Resumen de Temperature variability, predation pressure and zooplankton composition in Pyrenean hihg mountain lakes
In the context of current anthropogenic climate change and given the great number of Pyrenean lakes with introduced fish it is of great importance to know how they can change and affect zooplankton. Therefore, the aim of this thesis is to unveil the factors which explain water temperatures in the ice-free period and the ice phenology in the Pyrenean lakes to further understanding their effects on the zooplankton together with predation pressure of fish and other natural predators in relation to the environmental factors which explain zooplankton composition.
In order to understand the temperature variability in Pyrenean lakes we conducted a monitoring of 59 lakes from 2001 to 2014, from which we could study temperature conditions in the ice-free season and the ice phenology. With this data mixed models were developed in order to know which environmental variables can explain main thermal variables and ice phenology. With these models it was possible to project temperatures and ice-cover periods along the Pyrenees and in the future by downscaling air temperatures projections of Global Climate Models.
Following the models projections accumulated degree-days are expected to increase more in lowlands, whereas maximum temperatures are expected to show greater increases in higher altitudes. Mean ice-free period surface water temperatures are expected to increase an average of 2ºC from current mean temperatures of 11.3º C in Pyrenean lakes by 2090.
All the studied lakes froze in winter. Mean ice-cover duration was of eight months among the Pyrenees in average ranging from 4 months to 11. Using the models we foresaw future decrease in ice-cover duration of between 23 and 32 days in 2090, mainly due to the advance in ice-off.
Regarding the zooplankton communities in the Pyrenees we found that the dominant crustacean species were Daphnia longispina, Cyclops abyssorum, Eudiaptomus vulgaris and Chydorus sphaericus, and of the rotifers genera Kellicottia, Keratella, Asplanchna, Polyarthra, and Conochilus. The zooplankton composition was principally explained by geomorphological and chemical/phytoplankton variables. Also introduced fish species, temperature and ice phenology explained zooplankton. At Pyrenean scale salmonids explained zooplankton variability, whereas when analysing fish abundance effects on zooplankton minnows showed a negative effect. Different predation pressures were observed among predators of zooplankton, having minnows a greater impact. We could also observe differences in zooplankton sizes due to selective fish predation. Moreover fish had a negative effect on fecundity whereas fecundity could be recovered by lakes restoration removing invasive fish.
