1 µJ (ng CaCO3)−1. Regardless of the saturation state of aragonite (2.77 vs. 0.77), larvae utilize the same amount of total energy to complete first-shell formation. Even though there was a 56% reduction of shell mass and an increase in dissolution at aragonite undersaturation, first-shell formation is not energy limited because sufficient endogenous reserves are available to meet metabolic demand. Further studies were undertaken on larvae from genetic crosses of pedigreed lines to test for variance in response to aragonite undersaturation. Larval families show variation in response to ocean acidification, with loss of shell size ranging from no effect to 28%. These differences show that resilience to ocean acidification may exist among genotypes. Combined studies of bioenergetics and genetics are promising approaches for understanding climate change impacts on marine organisms that undergo calcification.

IJMS Editor’s Choice – the metabolic cost of calcification

The latest Editor’s Choice article from the ICES Journal of Marine Science is now available. Here, read about a study of the Pacific oyster and the role ocean acidification plays in how its metabolic energy is allocated and in shell formation.

​​​​​​​​​​As a group, oysters are the marine animals most raised in aquaculture. While there has been continued growth in global oyster production over the past decades, recent failures of larval Pacific oyster hatchery production along the U.S. West Coast highlight negative impacts of ocean acidification on marine aquaculture. As well as its importance as a source of seafood, the Pacific oyster is emerging as a model marine organism for study of development, physiology, and genetics. Responses to ocean acidification can involve high metabolic costs. In this study, the authors quantify the effect of ocean acidification on the allocation of metabolic energy and the cost of shell-formation during early larval development.

Within the first two days of development, the Pacific oyster grows a shell that is six times heavier than the mass of its whole body. Accomplishing this high rate of shell growth requires up to two-thirds of total metabolic energy. Yet, surprisingly, regardless of exposure to experimental ocean acidification, the amount of metabolic energy required and the maternally-endowed energy reserves utilized to complete development is the same. Consequently, decreased calcification rates resulting in smaller shells that are commonly observed under experimental ocean acidification are not caused by a limitation of biochemical energy reserves.

Despite the substantial impact of experimental ocean acidification on shell formation, different families of Pacific oyster range in their ability to make shell. Across a series of different larval families produced by controlled crosses of pedigreed lines, the effect of experimental ocean acidification ranged from no effect (resilience) to a 28% decrease in shell size. This insight shows, importantly, that genetic-based resilience to climate change may exist and that, moving forward, breeding programs could provide a potential long-term solution for commercial aquaculture.


​Sequence of first-shell formation in Pacific oyster. The image depicts the overlay of two fluorescence channels to distinguish cell nuclei (blue-stained DNA) from calcified shell (green) across three larval stages. On the far left is a trochophore larva (13-hours post-fertilization), showing localization of first calcification for each valve as two bright green regions. In the middle is a larva that is about half-way through extending its shell around the larval body (16-hours post-fertilization). On the far right is a 1-day-old veliger larva that has a fully developed shell of ~70 µm in length that now encompasses the entire larval body.  ​

ICES Journal of Marine Science, Editor’s Choice feature: