The study of cyst bank of 6 hypersaline lakes allowed us to give a
dimension to the unexpressed, potential biodiversity inhabiting such a
typology of stressed environments. A sensible portion of the
biodiversity of each lake rests during most of the year, and only a
portion of the species present result active in the water column at
each date. The accumulation of cysts of different species, generations
and genotypes with variable hatching rates leads to a mixed cyst bank
more bio-diverse than the active community sampled at any one moment.
Available information coming from the Vecchia Salina 
reported a total of 16 species in the water column (deriving from a
sampling effort which lasted over two years). The number of cyst types
(17) here reported from the bottom sediments of the same environment is
lower than that (24) reported by the same authors, but in that case the
investigation was carried out on a total of 14 cores collected in 14
different sites of the lake, while in the present study only the
central area of the lake was concerned by the collection of just 3
It is evident that such a light sampling effort (3 sediment cores at
one sampling date) devoted to the sediments gives more information than
a two-year period of sample collection in the water. Nevertheless, we
cannot ignore the fact that some species do not supply the sediment
cyst bank but overcome adverse periods differently (e.g. migrating as
insects do, or resting as sub-adults, as some harpacticoids do). Hence
the analysis of cyst banks cannot still completely substitute the
traditional investigation on active stages. It could be proposed,
however, as an indispensable additional source of information to
correctly evaluate the biodiversity of water environments [10,13].
A greater diversity of zooplankters are represented in the egg banks in
comparison to that present in the current water column, these are
dormant phases of the zooplankters life cycle and favourable hatching
conditions for those unique cohorts may or may not occur within a given
lake. The egg banks stored in sediments of each lake represent its real
potential diversity. This does not diminish their importance over time
because, as environmental conditions in a lake change its appropriate
zooplankter assemblage, it will be more (or less) dominant.
As regards the species composition of each assemblage, it can be
noted that Koyashskoe and Nartë were the poorest, while Vendicari pools
and Vecchia Salina saltworks were the richest lakes.
Some information about salinity [see Additional file 3]
suggests that this could be due to the high salt concentrations
characteristic of the first waters. The biodiversity of saline
habitats, in fact, seems to be inversely correlated with the salinity
As regards the species composition, we can note that both the
environments of Vendicari (Pantano Grande and Pantano Roveto) do not
host Artemia cysts, while they are the only habitats where diaptomid eggs have been found. As in the case described by ,
despite the proximity to the sea, the salt is probably not of marine
but of athalassohaline origin (underground brines). It has been proved
that the quality of salt content affects the biological community [6,7],
and a chemical analysis of dissolved anions in the Vendicari lakes
water will be the necessary future information to be collected to
confirm this rule. The sediments of both Vendicari lakes (Pantano
Grande and Pantano Roveto) sampled during the dry season (September
2005), did not show the presence of Artemia cysts, while there have been recognized eggs of other Anostraca (Phallocryptus sp.) and Calanoida (Arctodiaptomus sp.).
Although the two lakes are close to the sea, this taxonomic composition
of egg bank suggests their salinity is not entirely of marine origin,
but influenced by continental inputs.
Additional file 3. Table S3. Hypersaline lakes considered in the present study (listed in longitudinal order): salinity (‰) and depth (m) values.
Size: 21KB Download file
wide hatching patterns observed for most of the tested species is
thought to be an obligatory adaptation to the extreme variability of
the habitat. Hatching tests affirmed that the 5 tested species
inhabiting the present lakes dislike freshwater conditions. Hatching
has been found to be highly variable, even among cysts coming from the
same sediment level, as well as among different layers of each core,
probably due to the need to spread the risk of non successful hatching
over many attempts, according to the bet hedge theory of [17,18]
to ensure the persistence of populations in unpredictably stressed
environments. Indeed, most of cyst morphotypes here considered belong
to species that live in environments with a high level of stochasticity
, a condition in which bet-hedging is expected to evolve .
Cyst banks form an essential component of plankton ecology. As cyst
banks integrate seasonal and year-to-year variations in environmental
conditions, they represent the total species and genetic diversity in
any community better than the active component sampled at any one time.
Cyst banks can be considered the archive of the local habitat, and
overlooking the composition of the cyst bank in the study of
biodiversity and biogeography may result in erroneous patterns and
interpretations of the underlying processes.