Deutschen Gesellschaft für Limnologie e.V. Annual Meeting 2007 - Münster, Septembre 24th-28th, 2007.
Oral presentation : Lake typology based on functional characteristics of fish assemblages. Garcia XF, Mehner T.
Relationships between functional traits of organisms and their habitat deserve currently an increasing attention in freshwater ecology. It is assumed that life history traits summarise the strategy of the species to optimise the resource use and face spatio-temporal variability of the environments. The expected output of this approach is to develop new tools and models to assess the ecological status of freshwater ecosystems and predict the impact of environmental changes on faunal assemblages. In this study, we investigated the response of fish functional assemblages along natural and human disturbance gradients in north-eastern German lowland lakes.
For this purpose, 11 species traits with 39 attributes were collected for the 29 fish species found in the 67 lakes studied. Homogeneous functional groups of fish were identified by selecting that combination of traits minimizing the within-group heterogeneity while maximizing the between-group differences. Fish abundances, summed according to the functional groups identified, were used to ordinate the 67 lakes and were regressed against 55 variables describing environmental gradients in lakes.
Three functional types of fish assemblages were identified: species inhabiting warm water, small-size spring spawner species and large-size fall spawner species. Based on fish abundances, the three functional types accurately described three groups of lakes (NMS, final stress: 8.3, axis 1: 64 %, axis 2: 19.9 % of total variance explained) exhibiting distinct fish assemblages (MRPP, p<0.001 for all combinations). A first group of 26 lakes was correlated with high abundances of warm-water inhabiting species (Pearson's r=-0.58 with NMS axis 1). A second group of 33 lakes was correlated with high abundances of small-size spring spawner species (r=-0.62). The third group including 8 lakes was correlated with large-size fall spawners species (r=0.92). CRT and RDA analyses identified water depth and productivity as the best environmental descriptors to explain the observed patterns of fish functional abundances in lakes. Hence, warm-water inhabiting species and small-size spring spawner species rather inhabit shallow lakes (£ 17.2 m max. depth) characterised by chlorophyll a concentrations above 7 mg m-3, while large-size fall spawning species rather colonise deep clearwater lakes.
In this study, we could develop a lake typology based on fish functional traits which describes lakes exhibiting homogeneous fish functional assemblages. The relationships found between fish functional assemblages and environmental characteristics of the lakes were ecologically meaningful. Hence, shallow lakes are characterised by high temperatures and a fast spring water warming which favour species having a preference for warm water as well as spring spawner species. Conversely, deep lakes offer alternative cool deep areas allowing fall spawner species to escape the fast spring water warming. The 29 species considered in this study are mainly euryecious, which probably limited the number of fish functional groups identified and further reduced the number of relationships found between functional assemblages and environmental descriptors. Nevertheless, this study provides promising results to develop new management tools.