María Sahuquillo

Changes of life-history traits and size in Daphnia magna during a clear-water phase in a hypertrophic lagoon (Albufera of Valencia, Spain)

The rol.e o.flarge her?ivorous zooplankton, especially Dap~ma, m promotmg clear-water phases due to its grazmg effeet on phyroplankton is well doeumented (SoMMER et al. 1986, CARPENTER & KlTCHNEL 1996). The PGE model of plankton sueeession (SOMMER et al. 1986) deseribes both the produetion of the clear-water phase (CWP) and its decline. The latter results from two main meehanisms: (l) that the herbivorous woplankton beeomes food limited due to overpopulation, and (2) that fish predation a~eelerates ~e decline of the large woplankton speeJes. The aJm of the present study was to examine the ~opulati~n dynam!cs of Daphnia magna that eontnb~ted m produemg a CWP in the hypereutrophie shallow lake, Albufera ofValencia. Due to the high trophie level of the lake and the drastie ehanges that happen during this clear-water episode, the data presented herein clearly illustrate the operadon of the aforementioned meehanisms during the CWP and how they affeet the size strueture and lifehistory traits of the D. magna population.

Macroinvertebrates associated with reed stems

Macroinvertebrate communities associated with reed beds were studied in six wetlands along central Med1terranean coast o f the Iberian Península. Reed beds were chosen to provide quantitative data from a habitat common to all wetlands. The further aim of this study is to explore the viability o f these data as a means of assessing the ecological status o f the wetland. The project is part of a larger EC project (ECOFRAME). Also, this work is intended to be a contribution to the knowledge of macroinvertebrate fauna in western Mediterranean wetlands where these studies are scarce. The si tes sampled were shallow lagoons, two with brackish waters (Hondo and Cabanes). The freshwater lagoons showed an oligohypereutrophic gradient (Baldoví, Xeresa, Cap de Terme and Albufera, ordered by trophic Ievel); one (Baldoví) was a spring pool. Individual reed stems and surrounding water were collected with a 75 cm-long, 5 em interna! diametcr tu be (Kornijov & Kairesalo method); after cutting the stem the tube was closed with a sieve of 0.25 mm. Two areas o f reed bed were sampled in six lakes in July 200 l. Within each area, five stems werc collected separately but pooled together to give one sample per area. Length and diameter of each stem were measured to calculate their total area and express the density o f animal s per cm2 of the plants. Jndividuals were picked just after sampling and preserved in 70% ethanol. The remainder ofthe sample was filtered by a mesh s1ze smaller than the initial one to collect the smaller animals, which were also preserved in the same way. Macroinvertebrates were sorted and counted under stereoscope. All groups were identified to species level when possible. . Density o f macroinvertebratcs in reeds was higher m freshwater bodies than in brackish ones and increased with trophic level. In all samples and sites, the dominant group was clearly chironomidae. The proportion of chironomids increased with to tai density. Thirty-five taxa were recorded, chironomidae being the most diverse group (J O species). The highest diversity was observed in freshwater bodics fed by subterranean springs. The lowest diversity was found in the brackish water sites. The number of chironomid species i s no t related to the to tai number o f taxa especially in the richest si tes. Percentage of predator~ w1th respect to total number of individuals had the same trends as diversity. A detrended correspondence analysis (DCA) was apphed to the proportions of each chironomid species in each sample (pu) with ~ect to total chironomidae, followmg arcsen V P u transformation. DCA indicated that salinity was the most important feature responsible for chironomid species distributwn, whereas trophic level had a much reduced role. The second axis ofDCA separated the site with more fluctuating water levels (which can dry up in some years) from the re s t o f the wetlands, t h us indicating the Importance o f hydrological regime. . The sites were also studied looking at the proportions of different functional groups. The freshwater sites, except for the hypertrophic one, were characterized by big swimming insect larvae ( collectors and predators) and acari. Brackish water bodies (Hondo and Cabanes) and the spring pool (which has some marine influence) supported large numbers o f crustaceans: Gastropods becamc important only in sites WI!h h1gher water flow. A principal components analys1s (PCA) with the proportions of functional groups (arcsen VJ;; transformed proportions of orthocladins, chironomins, chironomid predators, small predators, nonpredator naidids+aelosomids big swimming collectors, big swimming predators: crustaceans, gastropods) distinguished three kinds o f environments: freshwaters, brackish waters and the spring pool. Each studied wetland had a distinct fauna. The main ecological factor responsible for species composition and distributions in this study was salinity, w!th flow and hydrological regime being secondary factors, whereas macroinvertebrate density was mainly related to eutrophy.