The Reproduction of the Red Sea Coral Stylophora pistillata. I. Gonads and Planulae

Abstract

The reproduction of Stylophora pistillata, one of the most abundant coral species in the Gulf of Eilat, Red Sea, was studied over more than two years. Gonads were regularly examined using histological sections and the planula-larvae were collected in situ with plankton nets. S. pistillata is an hermaphroditic species. Ovaries and testes are situated in the same polyp, scattered between and beneath the septa and attached to them by stalks. Egg development starts in July preceding the spermaria, which start to develop only in October. A description is given on the male and female gonads, their structure and developmental processes. During oogenesis most of the oocytes are absorbed and usually only one oocyte remains in each gonad. S. pistillata broods its eggs to the planula stage. Planulae are shed after sunset and during the night. After spawning, the planula swims actively and changes its shape frequently. A mature planula larva of S. pistillata has 6 pairs of complete mesenteries (Haicampoides stage). However, a wide variability in developmental stages exists in newly shed planulae. The oral pole of the planula shows green fluorescence. Unique organs ('filaments' and 'nodules') are found on the surface of the planula; these might serve as attachment organs. A hypothesis is offered for further examination suggesting a trend of brooding versus non-brooding species in sc\eractinian corals: Coral species which develop gonads in their body cavities (usually branching forms or small polyped corals) reduce the number of eggs during oogenesis, have small eggs and brood planula-larvae, while coral species which develop gonads within their mesenteries (usually massive growth forms or large polyped corals) have numerous and large ova per polyp and expel their eggs into the water.