Spawning behaviour in Platygyra daedalea off South Africa

Abstract

Coral spawning has never been observed in South Africa at the southernmost limit of scleractinian distribution along the East African Coast. Corals in the region are exposed to low temperatures (summer means of 26°C) and turbulent conditions (Schleyer et al. 2008), which may infl uence their spawning. Visiting the reefs at night is diffi cult, so 10 colonies of Platygyra daedalea (Ellis and Solander 1986) were collected on Two-mile Reef (27°31′376′′S, 32°41′181′′E) a few days before the Full Moon of February 2012 (07/02/12) and placed in open-water aquaria. The date of spawning in P. daedalea off South Africa was predicted from regular sampling of colonies from 2010. Spawning occurred over three consecutive nights (Full Moon +2 to +4 days) in 6-9 colonies at a water temperature of 26°C. The peak activity in spawning was observed at Full Moon +4days when 9 colonies spawn synchronously. Field sampling showed that in-situ colonies also spawned around these dates. Sperm and egg bundles were released between 19:00 to 22:00, with peak release at 20:30. Individual polyps released single bundles in synchronous waves, every 15-30 minutes. Each bundle of gametes was visible in the polyp mouth for 0.5-2 h before release (Figs 1A, B). During this time, they were rotated inside the polyp mouth, probably to compress the gametes and facilitate bundle expulsion (Fig. 1C). After release, the polyp mouth continued to gape for several minutes (Fig. 1D). This spawning behavior has been reported in several Platygyra species (Babcock et al. 1986). In the present study, the bundles averaged 2.2 mm (SE=0.2, N=25) in diameter and contained an average of 89.2 oocytes (SE=15.9, N=15). Each polyp released 2-3 bundles per spawning night. A single P. daedalea colony with an average diameter of 10 cm could thus re lease up to 10,000 oocytes per night. P. daedalea is known to spawn durSpawning behaviour in Platygyra daedalea off South Africa