Phenotypic differences may limit the potential for habitat restoration involving species translocation: A case study of shape ecophenotypes in different populations of Modiolus modiolus (Mollusca: Bivalvia)

Modiolus modiolus reefs have disappeared from most of their historical distribution range in Strangford Lough (Northern Ireland) while remnant populations are highly fragmented. This study investigated morphological differences in Strangford Lough and Irish Sea M. modiolus with an aim to provide sound scientific advice to managers involved in shellfish reef restoration programmes including translocation. By characterizing shape ecophenotypes within target and source areas it is possible to select morphologically similar source stocks to increase survival and self sustainability of the restored population. Linear and geometric shell shape analyses identified significant differences among M. modiolus populations from the Irish Sea and Strangford Lough. Three different phenotypes within the Strangford Lough metapopulation were identified. It is hypothesized that substrate type, tidal current strength and population thinning caused by mobile fishing gear influenced such morphological differences. This investigation confirmed, for the first time, phenotypic variability in M. modiolus which could affect future supplementation programmes aiming to restore degraded populations.