Sandra Brucet

Patterns of composition and species richness of crustaceans and aquatic insects along environmental gradients in Mediterranean water bodies

Differences in the dynamics of ecological processes between Mediterranean and colder temperate aquatic systems could imply different patterns in faunal communities in terms of composition and biodiversity (i.e. species richness and rarity). In order to identify some of these patterns the crustacean and aquatic insect composition and biodiversity of four water body types, classified according to their salinity and water permanence, were compared. Moreover, the relationships between species richness and water, pond and landscape variables were analysed. A total number of 91 water bodies located throughout Catalunya (NE Iberian Peninsula) were sampled. Three species assemblages were observed: one for permanent freshwaters, another for temporary freshwaters, and a third one for saline waters (SW), since permanent and temporary saline water bodies had similar composition. Differences in salinity were associated with proportion of crustaceans versus insects and with singularity. Thus, saline ponds had a higher proportion of crustaceans, and lower values of singularity. Conductivity was significantly related to total (crustaceans plus insects) richness, and also related to insect richness. The main difference between the models obtained for crustacean species richness and insect species richness is the significance of landscape variables in the latter, and this fact could be related to the different dispersion types of these two faunal groups: active for insects versus passive for crustaceans.

Predation in a temporary pond with special attention to the trophic role of Triops cancriformis (Crustacea: Branchiopoda: Notostraca)

Temporary ponds are described as environments with a low predation pressure. Notostracans inhabit these types of ponds, and some populations acquire a high proportion of larger individuals, whose feeding behaviour is mainly predatory. The predation nature of Triops cancriformis is not widely accepted, because its diet is still partly controversial. We analysed the diet of one population of T. cancriformis in a Mediterranean temporary pond (Espolla pond, NE Iberian peninsula) to evaluate its predation behaviour. The gut content of the individuals bigger than 10xa0mm is mainly composed of detritus, plant fibres and microcrustaceans (cladocerans, ostracods and copepods). The prey number increases with the body size of individual T. cancriformis as previously described. Sex-biased predation was observed for one copepod prey, but not for the other. Predation pressure in that community was monitored along six hydroperiods as the percentage of predator biomass (not only T. cancriformis) in relation to the non-predator biomass. The proportion of predator biomass is high, and this contrasts with the low predation pressure expected for a temporary system with short hydroperiods.

Comparative biodiversity of crustaceans and aquatic insects from various water body types in coastal Mediterranean wetlands

Coastal wetlands are characterized by a high biodiversity. At the same time, biodiversity is one of the main criteria used to establish protection policy priorities, or to propose management actions. In this study, crustacean and aquatic insect species richness in the Emporda wetlands was investigated. These two groups contribute in an important way to the total biodiversity, and still they are seldom taken into account in the management of natural areas. Representative samples (38 points) of all aquatic water body types in the Emporda wetlands were taken monthly (dip net with 250 μm mesh). Sampling was carried out between 1996 and 2000, but until present, only qualitative data have been extracted. A rich fauna of 125 crustacean taxa and 295 aquatic insect taxa were found. Some environments were characterized by low richness and high singularity (isolated artesian freshwater springs), some by high richness and high singularity (estuarine waters, brackish and meso-eutrophic freshwater wetlands), and others by low richness and low singularity (hypertrophic freshwater wetlands and hyperhaline wetlands). Factors determining singularity and richness are discussed. Comparison with crustacean richness of other western Mediterranean wetlands showed a similar high species richness in our study sites, probably due to high spatial heterogeneity of these areas.

Impact of different developmental stages of Daphnia magna (Straus) on the plankton community under different trophic conditions

Inxa0situ 24-h incubation experiments were performed to analyse the grazing effects of Daphniaxa0magna on a planktonic microbial community. Three field grazing experiments under different nutrient concentrations were carried out on treated effluents of a wastewater treatment plant. The grazing effects of three different D.xa0magna size classes (small (0.6–1.6xa0mm), medium (1.7–2.5xa0mm) and large individuals (2.6–3.7xa0mm)) were compared. The different sizes classes had similar effects on the plankton community. However, our results showed big differences in effects among experiments. Our findings suggest that in spite of D.xa0magna’s non-selective feeding behaviour and the fact that different developmental stages (i.e.xa0its size) had similar effects on the microbial planktonic community, these effects can differ according to the initial structure and composition of the community and the resulting cascading trophic interactions. Moreover, D.xa0magna effects can be direct through grazing (as is the case with ciliates), or indirect through trophic cascade interactions (as is the case with bacteria).