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Diel vertical migration of copepods in mountain lakes: The changing role of ultraviolet radiation across a transparency gradient
Author(s) -
Fischer Janet M.,
Olson Mark H.,
Theodore Nora,
Williamson Craig E.,
Rose Kevin C.,
Hwang Jin
Publication year - 2015
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.1002/lno.10019
Subject(s) - diel vertical migration , copepod , daytime , zooplankton , transparency (behavior) , environmental science , ecology , water column , predation , oceanography , atmospheric sciences , biology , crustacean , geology , political science , law
The transparency regulator hypothesis (TRH) proposes that water transparency determines the relative importance of visual predation vs. ultraviolet radiation (UVR) in driving zooplankton out of the surface waters during the day. To test this hypothesis, we used a combination of observational and experimental approaches to examine the effects of UVR, photosynthetically active radiation (PAR), fish, temperature, and food resources on the daytime vertical distribution and diel vertical migration (DVM) of the copepod Hesperodiaptomus arcticus in a set of lakes in the Canadian Rocky Mountains. Across lakes, H. arcticus daytime vertical distribution increased with both UVR transparency and depth of food resources, and was not related to PAR, thermal structure, or the presence of fish. We also observed a strong positive relationship between UVR and H. arcticus daytime depth distribution in a single lake that varied in transparency over time. The presence of substantial DVM in H. arcticus in two transparent lakes coupled with the lack of DVM in a less transparent lake indicated a weakening effect of UVR in lower transparency conditions. Finally, we deployed open‐bottomed vertical columns constructed of UVR‐blocking and UVR‐transmitting material overnight in two lakes of contrasting transparency. The following day, we observed significantly more copepods in UVR‐blocking columns in the more transparent lake but no UVR effect in the less transparent lake. Collectively, our results provide multiple lines of evidence supporting the TRH by highlighting the changing role of UVR as a driver of DVM across lakes of varying transparency.