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

Description/Abstract

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.