MEPS 298:251-260 (2005)  -  doi:10.3354/meps298251

ABSTRACT: The timing of larval release and the cues that control these rhythms (tidal, diurnal, or lunar cycles) were studied over a 2 mo period in the cirripeds Pollicipes pollicipes, Balanus spp. and Chthamalus spp., occurring on an exposed rocky shore in NW Spain. All of them showed rhythms of larval release, but the rhythms were different in each species. Chthamalus spp., which principally inhabit the upper intertidal zone, released their larvae mainly during diurnal high tides at the time of new and full moons. Larval release was greater during the afternoon than during the morning, because the amplitude of afternoon high tides was significantly higher than that of morning high tides. P. pollicipes larvae were released at morning high tide during waning moon and, to a lesser extent, during full moon. Nauplii of Balanus spp. were released during new and waning moons; almost no release occurred during full moon, and no larvae were found during the waxing moon, mainly during diurnal high tides. P. pollicipes and Balanus spp. usually began to release larvae after sunrise, which may be the factor inducing synchrony. In contrast, Chthamalus spp. released larvae at any time of day, but always coinciding with high tide, indicating that seawater may be the cue that triggers larval release in this species. Although larval release should occur during safe periods (e.g. night-time) in species such as those under study, with small unprotected colored larvae that are visible to predators, almost no larvae of any of the 3 cirripeds were found at night. Cirriped Nauplius I larvae respond positively to light, allowing larvae to travel upwards in the water column, away from congeners that could incidentally ingest their own larvae, and are transported offshore away from predators, which are more abundant close to the shore. At night this photopositive behavior does not take place, and thus the synchrony in the emission of larvae during daytime induces larval aggregation, which may increase larval survival because of the swamp effect over predators.

KEY WORDS: Larval release · Rhythms · Tides · Diurnal · Lunar · Cues · Barnacles · Nauplius