Journal of Limnology

vol. 63(2), 2004

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CONTENTS

1

Phototropic sulfur and sulfate-reducing bacteria in the chemocline of meromictic Lake Cadagno, Switzerland

Mauro TONOLLA, Sandro PEDUZZI, Antonella DEMARTA, Raffaele PEDUZZI and Dittmar HAHN

Lake Cadagno, a crenogenic meromictic lake located in the catchment area of a dolomite vein rich in gypsum in the Piora Valley in the southern Alps of Switzerland, is characterized by a compact chemocline with high concentrations of sulfate, steep gradients of oxygen, sulfide and light and a turbidity maximum that correlates to large numbers of bacteria (up to 107 cells ml-1). The most abundant taxa in the chemocline are large- and small-celled purple sulfur bacteria, which account for up to 35% of all bacteria, and sulfate-reducing bacteria that represent up to 23% of all bacteria. Depending on the season, as much as 45% of all bacteria in the chemocline are associated in aggregates consisting of different populations of small-celled purple sulfur bacteria of the genus Lamprocystis (up to 35% of all bacteria) and sulfate-reducing bacteria of the family Desulfobulbaceae (up to 12% of all bacteria) that are almost completely represented by bacteria closely related to Desulfocapsa thiozymogenes. Their association in aggregates is restricted to small-celled purple sulfur bacteria of the genus Lamprocystis, but not obligate since non-associated cells of bacteria related to D. thiozymogenes are frequently found, especially under limited light conditions in winter and early summer. Aggregate formation and concomitant growth enhancement of isolates of both partners of this association suggests synergistic interactions that might resemble a sulfide-based source-sink relationship between the sulfate-reducing bacterium that is able to sustain growth by a disproportionation of inorganic sulfur compounds (sulfur, thiosulfate, sulfite), with the purple sulfur bacteria acting as a biotic scavenger. The availability of these isolates opens up the door for future studies considering other facets of potential interactions in aggregates since both types of organisms are metabolically highly versatile and interactions may not be limited to sulfur compounds only.

2

Fragilaria and Staurosira (Bacillariophyceae) from sediment surfaces of 40 lakes in the Austrian Alps in relation to environmental variables, and their potential for palaeoclimatology

Roland SCHMIDT, Christian KAMENIK, Horst LANGE-BERTALOT and Rolf KLEE

The percentage distributions of Fragilaria and Staurosira taxa in surface sediment samples from 40 oligo- to ultra-oligotrophic, pH neutral to alkaline, mountain lakes of the central Austrian Alps (Niedere Tauern) were studied in relation to environmental variables using multivariate statistics. Selected taxa that were of uncertain taxonomy or that might be difficult to distinguish were illustrated in LM or SEM. The same statistics as they were applied to the total diatom data set were run on a Fragilariaceae subset with Fragilaria and Staurosira. These analyses emphasized on the high sensitivity of these genera to climate-driven environmental variables in mountain lakes. Canonical Correspondence Analyses (CCA) indicated that the pH, mean July water temperature (T_July), length of ice cover, and dissolved organic carbon (DOC) made significant contributions to explain the variation in the diatom assemblages. In addition, water depth affected the distribution of benthic and planktonic taxa. Differences or similarities in ecological preferences of taxa provided suggestions for taxonomy. Correlations between the mean valve length and summer water temperatures increase the overall high potential of Fragilaria and Staurosira for palaeoclimatological reconstructions in mountain lakes.

3

Biomass, composition and size structure of invertebrate communities associated to different types of aquatic vegetation during summer in Lago di Candia (Italy)

Celine TESSIER, Antonia CATTANEO, Bernadette PINEL-ALLOUL, Gaetano GALANTI and Giuseppe MORABITO

We compared the biomass, taxonomic composition, and size distribution of invertebrates associated to emergent (Schoenoplectus lacustris), submerged (Myriophyllum spicatum), and floating leaved (Trapa natans) vegetation at two depths (surface and water column) during summer in Lago di Candia, Italy. Invertebrate biomass was positively related to epiphyton biomass (Chl-a). M. spicatum supported higher invertebrate biomass per unit of plant weight than S. lacustris whereas T. natans was somewhat intermediate. Depth did not affect invertebrate biomass significatively. Surface sections of M. spicatum and T. natans supported invertebrate communities with similar taxonomic composition dominated by oligochaetes and ostracods. Large hirudineans and gastropods characterized the communities on the water column sections of M. spicatum. S. lacustris and the water column sections of T. natans (composed of stems and aquatic roots) were supporting invertebrate communities dominated by copepod nauplii and lacking large organisms. Changes in aquatic vegetation in Lago di Candia following harvesting of T. natans and removal of submerged vegetation by the invasion of the rodent coypu (Miocastor coypus) may affect the invertebrate biomass of its littoral zone.

4

Trophic conditions of marine coastal waters: experience in applying the Trophic Index TRIX to two areas of the Adriatic and Tyrrhenian seas

Franco GIOVANARDI and Richard A. VOLLENWEIDER

This paper is an extension of an earlier paper on a Trophic Index TRIX, a linear combination of the log of 4 state variables: ChA, aD%O, minN & TP (Vollenweider et al. 1998), to characterizing succinctly the trophic levels of coastal marine areas, and to discuss questions that since have arisen in applying and developing the index further. This entails in depth review of some proce¬dural aspects such as data processing including transformation of rough data; the statistical distribution of TRIX; comparisons over different spatial and temporal scales; discrimination limits between two contiguous means of TRIX; interrelationships between TRIX and its components, and between TRIX and other water related variables. Further to statistical properties of TRIX, attention is given to integrative features and other implicit functional relationships pertinent to the description of trophic characteristics of coastal systems, among which to mention the term "efficiency". This theoretical framework has been applied to data from two trophically different responding coastal systems, i.e. the Emilia-Romagna coastal area of the Adriatic Sea and the Tuscany coastal area of the Tyrrhenian Sea to illustrate some of the arising interpretative problems in using TRIX. Finally, analyses of the two system are juxta¬posed in an alternatively slightly modified reference diagram in which the trophic location and the extent of variability are shown in relation to the N/P ratio and related efficiency.

5

The influence of biological and environmental factors on the stable isotopic composition of ostracods – the Late Pleistocene record from Lake Albano, Central Italy

Claudio A. BELIS and Daniel ARIZTEGUI

The stable oxygen and carbon isotopic composition of ostracod valves is the result of the interaction of several variables. Understanding and identifying the biological and ecological factors influencing the life of these animals improves the interpretation of isotopical data, and leads to better paleoenvironmental reconstructions. Ostracod biostratigraphy and determinations of oxygen and carbon stable isotopes on ostracod valves were carried out on a short sequence of the Last Glacial Maximum from Lake Albano (Central Italy). The oxygen isotopic composition of adults of Candona neglecta ranged between 0.5‰ and 1.5‰, and in Ilyocypris bradyi between –2‰ and –0.5‰ . Isotopic values from adults of C. neglecta fell within the range –1.5‰ to –0.8‰ when corrected for vital effect. The carbon isotopic signal ranged from 9.4‰ to 10.8‰ in adults and juveniles of C. neglecta, and from 9.8‰ to 11.3‰ in I. bradyi. Differences between left/right valve and gender were negligible, whereas there appeared to be a marked influence of life stage and species-specific factors related to vital effect and differences in microhabitat and seasonality. We combined analyses on carbon and oxygen isotopes with information deriving from ostracod ecology to reconstruct short term oscillations in past lake water level. Seasonal changes in either the temperature or the isotopic composition of the lake water were also identified. Relatively high δ¹⁸O values in ostracod valves were probably associated with the lake location and source of moisture, while high δ¹³C values were most probably related to the input of volcanic CO₂ into the lake.

6

Genetic and morphometric differentiation among sympatric spawning stocks of whitefish (Coregonus lavaretus L.) in Lake Femund, Norway

Tor F. NÆSJE, Jukka A. VUORINEN and Odd T. SANDLUND

Lake Femund, Norway, contains several sympatric ecotypes of whitefish, Coregonus lavaretus L. Deepwater whitefish, river whitefish, and shallow water whitefish can be easily distinguished by spawning habitat and gillraker number. Variation in morpho¬logical and ecological characters and allozyme loci from 11 different spawning sites was analysed to compare the ecological poly¬morphism with possible genetic sub-structuring of whitefish in the lake. Of the individual morphological and ecological characters, gillraker number best separated the spawning populations, followed by body length. In a hierarchical cluster analysis based on gill¬raker number, body length and age of fish, the four deepwater sites grouped together as well as the three samples from, or closely related to, inlet rivers. The shallow water sites, however, were more dispersed. In the allozyme analysis, nine of the 38 enzyme loci were polymorphic at the 0.95 level. The amount of genetic variation was quite similar among localities with H_exp = 0.046 - 0.066. Allele frequencies differed significantly among localities at all polymorphic loci indicating distinct reproductive isolation between spawning sites. A consensus tree based on genetic distances grouped samples according to spawning depth and trophic morphology rather than regional proximity. All deepwater spawners grouped together with rather high support while geographically adjacent samples differing by their morphology or behaviour were dispersed. The patterns of differentiation based on allozyme variation and morphology are not fully concordant, but still the association between genetic differentiation and morphological and life history variables was highly significant. Thus, the morphological differences are not due to phenotypic plasticity within single spawning populations as is commonly seen in many other fish species. The possible evolutionary origins of reproductively isolated whitefish forms are discussed. The relatively close association between differences in gillraker counts and genetic difference indicates that the present management of Femund whitefish stocks based on gillraker counts is sensible.

7

Horizontal heterogeneity of seston, organic carbon and picoplankton in the photic zone of Lago Maggiore, Northern Italy

Roberto BERTONI, Roberta PISCIA and Cristiana CALLIERI

The horizontal heterogeneity of seston, dissolved (DOC) and particulate (POC) organic matter, Chlorophyll-a (Chl) and of autotrophic (APP) and heterotrophic (HPP) picoplankton was evaluated seasonally during a two-year period in Lago Maggiore, a large deep oligotrophic lake in Northern Italy. The dissolved fraction resulted homogeneously distributed in the epilimnion during the whole sampling period. The particulate fraction showed the higher heterogeneity in winter 2000 and 2001. For those years, POC and Chl heterogeneity was, respectively, 3-5 and 5-7 times higher than DOC. A similar trend was evident for Chl and for APP. The spatial heterogeneity of HPP resulted always smaller than the analytical variability, thus preventing any consideration about the spatial distribution of HPP. POC and Chl concentration exhibited a recurrent pattern of their spatial heterogeneity, possibly in relation with the location of the part of the drainage basin conveying higher amounts of nutrients to the lake.

8

First record and morphological features of Hemidiaptomus (Occidodiaptomus) ingens (Gurney, 1909) (Copepoda Calanoida) in Italy

Federico MARRONE and Luigi NASELLI-FLORES

During a survey, carried out to assess the consistency of microcrustacean fauna inhabiting temporary ponds in Sicily, Hemidiaptomus (Occidodiaptomus) ingens (Gurney, 1909), a large calanoid copepod up to now known only for North-African ponds, Camargue and Corse, was found in the north-western part of the island. Due to its central location in the Mediterranean Sea, Sicily represents a transition zone where several chorological zones of the West Palearctic merge and converge. A brief summary of the existing literature regarding this taxon is given with some morphological considerations on the recently found population which represents the first record for Italy. In particular, the morphological features of the Sicilian population are closely related to those described by Gurney for the specimens collected in the locus typicus (Oued Tindja, Tunisia) and slightly differ from the other European populations.