CACHE ITN Shell production for shellfish farming and biotech in a changing world

Shell thickness, shape, size and composition can vary significantly within species, depending on where they live and these are all strongly influenced by the local conditions. Understanding how shell characteristics vary in the natural environment is essential if we are to accurately predict how these animals will be affected when the environment changes. For example, if the sea warms up, will shells be thicker or thinner? We can test this by examining shells in animals from the Arctic, where sea temperatures can vary between freezing in winter and 6-8°C in the summer) and comparing them with animals from off the coast of Portugal (temperatures from 12°C  in winter and summer temperatures of up to 27°C in the lagoon by the research station). By studying the composition of shells from the same species obtained from different environments we can identify how local environmental conditions affect shell production and also identify if there are genetic factors associated with any observed differences. This will enable us to identify potentially resilient populations which can be selectively bred for future aquaculture production.

Throughout its life, a mollusc has to devote considerable amounts of energy to growth (of both shell and body tissue), reproduction and maintenance of essential cellular systems, such as immune functioning. It gets this energy from its food, but how the animal uses this energy  depends on the environmental conditions and time of year. In the winter there is not much food, so little growth occurs. In the summer, although there is much more food, the animal also has to reproduce, which is a considerable drain on energy reserves and the amount of growth is, to a certain extent , dictated by the balance of costs between these two essential activities. Also, if the animal is stressed, as can happen in Scottish lochs with fresh water run-off from pine forests temporarily lowering the salinity and pH of the water,  it will divert energy towards resisting  stress and boosting its immune system. By studying the same species of mollusc in different environments, in both  summer and winter and also manipulating conditions in the laboratory, we will be able to determine how molluscs allocate their energy under different conditions and how this impacts shell growth. This will enable us to better predict, how these animals will respond to our changing climate.

Individuals within a population are rarely genetically identical. All are slightly different and this produces variations in their ability to cope when the environmental conditions change. It follows that some animals will be better adapted to life under future climate change conditions than others and therefore identifying these more robust individuals and introducing them into aquaculture breeding programmes would be of considerable commercial benefit. This theme aims to identify how much genetic variability there is in the populations of our chosen species. We will identify genetic factors that may be associated with resistance to, or adaptation to climate change and to carry out selection experiments to identify more resilient strains for future aquaculture production.

Whilst we know a lot about how humans produce bone (which is essentially a mineralised structure, comprising a high percentage of calcium and bound together with a protein matrix), we know very little about how molluscs produce their equivalent structures: shells. Damaging shells via  drilling will allow us to monitor the genes and proteins that are produced during repair. Using this data we will be able to identify the biochemical pathways involved in shell production. Once an understanding of  the critical genes in this process is established, we can begin more targeted analyses to see how they are regulated in different environments and therefore identify potentially important genes in the adaptation to future climate change conditions. Because these biochemical processes, take a soluble form of calcium (in sea water) and turn it into an insoluble compound (shell) without heating or requiring the use of huge amounts of energy, we will explore how these processes may be used in the biotechnology industry.

Calcium is an essential ion in shell production. But we know little about how shells are produced and  have very little knowledge about how calcium is taken up: does it come from sea water and/or food and in what proportions? How is it moved around the body to end up in the shell? How is it controlled?  We will study in detail the tissue in the animal which ultimately makes the shell (the mantle tissue) to identify biochemical pathways involved in mobilising calcium from body tissues to produce the hard structure of the shell and how this is controlled. This will allow us to answer some fundamental questions: Can we induce more or less shell production by manipulating environmental conditions? What hormones are involved and how do they regulate shell production under different conditions? Are there genetic variants of these hormones in different populations which can be exploited in future breeding programmes?