Wave-induced variability of the underwater light climate in the littoral zone

Abstract

Underwater irradiance, here referred to as photosynthetically active radiation (PAR), undergoes strong temporal fluctuations. These fluctuations are not only caused by variations in the incoming light intensity but also by variations in the elevation and curvature of the water surface resulting from wave motion (SNYDER & DERA 1970, KIRK 1994, ZANEVELD et al. 2001). In addition, wave-induced resuspension of particles in the littoral zone can cause rapid changes of light attenuation within the water column. Thus, the variability of the light field is maximal at shallow depths (DERA & GORDON 1968, RØRSLETT et al. 1997, SCHUBERT et al. 2001). Light intensity is important for the growth of phytoplankton (FINGER et al. 2007), biofilms, and macrophytes (SCHEFFER et al. 1993) and affects habitat choice, food uptake, and predation pressure of fishes (UTNEPALM 2004, SCHLEUTER & ECKMANN 2006). The biological relevance of fluctuating light is not only determined by the intensity of the fluctuations, but also by temporal scales (WALSH & LEGENDRE 1983, PAHL-WOSTL 1992). We experimentally investigated the variability of the underwater light climate in the littoral zone with the intension of providing amplitudes and temporal scales of the intensity fluctuations resulting from wave focussing, change in surface elevation and resuspension.