Hatching success affects the timing of spawning by the intertidally spawning puffer Takifugu niphobles

Abstract

The puffer Takifugu niphobles, which is an intertidal spawner and deposits eggs in the upper intertidal zone, spawns on several days of every spring tide during spring to summer (i.e. the semilunar spawning cycle). As the season progresses, however, the timing of spawning events progressively shifts from just before to just after the new or full moon. This study explains why there is the seasonal shift in the timing of spawning from the viewpoint of larval hatching success. Larval sampling in the field and rearing experiments in the laboratory indicated that hatching occurred only when the nighttime high tides flood the stranded eggs. According to ambient temperatures, incubation periods tended to be shorter as the season progressed. Therefore, spawning occurs prior to the peak spring tides (dates of new and full moons) early in the season to allow sufficient time for completion of embryological development prior to the occurrence of neap tides, which may not flood the intertidal spawning site. The relationship between the zone of stranded eggs and the tidal regime at the site indicated that most of the completely developed embryos can be successfully submerged by nighttime high tides for the greater part of the season. Quadrat sampling of eggs showed that many embryos died because of temperature stress during intertidal incubation. The most advantageous time for embryo survival is, especially later in the season, after the peak spring tides when the intertidal zone is inundated at midday and temperatures are moderated by the water cover. The progressive shift in the timing of spawning is the result of a seasonal trade-off between the embryo survival during intertidal incubation and successful hatching during periods of submergence.