Dataset: Cell counts for 11 P. homomalla embryos taken every 5-10 minutes from fertilization to 13 hours after fertilization from adult corals collected in Round Bay, St. John, USVI in July of 2019

Methodology: 

Eleven female and four male branches of Plexaura homomalla were collected from adult colonies on an octocoral-dominated reef in Round Bay, St. John, USVI on July 14–15, 2019. All branches were about 15 cm long. Colonies were determined to be gravid in the field by cutting a 5-cm piece diagonally and looking for spermaries or eggs. Colonies were transported to the Virgin Islands Environmental Research Station and maintained in a sea table.

We monitored for signs of spawning for 5 hr starting at sunset starting one night after the full moon from July 17–23, 2019. Eggs and sperm were collected together with 60- mL syringes as they were released from the colonies and were stored in water from the tank for 30 min to ensure fertilization. We refer to the time at which gametes were collected as t = 0. On the third night of spawning detailed observations of embryo development were conducted by counting the number of cells in 11 embryos in triplicate every 10 min for the first 2 hr after fertilization, every 5 min for the next 4 hr, and every hour for the next 8 hr. Individual embryos were kept in separate containers. We stopped counting the number of cells after embryos reached 128 cells because further divisions became difficult to detect.

Instruments: 
dissecting microscope, hand lens