Impact of climate change on the future life history traits of economically important bivalves along the China coast

Abstract

The Pacific oyster, Crassostrea gigas (Thunberg 1793; also known as Magallana gigas), and invasive mussel, Mytilopsis sallei (Récluz 1849), are ecologically and economically important bivalve species along the China coast. It is, therefore, beneficial to predict changes in their performance and distribution, especially under climate change. To achieve this, the present study experimentally investigated variation in reproductive success of C. gigas under different scenarios and then used Dynamic Energy Budget (DEB) models to study how the two species allocate energy under varying environmental conditions. Based on different scenarios, the DEB models were used to determine variation in life history traits and to predict the future success of the two species along the China coast. Firstly, the consequences of thermal acclimation on the reproductive and larval success of oysters during different reproductive stages were investigated to understand the cause of post-spawning summer mortality, and how this may vary under climate change. The physiology and stress tolerance of oysters during gametogenesis was not affected by acclimation temperatures between 15 - 21 oC and no mortality was observed. High acclimation temperature (> 20 oC) was, however, a significant factor affecting mortality of post-spawned oysters, reducing their stress tolerance but also affecting the yield and viability of D-larvae. The differential responses of oysters during gametogenesis and post-spawning, as well as the variation in reproductive and larval success, is likely due to the low energy i reserves and high metabolic costs incurred during reproduction and spawning by high- temperature acclimated oysters. Understanding the responses of C. gigas at different reproductive stages is, therefore, valuable information as variation in temperature is a critical factor governing the success of aquaculture. The constructed DEB models were validated with biological field data and utilized to investigate the life history traits of Crassostrea gigas and Mytilopsis sallei at various spatial- temporal scales under climate change scenarios (conservative, RCP2.6; severe, RCP8.5) and three different food availabilities at each scenario (RCP2.6: 5, 10 and 20%; RCP8.5: 10, 20, and 30% reduction compared to present-day). DEB predictions showed there was the risk of losses of suitable areas for cultivation of C. gigas in northern China where food supply might become limiting under climate change. In contrast, in areas which are not food limited under present conditions, oysters were generally predicted to benefit from increasing temperatures when future declines in chlorophyll-a concentration was not beyond 10%. The DEB model for M. sallei predicted enhanced reproductive output under increasing temperatures even under poor food conditions; suggesting that M. sallei might increase its range, especially in regions south of the Yangtze River which is likely to impose a biogeographic barrier to extension northwards. Results from the present study illustrate the importance of coupling mechanistic and climate models to predict the effects of climate change on the future spatial-temporal dynamics of economically important bivalves, providing species-specific and locally relevant data which can be used to evaluate habitat suitability for aquaculture and predict biogeographic changes. This information is, therefore, useful for stakeholders to establish effective aquaculture practices, identify site specific management strategies, or to develop better mitigation and management strategies against invasive species.