UV-absorbing mycosporine-like compounds in planktonic and benthic organisms from a high-mountain lake
Sommaruga, Ruben; Garcia-Pichel, Ferran
Archiv für Hydrobiologie Volume 144 Number 3 (1999), p. 255 - 269
published: Mar 5, 1999
ArtNo. ESP141014403003, Price: 29.00 €
We investigated the occurrence, concentration and composition of mycosporines (mycosporine-like amino acids, MAAs) in planktonic organisms and epilithic cyanobacteria from a clear water high-mountain lake situated in the Central Alps, Austria. Two bi-substituted MAAs were identified by HPLC in extracts made of 1996 plankton samples with 90 % aqueous methanol, i.e. asterina-330 (Λmax = 330 nm) and shinorine (Λmax = 334 nm). Extracts with 20 % aqueous methanol for 2 h at 45 °C revealed the additional presence of another MAA tentatively identified as palythine (Λmax = 320 nm) in the 1998 planktonic assemblage. In the upper 3 m of the water column the total concentration of MAAs decreased exponentially with depth, but the maxima for both absolute and chlorophyll-a specific concentrations were observed close to the bottom at 8.5 m depth. This was explained by the accumulation of MAAs in the copepod Cyclops abyssorum tatricus that stays in deep water, during daytime. The copepodite III stage contained the 3 MAAs found in phytoplankton but also the mono-substituted compound, mycosporine-glycine (mycosporine-gly: Λmax = 310 nm). The concentration of MAAs in C. abyssorum tatricus was highest for shinorine (l.45 % of the dry weight) and lowest for mycosporine-gly (0.02 % of the dry weight). Epilithic cyanobacteria had a more diverse MAA spectrum than plankton, and produced not only asterina-330 and shinorine but also palythinol (Λmax = 332 nm), mycosporine-gly and two unidentified compounds with Λmax = 330 and 340 nm. The composition and also the relative abundance of the cyanobacterial MAAs changed with depth. Mycosporine-gly was found at the lakeshore where Gloeocapsa sp. dominates, but it was absent at 0. 5 and 2. 5 m depth dominated by Schizothrix sp. and Tolipothrix sp., respectively. We could not detect any MAAs in the cysts of the red snow alga Chlamydomonas nivalis, which develops on top of the winter cover shortly be fore ice-melt. These results expand to alpine lakes the range of ecosystems in which these compounds may play a significant biological role.