Meiofauna in closed coastal saline lagoons in the United Kingdom: Structure and biodiversity of the nematode assemblage

Coastal saline lagoons are rare in North West Europe and tend to be closed, brackish water systems. In the United Kingdom they are small and isolated, each exhibiting extremely variable habitat conditions, both spatially and temporally. This paper represents the first species-level study of lagoonal nematode assemblages in the UK. Samples were taken from seven ponds in a saline lagoon system on the south coast of England in order to describe the nematode assemblage in relation to habitat type and to assess the possibility of lagoonal specialisation. At each site samples were also taken, or data were already available, for salinity, sediment granulometry, sediment organic carbon content, photosynthetic pigments and lagoon topography. A lagoonal specialist nematode fauna was not identified, but it was found that the nematode communities strongly reflected the differences between environmental conditions in the lagoons. Sample and site diversity were found to be relatively similar, but the importance of habitat networks was indicated by the relatively high system diversity, species turnover being highest between lagoons with different salinity and/or granulometry regimes. Salinity was the principal factor correlated with assemblage structure and species diversity was highest at the higher salinity sites. Median salinity (averaged from weekly records over the previous 4 months) correlated more clearly with nematode assemblage structure than salinity at the time of sampling. This shows the importance of considering historical as well as contemporaneous data when undertaking ecological studies: Contemporary conditions may influence species fecundity, and therefore relative abundances, whilst historic conditions may influence species occurrence through the effects of recruitment and survival.