N.M.J.A. Dankers

Scale-Dependent Feedback and Regular Spatial Patterns in Young Mussel Beds

In the past decade, theoretical ecologists have emphasized that local interactions between predators and prey may invoke emergent spatial patterning at larger spatial scales. However, empirical evidence for the occurrence of emergent spatial patterning is scarce, which questions the relevance of the proposed mechanisms to ecological theory. We report on regular spatial patterns in young mussel beds on soft sediments in the Wadden Sea. We propose that scale‐dependent feedback, resulting from short‐range facilitation by mutual protection from waves and currents and long‐range competition for algae, induces spatial self‐organization, thereby providing a possible explanation for the observed patterning. The emergent self‐organization affects the functioning of mussel bed ecosystems by enhancing productivity and resilience against disturbance. Moreover, self‐organization allows mussels to persist at algal concentrations that would not permit survival of mussels in a homogeneous bed. Our results emphasize the importance of self‐organization in affecting the emergent properties of natural systems at larger spatial scales.

The influence of mussel beds on nutrients in the western Wadden Sea and eastern Scheldt estuaries

The uptake and release of materials by intertidal mussel beds were directly measured in two cultivated Dutch estuaries. Generally, chlorophylla, seston, and particulate organic carbon were taken up, while ammonium, orthophosphate, and silicate were released. The observed rates were higher than values computed from organismic observations and similar to those observed for intertidal oyster reefs in South Carolina. Specific estuarine material turnover rates varied from 1 week to 38 weeks when calculated with mussel bed fluxes. The fastest turnover rates were for chlorophylla and ammonium. These results support the idea that dense assemblages of bivalves are major components in the recycling of nutrients in estuaries.

Uptake and release of materials by a Wadden sea mussel bed

Abstract A flow-through plastic tunnel was used to determine the uptake and release of materials in the tidal waters passing over a mussel bed in the western Wadden Sea. There was significant uptake of total suspended sediments (4.4–7.2g · m−2 · h−1), Chl a (15.4–55.1 mg· m−2 · h−1), total organic C (0.8–1.1 g C· m−2· h−1) and nitrite + nitrate (0.02–0.08g N· m−2· h−1). There was a significant release of ammonium (0.04–0.11 g N· m−2· h−1) and o-phosphate (0.05–0.08 gP· m−2· h−1). The intertidal mussel bed removed particulate materials at high rates from the water column, transformed some of this material into biomass and released some constituents as dissolved waste products. This study supports the idea that mussel beds function as systems not just as populations of mussels which process estuarine materials. Even though the directions of material uptake and release on the mussel bed are similar to oyster reef systems, the magnitudes of material transports are generally higher on the mussel bed due to greater filter-feeder biomass, the existence of a substantial microbenthic algal component and a considerably different environmental setting.

The role of the mussel (Mytilus edulis L.) and mussel culture in the Dutch Wadden Sea

Mussel populations (Mytilus edulis) in the Dutch Wadden Sea (intertidal mussel beds, subtidal beds and culture plots), the culture methods, the extent of mussel culture, and the ecology of the mussel are described. Mussels filter suspended matter from the water column and deposit it as feces and pseudofeces. Mussel beds consume large amounts of phytoplankton and speed up the cycle of production and breakdown of organic matter. There are indications that the consumption of phytoplankton can lead to food shortage for several animal groups. Mussels serve as an important food source for a wide range of organisms (e.g., starfish, eider ducks, and oystercatchers). Because mussel culture increased the mussel biomass in the Dutch Wadden Sea, the impact also increased. The most obvious impact of the culture is the dredging of seed mussels. Overexploitation of intertidal mussel and cockle beds and bad spatfall of both mussels and cockles since 1988 had a negative impact on bird populations. The extent of positive and negative aspects of mussel culture depends on natural and human influences. The negative aspects may (partly) be overcome by appropriate measures. *** DIRECT SUPPORT *** A01BY069 00007

An analysis of mussel bed habitats in the Dutch Wadden Sea

Abstract. A habitat suitability analysis for littoral mussel beds in the Dutch Wadden Sea was carried out. The analysis was based on the presence of mussel beds in the years 1960–1970, and a number of environmental characteristics: wave action, flow velocity, median grain size, emersion times and distance to a gully border. The habitat model describes mussel bed appearance quantitatively. It predicts the distribution of mussel beds quite well, as well as the distribution of spatfall in the years 1994 and 1996. From the analysis we found that wave action (maximum orbital velocity) was the main structuring factor. A low orbital velocity was preferred. Neither very low, nor maximum flow velocities were favourable for mussel beds. Very coarse sands or silty environments were not preferred. Sites close to the low water line showed lower mussel bed appearance; when emersion time was above 50% , hardly any mussel beds could be found. The habitat suitability analysis and the construction of a habitat suitability map was performed in the framework of the discussions on a further or reduced exploitation of the tidal flats in the Dutch Wadden Sea by cockle and mussel fishery activities.

Seasonal variation in the filtration rates of a semi-natural mussel bed in relation to seston composition 1☆

Abstract In September 1988 a mussel bed, with a biomass of 1362 g ash-free dry weight· m−2, was created in a concrete tank with a continuous supply of natural seawater. Measurements of particulate matter uptake by the mussel bed were carried out monthly from December 1988 till December 1989. Fluxes of suspended particulate matter, particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphorus (POP) and chlorophyll-a, were significantly correlated with water column concentrations. A control experiment showed that sedimentation did not affect observed fluxes. Clearance rates of the mussel bed varied between 0.4 and 2.7 m3·m−2·h−1. Seasonal variation in the filtration activity of the mussel bed could be attributed to changes in the composition of the suspended particulate matter: individual clearance rates of the mussels were reduced in the period April–June, which coincided with a bloom of Phaeocystis sp. Moreover, clearance rates decreased with increasing SPM concentrations and showed a positive correlation with chlorophyll-a.

Large-Scale Spatial Dynamics of Intertidal Mussel (Mytilus edulis L.) Bed Coverage in the German and Dutch Wadden Sea

Intertidal blue mussel beds are important for the functioning and community composition of coastal ecosystems. Modeling spatial dynamics of intertidal mussel beds is complicated because suitable habitat is spatially heterogeneously distributed and recruitment and loss are hard to predict. To get insight into the main determinants of dispersion, growth and loss of intertidal mussel beds, we analyzed spatial distributions and growth patterns in the German and Dutch Wadden Sea. We considered yearly distributions of adult intertidal mussel beds from 36 connected tidal basins between 1999 and 2010 and for the period 1968–1976. We found that in both periods the highest coverage of tidal flats by mussel beds occurs in the sheltered basins in the southern Wadden Sea. We used a stochastic growth model to investigate the effects of density dependence, winter temperature and storminess on changes in mussel bed coverage between 1999 and 2010. In contrast to expectation, we found no evidence that cold winters consistently induced events of synchronous population growth, nor did we find strong evidence for increased removal of adult mussel beds after stormy winter seasons. However, we did find synchronic growth within groups of proximate tidal basins and that synchrony between distant groups is mainly low or negative. Because the boundaries between synchronic groups are located near river mouths and in areas lacking suitable mussel bed habitat, we suggest that the metapopulation is under the control of larval dispersal conditions. Our study demonstrates the importance of moving from simple habitat suitability models to models that incorporate metapopulation processes to understand spatial dynamics of mussel beds. The spatio-dynamic structure revealed in this paper will be instrumental for that purpose.

Seston dynamics and bivalve feeding in the Bay of Marennes-Oléron (France)

Within the framework of an investigation into the carrying capacity of the Bay of Marennes-Oléron (France) for bivalve culture, thein situ uptake of suspended particulate material by oysters (Crassostrea gigas) and mussels (Mytilus edulis) was determined in experiments with benthic ecosystem tunnels. Very high fluctuations in seston quantity and quality were observed within and between tidal cycles. The percentage of organic carbon was inversely related to seston quantity at low concentrations. Organic carbon was diluted by resuspension of material rich in inorganic matter. At high seston concentrations a constant level of about 2% organic carbon was found. The C/N ratio was relatively constant throughout the seasons and fairly low (6.5 to 8.4). Owing to the presence of bivalves large fluxes of suspended particulate material were observed in thein situ measurements. Selective retention of organic carbon or nitrogen could not be demonstrated. Clearance rates based on chlorophyll uptake were within a normal range compared to other studies. A large contribution to the food of the bivalves seemed to be formed by resuspended microphytobenthos. Judged by the low C/N ratio, the food was of good quality. Although its quantity was variable by dilution, it may support largely the carrying capacity of the Bay of Marennes-Oléron for the cultivation of bivalves.

The Wadden Sea in the Netherlands: Ecotopes in a World Heritage Barrier Island System

Publisher Summary The Wadden Sea forms the coastal strip bordering the North Sea in NW Europe. Along most of its length it is separated from the North Sea by a string of barrier islands. The system consists of many recognizable geomorphic units (here called ecotopes), such as islands, high sandbanks, sand dunes, salt marshes, subtidal and intertidal sand and mudflats, and channels of different depths and widths. The Wadden Sea intertidal flats are characterized by their location within tidal basins behind barrier islands. They contain a sequence of large to small ebb and flood gullies. The flats near the inlet are predominantly sandy and those near the coast are muddy. The Wadden Sea is a mesotidal barrier island system that only has minor river influences, fringing the flat and low-lying NW European coastal plain. In contrast to most mudflat systems in the world, the Wadden Sea area has not been formed as a river delta, nor is part of an estuary or bay, although there are some estuaries and bays within the Wadden Sea itself. The Wadden Sea consists of a number of very different habitats, ranging from islands to intertidal flats, salt marshes, and gullies and channels. Depending on the mapping scale, these can be further subdivided into smaller recognizable units. For management purposes, it is essential that the proper scale is adhered to when discussing specific issues. For mapping, it is important that elements can be distinguished based on discernable characteristics. When a single organism uses different habitats for different purposes, simple correlations between habitats and the occurrence of species are confounded.

11 – The Wadden Sea in the Netherlands: Ecotopes in a World Heritage Barrier Island System

Publisher Summary The Wadden Sea forms the coastal strip bordering the North Sea in NW Europe. Along most of its length it is separated from the North Sea by a string of barrier islands. The system consists of many recognizable geomorphic units (here called ecotopes), such as islands, high sandbanks, sand dunes, salt marshes, subtidal and intertidal sand and mudflats, and channels of different depths and widths. The Wadden Sea intertidal flats are characterized by their location within tidal basins behind barrier islands. They contain a sequence of large to small ebb and flood gullies. The flats near the inlet are predominantly sandy and those near the coast are muddy. The Wadden Sea is a mesotidal barrier island system that only has minor river influences, fringing the flat and low-lying NW European coastal plain. In contrast to most mudflat systems in the world, the Wadden Sea area has not been formed as a river delta, nor is part of an estuary or bay, although there are some estuaries and bays within the Wadden Sea itself. The Wadden Sea consists of a number of very different habitats, ranging from islands to intertidal flats, salt marshes, and gullies and channels. Depending on the mapping scale, these can be further subdivided into smaller recognizable units. For management purposes, it is essential that the proper scale is adhered to when discussing specific issues. For mapping, it is important that elements can be distinguished based on discernable characteristics. When a single organism uses different habitats for different purposes, simple correlations between habitats and the occurrence of species are confounded.