Spatio-temporal patterns in benthic macrofauna on a brackish mudflat (Schelde estuary, NW-Europe): results of ten years monitoring

Estuarine ecosystems are charac­terized by largely varying physicochemi­cal condi­tions, especially in the meso-/oligohaline zones. Knowledge of the environmental variability and related population effects on a range of spatio-temporal scales is fundamental to a better understanding of their functioning, stability, resilience and the way they are influenced by human impacts. This study combines spatial and temporal variations in macrobenthic populations (and their environment) on a brackish mudflat in the Schelde estuary (NW-Europe). From 1990 to 1999, long -term year-to-year variations were monitored on 24 sites, short -term monthly variations on two sites. The variation in macrobenthos and the physicochemical environment due to seasonal dynamics, spatial pattern, and annual as well as long-term trends, was quantified. The macrobenthic community on the mudflat was characterized by a few dominant species (Corophium, Heteromastus, Nereis, Oligochaeta), with spatial distributions related to sediment characteristics. Considerable year-to-year variation was observed and seasonality was evident for all species. It is argued that in the meso-/oligohaline zone, where salinity shows large seasonal fluctuations, benthic communities change frequently during the year, resulting in communities that seldom progress beyond early benthic-community succession. Annual variations are less pronounced. The impact of the construction of a containerterminal (1994), adjacent to the mudflat, on the macrobentic species distributions is discussed

10 jaar monitoring op het Groot Buitenschoor

The results of 10 years monitoring on the Groot Buitenschoor are reported. Macrobenthos data were analysed to explore both temporal and spatial trends in biomass and density, related to some abiotic parameters (sediment composition, altitude). Micro-pollution of the sediment was examined for several years. Evolutions in tidal marsh vegetation were assessed by comparison of two vegetation maps. Changes in wintering and migrating waterbird communities were analysed and related to environmental characteristics and macrobenthos populations. Finally an attempt was made to identify possible impacts of the construction and exploitation of the nearby container terminal

New crustacean invaders in the Schelde estuary (Belgium)

This paper reports on the first records of three non-indigenous crustacean species in the Zeeschelde estuary (Belgium). All three species are native to the Western Pacific Ocean and are probably transported in ballast water or hull fouling. The isopod Synidotea laevidorsalis has been recorded earlier in Europe from two locations, in the south of France and in Spain. The present records constitute a range extension of more than 1000 kilometres to the north. The crab Hemigrapsus takanoi and the prawn Palaemon macrodactylus were found for the first time in the brackish reaches of the Schelde estuary. The finding of these species demonstrates the vulnerability of the estuarine system to the invasion of exotic species

Tidal wetland restoration at Ketenisse polder (Schelde Estuary, Belgium): developments in the first year

Ketenisse polder is a former intertidal brackish marsh (30ha) situated in the mesohaline part of the Schelde Estuary. In the 19th century its central part was embanked as a polder. In the mid 1980’s the area was raised above intertidal level when it was used as a dumping site for the excavated soil from the Liefkenshoek tunnel. In 2002 the area was restored, it was levelled with a weak slope below mean high water level, creating the optimal starting conditions for the development of intertidal mudflats and marshes. Geomorphological changes, sediment characteristics and colonisation by phytobenthos, vegetation, zoobenthos, water birds and breeding birds at the restored site are monitored. The monitoring results of the first year after tidal restoration are presented. Sedimentation as well as erosion between 0 and 30cm was observed in the first year. Local changes in stream current patterns caused erosion on parts of the former mudflats; sheltered depressions filled up relatively fast. Median grain size showed large variation. Organic carbon content of the sediment varied between 0.5 and 15% and was closely related to sediment medium grain size. Chlorophyll a concentrations were negatively correlated with median grain size and tended to increase from the low water line to the shore. They were comparable to nearby intertidal areas and displayed similar seasonal variability with a maximum in spring. The large surface covered wtithVaucheria was indicator of initiated succession towards tidal marsh. Scirpus maritimus and transitional vegetations to Chenopodiaceae-vegetations established with increasing altitude. The Chenopodiaceae-vegetations were relicts of earlier vegetations before the tidal restoration, and will probably disappear. The macrobenthos community was dominated by Oligochaetes, which were present in 73% of all samples and attained an average density of about 40*103 ind. m-2. Other macrobenthos species found were nematods, copepods and Corophium. On the sheltered sampling stations macrobenthic densities were high compared to those on nearby intertidal areas. In the first season, 15 breeding bird species were recorded, the most common species being the Pied Avocet (Recurvirostra avosetta). The most common waterbirds were Common Shelduck (Tadorna tadorna), Greylag Goose (Anser anser), Pied Avocet (Recurvirostra avoset) and Lapwing (Vanellus vanellus), typical species for the mesohaline part of the estuary. The first year’s results suggest that Ketenisse polder has the potential to develop towards a varied and normal functional intertidal area