A floating mid-water coral nursery as larval dispersion hub: testing an idea

The global decline in reef health has prompted the need for effective management methodologies, including the development of active restoration measures. One such approach is the ‘gardening concept’ that involves use of underwater nurseries where coral fragments are farmed before their transplantation into denuded reefs. Here we document enhanced sexual reproduction in colonies of the coral Stylophora pistillata cultured in mid-water floating nursery situated in nutrient enriched water, near the fish farms in Eilat, Red Sea. We found that after 2 years of nursery, the average number of oocytes per polyp in farmed colonies was ca. 35% higher than in corresponding naturally growing colonies. Small branches in the nursery developed gravid colonies that released equal (or more) numbers of planula larvae as compared to similar size, 5-year old naturally growing colonies. These nursery-borne planulae possessed more zooxanthellae and contained more chlorophyll per larva. While settled and metamorphosed in equal rates compared to planulae originated from reef-grown colonies, the nursery borne planulae developed faster growing young colonies. We estimate that a coral nursery could generate, during the reproductive season, tens of millions of planula larvae and therefore should be regarded as a ‘larval dispersion hub’ that can be used as a management tool for natural recruitment enhancement.