The role of storms in the summer succession of the phytoplankton community in a shallow lake (Lake Balaton, Hungary)

The authors carried out day-to-day studies on the phytoplanktonof the largest shallow lake of Central Europe in the summerof 1976, 1977 and 1978. Data were analysed with diversity andcluster analyses. (i) Wind-induced stirring-up of the sedimentplays important role in the summer phytoplankton successionof the shallow lake. (ii) After storms algae with very smallcell sizes show synchronous development. In long calm periodsalgae with larger cell sizes exhibit organised population dynamics.(iii) In calm periods a shift from r-selection to predominantK-selection can be suspected. After the next storm importanceof r-selectionists again increases. (iv) Effect of changinggrowth- and loss rates on the population dynamics of the mostabundant species is discussed based on measured generation timesand calculated elimination. The phenomena discussed in the papercan appear to different extents in the summer phytoplanktonsuccession of other shallow, polimictic lakes.     

Composition,density and feeding of crustacean zooplankton community in a shallow,temperate lake (Lake Balaton,Hungary)

Composition density and filtering rates of crustacean zooplankton were studied in the open water and among the macrophytes of the oligo-mesotrophic part of Lake Balaton from 1981 to 1983. From the individual filtering rates of the different populations and the densities community grazing rates were derived.Copepoda made up 79–90% of crustacean plankton community in the open lake and 95–97% of it in littoral zone. Among them the nauplii dominated. At the end of summer 1982, when Anabaenopsis was in bloom, the filter-feeding species (Eudiaptomus, Daphnia) practically disappeared, being replaced by cyclopoids. Daphnia had the highest filtering rates followed by those of Eudiaptomus and Diaphanosoma. Among copepods, the filtering rates in decreasing order were: ovigerous > all adults > copepodites > nauplii. > . The filtering rates of the different species varied both seasonally as well as from year to year. In 1983, when the concentration of organic seston decreased, filtering rate increased compared with those in the earlier years. During the water bloom in 1982, the rates decreased by 70% on the average.The community grazing rate was very low (3% per day) in the open lake and among macrophytes, both in 1981 and 1982; also the share of crustacean zooplankton in grazing was very low. In 1983, together with the improving of water quality, the community grazing rate increased 4-fold. In 1981 and 1983 the rates were influenced by water temperature but in 1982 by seston concentration.     

Daily egg production ofTemora longicornis (Copepoda,Calanoida) during winter and early spring in the Marsdiep (Southern North Sea)

Mature females of the copepodTemora longicornis from the Marsdiep tidal inlet were incubated at ambient water temperature during the winter of 1989/1990 to estimate their egg production during 24 hours. Throughout winter this production remained at a level of 0 to 10 eggs per female. In March a steep rise to 60 to 80 eggs coincided with an equally steep rise in chlorophyll-a from 4 to 20 g.l^–1. Excess food given during incubation tended to increase the observed production rate only in October at relatively high temperature. Additive effects of rising food level and temperature on daily egg production were found in spring. In March and April 1988 and 1990 the observed maximum daily egg production per female increased from about 20 at 5°C and 5 g.l^–1 chlorophyll to 70 at almost 10°C and 20 g.l^–1. The egg production in winter gives a prebloom potential to maintain a stock of premature stages ready to utilize the algal spring bloom. Early spawning before April can also contribute to the development of the abundance peak of adults in May–June. Due to growth rates increasing with temperature in the months March and April, most of the adults at their peak density may have hatched from eggs before the period of maximum egg production rate at the end of April. The exceptionally high production rate observed at the end of March may be related to a developingPhaeocystis bloom.     

Life history of Corophium curvispinum G. O. Sars (Crustacea,Amphipoda) living on macrophytes in Lake Balaton

Samples of the amphipod Corophium curvispinum were collected from Myriophyllum spicatum twice a month during the vegetation period. The animals were sexed, their length measured and the eggs of females were counted. Length frequency histograms served to follow the life history of C. curvispinum.Reproduction lasts from May to October. The animals born in May–June reproduce in the same year while the summer-autumn generation reproduces the following year. The life span is about 1 year. The highest fecundity was found in June, the lowest in October.     

Phytoplankton nitrogen demand and the significance of internal and external nitrogen sources in a large shallow lake (Lake Balaton,Hungary)

Since the middle of 1990s the trend of Lake Balaton towards an increasingly trophic status has been reversed, but N₂-fixing cyanobacteria are occasionally dominant, endangering water quality in summer. The sources of nitrogen and its uptake by growing phytoplankton were therefore studied. Experiments were carried out on samples collected from the middle of the Eastern (Siófok) and Western (Keszthely) basins between February and October 2001. Ammonium, urea and nitrate uptake and ammonium regeneration were measured in the upper 5-cm layer of sediment using the ¹⁵N-technique. Ammonium was determined by an improved microdiffusion assay. N₂ fixation rates were measured by the acetylene-reduction method. Ammonium regeneration rates in the sediment were similar in the two basins. They were relatively low in winter (0.13 and 0.16 μg N cm^?3 day^?1 in the Eastern and Western basin, respectively), increased slowly in the spring (0.38 and 0.45 μg N cm^?3 day^?1) and peaked in late summer (0.82 and 1.29 μg N cm^?3 day^?1, respectively). Ammonium uptake was predominant in spring in the Eastern basin and in summer in the Western basin, coincident with the cyanobacterial bloom. The amount of N₂ fixed was less than one third of the internal load during summer when external N loading was insignificant. Potentially, the phytoplankton N demand could be supported entirely by the internal N load via ammonium regeneration in the water column and sediment. However, the quantity of N from ammonium regeneration in the upper layer of sediment combined with that from the water column would limit the standing phytoplankton crop in spring in both basins and in late summer in the Western basin, especially when the algal biomass increases suddenly.     

Stir-up effect of wind on a more-or-less stratified shallow lake phytoplankton community,Lake Balaton,Hungary

Microstratification of phytoplankton in the large shallow Lake Balaton (Hungary) was studied during a 24 h period. Dissolved O₂ showed biological stratification; flagellates exhibited a definite circadian rhythm. In the middle of the investigation a heavy storm broke out which was followed by the disappearance of differences between different layers of water. Storm-induced destratification is described by cluster-analysis. Abundances of dominant species changed differently in connection with the storm. Numbers of Nitzschia sp. increased due to stirring up from the sediment surface. Numbers of single-celled or colony-forming species (Cyclotella comta, Crucigenia quadrata, Coelosphaerium kuetzingianum) practically did not change. Numbers of all the three dominant filamentous species (Aphanizomenon fos-aquae f. klebahnii, Lyngbya limnetica, Planctonema lauterbornii) significantly decreased, which might be attributed to an unknown loss process and was followed by a competitive displacement by algae of small cell size.     

Mesozooplankton assemblage and first record of Paracartia grani Sars G.O., 1904 (Copepoda: Calanoida) in the Western harbour of Genova (Ligurian Sea).

Harbours are characterized by high pollutant charge and by the occurrence of well adapted and resistant species. This paper reports the results of an annual plankton survey (May 1997-June 1998) carried out in the western harbour of Genova (Ligurian Sea) and in its mouth. Plankton samples were collected by horizontal trawls using a WP2 net. Copepods were the bulk of plankton in almost all samples. Eight copepod species were recognized: Paracalanus parvus and Acartia clausi were the most abundant. The first record of Paracartia grani in the harbour of Genova is here reported; this species, which is known to occur in polluted harbour waters of the Mediterranean Sea and was found in semi-confined Mediterranean and Atlantic coastal areas, was dominant during October 1997. Also Clausocalanus spp., Centropages typicus, Oithona helgolandica, Oithona nana, Farranula spp., Eurytemora spp., Isias clavipes and Lucicutia spp. were frequently sampled. Among other zooplankters, cladocerans, ostracods and tunicates occurred frequently, while cnidarians, mysids and chaetognaths showed low densities. These results show the occurrence of a well defined harbour plankton and point out the differences between harbour and neritic plankton of the Gulf of Genova.     

Physiology and population structure of Calanus finmarchicus (Copepoda: Calanoida) during a Lagrangian tracer release experiment in the North Atlantic

A population of Calanus finmarchicus was followed in the opensea for a period of 10 days at the end of June 1996 using atracer release method. Gut fluorescence, egg production, carboncontent and stage specific abundance, together with phytoplanktonconcentration and composition, were measured during this period.Chlorophyll levels were less than 1 µg l^–1 and thephytoplankton population was dominated by coccolithophorids.Gut fluorescence decreased during a period with strong winds,whereas egg production remained constant. Estimated phytoplanktoningestion was too low to cover egg production requirements.However, the microzooplankton concentration seemed to be highenough to complement phytoplankton ingestion, enabling egg productioncarbon requirements to be covered. C/N ratios of adult femalesand stage CV were low, indicating low levels of lipid storage.The population was dominated by stage CIV, but shifted to adominance of younger stages during the study. Mortality calculatedfrom population structure indicates that higher death ratesoccurred at stage CV.     

Diversity patterns of trait-based phytoplankton functional groups in two basins of a large, shallow lake (Lake Balaton, Hungary) with different trophic state

The application of functional approaches in understanding phytoplankton community-level responses to changes in the environment has become increasingly widespread in recent years. Eutrophication is known to cause profound modifications in ecosystem processes; however, the underlying relationships between environmental drivers and phytoplankton diversity and functioning are complex and largely unknown. Therefore, in the present study, we investigated and compared the temporal diversity patterns of phytoplankton functional groups in the mesotrophic eastern and eutrophic western basin of the shallow Lake Balaton situated in Hungary. Diversity data were derived from taxonomic composition and biomass data corresponding to the years 2005–2006 and 2008–2009. With the use of cluster analysis, phytoplankton species were classified into eight distinct groups representing different combinations of functionally relevant traits including greatest axial linear dimension; surface-to-volume ratio; photosynthetic pigment composition; N₂ fixation; phagotrophic potential; growth form/complexity (unicell, filamentous, colony-, or coenobium-forming); and motility. Our results have revealed that there is a significant inverse relationship between the functional group diversity used in our study and trophic state (total phytoplankton biomass) as opposed to species diversity, where no correlation was observed. In addition, group evenness showed an even stronger negative correlation with trophic state, while species evenness yielded only a weak relationship. The observed variability in functional group diversity suggests that such an approach could provide an efficient means of revealing structural changes in phytoplankton communities, establishing new hypotheses and highlighting fundamental points in ecosystem functioning.     

Parasitic regulation in a population of Boeckella hamata Brehm (Copepoda: Calanoida)

SUMMARY. 1. The impact of parasitism by a fungus Aphanomyces sp. (Phycomycetes: Saprotegniaceae) on a population of Boeckella hamata in Lake Mahinerangi in New Zealand was studied over 20 months. The incidence of infection among adult female copepods exceeded 12% throughout winter (May-October) and was highest in autumn (46%) when population birth rates were depressed by 48.8%. During most of the study, parasitism lowered the rates of population recruitment and growth by more than 10%. These effects on the B. hamata population exceeded those of Aphanomyces on Boeckella dilatata Sars in another study.
2. It is hypothesized that the high incidence of parasitism by Aphanomyces and its importance at times in regulating populations of Boeckella in New Zealand lakes may be an ecological consequence of life in predator-poor ecosystems.     

Feeding of Boeckella gracilipes (Copepoda, Calanoida) on ciliates and phytoflagellates in an ultraoligotrophic Andean lake

The calanoid copepod, Boeckella gracilipes, is the dominantcrustacean zooplankton in South Andean deep ultra-oligotrophiclakes. Combining field and experimental data we explored thefeeding of the copepod and its access to the mixotrophic ciliate,Ophrydium naumanni, in Lake Moreno Oeste (Patagonia, Argentina).Phytoplankton was dominated by nanoflagellates throughout thewater column. Ophrydium naumanni, which accumulates much ofthe chlorophyll a, as do copepodites and adults of B. gracilipes,has a deep distribution during the day, with maximal abundancesaround 30 m depth. Mouth-part morphology analysis of B. gracilipesindicated that the copepod has an omnivorous diet. Laboratoryexperiments showed that B. gracilipes could access O. naumannionly when it is offered as a single food item. However, whennatural phytoplankton and ciliate assemblages (including O.naumanni)are offered, B. gracilipes did not eat Ophrydium and preyedon the oligotrich, Strombidium viride, and phytoflagellateslike Chrysochromulina parva. The range of ingested sizes wasbroad (3.9–33 µm of equivalent spherical diameter)but all selected particles were motile ones with distinctivemovements, which would enhance the copepod particle detection.     

Gladioferens Henry (Copepoda: Calanoida) discovered in Antarctica: G. antarcticus sp. nov. described from a lake in the Bunger Hills

A new species of Gladioferens is described from a freshwater lake in the Bunger Hills, Greater Antarctica. A key to the six species of Gladioferens is provided for both sexes. Most species of the subgenus containing G. antarcticus sp. nov. are remarkable in possessing asymmetries in the second legs (male) and fourth legs (female). This suggests that the mating behaviour of these species may be radically different from that in most heterarthrandrian calanoids and calls for further study. However, G. antarcticus is more primitive than its consubgeners in having, in the male, symmetrical second legs and 3-segmented endopods in the fifth legs. The genus shows a highly disjunct distribution (Australia, New Zealand and Bunger Hills) and its biogeography is now of outstanding interest.     

Population dynamics of the freshwater dinoflagellate Ceratium hirundinella in the largest shallow lake of Central Europe, Lake Balaton, Hungary

SUMMARY.

• 1 Horizontal distribution, long-term (1933–82) and short-term (day-to-day) changes in abundance, vertical stratification and circadian rhythm of the freshwater dinoflagellate Ceratium hirtmdinella were studied in Lake Balaton, the largest shallow lake of Central Europe.
• 2 The lowest abundance was consistently found in those areas of the lake which had the strongest currents.
• 3 The density of C. hirundinella seemed to be, at least in those parts of the lake above the level of fertility considered oligotrophic, insensitive to changes in trophic conditions; only its relative contribution to total biomass decreased with increased enrichment.
• 4 During the day the bulk of the population stayed at a level in which the light intensity was between 126 and 440 μE m^-2 s^-1 PAR.

     

Spatial distribution and short-term changes of benthic macrofauna in Lake Balaton (Hungary)

Spatial and short-term changes in the composition and density of the macrobenthic fauna were studied in Lake Balaton, a large shallow lake in Central Europe (Hungary). Spatial differences were examined along five transects and short-term changes at two stations of different trophic state. The macrobenthos consisted almost exclusively of Tubificidae and Chironomidae of the species Chironomus gr. plumosus, Procladius choreus, Tanypus punctipennis, Microchironomus tener and Cladotanytarsus sp. The Oligochaeta biomass showed a significant short-term decrease from 1995 to 1998, and their average biomass proved to be 0.86 and 0.79 g WFW (wet formalin weight) m-2 in 1996 and 1997, respectively. Chironomidae showed significant spatial and short-term differences following variations in primary production. Higher primary production resulted in higher biomass (up to 153.4 g WFW m-2 and 9785 ind. m-2 in 1995) of Chironomus-Procladius community, while lower primary production resulted in a very low biomass and abundance of the predatory Procladius-Tanypus-Microchironomus community (average: 3.16 g WFW m-2 and 1311 ind. m-2 in 1997). As compared to other lakes of similar climatic conditions, the total production of oligohaetes and chironomids proved to be very low in 1996 and 1997 (49.2 and 54.1 KJ m-2 yr-1, respectively). The 90% of the average chironomid production of Lake Balaton in 1996 and 1997 belonged to Ch. gr. plumosus (5.63 and 5.13 g m-2 yr-1), P. choreus (4.3 and 3.47 g m-2 yr-1) and T. punctipennis (0.27 and 2.21 g m-2 yr-1). This revised version was published online in July 2006 with corrections to the Cover Date.     

Some reflections on the structure of the mandibleplate ofEurytemora affinis (Copepoda,Calanoida)

The mandibleplates of several specimen of the copepodEurytemora affinis collected from the Westerschelde and the Gironde estuary were studied. Using the Edge index (ITOH, 1970) this species could be classified as an omnivore. Pictures obtained by light and scanning electron microscopy reveal that the mandible teeth ofE. affinis have a molar-like structure, which likely changes in functional morphology with developmental stage, sex and age of the adults. Based on these observations, the desirability to consider the three dimensional structure of copepod mandibles for feeding mode classification is discussed.Communication no. 540 of the Delta Institute for Hydrobiological Research, Vierstraat 28, 4401 EA Yerseke, The Netherlands.     

The seasonal cycle of Thermocyclops crassus (Fischer, 1853) (Copepoda: Cyclopoida) in a shallow,eutrophic lake

The seasonal cycle of Thermocyclops crassus was studied from 1985 to 1987, in the Gronne, a shallow, productive lake. T. crassus was present from late April to early October, while water temperature was above 10 °C. It produced three generations per year. Population peak was usually reached by the second generation, in August. Abundance was positively correlated with water temperature. Females carried 18.3 to 32.3 eggs on average. Reproduction rates were highest in July and August. Sex ratio was low, as females generally outnumbered males. Between October and April copepodites 4 went in diapause, predominantly in the deepest part of the lake and 0–4 cm deep in the bottom mud. Variations in body size were low across the year.T. crassus coexisted with the cyclopids, Cyclops vicinus and Mesocyclops leuckarti. In 1985 and 1986, abundances of M. leuckarti were low, while those of T. crassus and C. vicinus were high. In 1987 lower water temperatures, caused by cold weather, resulted in a marked decrease of the population density of T. crassus, while the abundance of M. leuckarti increased, and density of C. vicinus remained high. Comparison of the egg duration times of T. crassus, C. vicinus and M. leuckarti showed that at 15 °C and below T. crassus may be outcompeted by its comparatively longer egg development times. However, experiments in limnocorrals showed that T. crassus has an advantage over C. vicinus when fish predation is high.Department of Biology III, University of Ulm     

Meteorological factors affecting the bloom of Anabaenopsis raciborskii Wolosz. (Cyanophyta:Hormogonales) in the shallow Lake Balaton, Hungary

There was a heavy bloom of a nitrogen-fixing blue-green algaAnabaenopsis raciborskii Wolosz. in Lake Balaton in September-October1982. The authors studied the dynamics of the phyto- and bacterio-plankton of the lake by daily and weekly samplings. Some meteorologicalfactors were also considered. It could be concluded that thecauses of the bloom were accumulating nutrients being enrichedjust before the bloom-period suddenly washed into the lake byheavy rains, followed by windless warm days (water temperatures26–29°C). An expressed correlation between bacterio-and phytoplankton indicates their close trophic relationship.     

Population structure and reproduction ofCalanus helgolandicus (Copepoda,Calanoida) along the iberian and Moroccan slope

During three cruises, carried out in March 1991, October 1991, and January 1992 off the Iberian Peninsula and Morocco, the abundant calanoid copepodCalanus helgolandicus (Claus) was collected from a depth of 1000 m to the surface. Differences in depth preference were correlated with the life stage and geographically differing vertical salinity structures. In autumn and winter, only stage V copepodids (CV) and adults were found, in spring also younger copepodid stages. Within the range of the Mediterranean outflow water (MOW), a sharp decline of abundances of all stages was evident during all cruises. In autumn 1991, the bulk of the population was recorded south of the MOW, in winter 1992 north of it. During winter, numbers had declined by 70%, supporting the idea that winter individuals represent the same generation as was encountered in autumn, and that they had been transported northwards. CV stages preferred the depth layer 400–800 m, in autumn and winter. Adults were found in autumn at the same depth south of the MOW, while they preferred the 0–400 m layers north of it. In winter, the abundance of adults increased, males preferred the 400–600 m depth layer, while females stayed at 200–400 m. In spring 1991, stages younger than CV were found in high densities, all stages concentrating in the upper 200 m. During the crosslope survey in spring off Portugal, an absolute abundance maximum of females was found. In contrast, offshore densities were very low. On the basis of these findings, the hypothesis of a Mediterranean centre of distribution and dispersal into the Atlantic is questioned. It is suggested that a separate, reproductively active population ofC. helgolandicus exists off NW. Africa.