AN IN-SITU ENCLOSURE EXPERIMENT TO TEST THE SOLAR UVB IMPACT ON PLANKTON IN A HIGH-ALTITUDE MOUNTAIN LAKE - I - LACK OF EFFECT ON PHYTOPLANKTON SPECIES COMPOSITION AND GROWTH
S. Halac et al., AN IN-SITU ENCLOSURE EXPERIMENT TO TEST THE SOLAR UVB IMPACT ON PLANKTON IN A HIGH-ALTITUDE MOUNTAIN LAKE - I - LACK OF EFFECT ON PHYTOPLANKTON SPECIES COMPOSITION AND GROWTH, Journal of plankton research, 19(11), 1997, pp. 1671-1686
The effect of solar UVB radiation on the growth and species compositio
n of phytoplankton from a high-mountain lake (2417 m a.s.l.) was studi
ed in situ for 16 days in two enclosures of 1 m(3), receiving either f
ull sunlight or sunlight without UVB. A total of 20 species were ident
ified in both enclosures, consisting mainly of dinoflagellates, chryso
phytes and diatoms. During the experiment, there were no significant d
ifferences in phytoplankton species composition between the two enclos
ures. In both treatments, the abundance of phytoplankton increased con
tinuously, and chlorophyll a changed by similar to 5-fold. We observed
high fluctuations in the abundance of several species. However, these
fluctuations occurred in both enclosures, and hence they were not rel
ated to UVB radiation. Some species were affected by daily fluctuation
s of radiation (UVA + photosynthetically active radiation). Cyclotella
aff. gordonensis showed a robust positive correlation, whereas specie
s of Gymnodinium were negatively correlated. For most species, the sen
sitivity to radiation found during the experiment was consistent with
their diurnal vertical distribution in the lake. Our findings suggest
that the phytoplankton from this very clear lake (10% of the surface U
VB radiation at 305 nm reached 9.6 m depth) were well adapted to the h
igh UVB radiation characteristic of high-elevation sites.