Leeches associated to Hydrophyta in laguna Los Patos, Buenos Aires, Argentina.

Abstract

The  most  important   environmental    factors   influencing   the  number and  kind of leeches  in a given  habitat  are:  food's  availability,   nature  of the sub- strate,  depth, water  movements,   size   and nature  of the water  body,  hardness,  ph and  water temperature, disolved  oxygen, siltation,  turbidity,  and  water salinity. Leeches  are usually  less abundant at greater depths  primarily  because of the lack of vegetation,  suitable  substrates,  and  food. The  main  objective of this work  is to identify  the leeches associated to aquatic plants in Laguna Los Patos and to analyse   seasonal   population   variations   considering   mean  density,  species   rich- ness, dominance,  and frequency.  Quantitative   samples   were  taken  monthly,  from June  2000  to April  2002.  Temperature,   ph, conductivity,  and  dissolved   oxygen were  measured.   Twelve  species  were  found:  Helobdella  triserialis, H. lineata, H. hyalina, H. adiastola, H. diploides, H. duplicata. H. striata, H. simplex, H. michaelseni, Haementeria  eicchorniae,  Batracobdel/a  gemmata, and Orchibdella pampeana (Cyclobdellidae). Helobdella triserialis, H. lineara. H. adiastola, H. diploides, and  O. pampeana were  dominant  and constant  whereas  H  duplicata. H. striata, H. simplex, H. mtchaelseni,   Haetnenteria   eicchorniae, and Batracob­ della  gemmata were  occasional. Helobdel/a  triserialis and H. hyalina exhibited the  higher  mean  density  and occurred  around  ali year. Helobdella   duplicata. H. striata, H. simplex, H. michaelseni, Haementei  ia eicchorniae, and Batracobdella gemmata were scarce, being recorded  in spring,  summer  and autumn. Hydrocotyle ranunculoides housed  the highest  species  richness  (ten species)  while  the  lowest species  richness  was observed  in Azolla filiculoides (five specics).