Forty years of undisturbed change in the ground dwelling fauna in the Lauwersmeer, a reclaimed tidal estuary of the Dutch Waddensea

摘要

A tidal area of 9,000 ha in the north of the Netherlands was reclaimed in 1969. The presence of carabids, spiders, harvestmen, woodlice and myriapods has been monitored at two locations (Sennerplaat and Schildhoek) in the full period 1969-2008. The ecosystem could develop under undisturbed conditions, and desalinization and vegetation succession are the main processes. The characteristic salt marsh species disappeared after twelve years, indicating the fast desalinization. The succession from open soil (sandy or muddy) to a dense reed marsh with litter layer needed 15-20 years. More than 350,000 specimens have been captured in four series of two traps and identified to species-level; full data are presented in this paper. High numbers in specimens are present in the first years, but also after ten or twenty years in carabids and spiders. The first harvestmen, woodlice and myriapods invaded the system only after twenty years. Analyses in development of the catches in spiders indicate that the catches in the first twenty years are higher in the specimen numbers, the other twenty years remain on one lower level. Analyses in development of the catches in carabids indicate differences between the two locations. In Schildhoek the numbers are higher in 1970-1978 and on a constant lower level later. In Sennerplaat the numbers are higher with peaks around the years 1973,1983 and 1991, and on a constant lower level later. Higher numbers can be explained with some dominant species. The analyses on the species numbers, including loss and gain in yearly species, indicate that after some years the numbers remain on the same level for carabids at the four sub-locations and for the area as a whole. However, in the spiders the number of species rise from 20 to 45 with all data merged; in the four sub-locations the number remain on a constant level. Although many similar developments can be given for the two locations, some differences can be indicated that are related to abiotic conditions and dispersal. In the discussion, we conclude that during a forty-years period of succession we meet a constant arrival and disappearance of species in carabids, and after fifteen years also a gradual increase in spider species, that might be explained by dispersal capacity.