Integrated long term mid-water coral nurseries: A management instrument evolving into a floating ecosystem

Coral nurseries solve many of the technical and ecological problems that hamper long-term mass-farming of coral colonies, amenable for active reef restoration. Several types of nurseries have already been developed and tested. We outline here the operational summary of four mid-water, floating nursery prototypes in the Gulf of Eilat, Red Sea, that have been active for up to five years, yielding tens of thousands of healthy and large coral colonies from a number of coral species, a testimony to the long-term sustainability of these coral nurseries. Coral nurseries are similar to agriculture operations in that they require substantial investment of labor. Maintenance included routine checkups on the stability of the construction, the strength of the anchors and ropes and the constant adjustability of nursery's buoyancy. However, a well-designed nursery needs little alteration. Above outcomes relied on the availability of large numbers of coral fragments and nubbins produced at low cost, by low-tech, in the shortest possible culturing periods. The long-term maintenance of mid-water coral nurseries takes into account environmental and physical factors, the kind of coral species reared, ecological parameters and the nursery-specific "mini ecosystem" processes that delineate biological attributes for each mid-water nursery type. While covering a wide range of reef restoration needs, cumulatively, the coral nurseries manifested unique characteristics in comparison to terrestrial nurseries. One hallmark of a mid-water coral nursery is its integration into a de novo evolved floating reef ecosystem, ‘oases’ in blue waters, characteristic by a continuous influx of pests but also valuable reef organisms; this can also significantly improve performance and reduce maintenance costs. In contrast, terrestrial nurseries are designed as isolated and sterile entities. Floating coral nurseries also support practices and ecological services never seen in terrestrial nurseries. The nursery may serve as a hub for growing planula larvae from farmed corals, as a larval source production for other reef-dwelling organisms and as a reef management instrument that evolves into a rich floating ecosystem. Floating nurseries that become the focus of larval attraction from plankton can be used as a unique tool for enhancing connectivity between separated reef sites. Indeed, chains of nurseries can act as ‘stepping stone’ elements in regional reef complex planning. Nurseries situated away from anthropogenic impacts may also serve as mini MPAs, capturing drifted larvae of reef organisms from the plankton, enhancing development of communities that would otherwise lost when migrating to degraded reefs. The original perception of coral nurseries as a solely reef restoration instrument, the production of coral colonies for transplantation, can now be enlarged to include the above-mentioned management tools, developing a multiple-purpose restoration instrument. More study should be devoted to further developing this novel discipline of floating nurseries.