Changes in the aquatic moss Sphagnum denticulatum Brid. population abundance in a softwater lake over a period of three years

Józef Szmeja

doi:10.5586/asbp.2010.022

Abstract

Changes in population abundance of submerged Sphagnum denticulatum Brid. were studied in an acidic and oligotrophic lake in NW Poland over three years. Individuals were counted in a moss carpet at a depth of 2.5 m on 4 experimental plots, 1 × 1 m each, every 30 days for 36 months using the SCUBA method. PAR intensity was seasonally variable (in winter higher than in summer). Changes in water pH, conductivity, HCO3- concentration, hydration and sediment pH were statistically insignificant (p &gt; 0.05). In the summer of the second study year the moss carpet disappeared almost completely due to a massive bloom of filamentous green algae. Periods of growth, regression and regeneration were observed in the population. The stabilisation of population size took 24 months and followed the pattern: slight fluctuations, then rapid growth and repetition of slight fluctuations. The first stage lasted nine, the second four and the third nine months. These stages took place irrespective of seasons, temperature or PAR intensity. Each rapid increase in abundance lasted about 30 days, at PAR intensity &gt;20% and water temperature ranging from 11 to 16oC (in winter, spring or autumn). The regression stage brought about by the algal bloom started in the second year (in summer) and lasted six months (until the end of January in the third year). The population regeneration began in winter (in February, water temperature 3.0oC, PAR about 20%, ice cover 0.15 m) and finished with the end of spring. The population of S. denticulatum shows a repetitive pattern of abundance variations, which is seriously disturbed in summer, especially after a warm spring, by a massive bloom of filamentous green algae.

Highlights

Mosses are a common element of submerged vegetation in softwater lakes of northern Europe
The population of S. denticulatum shows a repetitive pattern of abundance variations, which is seriously disturbed in summer, especially after a warm spring, by a massive bloom of filamentous green algae
The macroscopic vegetation of lakes is to a great extent composed of perennials of which the phenology or population dynamics and structure, except for some species, have not been studied in detail

Summary

Introduction

Mosses are a common element of submerged vegetation in softwater lakes of northern Europe. They are mixed with higher plants or charophytes 1990), especially in oligotrophic lakes (Srivastava et al.1995; Toivonen and Huttunen 1995; Murphy 2002). The macroscopic vegetation of lakes is to a great extent composed of perennials of which the phenology or population dynamics and structure, except for some species, have not been studied in detail. One of such water plants is Sphagnum denticulatum Brid. This species is fairly common e.g. in the Scandinavian Peninsula, northwestern Russia (Karelia Republic), British Isles and coastal regions of the North and West European Plain (Murphy 2002), as well as some mountains including the eastern Pyrenees (Gacia et al 1994)

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