A comparative study of ultraviolet radiation tolerance in different populations of Diaptomus minutus

Abstract

A series of experiments was conducted to test the hypothesis that populations of Diaptomus minutus routinely experiencing high levels of ultraviolet radiation (UVR) are more tolerant of UVR than are those that routinely experience low levels of UVR. The relative degree of UVR tolerance was determined by monitoring mortality induced by either lamp or solar UVR. Diaptomus minutus from the low-dissolved organic carbon (DOC), high-UVR Lake Giles were consistently more tolerant of lamp and solar UVR than were those from the moderate-DOC, low-UVR Lake Lacawac. This differ- ence in UVR tolerance was apparent throughout the year in freshly collected animals, but it did not persist in cultured animals. The lamp UVR tolerances of cultured D.minutus were similar, except for those initiated from September collections. The September culture of Lake Giles animals was signifi- cantly more tolerant than the Lake Giles cultures initiated in December, May and June. The September culture of Lake Lacawac animals was significantly more tolerant than the June culture. The lamp UVR tolerance of freshly collected Lake Giles animals was greatest from late June through October, but the Lake Lacawac population was least tolerant in July and August. No differences in lamp UVR toler- ances were detected between animals collected from the surface and those collected from deeper water of either lake. It is concluded that the Lake Giles population was more tolerant than the Lake Lacawac population and that the period of greatest tolerance occurred several months after the time period with the highest ambient levels of solar UVR. Collectively, the experiments with both field and laboratory- cultured animals suggest that acclimation time plays a large role in UVR tolerance.