Low biodiversity in productive lakes

Posted on December 13, 2016

The over-supply of nutrients to lakes (through pollution, for example) stimulates the growth of plant plankton, which blocks light from reaching bottom-dwelling algae and higher plants. Therefore, nutrient excess has the potential to reduce habitat diversity and the associated biodiversity of animal plankton, macroinvertebrates and fish. An international team of biologists looked at the relationship between nutrient load (total phosphorus) and biodiversity by analyzing depth-stratified data sets from 53 Danish lakes. Average lake depths were 0.5 – 16.5 m. Phosphorus concentrations covered the range 0.02 – 0.41 mg/l, with a mean of 0.14 mg/l. The data sets included information on the abundance of fish (26 species, from 10 families), which were caught by electrofishing and gillnetting. In almost every case the compositional variability (species richness and diversity) of fish communities decreased with increasing nutrient concentration and depth, this being the case both at regional (between-lake) and local (within-lake) scales. The results therefore supported the nutrient-diversity hypothesis. Nutrient-induced reductions in the diversity of fish assemblages may make them less resilient to environmental disturbances.

Reference: Menezes, R.F. et al. 2015. Homogenization of fish assemblages in different lake depth strata at local and regional scales. Freshwater Biology 60, 745–757. http://onlinelibrary.wiley.com/doi/10.1111/fwb.12526/pdf