Adult oysters are stimulated to spawn by changes in the water temperature. Along the Southwest Florida coast, the Eastern Oyster begins to spawn in the spring when water temperatures reach about 68°F; it continues to spawn throughout the summer and into the fall; and stops spawning when water temperatures fall below the 68°F threshold. Eggs and sperm are released into the water where fertilization takes place. The eggs hatch within 24 hours after undergoing several embryonic stages and develop into free-swimming, planktonic trochophore larvae. Hair-like cilia on the surface of the larvae allow them to navigate horizontally and vertically in the water column to remain at the optimum salinity range. Over a 2-3 week period, the trochophore larvae remain free-swimming while undergoing 2 more larval stages before settling and becoming adults. Within 12-24 hours trochophore larvae begin to develop a shell and a foot and are called veliger larvae. The veliger larvae finally develop into pediveliger larvae which have a well-developed foot and eye spots that allow the larvae to find an appropriate place to settle out as spat – newly attached juvenile oysters. Depending upon conditions, it takes from 1-3 years for spat to grow into adult oysters.
Photo credit: Auburn University, Marine Extension and Research Center