Giuliano Bonomi

Relationship between sedimentary pigments and primary production: evidence from core analyses of twelve Italian lakes

A statistically significant correlation of the type y = axb between sedimentary plant pigments and contemporary algal primary production has been found in a study of the recent trophic evolution of twelve Italian lakes. The equation is used to assess baseline production levels in periods (50–70 years ago) when human influence was low.

Population Dynamics of Tubifex tubifex, Studied by Means of a New Model

The difficulties connected with the study of tubificid population dynamics and production have long been recognized (Kennedy, 1966; Johnson and Brinkhurst, 1971; Jonasson and Thorhauge, 1976; Waters, 1977; Bonomi and Adreani, 1978). The problems encountered are mostly of a taxonomic nature, as it is often difficult, if not impossible, to describe the populations in terms of biologically meaningful compartments. Even in the unusual case of a single species population, the complicated biological cycle strongly limits the possibility of a suitable description; indeed, it is well known that after the cocoon laying period, the tubificids undergo a regression of the reproductive system (Cernosvitov, 1930; Poddubnaya, 1971) that makes the regressed animals quite similar to the true young, that have not yet undergone any reproductive period. Only Poddubnaya and co-workers, as far as we know, have been able to account for the state of regression of the reproductive system in their work on the tubificids of Rybinsk Reservoir (Poddubnaya, 1972; Arkhipova, 1976). Moreover, the possibility of describing the cocoon (or egg) population numbers has been either neglected or not taken into consideration for the lack of description of the cocoons specific characters.

Cohort cultures of Psammoryctides barbatus (Grube) and Spirosperma ferox Eisen: a tool for a better understanding of demographic strategies in Tubificidae

Laboratory research on the tubificids Psammoryctides barbatus and Spirosperma ferox was done. Embryonic development time, growth, time required to attain the first cocoon laying and egg production were estimated at different temperatures and population densities. The results allow us to demonstrate some intrinsic density regulation mechanisms in the profundal tubificid communities and substantiate the hypothesis that the succession from oligotrophic to eutrophic species in the profundal of lakes undergoing eutrophication is mainly based on their biotic characteristics.

Toxicity of copper-spiked sediments to Tubifex tubifex (Oligochaeta, Tubificidae): a comparison of the 28-day reproductive bioassay with a 6-month cohort experiment.

Results from a 28-day adult reproductive bioassay using the aquatic oligochaete Tubifex tubifex (Müller, 1774) are compared with life table statistics obtained from a 6-month experiment on cohorts of the same species. This was done by simultaneously performing the two tests on copper spiked sediments. Five concentrations and a control were tested. The 28-day bioassay was performed 3 times in succession. Several endpoints were considered for each test and LOEC, IC10 and IC50 were calculated. IC50 estimates for the number of young produced in the 28-day bioassay range from 81 to 107 mg/kg; IC50 estimates for different endpoints of the cohort experiment ranged from 88 to 106 mg/kg. The 28-day bioassay showed essentially the same sensitivity as the cohort experiment to copper. This suggests that the 28-day reproductive bioassay does provide information that is relevant in assessing long-term toxic effects at the population level.

Progress in cohort cultures of aquatic Oligochaeta

Our laboratory work on the life cycle of aquatic Oligochaeta has been extended to the tubificids Potamothrix hammoniensis and P. heuscheri, as well as to the lumbriculid Bichaeta sanguinea.

Stratigraphy of specific algal and bacterial carotenoids in the sediments of Lake Varese (N. Italy)

A study on the succession of some phytoplankton populations in the very eutrophic Lake Varese over the past 80–100 years, was based on thin-layer chromatography of four group-specific carotenoids (echinenone, lutein, myxoxanthophyll and oscillaxanthin). The development of diatoms was traced by microscope counts of their frustules. In addition, the carotenoid okenone, peculiar to some Chromatium species, was identified and related to lake trophic conditions (the Chromatium species are obligate anaerobic bacteria, and use H2S).

Quantitative observations on the population ecology of Branchiura sowerbyi (Oligochaeta, Tubificidae)

Cohorts of Branchiura sowerbyi were reared at different temperatures and initial population densities in order to obtain data suitable for the interpretation of population dynamics in field populations. Percent hatching from cocoons reaches its maximum at 25 °C and decreases towards lower and higher temperatures. Embryonic development time, TE, was measured and the relative threshold temperature, 10 °C, calculated by extrapolation. The degree day requirement for embryo development is 195 °C d. The time of first cocoon laying (Tgm) was observed and the ratio TE/Tgm was seen to fit with that of other tubificid species cultured so far. Embryo mortality is rather high, while worm mortality is low or very low. Fecundity increases from 15 to 20 °C but decreases at 25 °C. A mathematical model for the simulation of population densities with four size-stage compartments is suggested. It could be used for the optimization of worm uptake (simulated as stage specific mortality) in mass cultures reared for the production of Branchiura, to be used as food for fish fingerlings.

Density-dependent processes in cohorts of Tubifex tubifex, with special emphasis on the control of fecundity

Laboratory cohort cultures of the tubificid Tubifex tubifex with different initial densities were carried out at 20° C with the condition of unlimited food. The main results were: 1) Intracocoon mortality was 37% of the laid eggs (observation of 689 eggs); 2) The principal bionomic parameters (generation time, r, R0) appeared to be density dependent; 3) Recruitment was regulated through the percentage of worms that actually attained the ovigerous stage, specific fecundity, and the duration of the egg laying stage, which appeared to be inversely correlated with density.

Observations on cohorts of Tubifex tubifex cultured at different food levels, using cellulose substrate

In order to clarify the relationship between food availability and population dynamics in aquatic oligochaetes, short term cultures and cohort cultures of Tubifex tubifex were reared using substrates with different food concentrations, obtained by mixing sand with different amounts of cellulose powder.

Population analysis in mass cultures of Tubifex tubifex

Mass cultures of Tubifex tubifex from Lake Orta were kept in the lab at 20 °C starting with different initial densities (10, 45, 86, 161 ind · jar−1), with the aim of evaluating the effect of density on population numbers and on population parameters. The results show that density mainly controls fecundity, growth, maturation and ovigeration rates. Growth rates and mean number of eggs laid/ovigerous (R0) are inversely related to density, but generation time appears to be directly related. Very low or very high initial densities display, at different times of the culture history, efficient density controls. Intermediate N0 seem to bring about situations of bad control, easily leading to numerical overshoots. A possible implementation of a population dynamics model (Bonomi & Di Cola, 1980), originally used for laboratory observations on T. tubifex cohorts was considered, including some density control functions derived from our observations on cohort and mass cultures in some transfer rates and in fecundity rate.