Weakly synchronized larval release maintained in the presence of predatory fishes

Abstract

a b s t r a c t a r t i c l e i n f oMany marine species minimize predation during hatching or spawning by releasing larvae or gametes synchronously during nocturnal spring ebb tides. Propagules are then rapidly transported away from high densities of predatory fishes into deeper waters under the cover of darkness. Females also suspend foraging in the presence of predators, but it is unknown whether they are able to delay releasing larvae. In a previous study, we found that larval release is only weakly synchronized to the safe period in a cold upwelling region, although the study was conducted on outdoor seawater tables in the absence of tides that reinforce endogenous rhythms. In this study, we experimentally determined whether larval release 1) is better synchronized in the field and 2) delayed in the presence of predatory fishes. Larval release was weakly synchronized to tidal amplitude, tidal and diel cycles, occurring from late flood to late ebb tide on both intermediate and spring tides during twilight as well as darkness. Weak synchrony likely arises because cold temperatures extend incubation of externally brooded embryos, increasing exposure to environmental variation. Larval release was not delayed in the presence of predatory fishes; nor was refuge use or other behaviors of females altered by fishes. Behaviors were not affected by predators presumably because larvae are already being released near the safe period from refuges. Our results likely apply to other cold regions of the world, but it remains to be determined whether predators alter the activities of nonovigerous female and male shore crabs, which may not spend as much time in refuges as ovigerous females, potentially resulting in cascading effects on communities.

Investigating the timing of spawning of two sea urchins (Tripneustes gratilla and Toxopneustes pileolus)

“…Why should organisms achieve synchronization of spawning time without using cyclic factors that fluctuate rhythmically, for example, as in the lack of lunar/semilunar spawning patterns of the two sea urchins in this study? One explanation is that rhythmic factors could easily be predicted by predators (Lane & Mahony, 2002; Rasmuson et al., 2014). Thus, loss to predation may be a strong selective force and could not be compensated for by spawning synchronization (Kao et al., 2010).…”

Decreased temperature results in daytime larval release by the fiddler crab Uca deichmanni Rathbun, 1935

“…maintain the timing of larval release during darkness by switching from the morning to the evening high tide when the morning tide occurs after sunrise (Christy, 2003;Christy and Backwell, unpublished data). Other crabs that live in colder water and have low synchrony of larval release among individuals also release during either evening or morning high tides, thus maintaining release during darkness or twilight for the most part (Rasmuson et al, 2014). A few other species do release larvae, at least partially, during the day.…”

“…This timing of larval release therefore likely reduces the risk of predation on females and larvae by diurnally feeding fishes that are abundant nearshore (Morgan, 1990(Morgan, , 1995Christy, 1995, 1997;Hovel and Morgan, 1997;Kerr et al, 2014a). A few crab species nevertheless release larvae during both day and night, or release during the day, if the largest amplitude tides do not occur at night (Morgan and Christy, 1995;Kellmeyer and Salmon, 2001;Yamaguchi, 2001;Christy, 2011;Rasmuson et al, 2014). In addition, there are conditions under which females may be unable to match the timing of larval release with the best tides, the nocturnal high tides with large amplitude, and must release during suboptimal tides.…”