Environmental change in the coastal environment: challenges for the selection and propagation of filter feeding species in aquaculture, stock enhancement and environmental rehabilitation
Selection of species for aquaculture, fishery stock enhancement and environmental rehabilitation or restoration in the coastal zone requires consideration of the fact that species have evolved over geological time whereas changes in the coastal environment have occurred predominantly over recent historical time, often with the largest changes occurring within the past decades of human activity. The evolutionary issue is particularly noted with filter feeding molluscs, where extant species supporting both major natural fisheries and aquaculture have ancient lineages and evolved in environments that may have differed considerably from the locally turbid, nutrient enriched, disturbed (through watershed change and local activity) waters in which they now survive. We cannot presume that native species are strongly selected to survive in the environments in which they currently reside. Neither can we presume that they will be successful candidates for aquaculture, fishery stock enhancement, environmental rehabilitation (the restoration of ecological services in community structure), or environmental restoration (restoration of native community structure with associated ecological services). Watershed and coastal use impacts have, over recent human history, altered community structure in coastal waters, and diminished the ability of surviving community members to perform the ecological services that are one end product of their evolution. A challenge is therefore presented to students of intensive species culture, extensive fishery enhancement, and ecological rehabilitation or restoration: how to best use the tools of husbandry in concert with large and small scale environmental manipulation to promote progress in the designated area of interest? Ecological rehabilitation or restoration centered on cornerstone filter feeding species must employ local environmental rehabilitation, but this will only be successful if it is accompanied by a wider commitment to watershed management protocols that protect all life history stages, including the delicate early stages. A numerical argument for this approach, based on Paulik life history models, will be presented. Intensive aquaculture, by comparison, may be able to progress in marginal environments where delicate early life history stages are cultured in controlled situations, thus limiting mortality, before transfer to open systems. Fishery enhancement resides between these options, where a dual role of supplementing local reproduction is balanced against increased exploitation of commercial product
