Influence of heterotrophic feeding on the sexual reproduction of Pocillopora verrucosa in aquaria

Recent research has shown that heterotrophic feeding has a strong effect on both maintenance and growth of corals by providing mainly a nutritional source of nitrogen and phosphorus. Nevertheless, no study has yet been undertaken on the interactions between feeding and sexual reproduction in corals. This study examines the effects of heterotrophic feeding on the sexual reproduction of Pocillopora verrucosa in aquaria. Rotifers were used as a live food source at two concentrations ((LFC = low feed colonies) = 5 × 102 organisms l− 1; (HFC = high feed colonies) = 15 × 102 organisms l− 1) with an unfed control (UC = unfed colonies). Three replicates of five colonies were used for each treatment. Rotifers were distributed among the nine aquaria four times per week for 3 h. Histological sections of coral polyps were prepared to monitor the development of gametogenic stages and the fecundity of the colonies. The number and size of oocytes, sperm sacs and gonad stages were determined in each polyp. Both fed and starved colonies of P. verrucosa proved to be simultaneous hermaphrodites and broadcast spawners. The gametogenesis period was short (3 months) and occurred from October to December 2007. No spawning event was observed in the aquaria. However, the disappearance of mature oocytes in samples collected in January 2008 suggested that spawning took place between December 2007 and January 2008. Heterotrophic feeding appeared to have a negative effect on reproduction in P. verrucosa. The results showed that both the proportion of polyps with gametes and the reproductive effort were lower in the fed than in starved colonies. It is likely that an energetic trade-off occurred between reproduction and other metabolic functions. However, oocytes were bigger in fed corals compared with the unfed controls. Several hypotheses are proposed to explain these metabolic/energy distribution patterns.