Proteomic analysis of oyster larvae reveals molecular mechanism of ocean acidification and multiple stressor effects

Abstract

The increase in carbon dioxide emissions due to human activities has led to drastic variations in global climate. In addition to global warming and extreme weather patterns, the high CO2 levels have been leading to progressive ocean acidification. Compounded with other climate change related stressors, ocean acidification will hinder the ability of marine organisms to adapt to the ensuing changes and might affect human dependence on oceans as a source of food. Most marine organisms have complex life cycles, involving metamorphosis from larval to adult forms. In the early stages of life, oysters have calcium carbonate shells that are particularly sensitive to low pH, and the rapid climatic changes can compromise their metamorphosis. High temperature, low salinity and low pH resulting from ocean acidification are detrimental to both native and cultivated oyster populations. Although mechanistic studies to understand the tolerance responses of closely related species would be significant in this context, none have been reported to date. Therefore, this thesis aims to reveal the mechanisms that distinguish the “winners” from the “losers” among the selected aquatic species of commercial importance, in withstanding the stress induced by climate change.

The present study employed molecular approaches to evaluate the interactive and cumulative effects of multiple stressors on large-scale cultures of pediveliger larvae from two oyster populations, Crassostrea hongkongensis and Crassostrea gigas. The study undertook transcriptomic and proteomic profiling of changes induced by ocean acidification in the larvae. The results revealed that oyster larvae could adopt an energy ‘trade-off’ strategy through metabolic suppression and adjust cell signalling pathways to overcome the stress induced by ocean acidification.

Information from the oyster genome database facilitated the shotgun proteomics investigations on oyster larvae remarkably revealed over 1350 proteins in both the species. The study identified species- and stressor-specific tolerance responses, and survival mechanisms that preserved calcification, in oyster larvae. The larvae showed depletion of energy reserves due to enhanced metabolism, oxidative damage-induced immune response and metabolic suppression.

The study reveals the existence of tolerance mechanisms in oysters that help them adapt to stresses resulting from climate change. It pioneered the use of a proteomics approach to understand the impact of multiple stressors on oyster larvae and the molecular mechanisms underlying their successful adaptation to them. Highlighted several potential possible biomarkers in this study will likely to play an important role in identifying oyster species showing heritable tolerance for future aquaculture.