Pesticides Research, 85 – Effects of Pesticides on Bombina bombina in Natural Pond Ecosystems

Effects of Pesticides on Bombina bombina in Natural Pond Ecosystems

Summary

Aim

The aim of this investigation was to investigate effects of pesticides on growth and survival of Bombina bombina eggs and tadpoles and survival of adult B. bombina in the field.

Over a period of three years (1993-95) a field investigation was established from May to August in 8 ponds on Avernakø (Fyn County) and 3 ponds on the east coast of Fyn. The ponds were selected among existing ponds in conventional agricultural areas, except for two of the ponds on the east coast of Fyn. The investigators had no influence on spraying of pesticides on fields surrounding the ponds.

Two types of experiments were conducted to investigate the effects of pesticides on survival of eggs and small tadpoles (<0.2 g) and growth and survival of large tadpoles (>0.2 g). Eggs of Bombina bombina were placed in bags (35 l) placed inside cages (1.25*1.25*0.6 m) in each pond and hatching success and survival of tadpoles were monitored. B. bombina tadpoles were reared in an aquarium till a weight of 0.2 g. The tadpoles were then transferred to the cages where growth (weight) and survival were monitored till metamorphosis. Eggs and tadpoles were monitored on a weekly basis. Predators of tadpoles were noted and removed from the cages weekly. Water level in cages and max./min. water temperature were registered at every visit. Samples of epiphytic coverings of algae, bacteria, rotifers and protozoa in the ponds were taken weekly from plastic sheets for determination of amount and diversity of potential food sources to the tadpoles (only in 1994 and 1995).

Samples for analysis of pesticides were taken from the 0.5 cm top surface water of the ponds weekly. The farmers gave a thorough report of use of pesticides and fertiliser (compound, dose, date) at the end of each season.

Results on survival of adult Bombina bombina on Agersø, Avernakø, Hjortø, Knudshoved Odde and Nekselø were collected and analysed for evaluation of effects of cultivation on adult survival.

Herbicides were found in 10 out of the 11 ponds, including one finding in each of the two ponds situated in non cultivated areas. Insecticides and fungicides were found in 6 of the ponds and only in the agricultural areas. Only three insecticides and two fungicides were detected in the ponds whereas 14 herbicides were found. Peak concentrations of herbicides ranged up to 11.440 g/l whereas insecticides and fungicides reached 460 ng/l and 7.475 g/l respectively. Herbicides were found to be much more persistent than insecticides and fungicides.

Frequency of pesticide findings decreased significantly with increasing width of buffer zone and peak concentrations of pesticides tended to decrease with increasing width of buffer zone (1-10 m). No effect of height of the vegetation in the buffer zone (0-1 m) could be demonstrated. Not even a 10 m wide buffer zone was sufficient to provide complete protection of ponds against spray drift of pesticides.

Only in one case an effect of pesticides on Bombina bombina tadpoles was found. Heavy contamination of a pond with herbicides probably caused the death of the macrophytes in the pond. Epiphytic coverings of algae, protozoa, rotifers and bacteria, on which the tadpoles depend for feeding, almost disappeared and was replaced by filamentous algae. The result was very poor survival of both small and large tadpoles.

Correlations between pesticide contamination and growth parameters of tadpoles were found but the results were not consistent.

Hatching of eggs was generally successful and not affected by pesticides.

The newly hatched tadpoles were very vulnerable and survival was highly variable.

In 3 out of 8 cases there was a significant positive correlation between abundance and quality of suitable food for the tadpoles and growth and survival of the tadpoles. The quality and thickness of epiphytic coverings on stems of higher plants are therefore probably of vital importance for the fitness of the tadpoles of Bombina bombina.

On average half of the tadpoles released in the cages survived till metamorphosis, but the results were highly variable and offered only little basis of conclusions.

The survival of adult Bombina bombina were generally lower in intensively cultivated agricultural areas than in uncultivated areas.