The higher taxonomic structure of a meiofaunal community was investigated in an Eastern Mediterranean lagoon (Gialova lagoon, Ionian Sea). Seven stations were sampled on a seasonal basis during 1995-1996. Stations within the lagoon were found to support a maximum of 14 meiofaunal taxa with densities ranging from 17 to over 2000 individuals per 10 cm 2 . Nematodes were not always the most abundant taxa, although they dominated about half of the total 28 samples. Uni-and multivariate analyses were employed to study the community structure. The distribution pattern of the meiofaunal community varied both across the lagoon and over the seasons. On the basis of the spatial differences a meiofaunal coenocline, correlated with the degree of isolation, was observed, composed of mainly two zones: one defined by the area close to the marine channel and the other the more isolated area in the inner lagoon. Meiofaunal distribution pattern was not clearly correlated to one environmental variable, but rather to many, and spatial and seasonal effects could be seen.

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Lagoonal mud snails have been shown to suffer approximately 50% mortality between hatching and adulthood. Experiments were conducted in the laboratory to assess the role of predators on the survival of juvenile Hydrobia neglecta (Mollusca: Gastropoda). Adult snails were collected from a lagoon in the Reedland Marshes system at Dunwich, Suffolk, and their eggs hatched in the laboratory, providing a population of juvenile snails which could be presented as a food source. The vessels, kept at environmental regimes close to that of the natural environment, were seeded with juvenile snails at field density. Predator preference was established by exposing the juvenile snails to combinations of potential predators found in the lagoon. One experiment also gave predators a choice of various juvenile snail sizes and other prey species. Juvenile snails remaining alive after the four week exposure to predators were removed, counted and measured. In the absence of other prey, the opisthobranch snail Retusa obtusa preferentially consumed 50% of the available juvenile H. neglecta over a four week period and the nemertean Lineus ruber up to 90%, making them the major contributors to juvenile H. neglecta mortality. The infaunal anemone Nematostella vectensis, did not have a significant impact on snail survival in the experiments but was observed (incidentally) in a separate non-experimental situation engulfing juvenile H. neglecta. The stickleback Gasterosteus aculeatus and the lagoonal prawn Palaemonetes varians, did not contribute directly to the observed mortality of juvenile mud snails, but were found to consume other predators, producing a system of prey preferences in the food chain. Understanding the role of predation contributes to the understanding of ecological processes occurring in rare lagoonal systems.