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In this study, performed in Mediterranean brackish ponds during spring season, we assessed the effects of biotic interactions and abiotic factors on the size and taxonomic structure of the phytoplankton and zooplankton. We used a taxonomic and a size diversity index as a descriptor of the community structure. We predicted that the size diversity of each trophic level would be mainly related to biotic interactions, such as size-based fish predation (in the case of zooplankton) and food resource availability (in the case of phytoplankton), whereas taxonomic diversity would be more affected by abiotic variables (e.g., conductivity, pond morphology). Our results showed a negative relationship between phytoplankton size diversity and food resource availability leading to low size diversities under food scarcity due to dominance of small species. Conductivity also negatively affected the phytoplankton size diversity, although slightly. Regarding zooplankton size diversity, none of predictors tested seemed to influence this index. Similar fish size diversities among ponds may prevent a significant effect of fish predation on size diversity of zooplankton. As expected, taxonomic diversity of phytoplankton and zooplankton was related to abiotic variables (specifically pond morphometry) rather than biotic interactions, which are usually body size dependent, especially in these species-poor brackish environments.

Environmental factors accountable for bacterioplankton or phytoplankton biomass dominance were analysed in a confined Mediterranean salt marsh (Emporda Wetlands, NE Spain). Two basins located in the same salt marsh, and with differences in size and catchment's area were compared, during four characteristic situations of the hydroperiod. Since bacterio- or phytoplankton relationships may be affected by other factors such as diel variations or vertical differences in nutrient composition and distribution, high frequency fluctuations due to these factors were also taken into account. Differences in catchment area appeared to be the more plausible explanation of differences in nutrient and organic carbon accumulation among basins, since during confinement basins essentially accumulate the allochthonous nutrient and organic matter supplies that previously entered by runoff. DOC (Dissolved Organic Carbon) favoured the bacterioplankton biomass increase, but also was the main variable significantly affecting phytoplankton biomass. Basins showed marked differences in bacterio- and phytoplankton dominances. Relationships between phytoplankton and bacterioplankton were positive, negative or not significant, depending on the basin and on the period of the year. The phytoplankton mixotrophic capabilities, both phagotrophy and osmotrophy, and their production of UV-screening compounds, as sunscreen, may explain the significant correlation between DOC and phytoplankton biomass, and the significant effect of phytoplankton on bacterioplankton found in these ecosystems.

The most suitable method for estimation of size diversity is investigated. Size diversity is computed on the basis of the Shannon diversity expression adapted for continuous variables, such as size. It takes the form of an integral involving the probability density function (pdf) of the size of the individuals. Different approaches for the estimation of pdf are compared: parametric methods, assuming that data come from a determinate family of pdfs, and nonparametric methods, where pdf is estimated using some kind of local evaluation. Exponential, generalized Pareto, normal, and log-normal distributions have been used to generate simulated samples using estimated parameters from real samples. Nonparametric methods include discrete computation of data histograms based on size intervals and continuous kernel estimation of pdf. Kernel approach gives accurate estimation of size diversity, whilst parametric methods are only useful when the reference distribution have similar shape to the real one. Special attention is given for data standardization. The division of data by the sample geometric mean is proposed as the most suitable standardization method, which shows additional advantages: the same size diversity value is obtained when using original size or log-transformed data, and size measurements with different dimensionality (longitudes, areas, volumes or biomasses) may be immediately compared with the simple addition of ln k where k is the dimensionality (1, 2, or 3, respectively). Thus, the kernel estimation, after data standardization by division of sample geometric mean, arises as the most reliable and generalizable method of size diversity evaluation.

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.

The influence of hydrology, nutrient composition, food resource availability and predation on zooplankton taxonomic and size diversity was analyzed in several shallow lagoons of a Mediterranean salt marsh (Baix Ter Wetlands, NE Iberian Peninsula). Taxonomic diversity correlated better with variables related to the trophic state, such as nutrient concentrations, whereas size diversity was more sensitive to fish predation. However, the fish predation influence on the size diversity was only significant when fishes reached high densities. Under low fish densities no predation effects were observed and the food resource availability (FRa) appeared to be more important in structuring the zooplankton community. Nevertheless, the two diversity indexes showed opposite responses to this factor. With increasing FRa the taxonomic diversity increased and the size diversity decreased. Neither taxonomic nor size diversity of the zooplankton community correlated with other physical or biotic factors such as hydrological variability or macroinvertebrate predation. The relationships found suggest that the size diversity is mainly related to biotic interactions, such as fish predation or inter/intraspecific competition, while the taxonomic diversity appears to be more sensitive to abiotic factors such as the nutrient composition Financial support was provided by a LIFE-Nature project (LIFE 99 NAT/E/00 6386), by a grant from the Ministerio de Ciencia y Tecnología of the Spanish government, Programa Nacional de Biodiversidad, Ciencias de la Tierra y Cambio Global (ref. CGL2004-05433/BOS) and by a predoctoral grant (ref. FPU AP2001-3933) from the Ministerio de Educación, Cultura y Deporte of the Spanish government

Differences in size and species diversity were analysed in a zooplankton community of a Mediterranean salt marsh (Emporda wetlands, NE Iberian Peninsula), where the dominance of a single species was frequent. In the permanent salt marsh, species diversity and size diversity had similar patterns along zooplankton succession. In the temporary salt marsh species diversity was high after flooding and diminished once water inputs ceased. As species diversity declined size diversity increased. Eventually, one species of calanoid dominated the zooplankton community. The high size diversity in situations of calanoid dominance was possibly due to the co-occurrence of different developmental stages, each of which have different diets. Size diversity would thus indicate trophic niche segregation among different sizes. The combined use of species and size diversity values allows the identification of the successional phases.

Pigment composition and size distribution of phytoplankton were analysed in a group of Mediterranean salt marshes, where hydrology is dominated by sudden inputs during sea storms, followed by long periods of confinement. These marshes are characterized by a low inorganic–organic nutrient ratio, and inorganic nitrogen is especially scarce due to denitrification. Nutrients were the main factor affecting phytoplankton biomass, while zooplankton grazing did not control either phytoplankton community composition, or their size distribution. The relative abundance of the different phytoplankton groups was analysed by correspondence analysis using the pigment composition measured by high-performance liquid chromatography (HPLC) and analysed with the CHEMTAX programme. In this analysis, phytoplankton pigment composition was correlated with two nutrient gradients. The first gradient was the ratio of nitrate–total nitrogen (TN), since the different phytoplankton groups were distributed according to their eco–physiological differences in nitrogen uptake. The second gradient was correlated with total nutrient loading. Biomass size distributions frequently showed a lack of intermediate sized nanophytoplankton (2.5–4 μm in diameter), and the importance of this lack of intermediate sizes correlated with dinoflagellate biomass. These results suggested that in confined environments, where nutrients are mainly in an organic form, dinoflagellates take advantage of their mixotrophy, by competing and grazing on smaller phytoplankters simultaneously.

The role of the hydrological regime in the nutrients and zooplankton composition and dynamics has been analysed in five lagoons of La Pletera salt marshes (NE Iberian Peninsula) during a complete hydrological cycle (2002–2003). Two of the lagoons have their origin in the old river mouths while the other three were recently created in the framework of a Life Restoration project. This fact has also allowed us to study the effect of the lagoon age on nutrient and zooplankton composition and dynamics. The salt marsh hydrology is determined by a prolonged period of confinement without water inputs, irregularly interrupted by sudden water inputs due to flooding events (sea storms or intense rainfalls). While the dynamics of oxidized nitrogen compounds in the lagoons depends on the water inputs variability within each hydrological cycle, the internal load of phosphorus, total nitrogen and organic matter is related more to the cumulative mechanisms during the confinement periods. Accumulation processes may be easily related to lagoon age, since old lagoons have higher content of nutrients and organic matter, suggesting that these lagoons progressively accumulate nutrients during the successive confinement events. This is the usual case for most Mediterranean salt marshes without an artificially manipulated water regime. The zooplankton community in La Pletera integrates the effects of both the hydrological regime and the lagoon age since the former determines the temporal pattern of the main zooplankton species and the latter explains differences in composition and structure between old and new lagoons.

Changes in amino acid composition (AAC) during ontogeny of some planktonic crustacean species commonly found in fresh and brackish coastal waters were compared. For these comparisons two calanoid copepods (Eurytemora velox and Calanipeda aquae-dulcis), two cyclopoid copepods (Diacyclops bicuspidatus odessanus and Acanthocyclops robustus) and two Daphnia (Daphnia pulicaria and Daphnia magna) species were selected. A discriminant analysis was performed to determine whether there were significant differences between the AAC of the different stages of each species. Results show gradual changes in AAC during ontogeny of the copepod species. Calanoids showed the greatest differences in AAC between stages, followed by cyclopoids. Gradual changes in AAC were due to the increase in some amino acids such as alanine, valine, glutamic acid, glycine, arginine, proline and tyrosine from nauplii to adults. The latter showed a remarkable increase in all copepod species. In contrast, Daphnia species showed a relatively constant AAC during development, with only minor changes being detected, and not related with ontogeny. Differences in the physico-chemical variables of the lagoons do not seem to be the cause of copepod ontogenic changes in AAC. Data suggest that AAC differences found between stages of copepod species could indicate a gradual change in diet during the life cycle of these copepods.

Differences between zooplankton structure (species abundance and size distribution) and dynamics of permanent and temporary basins of a Mediterranean salt marsh (Emporda Wetlands, NE Spain) were analysed by means of taxon-based and size-based approaches. These basins are shallow bodies of water which are occasionally connected. They were isolated after water retreat from a broadly flooded, low-lying area close to the open sea. Although temporary and permanent basins show no differences in the most abundant zooplankton species, they differ in their zooplankton diversity, temporal pattern and size structure. The zooplankton assemblages of temporary basins exhibit a temporal pattern with six phases, which are conditioned to the hydrological cycle, each one dominated by one species, whereas in the permanent basin this temporal pattern shows only two phases. Zooplankton size distribution of the temporary basins is dominated by large sizes (copepodites and copepods) while the permanent basin is dominated mainly by small sizes (rotifera and nauplii of copepods). In the temporary basins, the shape of the biomass size spectrum changes according to the hydrological cycle and reflects the dynamics of the ecological interactions among zooplankton species. Differences in the zooplankton composition and dynamics of the permanent basin are not a consequence of water permanence but of the ecological interactions among species involved. The presence of a stable fish population in the permanent waters may explain the high values of zooplankton diversity and the low densities of large zooplankton.

We compared the reproductive effort of perennial and annual Ruppia cirrhosa (Petagna) Grande in a mediterranean coastal lagoon where the species develops in permanent waters as well as in shallow areas which dry up during some months. In permanently flooded areas, Ruppia cirrhosa was perennial with biomass maxima up to 800 g DW m −2 . Here, the reproductive period lasted 8–10 weeks (between April and June), the reproductive effort was low (with 4–8 fl g −1 DW) and mature fruit development was practically absent. In temporarily flooded areas, in contrast, Ruppia cirrhosa developed in an annual cycle which was completed in less than 8 weeks (maximum biomass of 137 g DW m −2 ); reproductive activity began later in the year (June) and lasted 3–4 weeks, but led to more flowers (17 fl g −1 DW) and a high fruit production (up to 590 fr m −2 ). We conclude that reproductive effort in Ruppia cirrhosa is highly plastic and interpret this as an adaptation to temporay flooding.

Body size has been widely recognised as a key factor determining community structure in ecosystems. We analysed size diversity patterns of phytoplankton, zooplankton and fish assemblages in 13 data sets from freshwater and marine sites with the aim to assess whether there is a general trend in the effect of predation and resource competition on body size distribution across a wide range of aquatic ecosystems. We used size diversity as a measure of the shape of size distribution. Size diversity was computed based on the Shannon-Wiener diversity expression, adapted to a continuous variable, i.e. as body size. Our results show that greater predation pressure was associated with reduced size diversity of prey at all trophic levels. In contrast, competition effects depended on the trophic level considered. At upper trophic levels (zooplankton and fish), size distributions were more diverse when potential resource availability was low, suggesting that competitive interactions for resources promote diversification of aquatic communities by size. This pattern was not found for phytoplankton size distributions where size diversity mostly increased with low zooplankton grazing and increasing nutrient availability. Relationships we found were weak, indicating that predation and competition are not the only determinants of size distribution. Our results suggest that predation pressure leads to accumulation of organisms in the less predated sizes, while resource competition tends to favour a wider size distribution his work was supported by grants from the Comision de Investigacion Cientifica y Tecnica (CICYT), Programa de Investigacion Fundamental (CGL2008-05778/BOS and CGL2011-23907). We thank Dr. Dietmar Straile, who provided zooplankton data on Lake Constance. S. Brucet's contribution was supported by the Marie Curie Intra European Fellowship No. 330249 (CLIMBING)

Over 30 years after drainage for agricul- ture, a 2700 ha temporary marshland was recently restored in Don˜ ana National Park. We describe the recovery of zooplankton communities (copepods, cladocerans and rotifers) in 47 new temporary ponds excavated as part of the restoration project during the first two hydroperiods (April 2006 and 2007), and compare them to those of eight reference sites in the surrounding marshland. Major changes in the species composition and abundance occurred in new ponds between years. While rotifers and cyclopoid cope- pods dominated in terms of number of individuals in 2006, calanoid copepods and cladocerans were the most abundant groups in 2007. Rotifer species richness was significantly lower in 2007, but there was an increase in Simpson and b-diversity in 2007 owing largely to a dramatic decline in the abundance of Hexarthra cf. fennica (rare in reference sites) from 93% of all rotifer individuals in new ponds in 2006 to only 32% in 2007. In contrast, species richness of copepods and cladocerans was significantly higher in new ponds in 2007, but there were no changes in Simpson diversity. b-Diversity of cladocerans was also significantly higher in 2007. In 2006, the species richness of cladocera and copepods was significantly lower in new ponds than in reference sites, but by 2007 there were no differences in richness or Simpson diversity. Overall, 7 copepod, 13 cladoceran and 26 rotifer taxa were recorded in new ponds, including 80% of taxa recorded in reference sites. These results indicate that zooplankton communities can be rapidly restored in Mediterranean temporary wetlands, at least when large source populations in the surrounding area reduce dispersal limitation. They also illustrate the importance of comparing different metrics of richness and diversity in studies of zooplankton restoration.

We sought to identify environmental factors influencing crustacean zooplankton species richness in brackish lagoons and to elucidate whether crustacean zooplankton species richness and trophic structure of brackish lagoons differ among two regions with contrasting temperatures. We sampled 35 and 42 brackish lagoons (salinity ranging from 0.3 to 55‰) in Mediterranean Catalonia (NE Spain) and northern-temperate Denmark, respectively. No significant differences were found in total crustacean zooplankton species richness or cladoceran richness between the climatic regions. Calanoid richness was higher in Denmark than in Catalonia, while cyclopoid richness was higher in Catalonia. Salinity was the most important variable associated with zooplankton species richness in both regions, richness of total zooplankton species, cladocerans and cyclopoids being negatively related with salinity. In both regions, a shift occurred from dominance of large filter feeding cladoceran species at low salinities to copepods and small cladoceran species at higher salinities. Cladoceran richness increased with increasing total phosphorus, but was not influenced by total nitrogen or chlorophyll-a. Trophic structure in Mediterranean brackish lagoons showed a more pronounced seasonal variation than in north temperate brackish lagoons. Our results imply that the indirect effects of climate warming, such as changes in salinity and hydrology, will have a larger impact on brackish lagoon ecosystems than the increase in temperature per se.

1. The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon that has been mostly flooded by excessive irrigation water during recent decades. During 2001 and 2002 the lagoon was subject to several water management actions, the main consequence of which was a change in the hydrological regime due to drastically reduced irrigation water inputs to the lagoon. 2. In order to comply with the Water Framework Directive, all the management actions in an ecosystem should be focused on protecting and, where necessary, improving its ecological status. 3. The aims of this study were (1) to analyse whether the hydrological change caused by management actions have affected the ecological status of the lagoon, and (2) to discuss the suitability of several physicochemical and biological indicators for the assessment of the ecological status in this kind of coastal ecosystem. 4. After the change in the hydrological regime, a general improvement of the ecological status was observed mainly as a result of the significant decrease in the nitrogen Trophic State Index and in the abundance of rotifer indicative of eutrophy, and in turn by the significant increase in the water quality index QAELS, based on crustaceans and insect assemblages. 5. Contradictory results emerged with regard to some of the indicators used. After the hydrological change, the increase in the phosphorus Trophic State Index was related with the fact that Mediterranean confined coastal ecosystems are typically P-enriched. In contrast with general assumptions, low diversity and richness of the zooplankton and the dominance of a few species have been related with an improvement of the ecological status after the hydrological change, when freshwater inputs were reduced and the lagoon became more confined. Copyright © 2008 John Wiley & Sons, Ltd.

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.

The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon which has been flooded by the excess irrigation water and the agricultural runoff during the last decades. Between 1999 and 2003, restoration measures were applied to improve its water quality. At the same time, but independently, agricultural water management drastically reduced the freshwater inflow. The short-term effects of these management actions on the limnological characteristics of the lagoon were analysed by comparing two hydrological cycles, one before (1999/2000) and the other one after (2002/2003) the actions. The two cycles are illustrative of opposite situations in the hydrological functioning of coastal wetlands. In the first, the lagoon was exorheic, with prolonged flooding periods and a low residence time; in the second, it had a more endorheic character, with scarce water inputs and prolonged periods of confinement. Consequently, nitrogen inputs diminished and organic load and salinity increased as the internal loading and the accumulation effects became more relevant. These effects were actually caused by the drastic reduction in the freshwater inflow which prevented, in turn, the success of the restoration measures. The zooplankton community of the Ter Vell lagoon was not significantly altered by the hydrological change, at least in the short-term, and rotifers and cladocerans, mainly those species indicative of eutrophy, dominated the community.

12 pages, 7 figures, 1 table, The taxonomic structure of phytoplankton populations in two Mediterranean coastal lagoons were compared with those of nearby marine waters (external waters). Mediterranean confined lagoons remain isolated for most the year and concentrate phytoplankton to a very high biomass. Coastal lagoons on the Mediterranean may, therefore, act as accumulators of neritic phytoplankton (including species related to harmful algal blooms). We examined whether coastal lagoons act as concentrators of marine toxic dinoflagellates during confinement periods, and the common environmental factors that favour growth of specific harmful species in the two ecosystems considered: coastal lagoons and external waters. An alternation between the dominance of diatoms and dinoflagellates was observed, coinciding with that described in Margalef's mandala, occurring in external waters as well as in coastal lagoons. Moreover, the temporal patter was different in the two ecosystems. Dinoflagellate species composition and their bloom period were highly variable in time and space, thus, species had to be analysed individually. Most of the dinoflagellate species found in this study were potentially harmful and high biomass producers. Harmful dinoflagellate species performed well in both, external waters and lagoons, but the specific species-dependent affinity to each of these environments determined which organisms bloom there. Thus, expansion of harmful algal blooms (HAB) to inland waters is not likely and some environmental factors such as the oxidised state of available nitrogen, became determinant to the success and bloom of a species in the coastal lagoon ecosystem, This study has been supported by the EU financed Research Project STRATEGY EVK3-CT-2001-00046; by the contract between Agencia Catalana de l’Aigua (Departament de Medi Ambient, Generalitat de Catalunya) and CSIC; by a grant from the Comisión de Investigación Científica y Técnica (CICYT), Programa de Recursos Naturales (CGL2004-05433/BOS) and by a BR grant of the University of Girona