The response of a harpacticoid copepod community to sediment disturbance in a semi-enclosed lagoon

The harpacticoid fauna of a sandy sediment in the Sluice Dock of Ostend, Belgium, was dominated by a single species, Canuella perplexa, that attained an average annual density of over 400 ind. 10 cm^–2 in 1976 and 1977, whereas other species had a total mean density of less than 10 ind. 10 cm^–2. In the summer of 1979 a dystrophic crisis with abundant growth of Ulva occurred and in March 1980 the lagoon was drained. After refilling of the lagoon, the sediment was immediately colonized by good swimming harpacticoids, that attained densities of 200 ind. 10 cm^–2. Three months after refilling Canuella perplexa reappeared and the system returned to its original state within one month.     

Community structure and functional roles of meiofauna in the North Sea

Knowiedge on community structure of North Sea meiofauna has greatly increased recently. A quasisynoptic picture of meiofauna densities and copepod community structure from 171 stations of the southern North Sea, sampled in April–May 1986, has been obtained during the North Sea Benthos Survey. Latitudinal patterns in meiofauna abundance and copepod weight, abundance and diversity exist in an area between 51°30′N and 58°30′N. Using TWINSPAN-classification five major groups of copepod species can be recognized which are related to sediment type, latitude and depth. The part of the meiofauna in total benthic energy flow, their role in the benthic food web and in biogeochemical cycles is discussed based on existing literature. There are still considerable gaps in knowledge and the field is not progressing rapidly. Publication no. 599 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

Benthic communities in the Southern Bight of the North Sea and their use in ecological monitoring

Macrobenthic and meiobenthic communities of an area off the Belgian coast of the North Sea were studied from 1970 until 1975 at 74 stations. On the basis of both macro- and meiobenthos, three zones can be distinguished in the area. The coastal zone is characterized by the macrobenthicAbra alba community, corresponding to the meiobenthicMicroarthridion littorale — Halectinosoma herdmani community, and the open sea zone by the macrobenthicVenus gallina community and the meiobenthicLeptastacus laticaudatus — Paramesochra helgolandica community. In between is a transient zone where elements of both other zones mix. The distribution of these zones is governed by the hydrodynamical regime of the region, especially by the residual and tidal current system of the Southern Bight. Within the coastal zone, the composition of the community is influenced by pollution which especially affects the epibenthic detritus-feeders of the meiobenthos. The spatial stability of parameters describing community structure can be used for monitoring changes. Temporal characteristics of these parameters could not be investigated properly, but diversity seems to be much stabler than biomass.     

The influence of Corophium volutator abundance on resuspension

Two experiments were performed to test the hypothesis that Corophium volutator affects the turbidity of water in estuaries through active resuspension of sediment. One experiment was done in a flume system under different flow velocities, and one in aquaria. A diatom film developed at the sediment surface in both experiments before Corophium was added. This diatom film was supposed to have a stabilising effect on the sediment. In both experiments, the concentration of suspended solids in the water column increased with the density of Corophium individuals. No effect of flow velocity on suspended solids concentration was found. This indicates that, in our flume experiment, active resuspension by Corophium was more important than physical resuspension, at least at low flow velocity (<20 cm s^-1) and in the presence of a diatom film. The critical erosion threshold decreased with increasing Corophium density in the aquarium experiment, indicating that indirect effects of Corophium grazing may become more important at high levels of bottom shear stress. The implications of our findings for suspended solids concentration in estuarine systems are discussed.     

Growth and respiration of Cyprideis torosa Jones 1850 (Crustacea Ostracoda)

Summary The ostracod Cyprideis torosa Jones 1850 is a dominant species in brackish water habitats. To assess its importance, growth and respiration were measured. The shells form an increasing part of total weight as the animals grow but there is no correlation between shell weight and soft parts weight in the adults, indicating that tissue growth is a continuous process in these ostracods.Respiration was measured at 20° C. The slope of the log-log regression of respiration on dry weight was 0.746, showing that Cyprideis torosa follows the general rule for this relationship. The respiration rate per unit biomass was 0.246 nl O₂ g^-1 h^-1, which is low but well within the range of observed meiobenthic respiration rates.The Q₁₀, expressing the temperature dependence of respiration, was 2.15. The general validity of Price and Warwick's (1980) hypothesis relating Q₁₀ to stability of food supply is questioned.     

The predictability of biological populations and communities: an example from the meiobenthos

The predictability of temporal changes was analysed in the population density of three meiobenthic copepod species, and for three parameters characterizing this community. For Paronychocamptus nanus and Tachidius discipes a large part of the variation in time scales longer than 1 year is explainable as cyclic factors. In P. nanus clear cyles with periods of 2 years and 1.5 years were found. These cyclic factors can be extrapolated for prediction. In Canuella perplexa almost all the variation was due to unpredictable long-term drift. Community parameters are generally better predicted than population densities. In our data set total density of the copepods was the best parameter to monitor. Monitoring does not necessitate a strict sampling scheme; irregular quarterly sampling from the P. nanus series showed that the essential features of the series were still discernible.     

Biophysical characterization of Artemia salina (L.) extracellular haemoglobins.

Sedimentation coefficients (s0 20,w) of 11.57 +/- 0.10 S and 11.52 +/- 0.09 S were assigned for Artemia salina (L.) extracellular haemoglobins II and III respectively. These values are not significantly different. The molecular weights, M0w and M0z, of the native haemoglobins as determined by the high-speed sedimentation-equilibrium method were for haemoglobin II 239 400 +/- 7200 and 240 400 +/- 2600 respectively, and for haemoglobin III 216 300 +/- 6500 and 219 300 +/- 4500 respectively. The observed increase of Mapp. with concentration suggested that association was occurring over the concentration range investigated. Exposure of haemoglobin II to either 6 M-guanidinium chloride or to low pH (pH 4) resulted in dissociation to units of approximately half the size of the native protein, with molecular weights approx. 115 000. Electron-microscopic observations indicated a molecular structure composed of two stacked lobed discs. These results strongly support the dimeric model for Artemia haemoglobins proposed by Moens & Kondo [(1978) Eur. J. Biochem. 82, 65-72].