Epi- and hyperbenthic communities of Belgian sandy beaches: summary

This is the first study on the epi- and hyperbenthic fauna of the surf zone of sandy beaches of the Belgian coast. Therefore, as a first objective of this thesis, a lot of attention has been paid to the inventarisation (species composition), and to the investigation of the temporal and spatial distribution patterns of both communities. A temporal and a spatial campaign were performed during which the hyper- and epibenthos was sampled. During the temporal campaign monthly samples were taken at 4 selected stations and the spatial campaign involved sampling of 12 stations along the Belgian coast. All in all, the surf zone of the Belgian coast is a habitat for a considerable number of species. The surf zone harbours a rich hyperbenthic fauna and also the epibenthic assemblage is diverse. Total hyper- and epibenthic densities were comparable or even higher than those of the adjacent, subtidal regions. It seems that the Belgian surf zone can be seen as an extension of the rich shallow sand bank system in front of the coast. Differences in total hyperbenthic densities with other European sandy beaches might be linked to the degree of exposure.An attempt was made to elucidate the major environmental variables structuring the communities. Therefore several environmental variables were measured at the moments of sampling. Different uni- and multivariate statistical techniques were used for the analyses of the data. Although clear temperature-related seasonal distribution patterns were observed, the hyper- and epibenthic communities of the surf zone can also be influenced severely by hydrodynamic factors and this both by short-term events (e.g. storm) and long-term effects (influence on morphodynamics of the beach). Spatial differences were found both in species richness and in density. In general, highest hyper- and epibenthic densities were found on flat, wide beaches, but also intermediate sites and sites with a high turbidity were characterised with high densities and a high number of species. Although clear distribution patterns could be observed, the much lower densities of the epibenthos compared to the hyperbenthos, might require a higher sampling effort with replicate sampling in future research. Furthermore, this study indicates that both intertidal and subtidal characteristics should be considered if the (mobile) surf zone fauna is investigated.Stomach/gut content analyses were performed on five common flatfish fish species from epibenthic samples taken during the temporal campaign in order to unravel part of the surf zone food web. Additional fish were obtained from commercial fishermen. Prey items of all species included hyperbenthic (e.g. mysids), endobenthic (e.g. polychaetes) and epibenthic (e.g. shrimps) species. Little dietary overlap was observed. If diet overlap did occur, it mainly involved prey species that are dominant in the surf zone of the studied beaches, such as shrimps and mysids. These results confirm the opportunistic utilisation by flatfish of the available food resources in surf zone ecosystems. Such opportunistic utilisation of food resources can be important for teleosts frequenting physically stressed environments such as surf-exposed beaches. The diets of turbot Scophthalmus maximus and brill Scophthalmus rhombus reveal part of the main interactions between the hyper- and epibenthos, whereas those of plaice Pleuronectes platessa, dab Limanda limanda and sole Solea solea reveal important links between the epibenthos and the macro-endobenthos within the local surf zone food web.Three 24-hours sampling cycles were performed to study short term migration patterns. Again the hyper- and epibenthos was sampled alternatingly each hour. Stomach content analyses were performed on juvenile plaice Pleuronectes platessa of the first 24h-cycle (spring tide). Possible interactions between the epi- and hyperbenthic organisms are discussed. Despite the turbulent conditions of the studied sites, clear tidal (e.g. I-group plaice Pleuronectes platessa, the brown shrimp Crangon crangon) and diurnal (e.g. juvenile sole Solea solea) periodicities were observed in many macrocrustacean and demersal fish species. An opportunistic utilisation of available food resources is again suggested as I-group plaice clearly migrate high up the beach during flood to disperse in order to profit from the rich macrobenthic area (mainly the polychaete Scolelepis squamata and ends of Arenicola species), while the 0-group feeds mainly on the most abundant hyper- and macrobenthic organisms from somewhat deeper water (mainly palps of the polychaete Magelona papillicornis and cyprid larvae).Finally, it can be concluded that the Belgian surf zone functions as a nursery and/or transient area for hyper- as well as epibenthic stages of several species

The Scheldt Informationcenter: an information platform for the estuary of the River Scheldt

The Scheldt InformationCenter acts as an information platform for the estuary of the River Scheldt. This center is active in both Flanders and The Netherlands. Its area of interest concerns the tide-related part of the River Scheldt, information about the estuary area at the disposal of everybody interested in thesubject.Additionally, the institute acts as a contact point. The Scheldt InformationCenter contributes also in popularising less accessible reports and publications and has therefore an interface function between the public authorities, the scientific community and the public at large. Coordinating Scheldt-related projects is another task of the institute. In all activities, the different functions of the estuary, safety, policy and management are central issues.By informing everybody about the River Scheldt, the institute hopes to enlarge the involvement and public awareness of this estuary, a river so important for Sealand (NL) as well as Flanders (B)

Het Schelde Informatiecentrum: een informatieplatform voor het Schelde-estuarium = The Scheldt Information Center: an information platform for the estuary of the River Scheldt

The Scheldt InformationCenter acts as an information platform for the estuary of the River Scheldt. This center is active in The Netherlands and in Flanders. Its area of interest concerns the tide-related part of the River Scheldt, i.e. from Ghent (B) to the mouth in Vlissingen (NL). The main task of the Scheldt InformationCenter is putting information about the estuary area at the disposal of everybody interested in the subject. Additionally, the institute acts as a contact point. The Scheldt InformationCenter coordinates (with or without cooperation of other institutes) Scheldt-related projects. In all activities, the different functions of the estuary, safety, policy and management are central issues. By informing everybody about the River Scheldt, the institute hopes to enlarge the involvement and public awareness of this estuary, a river so important for the delta-area in the South-West of The Netherlands as well as for Flanders, Belgium

Factors influencing fish and macrocrustacean communities in the surf zone of sandy beaches in Belgium: temporal variation

Monthly samples were taken in the surf zone of sandy beaches along the Belgian coast from May 1996 until July 1997 at four selected stations. Temporal patterns of the macrocrustacean and fish species residing the surf zone were investigated, as well as the abiotic variables structuring the community. In total 34 species were recorded belonging to caridean shrimps (3), anomuran and brachyuran crabs (5), cephalopods (2) and fish (24). The brown shrimp Crangon crangon dominated almost all samples (>80%). Total densities often exceeded 400 ind per 100 m², and if C. crangon was excluded 10 ind per 100 m². Notwithstanding the harsh hydrodynamic conditions, the surf zone of Belgian sandy beaches is used intensively by a number of epibenthic macro-crustaceans and demersal fish species. Seven resident and ten migrant species were identified. As mainly juvenile fishes were present, the surf zone of the Belgian sandy beaches may act as a nursery for longer (e.g. plaice Pleuronectes platessa) or shorter (e.g. brill Scophthalmus rhombus) periods. However, its nursery function should be studied in more detail, since the highly dynamic circumstances and more specifically wave height and wind speed may be important structuring factors for the epibenthic communities. The surf zone of Belgian sandy beaches also seems to function as a transient area to other nurseries (e.g. bass Dicentrarchus labrax) or between a nursery and the true marine environment (e.g. dab Limanda limanda). Temporal variation in community structure was greatly masked by spatial differences between sites. Although variables such as salinity and hydrodynamic factors may have influenced the data, clear temperature-related, seasonal patterns occur. Most likely, extreme winter conditions and subsequent migration of organisms to deeper waters caused a decline in winter in both density and diversity

Epi- en hyperbenthische gemeenschappen van Belgische zandstranden = Epi- and hyperbenthic communities of Belgian sandy beaches

This is the first study on the epi- and hyperbenthic fauna of the surf zone of sandy beaches of the Belgian coast. Therefore, as a first objective of this thesis, a lot of attention has been paid to the inventarisation (species composition), and to the investigation of the temporal and spatial distribution patterns of both communities. A temporal and a spatial campaign were performed during which the hyper- and epibenthos was sampled. During the temporal campaign monthly samples were taken at 4 selected stations and the spatial campaign involved sampling of 12 stations along the Belgian coast. All in all, the surf zone of the Belgian coast is a habitat for a considerable number of species. The surf zone harbours a rich hyperbenthic fauna and also the epibenthic assemblage is diverse. Total hyper- and epibenthic densities were comparable or even higher than those of the adjacent, subtidal regions. It seems that the Belgian surf zone can be seen as an extension of the rich shallow sand bank system in front of the coast. Differences in total hyperbenthic densities with other European sandy beaches might be linked to the degree of exposure. An attempt was made to elucidate the major environmental variables structuring the communities. Therefore several environmental variables were measured at the moments of sampling. Different uni- and multivariate statistical techniques were used for the analyses of the data. Although clear temperature-related seasonal distribution patterns were observed, the hyper- and epibenthic communities of the surf zone can also be influenced severely by hydrodynamic factors and this both by short-term events (e.g. storm) and long-term effects (influence on morpho- dynamics of the beach). Spatial differences were found both in species richness and in density. In general, highest hyper- and epibenthic densities were found on flat, wide beaches, but also intermediate sites and sites with a high turbidity were characterised with high densities and a high number of species. Although clear distribution patterns could be observed, the much lower densities of the epibenthos compared to the hyperbenthos, might require a higher sampling effort with replicate sampling in future research. Furthermore, this study indicates that both intertidal and subtidal characteristics should be considered if the (mobile) surf zone fauna is investigated. Stomach/gut content analyses were performed on five common flatfish fish species from epibenthic samples taken during the temporal campaign in order to unravel part of the surf zone food web. Additional fish were obtained from commercial fishermen. Prey items of all species included hyperbenthic (e.g. mysids), endobenthic (e.g. polychaetes) and epibenthic (e.g. shrimps) species. Little dietary overlap was observed. If diet overlap did occur, it mainly involved prey species that are dominant in the surf zone of the studied beaches, such as shrimps and mysids. These results confirm the opportunistic utilisation by flatfish of the available food resources in surf zone ecosystems. Such opportunistic utilisation of food resources can be important for teleosts frequenting physically stressed environments such as surf-exposed beaches. The diets of turbot Scophthalmus maximus and brill Scophthalmus rhombus reveal part of the main interactions between the hyper- and epibenthos, whereas those of plaice Pleuronectes platessa, dab Limanda limanda and sole Solea solea reveal important links between the epibenthos and the macro-endobenthos within the local surf zone food web. Three 24-hours sampling cycles were performed to study short term migration patterns. Again the hyper- and epibenthos was sampled alternatingly each hour. Stomach content analyses were performed on juvenile plaice Pleuronectes platessa of the first 24h-cycle (spring tide).Possible interactions between the epi- and hyperbenthic organisms are discussed. Despite the turbulent conditi

Tidal and diurnal periodicity in macrocrustaceans and demersal fish of an exposed sandy beach, with special emphasis on juvenile plaice <i>Pleuronectes platessa</i>

Macrocrustaceans and juvenile demersal fish were sampled in spring of 1997 in the surf zone of an exposed sandy beach on the Belgian coast. Three consecutive 24 h cycles were sampled to investigate tidal, diurnal and semi-lunar distribution patterns within the epibenthic community. Multivariate statistical techniques and 3-way ANOVA were used to evaluate the effects of the environmental variables measured. The most important variable correlated with the variation in epibenthic catch density was the state of the tide (ebb and flood), but light intensity (day and night) was also important. The individual catch density of several species differed significantly over the three 24 h cycles. Despite the strong turbulent conditions of the site studied, clear tidal (e.g. the brown shrimp Crangon crangon, juvenile plaice Pleuronectes platessa) and diurnal (e.g. juvenile sole Solea solea and clupeids, caught mainly during the night/day respectively) periodicities of many macrocrustacean and demersal fish species were observed. Nevertheless, the extremely turbulent conditions of the surf zone possibly affect the behaviour of many species (e.g. juvenile brown shrimp are not able to bury themselves as the water retreats). To investigate whether the high dynamics of the surf zone suppress the ability of juvenile plaice to actively search for food, stomach contents were analysed. Also, the interaction with potential prey was investigated: the hyperbenthic fauna was sampled simultaneously and macrobenthic data were available from the literature. Clearly, the Belgian sandy beaches are used as a feeding ground by I-group plaice. An opportunistic utilisation of available food resources is suggested. I-group plaice migrate high up the beach during the flood tide to profit from the rich macrobenthic intertidal area, while the 0-group feeds mainly on the most abundant hyperand macrobenthic organisms from somewhat deeper water. The presence of the 0-group in the intertidal area is possibly linked to refuge for predators or influenced by the strong surf zone currents

Surf zone hyperbenthos of Belgian sandy beaches: seasonal patterns

Since surf zone hyperbenthos, although highly important in local food webs, has often been neglected and very little information is available, a survey of the Belgian sandy beaches was carried out from May 1996 until July 1997. Monthly samples were taken to give a complete record of hyperbenthic organisms occurring in the surf zone of Belgian sandy beaches and to evaluate the intensity by which this surf zone is used. In total 172 species were recorded. The number of species occurring in the surf zone is comparable to that of adjacent areas. As weIl as true hyperbenthic species, endobenthic and planktonic organisms were sampled. More than 75% of the average total sample composition consisted of mysids, mainly Mesopodopsis slabberi, Schistomysis spiritus and Schistomysis kervillei (holohyperbenthos). Apart from several resident species, active and passive seasonal migration towards the surf zone by a number of species is suggested. A large number of sporadic species adds to the composition of surf zone hyperbenthos. Within the merohyperbenthos, postlarval decapods and fish were the dominant organisms. During the year three recruitment peaks were observed. Average densities per month exceeded 1500 ind. 100 m-2. Yearly biomass averages ranged from 300 to over 3000 mg ADW 100 m-2. Densities of the common species are slightly higher in the surf zone than in other habitats, emphasising the importance of the area. Besides a possible nursery function, the surf zone may also be used as a transient area between different habitats. Finally, the influence of several abiotic factors on the hyperbenthic assemblages was evaluated. The main structuring variables determining the occurrence of most of the organisms are water temperature and hydrodynamic factors such as wave height and turbidity. The influence of wave height seems to be two-fold: several good swimmers such as mysids and some fish species are suggested to be able to actively avoid severe wave conditions, whereas other, more planktonic organisms, are passively transported towards the area if wave height increases