Larval release and photobehavior were studied in the colonial ascidian Polyandrocarpa zorritensis. The test hypothesis was that if larval release is induced by light, then larvae should be attracted to settlement areas where light is sufficient for larval release. Light induced larval release but the time course varied with light intensity. As the intensity of either sunlight or blue-green light decreased (1) the time until the beginning of larval release (latency) became longer, (2) the mean time of larval release increased, and (3) the time interval over which larvae were released increased. The threshold light intensity to induce larval release in blue- green light (8.75 x 1012 photons cm-2 s-1) was lower than that in sunlight (3.6 x 1013 photons cm-2 s-1). Light induced larval release was not affected by currents up to 15 cm s-1. Larvae aggregate in light when given a choice between light and dark. This response did not vary with larval age. The lowest light intensity, at which larvae could distinguish between light and dark was 5.0 x 1012 photons cm-2 s-1 in blue-green light and 2.9 x 1014 photons cm-1 s-1 in sunlight. Thus, the hypothesis is supported because larvae are attracted to areas where light intensity is sufficient for larval release. (C) 2000 Elsevier Science B.V. All rights reserved.
Forward, R. B., Welch, J. M., & Young, C. M. (2000). Light induced larval release of a colonial ascidian. Journal of Experimental Marine Biology and Ecology, 248(2), 225–238. https://doi.org/10.1016/S0022-0981(00)00168-4