Ecology of parasites in mudflat ecosystems

Mudflats are not only home to large numbers of bivalves, polychaetes,crustaceans, fish and birds, but also to diverse communities of parasites. In thischapter, we illustrate and explore how the resulting parasite-host interactions canaffect host populations, communities and food webs in mudflat ecosystems, equallingin importance the effects resulting from other species interactions, such as predation and competition. We first give an overview of the distribution and ecologyof typical parasites occurring in mudflat ecosystems. Then we illustrate the mainabiotic and biotic drivers of parasite infection levels in mudflat hosts. Following this,we conceptualise and illustrate the many direct and indirect effects of parasite-hostinteractions on host populations, communities and food webs in mudflat ecosystems.Finally, we highlight the potential impact of ongoing global changes such asincreasing temperature and species introductions on parasite-host interactions inmudflat ecosystems. With this condensed overview of the presence and ecologicalrole of parasites in mudflat ecosystems, we hope to increase the appreciation of themanifold ecological effects of parasite-host interactions on host populations, communitiesand food webs of mudflat ecosystems, and to spark further research in this fiel

Resource tracking in marine parasites: going with the flow?

Understanding how diversity interacts with energy supply is of broad ecological interest. Most studies to date have investigated patterns within trophic levels, reflecting a lack of food webs which include information on energy flow. We added parasites to a published marine energy-flow food web, to explore whether parasite diversity is correlated with energy flow to host taxa. Parasite diversity was high with 36 parasite taxa affecting 40 of the 51 animal taxa. Adding parasites increased the number of trophic links per species, trophic link strength, connectance, and food chain lengths. There was evidence of an asymptotic relationship between energy flowing through a food chain and parasite diversity, although there were clear outliers. High parasite diversity was associated with host taxa which were highly connected within the food web. This suggests that energy flow through a taxon may favour parasite diversity, up to a maximal value. The evolutionary and energetic basis for that limitation is of key interest in understanding the basis for parasite diversity in natural food webs and thus their role in food web dynamics

Enhanced erodibility of fine-grained marine sediments by <i>Hydrobia ulvae</i>

The common mud snail Hydrobia ulvae is a widespread and dominant deposit feeder on fine-grained substrata along the European Atlantic coastline. Previous studies have shown that mud snail activities such as grazing, faecal pellet production and mucous production may influence physical properties of the surface sediment layer and thus depositional and erosional processes. To quantify the influence of Hydrobia density on key parameters such as erosion threshold and erosion rate, a short-term laboratory experiment was conducted. Snails were placed on fine-grained sediment at densities of 10000 and 50000 ind m-2 and erosion experiments were carried out one, three and five days after establishment of the sediment beds. Controls without H. ulvae were treated the same way. The presence of H. ulvae significantly increased the erosion rate and decreased the erosion threshold compared to snail-free control plots. The erosion rate was increased by a factor of 2 to 4 when H. ulvae were present and showed stronger influence by the snail than the erosion threshold. Snail density did not affect the erosion threshold, but the erosion rate doubled with an increase in density from 10000 to 50000 ind m-2. The erosion rate was only marginally different after one day but the difference increased over time and the erosion rate was significantly different for all treatments after five days. No significant time dependence was observed for the erosion threshold. The results generally confirm results obtained in situ and differences can be related to different hydrodynamic conditions under field and laboratory conditions

Use of ITS rDNA for discriminating of larval stages of two microphallid (Digenea) species using <I>Hydrobia ulvae</I> (Pennant, 1777) and <I>Corophium volutator</I> (Pallas, 1766) as intermediate hosts

International audienceDigenean trematodes encompass several species with little morphological differentiation in the larval stages and, as a result, uncertainty prevails regarding species identification. The microphallid trematode Maritrema subdolum occurs widespread geographically in mud snail and crustacean hosts in European marine shallow-water ecosystems. Larval stages of this and other congeneric species are, however, difficult to separate morphologically. To verify the species status and to secure identification of two co-occurring microphallids, M. subdolum and microphallid sp. no. 15 (Deblock, 1980), we examined the nucleotide sequences of the internal transcribed spacer regions (ITS1, ITS2). From fragments consisting of both ITS regions and the 5.8S gene (nearly 1,200 bp), a sequence divergence of 2.9% between the two types was recorded. In accordance with the morphological traits of the cercariae (stylet shape, length), the results support the view that the two types actually represent different species. Species-specific primers were prepared for each species. They proved to be efficient diagnostic tools for identifying single larval-stage individuals. Using these primers, infections in host organisms were also verified without performing a dissection of the host individuals