The immunobiology of Crepidula fornicata and its potential to act as a harbourer of infectious disease

Abstract

Invasive alien marine species have garnered a negative reputation outside of their native ranges, often due to them translocating disease from their native areas to their new environment. Much of the currently available resources on the disease status of marine species is focused on species of commercial importance such as the Blue mussel Mytilus edulis, Pacific oyster Crassostrea gigas or farmed abalone species e.g., Haliotis spp. The slipper limpet Crepidula fornicata is an invasive alien species, originating from the east coast of the United States. Crepidula fornicata is now found throughout the coastal waters of southern England and Wales, U.K. Crepidula fornicata is often thought of as a pest when found in commercial shellfish areas. However, despite this negative reputation, little is known about its disease status or immunobiology. Therefore, the aim of this thesis was to study the immunobiology of C. fornicata and to understand its potential as a harbourer of infectious disease. To address the lack of information available with regards to the immunobiology of C. fornicata in Chapter 2 haemolymph (blood) was isolated and examined for the presence of the immune-enzyme phenoloxidase. The presence of laccase and catecholoxidase activities were confirmed. Importantly, it was shown that products derived from laccase and catecholoxidase activities reduced the numbers of colony- forming units of bacteria in vitro. Tissue was also examined histologically, and the presence of eumelanin-like pigments and lipofuscin was visualised in a number of regions e.g., digestive gland, connective tissues, and gills. A year-long multi-resource disease survey was carried out at two sites in South Wales, Swansea Bay, a native oyster Ostrea edulis restoration site, and Milford Haven, an area of commercial shellfish activity. In Chapters 3 & 4 a combined PCR and histological approach was taken to screen C. fornicata for the presence of diseases potentially harmful to shellfish and/or humans e.g., Vibrios, haplosporidians, microsporidians, and paramyxids. Chapter 3 found that a large proportion of individuals were PCR positive for Vibrio-like bacteria. However, it was found through a histological screen that few disease signatures could be observed, suggesting that C. fornicata are not particularly sensitive to bacteriosis at the sites surveyed. Chapter 4 found no clinical signs of C. fornicata being infected with haplosporidians, microsporidians or paramyxids. Histology revealed the presence of trematodes, turbellarians, and an apicomplexan-like parasite. The data suggested that C. fornicata are not susceptible to major parasitic infections outside of the native range. A Species Distribution Model (SDM) was constructed in Chapter 5 to aim to understand the potential future distribution of C. fornicata under predicted climate change. Areas further north in North America, Europe, and Northeast Asia were identified as areas most at risk for future introductions of C. fornicata.