Steps in the construction of underwater coral nursery, an essential component in reef restoration acts

Abstract

Many coral reefs worldwide are rapidly declin- ing, but efficient restoration techniques are not yet available. Here, we evaluate methodologies for reef res- toration based on the ''gardening concept''. A floating mid-water prototype nursery was placed at 6 m depth (14 m above sea-bottom) within the nutrient-enriched environment of a fish farm (Eilat, Red Sea). Ten colonies from five branching coral species provided 6,813 frag- ments (0.5-3 cm height). The fragments, each attached to a plastic pin, were inserted into plastic nets that were tied to a rope-net floating nursery. After 144 nursery days, only 13.1% of the fragments died and 21.2% were de- tached by mechanical forces. Small colonies ready for transplantation developed within 144-200 days. Ramets' ecological volumes increased 13-46 folds and their heights by a factor of 3.5. After 306 days, the ecological volumes of the colonies increased 147-163 fold as com- pared to original volumes (revealing a daily growth rate constant of 1.67% during the first 5-10 months) and height values by a factor of six. Building and maintenance costs of the nursery were low. This nursery prototype demonstrates the feasibility of the coral ''gardening concept'' by fulfilling several important needs, namely, mass production of coral colonies at low costs, high survivorship, fast growth, short nursery phase and im- proved methodologies for handling farmed colonies.