Pedro Sánchez-Castillo

Freshwater biodiversity in the rivers of the Mediterranean Basin

We review the diversity of freshwater organisms in the Mediterranean Basin (hereafter Med), particularly from streams and rivers. We present available information on the richness, endemicity, and distribution of each freshwater organism group within the Med, and make a comparison with Palearctic diversity. Approximately 35% of known Palearctic freshwater species and more than 6% of the World’s freshwater species are present in the Med. A high degree of endemicity is found in the Med freshwater biota. These data, together with the degree to which many freshwater species are threatened, support the inclusion of the Med among World biodiversity hotspots. Nevertheless, knowledge of Med biodiversity is still incomplete, particularly for some taxa. Regarding to the spatial distribution of species within the Med, the richest area is the North, although patterns differ among groups. A comparison of the ecological and biological traits of endemic and non-endemic species of three riverine groups (Ephemeroptera, Plecoptera, and Trichoptera) revealed that endemic species have several strategies and mechanisms to face typical mediterranean-climate conditions, such as drought, when compared to non-endemic species. We briefly analyse the conservation status of the region’s biodiversity. Finally, we present some future challenges regarding the knowledge and protection of Med freshwater biodiversity.

Influence of nutrients, submerged macrophytes and zooplankton grazing on phytoplankton biomass and diversity along a latitudinal gradient in Europe

In order to evaluate latitudinal differences in the relationship of phytoplankton biomass and diversity with environmental conditions in shallow lakes, we sampled 98 shallow lakes from three European regions: Denmark (DK), Belgium/The Netherlands (BNL) and southern Spain (SP). Phytoplankton biomass increased with total phosphorus (TP) concentrations and decreased with submerged macrophyte cover across the three regions. Generic richness was significantly negatively related to submerged macrophyte cover and related environmental variables. Zooplankton:phytoplankton biomass ratios were positively related to submerged macrophyte cover and negatively to phytoplankton generic richness in DK and BNL, suggesting that the low generic richness in lakes with submerged macrophytes was due to a higher zooplankton grazing pressure in these regions. In SP, phytoplankton generic richness was not influenced by zooplankton grazing pressure but related to conductivity. We observed no relationship between phytoplankton generic richness and TP concentration in any of the three regions. The three regions differed significantly with respect to mean local and regional generic richness, with BNL being more diverse than the other two regions. Our observations suggest that phytoplankton diversity in European shallow lakes is influenced by submerged macrophyte cover indirectly by modulating zooplankton grazing. This influence of submerged macrophytes and zooplankton grazing on phytoplankton diversity decreases from north to south.

Temporal occurrence of Ceratium hirundinella in Spanish reservoirs

Ceratium hirundinella has traditionally been characterised as a species that thrives in warm waters and in stratified conditions. In our study, however, we found that the temporal occurrence of C. hirundinella in Spanish reservoirs greatly differs from that typically described in temperate zone aquatic systems. We analysed the temporal occurrence of C. hirundinella populations as well as physical and chemical variables in one hundred Spanish reservoirs. C. hirundinella was present in most (74%) of the reservoirs. In 78% of the reservoirs with C. hirundinella occurrence, the species was present during winter time and in 70% it was present during all four seasons.C. hirundinella was very commonly present in Spanish reservoirs in winter time despite the mixing conditions and lower temperatures and light availability. The presence of the species was positively related to water ionic content (HCO3−, SO42-, Ca2+, Mg2+). We conclude that C. hirundinella temporal occurrence in southern north-temperate systems greatly differs from the seasonality typically described for the temperate zone and could be regulated by different factors than those operating in the northern north-temperate zone.

Utilization of immobilized benthic algal species for N and P removal.

Laboratory experiments were performed to study the growth rate and phosphorus (P) and nitrogen (N) uptakes of eight benthic microalgae species isolated from different sources of pig manure. Cells immobilized in calcium alginate beads were cultured with three replicates for each species. P removal rates obtained for the unicellular self-aggregating benthic species (Palmellopsis gelatinosa, Chlorosarcinopsis sp., and Macrochloris sp.) were markedly higher than those obtained in previous published experiments. N removal rates were highest for Macrochloris sp., Chlorosarcinopsis sp., and Euglena sp. 2 and comparable to the maximum rates obtained by other authors. Our results show an excellent efficiency of autochthonous benthic species for nutrient removal, especially for P, and call attention to their use for wastewater treatment.

Analysis of phytoplankton-zooplankton relationships in an oligotrophic lake under natural and manipulated conditions

During August, 1987, we performed a series of Limnocorral experiments in lake La Caldera, a small winter-kill lake in which phytoplankton is strikingly nutrient-limited. The effects of biomanipulation on zooplankton-phytoplankton relationships were assessed by monitoring both individual species and whole-assemblage responses. Two sizes of enclosures were used (15 and 350 litres) and two treatments were assayed: 1) removal of zooplankton by 45 µm filter net and 2) doubling the natural grazing pressure by increasing the zooplankton concentration. Results show the two enclosure types to differ strikingly: flagellates disappeared from the small enclosures, resulting in four- to six-fold changes in chlorophylla concentration and three- to four-fold changes in number of individuals. Most species were grazed (a prey selectivity based on criteria other than size was observed) and their net growth rate increased with zooplankton concentration, causing a net increase in the phytoplankton growth, a stimulatory effect probably through nutrient regeneration that overrides the losses due to grazing.

Biodiversity in European Shallow Lakes: a Multilevel-Multifactorial Field Study

This chapter is based on the premise that the precipitous decline in freshwa- ter wetlands and species can only be arrested through conservation and sus- tainable management at a large scale, based on water (usually river) basins. A number of approaches to large-scale freshwater wetlands conservation are presented and assessed to draw conclusions on future conservation priori- ties.

AUXOSPORULATION IN CYCLOTELLA OCELLATA (BACILLARIOPHYCEAE) UNDER NATURAL AND EXPERIMENTAL CONDITIONS1

Growth and sexual reproduction in a population of Cyclotella ocellata Pantocseck were studied during one annual cycle in a reservoir and in short‐term enclosure experiments performed in situ involving different nutrient conditions and concentrations of zooplankton species. Three phases of auxosporulation in this diatom were distinguishable morphologically: 1) preauxospore, from the beginning of zygote formation until the valves were longitudinally separated, 2) primary auxospore, when the zygote grew too large to fit inside the valves and before it reached its full size, and 3) mature auxospore, characterized by a well‐developed, markedly scalloped edge. Under experimental and natural conditions, sexual reproduction was associated with changes in cell size. In the natural system, the auxospore appeared to act as a resting structure during conditions adverse for population growth. A threshold population of small cells appeared to be necessary for sexual reproduction in the natural system, whereas auxosporulation was associated with phosphorus fertilization in the enclosures. In both environments only cells smaller than 9.5 μm in diameter were capable of auxospore formation. Our results suggest that, once having reached the critical cell size, the factors that trigger sexual reproduction may depend on ambient environmental conditions.

DISPERSAL AND COLONIZATION OF THE EPIBIONT ALGA KORSHIKOVIELLA GRACILIPES (CHLOROPHYCEAE) ON DAPHNIA PULICARIA (CLADOCERA)

The dispersal and colonization of Korshikoviella gracilipes (Lambert) Silva on Daphnia pulicaria Forbes collected from a small high mountain lake in southern Spain were investigated in a series of laboratory experiments. Results of these laboratory experiments were related to previous field data. Massive release and detachment of zoospores, which is the dispersal stage of the epibiont, occurred just before molting. A lower number of zoospores was dispersed from the discarded molts and a scant number dispersed during the intermolt period. Release of cysts, which is the overwintering stage of the epibiont, mainly occurred immediately after the molt was discarded. The production of dispersal forms (zoospores and cysts) shows precise temporal synchronization with the molting process in Daphnia. The colonization of uninfected individuals from infected molts and from infected individuals was rapid. Our results suggest that colonization of field animals in this lake is efficient and is facilitated by the coincident aggregates of substrate and epibiont.

Amphora margalefii Tomàs var. lacustris P. Sánchez var. nova, a new brackish water diatom

A new variety of Amphora margalefii is described as: A. margalefii var. lacustris P. Sánchez var. nov. It is identifiable by its narrow, elliptical frustule (18–27 × 6.5–10 µm) with dorsal striae consisting of a double row of puncta. This taxon inhabits epipelic communities which develop in the litoral zone of several brackish water lakes in the province of Málaga (Spain). Maximum population densities are observed between December and February.

Physical, chemical, and management-related drivers of submerged macrophyte occurrence in Mediterranean farm ponds

The construction of ponds for irrigation has proliferated during last decades in Mediterranean regions. If properly constructed and managed, ponds may simultaneously meet conservation and agricultural objectives: the preservation of certain macrophytes might improve water quality for irrigation purposes. However, the effects of management are often neglected when analyzing the main drivers of organisms community structure. Here we investigated the effect of environmental variables, construction type and management practices on the occurrence of submerged macrophytes (vascular plants, charophytes, filamentous algae). Total submerged macrophyte coverage and richness did not vary with pond type, but the presence of submerged macrophytes was significantly higher in embankment ponds. Artificial ponds showed the highest charophyte richness but lowest vascular plant occurrence. Total submerged macrophyte occurrence mainly correlated with conductivity and littoral vegetation, whilst the relative importance of environmental factors was higher than variables related to pond type and management. However, embankment ponds showed the highest richness of vascular plants and filamentous algae, and artificial ponds contributed to the regional pool of charophyte species. Thus, construction pond type and management levels might be relevant to understand submerged macrophytes occurrence in man-made ponds, since the three pond types contributed to the local and regional species pool.