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Time of Chironomus plumosus (L.) generations in natural conditions of lowland reservoir

Kajak Z., Prus P.

Polish Journal of Ecology

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2004

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Vol. 52, nr 2

211-222

EN

The time of Chironomus plumosus generation in the field conditions (shallow, eutrophic dam reservoir) was estimated tobe about 3 weeks in the spring. This estimate has been possible due to simultaneous mass appearance of young larvae (the new generation) and the lack of older larvae at this time. Later in the season usually there was some amount of the youngest larvae, indicating the permanent emergence of imagos and the egg-laying, but without clear peaks of numbers and boundaries between successive generations. This regularity and the relatively low total numbers of larvae during the summer indicate the heavy fish pressure on the benthos, not allowing for the mass appearance of young larvae and the estimate of the generation time. Fish pressure is probably weak in spring, during a spawning period, but then increase in the summer. The generation number could be theoretically as high as 5 during the vegetation season (May-October), assuming about 3 weeks for full larval development, as it was estimated at optimal feeding and oxygen conditions and low fish pressure in the spring. However some limiting factors like: oxygen defficits, the annoyance by fish and bestrewing of larval tubes with the mud transported by the water flow (range 150-500 m^3 s^-1 of the total inflow) increase in the summer. These factors can slow down larval development, resulting in observed lower generation number: 3 to 4 during a year.

2

Influence of the population density and the amount of food on Chironomus plumosus (L.) and Tubificidae. Laboratory experiments

Kajak Z., Prus P.

Polish Journal of Ecology

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2004

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Vol. 52, nr 1

47-53

EN

The aim of this paper has been to examine experimentally the importance of the density of larvae and of the addition of the food for Chironomus and Tubificidae using selected parameters and indices of their populations. Increase of the density of Chironomus plumosus larvae (0.5-50.0 thousands ind. m^-2) in laboratory experiments resulted in the decrease of emergence of imagos, number of tube apertures (3.5-0.4 apertures ind.^-1), and in the lower rate of tubes building. The addition of the food (powdered dry daphnids or food tablets for aquarial fish) had only slight effect on tube numbers but it decreased clearly the getting out of larvae from tubes (probably due to improved feeding conditions inside tubes). It had also a slight negative effect on the survival of larvae. Numbers and individual growth of Tubificidae were positively dependent on the addition of the food (also in the form of naturally dead Chironomus larvae) and negatively - on the density of Chironomus

3

Seasonal and year-to-year variation of numbers of Chironomus plumosus L. and Tubificidae in a lowland reservoir : regularities, causes, mechanisms

Kajak Z., Prus P.

Polish Journal of Ecology

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2003

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Vol. 51, nr 3

339-351

EN

During 9 years of studies very regular Chironomus population dynamics was stated in a eutrophic, lowland dam reservoir. There were usually two peaks of the abundance: the higher one at spring (up to 80 thousands ind. m^-2) and the much lower in autumn. The duration of the spring Chironomus generation was about 3 weeks. The constant presence of young larvae during the summer did not result in the high total abundance of larvae, mainly due to the strong predation of fish and swallows on various stages of Chironomus. The smaller predators pressure in the spring (due to fish breeding) and in the autumn (due to lower temperatures) resulted in the mentioned two peaks. The spring peak abundance was positively correlated with the chlorophyll concentration in water (feeding resource for larvae) and negatively with the water flow. There was also negative correlation of the water flow and the chlorophyll concentration, as well as abundance of Chironomus and Tubificidae during the vegetation season (April-October). Tubificidae correlated strongly positively with the spring Chironomus numbers (with a month lag). The slight positive correlation of these benthic components abundance occurred for the whole vegetation season. Tubificidae occurred in generally high numbers up to 400 thousands m^-2, but various in different years, and with no regular changes during the season.

4

Field experiment reveals no relation between substrate composition and Chironomus abundance

Kajak Z., Prus P.

Polish Journal of Ecology

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2001

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Vol. 49, nr 1

19-27

EN

In the field experiment no relation between organic matter content (0-83%) in substrates provided and Chironomus plumosus (L.) abundance was found. Numbers of larvae and their age structure were usually similar on the mineral substrate and various bottom sediments but sometimes differed up to 2-3 times (at the same site and date of sampling); there was howerver no correlation with the quality of substrate. This indicates that the feeding of Chironomus plumosus did not depend on the bottom deposit the larwae lived in, but mostly on sedimenting tripton, which formed a thin layer on the top of substrates provided. Also mutual relations of individuals and the period of exposure of the sediment (from 3 weeks to few months) did not matter. Very high abundance of Ch. plumosus (up to 90 thousands ind. m^-2) found already after 3 weeks exposition in the sediment initially without that species indicates a very high growth potential of the Chironomus population at the study site.

5

Effects of the density of larvae and type of substrate on Chironomus plumosus L. (Diptera: Chironomidae) population. Laboratory experiments

Kajak Z., Prus P.

Polish Journal of Ecology

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2001

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Vol. 49, nr 4

369-378

EN

Strong dependence of larval tube numbers on the population density, the condition of larvae and feeding situation occurred, but no correlation with the type of substrate was found. Numbers of larval tubes per individual were on the average 2.6 times lower at high (20 and 40 thousands ind. m^-2) than at low (2 - 2.5 thousands ind. m^-2) initial densities of larvae. They fluctuated strongly, but only at low densities, indicating the very high activity of larvae; high densities probably restrained this activity. The grown up larvae succeeded in finishingtheir full development in the mineral substrate with the tiny (<0.1 mm) layer of the natural mud at the top of it. No conical nettings (inside larval tubes) for food filtration were observed. The larvae fed mostly on the internal walls of their tubes; sometimes they also collected particles from the surface of the substrate (especially of substrates poor in the organic matter), after the food was furnished. The emergence of imagines depended on the larval density but quite differently than the numbers of tubes. The threshold for the decreased tube numbers per individual was between 2.5 and 20 thousands individuals m^2, while that for the emergence of imagines - between 20 and 40 thousands individuals m^2.