Branching Coral Nurseries

Branching corals are propagated in rope nurseries.

Nursery Number

The number of standardised nurseries is determined by the size of the restoration area. ReefManager calculates the number of corals required based on the goal of 50% live coral cover of appropriate substrate at a density of 7–10 corals/m² of available restoration substrate. Using the standard nursery size for each branch, ReefManager sets the number of tables required in the nursery (default size is 2× standardised nursery). Large restoration sites will be divided into manageable smaller units that will be restored over time.

Nursery Fragment Size

Branching corals: fragments put on ropes should be at least 10 cm minimum length.

Residence Time

From our experience in Moorea, the optimal length of time in the nursery is estimated to be ~2–3 years. Current analysis by Coral Gardeners Labs is comparing survival/bleaching resilience vs. age/size in nursery for each species to test this hypothesis and identify the ideal age of outplants.

Coral Gardeners French Polynesia observed that nurseries with larger colonies (2–3 years old) also act as fish (and invertebrate) nurseries by supplying a place for larvae that might otherwise not find a suitable settlement area and either die from lack of habitat or predation. We know from coral ecology that associated organisms create resilience, and settled organisms signal conspecifics via sound, chemical, and visual cues that also attract other species generally.

Staggering

We are staggering the age of corals in our nursery, always having 1–2–3 year old corals mixed in among new fragments. This requires:

• Outplanting part of the nursery each year (older corals — 2–3 year olds)
• Holding the rest in the nursery
• Re-filling the outplanted part

This ensures that the community of associated organisms that have established in the nursery are maintained from year to year, and their services are continued — rather than outplanting everything every year, losing all the fish and invertebrates from the nursery, and having to start over to rebuild these communities. Alternate/additional strategies to maintain associated species near the nurseries will also be considered and developed.

Re-Use of Nursery Corals

Re-use of nursery corals to re-seed a nursery may be required if the natural reef is unable to provide enough material, permit restrictions require it, as part of the best practices of coral fusion workflow, or if we decide to propagate again a very resilient coral. Re-seeding should be accomplished by fragmenting several colonies/genotypes, or from an intentionally established "orchard", and not partial sampling from a colony about to be outplanted. The number of generations should be monitored, considering biodiversity and the number of genetically identical colonies planted in a particular area.

Cleaning

Minimum 1× per month or as directed by the Restoration Manager, and may change seasonally. 1× per week may be required during hot seasons. Cleaning is essential to keep disease and overgrowth from damaging our corals. All parts of the nursery must be cleaned, including ropes, wire, support structures, cable ties (marking dead corals), shade structures, etc., to prevent creating sources for rapid re-fouling. Cleaning should be tracked per nursery and per table, and recorded in the ReefApp.

Removal of Dead/Sick Corals

Dead and/or dying corals should be removed from the nursery immediately after monitoring has identified them. Any coral that has reached a health score of 3 (or more) should be removed, and a placeholder (cable tie) put in its place.