The California grunion, Leuresthes tenuis, spawns on shore during spring high tides and fertilized eggs incubate 9-14 days until wave action stimulates hatching during the next spring high tide series. Embryos that are not washed out can remain viable for at least 35 days and may hatch during subsequent spring high tides. We hypothesized that larvae fertilized at two different also monitored the environmental conditions that grunion embryos experience on three beaches in southern California.
Egg masses were located, their depths recorded, and tidal heights measured. Sand movements and temperatures at two depths (15 and 25 cm) were monitored at each beach for 32 h during a spring tide series. Mean sand temperature at depths where we found grunion egg masses ranged from 17.5°C to 23.7°C. Temperature fluctuated by as much as 11.4°C and varied more at shallower depths. These differences in temperature will affect the rate of grunion embryonic development and when they are ready to hatch.
Based on measured tidal heights of the egg masses, predicted tides and sand movements within the environment, embryos at all three beaches may be forced to delay hatching. We compared development and swimming speed in 30-days-post-fertilization (dpf ) larvae and 14-dpf larvae. The 30-dpf larvae were significantly longer, had less yolk, and fewer myotomes than the 14-dpf larvae, but swimming speed did not differ between the two groups. Delayed hatching resulted in larger, more developed larvae with reduced energy reserves, which may impact post-hatching survival in Leuresthes tenuis.