Interaction between seston quantity and quality and benthic suspension feeders in the Oosterschelde, the Netherlands

134

107

Annular flumes were used to quantlfy benthic-pelaqc exchanges in relation to changes in current velocity and sediment biota. Various physical, chemical and biological parameters were determined for 4 sites on the Molenplaat tidal flat in the Westerschelde (The Netherlands) during 2 field campaigns in May-June and August-September 1996. These Pcluded: the mass of sediment eroded, maximum and mean erosion rates, critical erosion velocity (Ucfi,), suspension feeding/biodeposition rate, oxygen and ammonium fluxes, density of macrofauna species, chlorophyll a (chl a), colloidal carbohydrate, and physical properties of the sediment. The study showed marked and statistically significant spatial and temporal differences in the potential for sediment erosion. Sites in the centre of the tidal flat were less erodable than those on the edge. All sites on the tidal flat had a significantly (p < 0.001) lower erosion potential in June (i.e. higher U,,, and lower erosion rates) compared to September.The presence of a well-developed microphytobenthos community in June resulted in a statistically significant relationship between U,,, and chl a/colloidal carbohydrate (r = +0.85, p = 0.01). There was a significant relationship (r = +0.88, p = 0.005) between sediment erodab~lity (mass of sediment eroded and erosion rate) and the density of the clam Macoma balthica, a major bioturbator of the surface sedi m e n t~. Analysis of the data also demonstrated significant relationships between clearance rate and Cerastoderma edule biomass (r = +0.91, p < 0.001), and between sedment chl a/colloidal carbohydrate and C. edule biomass (r = +0.92; p < 0.001), reflecting the influence of suspension feeders on both the water column and the sediment, through their biodeposits. The significant increase in sediment erodability between June and September reflected the shift in the overall balance between the major 'biostabilisers' (microphytobenthos) and 'bio-destabilisers' (bioturbating bivalves). T h s interpretation of field-derived correlations is consistent with previously established relationships and mechanistic understanding derived from controlled flume experiments.

“…1.64 g m-' h-' for 78 ind. m-2 in the Oosterschelde at 20 mg SPM I-': Smaal et al 1986, and 6 g m-2 h-' for 50 ind. m-2 in the Humber at 52 mg SPM I-': Widdows et al 1 9 9 8~) .…”

Section: Biodeposition and Sediment Propertiesmentioning

confidence: 99%

Influence of biota on spatial and temporal variation in sediment erodability and material flux on a tidal flat (Westerschelde, The Netherlands)

Widdows¹,

Brinsley²,

Salkeld³

et al. 2000

134

107

“…Although biomass and production values have been reported for mussel populations from several coastal regions (Milne & Dunnet 1972, Dare 1976, Bayne & Worall 1980, Kautsky 1981, Briggs 1982, Rodhouse et al 1985, Craeymeersch et al 1986, Smaal et al 1986), up to now no attempt has been made to calculate the secondary production of a total mussel bed community. Such an investigation is necessary in order to estimate the amount of energy made available by community members to higher trophic levels.…”

Section: Introductionmentioning

confidence: 99%

Secondary production of an intertidal mussel bed community related to its storage and turnover compartments

Asmus¹

1987

121

Macrofaunal b~o n~a s s and production were studied at 6 sites on an intertidal mussel bed in the northern Wadden Sea near the island of Sylt (North Sea) in 1984 Mean biornass of the community w a s about 25 times h~g h e r (1243 g AFDW m-') than in other commumties of the Wadden Sea Of t h s biomass, 97 % was represented by the mussel M y t~l u s e d u l~s L Although associated fauna had a share of only 3 %, their absolute biomass of 35 g AFDW m-' is in the range reported for other intertidal communities of the Wadden Sea Annual producbon of the rnacrofaunal community (468 g AFDW m-2 yr-') was dominated by n~ussels (436 g AFDW m-2 yr-') P/B-rabo was very low for the total community (0 36) Annual production of associated macrofauna was much lower (31 g AFDW m-'yr-') but the P/Bratio (0 89) indicates a higher turnover rate Suspension feeders had the greatest share in secondary production followed by grazers Predators and detr~tus feeders were of lesser importance Biomass and production of individuals of higher mass dominated overwhelmingly over smaller size groups The main productive potential of the communlty is formed by the larger size classes These are of only minimal importance for predation Therefore the communlty can be divided into 2 functional compartn~ents (1) a storage compartment with a high productive potenbal leading to further increase in biomass or being spent for metabolic and reproductive requirements and (2) a turnover compartment with relatively low biomass and production but higher turnover The production of the turnover compartment is available to most predators

“…The bottom-cultivation of mussels creates very high densities of suspension-feeding bivalves that are capable of filtering large volumes of water (Smaal et al 1986). They increase the sedimentation of particulate material (Prins & Smaal 1994, Smaal 1994, which becomes bound with their pseudofaeces and entrapped within the mussel matrix.…”

Section: Introductionmentioning

confidence: 99%

Effects of intertidal mussel cultivation on bird assemblages

Caldow¹,

Beadman²,

McGrorty³

et al. 2003

Mussel Mytilus edulis cultivation on intertidal flats affects the invertebrate community, often adversely, and this may have detrimental consequences for shorebirds. Here we present the results of an experimental study to quantify the effects of intertidal mussel cultivation on shorebirds. A study area of 4.32 ha, comprising experimental plots and control plots, was laid out in summer 1999 on the mudflats of the Menai Strait in Wales. Regular counts throughout winter of 1999/2000 established pre-cultivation patterns of bird usage. Mussels were laid in the experimental plots in April 2000 and bird usage in these plots and the controls was monitored over the 2 subsequent winters. Although no species were lost from the experimental plots, the bird assemblage in them changed. This reflected variation in the distribution of the 5 most abundant species. However, none of these key species declined in abundance following the laying of mussels. Curlew Numenius arquata and redshank Tringa totanus increased in abundance, although, unexpectedly, oystercatchers Haematopus ostralegus did not. At this study site, commercial mussel cultivation may have beneficial effects, not just for the birds that eat mussels, but also for other species that can take advantage of the associated changes to the benthic fauna and habitat complexity. However, features of conservation interest at other localities may mean that bottom cultivation of mussels will have detrimental rather than beneficial effects. The environmental effects of proposals to initiate or expand bottom cultivation of mussels need to be assessed on a case-by-case basis.