Dynamics Of Aquatic Communities Research Articles

Effects of sewage discharges on microbial components in tropical coastal waters (Senegal, West Africa)

Coastal ecosystems are frequently submitted to anthropogenic pressure but little is known about how the dynamics of aquatic communities can be altered. The impact of urban and industrial discharges on microbial plankton was studied in Hann Bay near Dakar (Senegal) on the Atlantic Ocean. Spatial patterns were studied using three transects, with a total of 20 stations, during two periods in May and November (before and after the seasonal upwelling), revealing a clear contrast between near shore stations and the intermediate and seaward stations. In November, phytoplankton were associated with dissolved nutrient availability (e.g. with nitrate, r = 0.76) whereas in May, phytoplankton were more correlated with microbial variables (e.g. with heterotrophic nanoflagellates, r = 0.63). Most samples (40) failed to meet the quality levels for the faecal indicator bacteria (FIB) defined by the European Union bathing water quality directive. The topography plays a major role in water circulation explaining the presence of FIB at the seaward stations. The high prevalence of FIB during the two periods suggests chronic pollution and a potential risk to recreational swimmers and fish consumers in Hann Bay. Thus, as demonstrated in various temperate systems, the decline of water quality constitutes a serious problem in many West African countries.

Ammonium uptake by seagrass communities: effects of oscillatory versus unidirectional flow

Nutrient dynamics of aquatic communities are dependent on the flux of nutrients to organisms within the communities. Flux is dependent on water column concentration and hydro- dynamic factors that affect both advection of nutrients through the community and rates of diffusion at the surfaces of organisms. In this study, we measured rates of ammonium uptake for a seagrass community under various hydrodynamic conditions and determined the effects of water velocity and oscillatory flow on uptake rates. Experiments were conducted using a portable flume deployed in natural Thalassia testudinum communities. Uptake rate constants ranged from 9.9 to 25.4 × 10 -5 m s -1 and were ~1.5 times higher in oscillatory flow than in unidirectional flow. Uptake rate constants were positively dependent on both water velocity and turbulent energy in the water column. These results demonstrate the importance of hydrodynamics on biogeochemical cycling in seagrass beds and pro- vide evidence of the efficacy of merging research on hydrodynamics and biogeochemistry in under- standing nutrient processes in complex nearshore communities.

Time series of multivariate data in aquatic ecology

Coupling of multivariate methods and time series analysis can be ueful for studying dynamics of aquatic communities. This is demonstratred with a data set from the pelagic area of an oligo-mesotrophic lake in Central Spain during 61 consecutive days of Autumn overturn. Abiotic variables, phytoplankton species and their total biomass were traced. Species abundance and specific biomass were considered as indices of community structure and resource partitioning, respectively. Abiotic and algal data sets were subjected to factor analyses of cases separately. Atmospheric forcing and nitrogen could be considered as the main (2) driving variables of the abiotic matrix. The coupling of motile abilities and cell size was associated to the main factors of the community structure matrix whereas phosphorus limitation and species responses to buoyancy represented the main factors of the biomass matrix. Coordinates of the two first factors could be used to mimic the trajectories in the data space. Significant short term lags (1–4 days) were found in most time series. Lagged responses of atmospheric forcing and nitrogen on phytoplankton community structure and resource partitioning at scales of 1–7 days were also shown. Overall phytoplankton biomass did not show significant delayed responses, thereby suggesting that it might be resulting from the interplay of other non-studied factors.

Competition and allelopathy in aquatic plant communities

The paper reviews the published literature on the studies of competition and allelopathy in aquatic plant communities. Taking a broader view of the community, the studies on interactions between macrophytes and microphytes, macrophytes and macro-invertebrates and microbial communities are also reviewed. The role of these interactions in the structure and dynamics of aquatic communities has been discussed in light of the current hypotheses concerning competition in terrestrial communities. The available information suggests that the aquatic plants of various growth forms differ greatly among themselves in their responses and adaptations to competition and allelopathy. The possible application of these interactions in biological control of plant pests and in agriculture is also summarized. We conclude that the observed differences in these interactions between the terrestrial and aquatic environment are due to the effects of water as a non-resource variable as well as due to special adaptive characteristics of aquatic plants. Further we hypothesize that the aquatic plants adopt both competitive and allelopathic strategies under different conditions and in interactions with different plants. The review highlights that our knowledge of both competition and allelopathy among aquatic plant communities is inadequate and fragmentary, and therefore, both extensive and intensive studies are required.

A study of aquatic community dynamics in a karstic system by the use of artificial substrates

Mise en evidence du role de l'hydrologie dans la dynamique des peuplements d'un systeme karstique a l'aide de substrats artificiels immerges pendant un mois ou exposes pendant deux mois.Cette etude souligne le fait que la duree d'immersion est moins importante que la periode hydrologique pendant laquelle le substrat est immerge.L'utilisation de cette methode permet de souligner l'importance des processus de colonisation des differents habitats du milieu.De plus, les substrats artificiels rendent possible l'etude de l'installation des organismes epiges dans le systeme souterrain karstique