| Title | Dynamics of bacteria and mixotrophic flagellates in an Alpine lake in relation to Daphnia population development |
| Abstract | In a fishless oligotrophic Alpine lake (Lago Paione Superiore: LPS), with a simple trophic food web, the relationships between microorganisms and zooplankton have been studied. During the ice-free period 1999, bacterial grazing by mixotrophic flagellates (MxFl), autotrophic carbon fixation and excretion (EOC), bacterial production, and zooplankton abundance and biomass were measured weekly. After ice-melt, MxFl, which constituted 94% of total phytoplankton, increased in number until the appearance of Daphnia longispina, the dominant crustacean zooplankton species in LPS. Gross primary production and EOC ranged from 0.2 to 2.5 and from 0.1 to 1.8 ?g C l-1 h-1, respectively. EOC accounted for 45 to 90% of total autotrophic production. Community grazing rate of MxFl was higher at 9 m in comparison with 1 m and ranged from 3 to 62 × 103 bact ml-1 h-1. MxFl ingested 0.2 to 8% of the natural bacterioplankton per hour, in summer. The community grazing rate of mixotrophic flagellates was significantly correlated
with the phytoplanktonic photosynthetic activity (P = 0.006) and with the bacterial production (P = 0.037). In August, Daphnia grazing caused a rapid decrease of both bacteria and MxFl and of their activities. Phytoplankton photosynthetic efficiency increased in late summer after a phosphorus pulse. Although P excretion by zooplankton was not measured, it is speculated that Daphnia play an important role in the availability of this element firstly by grazing bacteria and MxFl in the water column and, after the exhaustion of such food, by browsing algae at the water-sediment interface. |
| Source | Journal of limnology (Online) 61 (2), pp. 177–182 |
| Keywords | Alpine lakesmicrobial food webmixotrophic flagellate grazingDaphnia longispina |
| Journal | Journal of limnology (Online) |
| Editor | Istituto per lo Studio degli Ecosistemi, Pavia, Italia |
| Year | 2002 |
| Type | Articolo in rivista |
| Authors | Callieri C., Bertoni R., Corno G. |
| Text | 71782 2002 Alpine lakes microbial food web mixotrophic flagellate grazing Daphnia longispina Dynamics of bacteria and mixotrophic flagellates in an Alpine lake in relation to Daphnia population development Callieri C., Bertoni R., Corno G. C. Callieri CNR Istituto per lo Studio degli Ecosistemi, Verbania Pallanza R. Bertoni CNR Istituto per lo Studio degli Ecosistemi, Verbania Pallanza G. Corno Max Planck Institut fur Limnologie, Plon, Germany In a fishless oligotrophic Alpine lake Lago Paione Superiore LPS , with a simple trophic food web, the relationships between microorganisms and zooplankton have been studied. During the ice free period 1999, bacterial grazing by mixotrophic flagellates MxFl , autotrophic carbon fixation and excretion EOC , bacterial production, and zooplankton abundance and biomass were measured weekly. After ice melt, MxFl, which constituted 94% of total phytoplankton, increased in number until the appearance of Daphnia longispina, the dominant crustacean zooplankton species in LPS. Gross primary production and EOC ranged from 0.2 to 2.5 and from 0.1 to 1.8 g C l 1 h 1, respectively. EOC accounted for 45 to 90% of total autotrophic production. Community grazing rate of MxFl was higher at 9 m in comparison with 1 m and ranged from 3 to 62 × 103 bact ml 1 h 1. MxFl ingested 0.2 to 8% of the natural bacterioplankton per hour, in summer. The community grazing rate of mixotrophic flagellates was significantly correlated with the phytoplanktonic photosynthetic activity P = 0.006 and with the bacterial production P = 0.037 . In August, Daphnia grazing caused a rapid decrease of both bacteria and MxFl and of their activities. Phytoplankton photosynthetic efficiency increased in late summer after a phosphorus pulse. Although P excretion by zooplankton was not measured, it is speculated that Daphnia play an important role in the availability of this element firstly by grazing bacteria and MxFl in the water column and, after the exhaustion of such food, by browsing algae at the water sediment interface. 61 Published version La ricerca sulle catene alimentari microbiche dei laghi alpini e un ambito privilegiato di sviluppo e verifica di teorie ecologiche perche in tali ambienti talune variabili sono naturalmente forzate dalle condizioni climatiche estreme. Journal of Limnology 61 2 177 182 Journal_of_Limnology_61_2_177_182.pdf Articolo in rivista Istituto per lo Studio degli Ecosistemi 1723 8633 Journal of limnology Online Journal of limnology Online J. limnol. Online Journal of limnology. Online roberto.bertoni BERTONI ROBERTO cristiana.callieri CALLIERI CRISTIANA |
