General description

Aquatic soldiers, Stratiotes aloides (Hydrocharitaceae), are floating plants that form often wide plantations in river bays and floodplain lakes. It is assumed (e.g., Sugier et al., 2010) that common occurrence of these plants may be considered to be evidence for good status of an aquatic ecosystem and diversity of aquatic vegetation. According to Suutari et al. (2009), occurrence of S. aloides indicates first of all the relatively low level of the water eutrophication.

S. aloides is one of the most available aquatic substrates for macroinvertebrate colonization and can be used as an indicator of valuable habitats in terms of macroarthropod diversity and species richness (Suutari et al., 2009). In southern Finland (Suutari et al., 2009), invertebrate communities in lakes with S. aloides include 257 species of 10 taxa, at 23 species more than invertebrate communities with the same taxa in lakes without these plants.

According to faunistic studies (e.g., Kiss & Juhász, 1996; Linhart, 1999; Obolewski, 2005), numerous epiphytic and mining invertabrates of 22-33 taxa inhabit rosettes of S. aloides. Practically in all studied localities, Chironomidae larvae are most abundant. The total abundance of phytophilous macroinvertebrates (> 300 μm) is estimated (in Poland’s lake) to be 8,328 individuals per m² for epiphytic invertebrates and 11,800 individuals per m² for all animals, including mining Chironomidae that have 40% of all chironomid larvae found in samples (Linhart, 1999). These numbers are higher than those given by Deák et al. (2008) for Balaton. According to observations (e.g., Obolewski, 2005), biomass of invertebrates can achieve 3-6 gr per 1 kg of fresh plants being determined by large invertebrates, Gastropoda and Bivalvia first.

Conservation

In southern Finland, lakes with S. aloides harbour more species of conservation priority than lakes without these plants (Suutari et al., 2009). Such endangered species as Aeshna viridis, Leucorrhinia caudalis and Leucorrhinia pectoralis (Odonata) are strongly associated with S. aloides.

Females of A. viridis mainly lay eggs on the leaves of  S. aloides and occasionally on some other aquatic plants, such as Typha spp. and Sparganium spp. (Matushkina & Gorb, 2003; Rantala et al., 2004). Adult dragonflies have been found occasionally by water without S. aloides, but larvae have only been recorded in lakes with these plants (Rantala et al., 2004). In accordance with field and laboratory data of the same authors, this is possibly because the spiny leaves of S. aloides protect effectively A. viridis larvae against predatory fish (like perch, Perca fluviatilis).

Intraguild predation of larvae of A. viridis with larvae of sympatric A. grandis and A. juncea is possible, with the susceptibility of larvae of the first species (Suutari et al., 2004). This conflict can be partially solved through spatial divergency, because larvae of A. viridis prefer inner parts of S. aloides rosettes. On the other hand (see Suutari et al., 2004), A. juncea prefer more oligotrophic and slightly acid waters. There are also strong differences between the foregoing species on substrates for oviposition (Matushkina & Gorb, 2003): females of A. grandis and A. juncea prefer dead plant materials. In accessible literature sources, we have not found direct indications on co-occurrence of A. viridis and A. grandis larvae in the same S. aloides rosettes.

Owing to the decline during last decades of S. aloides in Europe due to eutrophication and environmental stresses (e.g., Roelofs 1991; Smolders et al. 1996), A. viridis become scarcer and disappear from many former distribution areas (Sahlén et al., 2004).

Basic References

Deák C., Gór D., Lakatos G. 2008. Phytophil ... Read more »