Fig 1.
Reef structures to help stabilise damaged reef.
Examples of structures used to stabilise and restore rubble-dominated habitats. Reproduced with permission of the Reef Restoration and Adaptation Program.
Fig 2.
Stages in the stabilisation and binding of rubble.
Stages of the natural stabilisation of rubble fields and eventual conversion to reef framework. A) shelter from strong hydrodynamic activities, a depression in bathymetry or particle organisation into stable bedforms allows the rubble pieces to settle, interlock and stabilise; b) pioneer binding organisms such as fleshy and calcareous algae settle on the rubble; c) intermediate binders such as cryptic and erect sponges create greater stability; and d) late stage binders and coral settlement.
Fig 3.
Where does active intervention fit into the disturbance and recovery cycle?.
Schematic diagram showing formation of coral rubble, and stages that might require intervention. In the inner ring of the circular progression, the substratum is affected by disturbance, and, given favourable conditions, transitions from loose rubble to stable reef matrix onto which corals (outer ring) can recruit. When the transition from rubble creation to binding cannot occur naturally, it can be artificially induced through active restoration. Further intervention is possible through the seeding of coral larvae or attachment of coral fragments. When the cycle occurs naturally, passive management (e.g. through protected areas) can occur.
Fig 4.
Methods and structures for rehabilitation of rubble fields.
Rubble stabilisation techniques: (a) rocks used to consolidate rubble in Indonesia, photo by Helen Fox, (b) the same area 14 years later, photo by Emily Darling, (c) metal mesh used to stabilise rubble in Australia, photo by Ian McLeod, (d) the same mesh with corals added, photo by Nathan Cook. (e) Reef Stars deployed over a rubble bed in Indonesia, photo by Biopixel. (f) Reef Stars with coral growth, Indonesia, photo by Marie-Lise Schlappy, (g) reef bags used to consolidate rubble in Australia, photo by Tom Baldock, (h) corals growing on reef balls in Thailand, photo by Margaux Hein. Note that many of these methods have not been subject to rigorous scientific testing for effectiveness, and are shown here as examples.
Table 1.
Rubble stabilisation and small structures: Summary of methods.
Fig 5.
Costs and benefits of rubble field restoration methods.
A stylised visual representation of the relationship between time required to gain restoration benefits and the level of technology required. Techniques in the top left quadrant require a higher level of technology, but are likely to yield immediate benefits. Techniques in the top right quadrant are more technologically advanced and will take a relatively long time before recovery occurs (i.e. through natural recruitment and growth of corals). Techniques in the bottom right quadrant are relatively low-tech but are expected to take a long time to yield benefits. Finally, techniques in the bottom left are low-tech and may see immediate or fast benefits to coral communities. Most techniques can reduce the time until benefits (moving right to left along x-axis) by adding transplanted corals.
Table 2.
Questions to guide monitoring and research priorities.
Questions arising from current knowledge gaps, and examples of ecological and socio-economic metrics to tailor monitoring to the questions for each stage of a rubble field repair intervention.
Fig 6.
Decision tree showing considerations to be made in rubble stabilisation interventions.
The tree shows a framework for making decisions at two stages of restoration planning: when i) determining whether active intervention is suitable and likely to effectively restore a rubble field on a damaged reef, and ii) deciding which active intervention method to employ.