Charophytes of the lake Garda (Northern Italy): a preliminary assessment of diversity and distribution

Abstract

Charophytes (stoneworts and bassweeds) are a typical macrophytic component of inland water ecosystems. Well-developed submerged meadows of charophytes are expression of clear water and rather low phytoplankton concentrations. Consequently, among aquatic macroscopic primary producers, charophytes are one of the most threatened groups being very sensitive to phosphorous availability, turbidity and water level perturbations. Accordingly, charophytes have been suffering a massive diversity loss worldwide over the last century, mainly because of human-induced pressures. During summer 2011, detailed field surveys were carried out with the main purpose of filling knowledge gaps concerning aquatic flora and vegetation of the lake Garda – the largest lake in Italy and one of the deepest in Europe. Along randomly selected transects, floristic data were collected following standard procedures, as imposed by the Water Framework Directive. Overall, 12 different species of charophytes were recorded, which accounts for 36% of total Italian charophytes and 19% of European species. The most diffuse species were <em>Chara globularis</em> and <em>C. intermedia</em>; whereas, the most interesting taxa were <em>Chara polyacantha</em> and <em>Nitella hyalina</em>, two species with narrow distribution in Italy. Overall in the lake Garda, dense stands of charophytes covered almost homogeneously the littoral sectors at a water depth between 3 and 12 m. The deepest species was <em>C. globularis</em>, which reached a maximum depth of colonisation of about 17.5 m. Charophytes represent a major element among the primary producers in the lake Garda. The high local charophyte diversity and the rather wide most colonised areas (~1000-1200 ha) confirm that the lake Garda is an important reserve for many rare and threatened charophytes. For the first time, these results highlight the key role of the lake Garda for charophyte diversity at a national and European level

Short‐term dynamics of submerged aquatic vegetation diversity and abundance in deep lakes

“…; Bolpagni et al. ). Macrophyte diversity is highest between 1 and 5 m depth, in the presence of intermediate levels of disturbance.…”

A preliminary evaluation of lake morphometric traits influence on the maximum growing depth of macrophytes

“…During the last century, aquatic plants have experienced a widespread decline and a marked decrease in diversity and representativeness, especially in developed countries (Schmieder, 2004;Dudgeon et al, 2006;Bolpagni et al, 2013a). Eutrophication and water over-exploitation, land use changes and littoral and shoreline modifications are the main factors forwarding critical regime shifts in aquatic primary producers that have promoted the replacement of submerged plant species by pleustophytes or phytoplankton (Scheffer et al, 2003;Bolpagni et al, 2007Bolpagni et al, , 2013bBolpagni et al, , 2014Sayer et al, 2010;Azzella et al, 2013aAzzella et al, , 2014Tombolini et al, 2014).…”

Untitled

“…In 1959 six of the eight lakes possessed good ecological status and two, Bikcze and Mytycze were considered to be in very good This index is based mainly on submerged macrophytes and floating-leaf plants, which are more sensitive to changes in water conditions (Radwan & Kornijów, 1991;Søndergaard et al, 2010;Bolpagni, et al, 2013). In lakes where index values were low, hence qualified as of poor ecological state, submerged macrophytes were virtually absent and frequent phytoplankton blooms occurred.…”