Original paper

Epiphyton, phytoplankton and macrophyte ecology in a shallow lake under in situ experimental conditions

Romo, Susana; Villena, Marí a-José Garcí a-Murcia

Abstract

The present experimental research reports the responses of phytoplankton, epiphyton and charophytes in a shallow characean Mediterranean lake under different nutrient levels (nitrogen and phosphorus) and planktivorous fish densities in two in situ mesocosm experiments. How these factors affected biomass, dominance and replacement of these primary producers were quantified and detailed. Diversity and the structure of phytoplankton and epiphyton were also examined, as well as algal selectivity between habitats determined by daily recruitment of the epiphyton in the water column under different nutrient and grazing conditions.Our findings indicated that epiphyton biomass underwent a logarithmic increase at lower nutrient levels than phytoplankton, which increased linearly and dominated with total phosphorus above 0.35 mg L−1. Both phytoplankton and epiphyton correlated negatively to submerged plant biomass, while phosphorus levels above 0.1-0.2 mg L−1 prevented the co-existence of charophytes, epiphyton and phytoplankton. Charophyte biomass was highest with total phosphorus below 0.06 mg L−1 when phytoplankton chlorophyll-a was below 35 μg L−1 and epiphyton chlorophyll-a below 200 μg g−1 plant dry mass. Planktivorous fish densities exerted a minimal effect on the biomass and composition of epiphyton and phytoplankton and on the biomass of charophytes. Diversity of planktonic and epiphytic algae significantly decreased with nutrient additions. Epiphyton and phytoplankton shared 85-88% of the species composition, suggesting that most of them were tychoplanktonic. Daily algal recruitment from the periphyton in the water column was higher at intermediate nutrient levels of 0.6 mg L−1 N and 0.06 mg L−1 P, especially for filamentous cyanobacteria.

Keywords

mesocosmsfertilizationplanktivorous fishcyanobacteriacharophytesalgal recruitmentshallow mediterranean lake