Flexing Mussels: does Mytilus edulis have the capacity to overcome effects of ocean acidification? (Regional)
This project has two objectives:
1) To test for cross-generational adaptation to the impacts of increasing ocean acidification in blue mussels, either through phenotypic acclimation or through heritable changes.
2) To determine if there are tradeoffs in growth and development across life stages in response to stress induced by ocean acidification in blue mussels.
1. Collect and mark blue mussels, Mytilus edulis, from multiple populatons around Long Island Sound that experience very different environments (e.g., salinity, temperature, hypoxia, nutrient concentrations).
2. Condition reproductive animals from each population to three Ocean Acidification (OA) stress treatments produced by bubbling a CO2/air mixture into the seawater: aragonite saturation Ω 2.0 (pH 8.0, C); Ω 1.0 (pH 7.7, M); and Ω 0.7 (pH 7.4, L).
3. Experiment 1: Spawn animals from each population conditioned in each OA treatment; create larval (F1s) population lines; rear larvae (5 replicates for F1 offspring of each population in each treatment) in the same treatment as parents were conditioned in.
4. Quantify performance of larvae: survivorship, growth, time of development, lipid accumulation, shell shape and shell microstructure.
5. Once metamorphosed, F1 juveniles marked with a fluorescent marker, kept in the same OA stress treatment as they have been reared in, and performace quantified: survivorship, growth, shell shape and microstructure, and time to production of gonads.
6. Sample of larvae and juveniles from each treatment for each population preserved so that if funds become available in the future, genetic analyses can be conducted.
7. Once F1 animals reproductive, conduct Experiment 2 with the same OA stress treatments. F1 animals spawned within populations and treatments, producing a second generation of offspring, F2s.
8. Experiment 2: F2 offspring from each treatment for each population allocated to each of the three OA treatments. Includes the treatment their parents were reared in (C1 M1, L1) and the other two OA treatments (C1C2, C1M2, C1L2, M1C2, M1M2, M1L2, L1C2, L1M2, L1L2). Same performance metrics quantified as in Experiment 1 for both larvae and resultant juveniles. Samples collected and preserved so that that if funds become available, genetic analyses can be conducted in the future.
9. Test for performance differences among populations, among treatments, and population x treatment interactions. Experiment 1: Differences among treatments will indicate levels of OA stress that blue mussels are resilient to and which levels induce stress.
10. Differences among populations for F1 animals may mean that history (phenotypic acclimation or epigenetic effects) or genetic differences among poulations affect perfomance.
11. Statistical tests on F2 animals (Experiment 2) will separate the roles of recent past enviorment, source location (could represent genetic differences) in the responses of blue mussels to OA stress.
12. Increased performance overall in F2 animals will suggest that blue mussels have the capacity to be resilient and adapt to OA stress.
14. Test for tradeoffs in performance metrics associated with OA stress, look for bottlenecks during development that could have large impacts affecting resilience of blue mussels to OA stress.
Ocean acidification (OA) conditions have already been shown to affect a wide variety of marine organisms. Shoreline systems, including estuarine areas where most shellfish aquaculture is conducted, experience greater rates of change in water chemistry than are seen or projected in the open ocean. Not all species or developmental stages within species are inhibited by higher pCO2. In some cases, differences among individuals within a given species in response to OA stressors have been found, indicating variation in the capacity to respond to OA. Thus, predicting the impacts of OA on coastal systems and species, including species use in aquaculture, remains challenging. Legacies of historic conditions may result in some species being more resilient to elevated CO2 conditions, or more able to adapt to changing conditions. Although most studies focus on the average response within a species to experimental conditions, all studies show a variance in response; this variance may be due to measurement error, small differences in the local conditions of individuals, or it may reflect real differences among individuals in response, with some individuals much more robust than others to environmental stressors. "Winners" and "losers" will likely exist not only among species, but also among individuals within species. Studies are needed to determine what driving factors are resulting in variance in responses seen within species to OA stress, especially long term, cross-generational studies. We will use cross-generational experiments with the common blue mussel, Mytilus edulis, to test for its capacity to display resilience or adapt to different OA conditions. The blue mussel is one of the most extensively studied marine organisms, and has been used as a model for physiology and a variety of other studies, and it is an important aquaculture species in many northern areas in the Atlantic. The short generation time of the blue mussel relative to many other aquaculture species also makes it ideal for cross-generational studies of the impacts of OA conditions. We will examine multiple metrics of performance at different life stages, test for tradeoffs in performance under different OA conditions, and assess the potential for M. edulis to show resilience or adapt to changing environments. Our experimental design will allow us to determine if blue mussels in LIS have the capacity to acclimate or adapt to OA. If responses are phenotypic, we should see similar responses in the experiments with F2s in each treatment, irrespective of their parental OA treatment (and variance among individuals within treatments should be lower, erasing maternal effects present in the F1). If there are heritable or inducible long term responses, we expect to see differences in response of F2 individuals based on their parental OA treatments. Lasting tradeoffs due to OA will be tested for by examining juvenile responses in both F1 and F2 individuals. The results of our experiments can then be used to develop management practices for wild populations and more robust aquaculture practices for blue mussels. From an aquaculture perspective, if animals from certain source populations are more resilient to OA stress, those locations could be targeted for collection of wild seed that will produce resilient mussels in aquaculture leases. Furthermore, the environmental characteristics of these advantageous site(s) could then be characterized to predict other sites that may also produce resilient mussels. Overall, the data obtained from this proposed work could be used to enhance mussel culture, an economically important activity of growing importance in our region.