Photomovement of Aquatic Organisms in Response to Solar UV

Abstract

Photomovement in response to sunlight has been reported in many species of planktonic organisms. The literature includes numerous studies of vertical migration patterns of planktonic species, but relatively few studies examine the role of solar UV in influencing these movements. Studies by Cowles and Brambel (1936), Hasle (1950, 1954) and Barcelo and Calkins (1979) suggest that UV light may influence movements during the day, particularly avoidance of the surface at midday. These daily movement patterns were observed to change in varying climatic conditions e.g. the amount of cloudcover, intensity of irradiance, etc. changed the distribution pattern (Hasle 1950, 1954; Eppley et al. 1968; Goff 1974). Other examples of this phenomenon were reported by Cowles and Brambel (1936) in which they observed that Gonyostomum were distributed lower in a pond on bright clear mornings than on other somewhat less bright mornings, while on cloudy mornings the maximum counts were at the surface. Agamaliev and Bagirov (1975) also observed a similar pattern by ciliates in the Caspian Sea. Barcelo and Calkins (1979) examined various external and internal environmental factors (i.e. light, temperature, wind, etc.) to determine if it is indeed sunlight, solar UV, or some other factor which is most important in influencing the vertical distribution of certain aquatic species. In this particular study the distribution of the ciliate, Coleps was examined and low correlation was found between the location of the animals and wind, temperature gradients, food gradients, etc. On the other hand, irradiance factors (both total solar irradiance and the UV-B component of sunlight) showed high correlations with the location of the protozoan, in good agreement with the aforementioned studies.