Angel Baltanás

Impact of an introduced Crustacean on the trophic webs of Mediterranean wetlands

Based on a review and our own data, we present an overview of the ecological impacts on the trophic web of Mediterranean wetlands by an introduced Decapod Crustacean, the red swamp crayfish (Procambarus clarkii). P. clarkii lacks efficient dispersal mechanisms but is very well adapted to the ecological conditions of Mediterranean wetlands (fluctuating hydroperiods with regular intervals of drought). As an opportunistic, omnivorous species, which adapts its ecology and life history characteristics, such as timing and size at reproduction to changing environmental conditions, it became readily established in most of the Mediterranean wetland environments. High reproductive output, short development time and a flexible feeding strategy are responsible for its success as an invader. Like most crayfish, it occupies a keystone position in the trophic web of the invaded system and interacts strongly with various trophic levels. It efficiently grazes on macrophytes and is one of the main factors, besides the impact of flamingos, cattle and introduced fish, of the change of many water bodies from a macrophyte dominated, clear water equilibrium to a phytoplankton driven turbid water balance. Juveniles feed on protein rich animal food with the corresponding impact on the macroinvertebrate community in competition with other crayfish or fish species. At the same time, it serves as a prey for mammals, birds and fish. Due to its predatory and grazing activity, it efficiently canalises energy pathways reducing food web complexity and structure. Feeding also on detritus it opens, especially in marshlands, the detritic food chain to higher trophic levels which results in an increase of crayfish predators. As a vector of diseases, it has a severe impact on the preservation and reintroduction of native crayfish. P. clarkii accumulates heavy metals and other pollutants in its organs and body tissues and transmits them to higher trophic levels. Due to the long history of its presence, the complex interactions it established within the invaded ecosystems and the socio-economic benefits it provides to humans, prevention and control seem the most promising management measures to reduce the negative impact of this crayfish species.

Diet of the Red Swamp Crayfish Procambarus clarkii in Natural Ecosystems of the Doñana National Park Temporary Fresh-Water Marsh (Spain)@@@Diet of the Red Swamp Crayfish Procambarus clarkii in Natural Ecosystems of the Donana National Park Temporary Fresh-Water Marsh (Spain)

As a result of the introduction of the crayfish Procambarus clarkii, the functioning and structure of the fresh-water marsh in the Dofiana National Park have been dramatically altered. Because those changes have been attributed mostly to trophic interactions between the crayfish and existing food webs, the aim of this study was to explore the diet of this species in natural ecosystems in this park. A total of 502 stomachs was analyzed from 3 sites on 2 dates (March and May). The stomach contents were classified into 13 food categories. The most frequent food item in the population was non-green plants (80% occurrence in the pooled data), followed by rhizomes of Scirpus sp. (50%), green plants (36.8%), and organic sediment (30.1%). Animal food items were represented mainly by insects (24.9%), which included a wide variety of aquatic larvae, cladocerans (16%), and Gambusia holbrooki (14%). Both immature and adult size-classes of this crayfish ingested mainly plants and organic detritus, but a higher proportion of food of animal origin has been found in young ( 0.05), except for March when we found lower means in the Manecorro and La Rocina stations than during May. The trophic index calculated was D = 25.3. Thus, the diet of P. clarkii indicates that this crayfish is a polytrophic species.

Ontogenetic changes in the carapace shape of the non-marine ostracod Eucypris virens (Jurine)

Developmental changes in carapace form (size+shape) during ontogeny have been explored in Eucypris virens (Crustacea, Ostracoda) using elliptic Fourier analysis. Clones from different geographic localities raised under controlled constant conditions (temperature and photoperiod) were used to characterize developmental pathways in the species. A larger data set including field populations and laboratory populations cultured under a range of environmental conditions were used to infer influence of environmental factors on carapace shape changes during ontogeny. Size changes between consecutive juvenile stages support empirical laws describing the doubling of ostracod volume at each moult. Ontogenetic changes point out the remarkable influence of environmental conditions on carapace shape.

Techniques for Collection and Study of Ostracoda

The chapter introduces practical methods to sample and study living and fossil marine and non-marine ostracods. Special emphasis is given to sample processing and the analysis of ostracod data. Finally we deal with laboratory culturing methods. Both qualitative and quantitative sampling methods and sampling strategies are recommended and several effective techniques are described. Protocols for preservation of samples containing ostracods and further for extraction of the latter are presented. Special emphasis is given to sub-sampling techniques and to the preparation of ostracods for analysis of species assemblages and geochemical analysis of the valves. The data-analysis section reviews information on the distribution of species abundances, on the adult-juvenile ratios and their usefulness for ecological and palaeoecological interpretation, on adult sex ratios, on the seasonal variation in carapace size, on the preservation state of the ostracod valves and on the application of morphometric analysis to the ostracod carapace shape. The last part deals with laboratory culturing ostracods. It is shown why culturing ostracods is important and how one can start and maintain for long periods batches and/or single specimen cultures of both marine and non-marine ostracods.

Developmental trajectories in geographically separated populations of non-marine ostracods: morphometric applications for palaeoecological studies

Developmental trajectories refer here to patterns of size and shape changes in ostracod valves during the sequence of post-embryonic growth stages. The information obtained from the study of such patterns has significant applications for evolutionary biology and/or (palaeo) ecology. Using geometric morphometrics methods, we describe the developmental trajectories of three ostracod species with valves retrieved from the sediments of lakes Mondsee (Austria), Hańcza (Poland) and Iseo (Italy). Size and shape data result in distinct developmental trajectories. Ontogenetic changes agree with predictions of Prizbram’s and Brooks’ laws. Patterns of valve shape change provide information which might be of use to the taxonomic definition of evolutionary lineages and to the development of studies of allometry and heterochrony in non-marine ostracods.

Limnology of Crater Lakes in Los Tuxtlas, Mexico

The purpose of this study was to characterize five crater lakes in Los Tuxtlas, Mexico, on the basis of morphological, physical, chemical, and biological features. A bathymetric map of each lake was obtained and morphometric parameters were calculated. Physical and chemical parameters (temperature, transparency, nutrients, pH, conductivity, cations) and chlorophyll a were measured for three periods: the cold season (January), the dry season (May), and the rainy season (October) of 2000. The trophic state of each lake was determined using Carlson’s indices for transparency and chlorophyll a. The lakes studied have the morphometric characteristics of maar-type volcanic lakes. Majahual, Chalchoapan, and Manantiales are the deepest lakes with elliptical basins and are classified as warm monomictic systems; Verde and Mogo are shallow lakes with conic basins and are warm polymictic. Majahual and Chalchoapan had an anoxic hypolimnion, while at Manantiales a metalimnetic oxygen maximum was measured. Sodium was the dominant cation in the five lakes, while bicarbonate was the dominant anion. Nutrient and chlorophyll a concentrations, transparency, and trophic indices suggest that Chalchoapan, Verde, and Mogo are eutrophic lakes with tendencies toward hypereutrophy; Manantiales and Majahual, in contrast, can be classified as mesotrophic lakes. The trophic state of lakes was indirectly related to deforestation and to the use of agricultural fertilizer in Los Tuxtlas as well as to certain morphometric characteristics.

Food-web structure in two shallow salt lakes in Los Monegros (NE Spain): energetic vs dynamic constraints

Energetic and dynamic constraints have been proposed as rival factors in determining food-web structure. Foodweb length might be controlled either by the amount of energy entering the web (energetic constraints) or by time span between consecutive disturbances relative to time needed to build up a population (dynamic constraints). Dynamic constraints are identified with processes functioning at a regional scale such as climate, lithology and hydrogeology. Energetic constraints are related with processes operating both at a regional and a local scale. We studied the contribution of energetic constraints to food-web organization in two temporary saline lakes with similar dynamic constraints. Lakes were sampled fortnightly during two hydroperiods (1994/1995 and 1995/1996). Differences in energetic constraints between lakes result in divergent assemblages of primary producers. Consumer assemblages in both lakes, however, are similar in species composition although differ in total biomass and species abundances. Food-webs are short with a high proportion of omnivores. To simulate an increase in the energy input entering to these systems, an addition of nutrients (to a final concentration of 100 μg·1−1 P-PO4 3−) was done in mesocosms placed within the lakes in order to obtain an increase in the phytoplankton biomass. No significant response to nutrient enrichment was found in food-web structure (composition, density or biomass).

Geographical variation in shell morphology of juvenile snails (Concholepas concholepas) along the physical-chemical gradient of the Chilean coast

Changes in phenotypic traits, such as mollusc shells, are indicative of variations in selective pressure along environmental gradients. Recently, increased sea surface temperature (SST) and ocean acidification (OA) due to increased levels of carbon dioxide in the seawater have been described as selective agents that may affect the biological processes underlying shell formation in calcifying marine organisms. The benthic snail Concholepas concholepas (Muricidae) is widely distributed along the Chilean coast, and so is naturally exposed to a strong physical-chemical latitudinal gradient. In this study, based on elliptical Fourier analysis, we assess changes in shell morphology (outlines analysis) in juvenile C. concholepas collected at northern (23 degrees S), central (33 degrees S) and southern (39 degrees S) locations off the Chilean coast. Shell morphology of individuals collected in northern and central regions correspond to extreme morphotypes, which is in agreement with both the observed regional differences in the shell apex outlines, the high reclassification success of individuals (discriminant function analysis) collected in these regions, and the scaling relationship in shell weight variability among regions. However, these extreme morphotypes showed similar patterns of mineralization of calcium carbonate forms (calcite and aragonite). Geographical variability in shell shape of C. concholepas described by discriminant functions was partially explained by environmental variables (pCO(2), SST). This suggests the influence of corrosive waters, such as upwelling and freshwaters penetrating into the coastal ocean, upon spatial variation in shell morphology. Changes in the proportion of calcium carbonate forms precipitated by C. concholepas across their shells and its susceptibility to corrosive coastal waters are discussed.

Assessing the trophic ecology of crayfish: a case study of the invasive Procambarus clarkii

INTRODUCTIONFreshwater crayfish, among the largest invertebrate members of biologicalcommunities in non-marine ecosystems throughout the world, have a func-tional role that is tightly linked to their trophic ecology both as consumers of alarge variety of food sources and as prey for a number of vertebrate predatorsranging from fish to mammals (Hogger 1988). Although the low diversity ofcrayfishspeciesinEurope,ascomparedtothatinNorthAmerica,mightsuggesta low significance of this group to the functioning of ecosystem, the recentintroduction of several non-indigenous species has changed this view dramati-cally (Chapter 28).Severeenvironmentalimpactsatboththepopulationandtheecosystem levelfollowed those introductions. Impacts produced on other (indigenous) crayfishshould be distinguished from those impacts affecting non-crayfish species. Theformer ones are frequently related to the spread of diseases (mainly the crayfishplague, Aphanomyces astaci Schikora) and to competitive interactions; whereas

Ostracods of the Paratethys Sea and Lake Pannon — Perspectives for renewal of cooperative projects

Ideas from a workshop with the title ‘Ostracods of the Paratethys Sea and Lake Pannon‘, organised during the 6th European Ostracodologists’ Meeting (EOM-VI), are briefly presented. The necessity to start a new active communication between palaeontologists and neontologists on the evolution and palaeoecology of ostracods of the marine Paratethys and Lake Pannon during the Cenozoic in Europe and Asia is stressed. This should continue and extend studies of earlier generations of ostracodologists who contributed to the chronostratigraphic and palaeobiogeographic understanding of this domain. Several research topics are proposed and their importance is supported by such arguments as: (1) the high relevance of studies dealing with the origin and diversification of the fauna of (palaeo)ancient lakes; (2) the reconciliation of the systematics of fossil and Recent ostracod taxa, for a better reconstruction of evolutionary histories; (3) a better perception of the developmental trajectories of various Recent and fossil ostracod taxa to facilitate the application of ostracods for palaeoecological studies. Finally, topics for future workshops dealing with Cenozoic ostracods are proposed.