THE EFFECTS OF IRRADIANCE LEVELS AND SPECTRAL COMPOSITION ON MATING STRATEGIES IN THE SNOW ALGA, CHLOROMONAS SP.-D, FROM THE TUGHILL PLATEAU, NEW-YORK-STATE

Studies have related changes in snow albedo to snow crystal structure and to the presence of surface debris (i.e, pine needles), but there h as been less attention given to the existence of algae in snow. An inc rease in the number of snow algae could also decrease albedo and incre ase snowmelt rates. The primary purpose of this paper is to document h ow solar irradiance serves to control the developing stages of algae i n snow. Snow algae do not appear near the surface until there is meltw ater in the snowpack. Low levels of solar irradiance penetrate through the snowpack and germinate snow algal resting stages that lie underne ath, and snow algal growth is enhanced by available gases and nutrient s. Flagellate cells swim through the snowpack in the meltwater around the snow crystals, and cells are positioned according to irradiance an d spectral differences. In this study, Chloromonas sp.-D strains 582C and 582D, isolated from the upper 20 cm of snowpacks in the Tughill Pl ateau, Whetstone Gulf State Park, NY, were used to investigate mating strategies under different irradiance levels and spectral compositions in the laboratory, and the irradiance levels used in the experiments correlated with those recorded from the upper 20 cm of snow. Using sim ilar irradiance levels, blue light regimes produced more matings than green and red light regimes. There were no trends in mating when compa ring green and red light regimes. When red light regimes of higher pho ton irradiance (85 mu mol m(-2) s(-1)) were compared with those of blu e light regimes of lower irradiance (30 mu mol m-2 s(-1)), more mating occurred under red light. A photon irradiance of 95 mu mol m(-2) s(-1 ) [photosynthetically active radiation (PAR) of 400-700 nm] produced t he most mating under both wide-spectrum (WS) and cool-white (CW) regim es, but more mating occurred under CW in all irradiances tested. Matin g pairs of three types were observed: oblong-oblong (o-o), oblong-sphe re (o-s) and sphere-sphere (s-s). Cell packs that produced mating type s and o-o mating pairs diminished through the eight-hour time duration of the experiments. However, o-s and s-s mating pairs peaked at six t o seven hours after the experiments began, while quadriflagellate zygo tes produced from the mating pairs continued to increase throughout th e eight hours. (C) 1998 John Wiley & Sons, Ltd.