Testing coir (coconut) fiber as a novel, biodegradable material for coral reef restoration: coir interactions with larval and juvenile corals

Coral populations have declined in recent decades, largely due to anthropogenic climate change. In response, coral restoration projects are being implemented, and rubble stabilization is one such approach. Rubble beds form when dead coral fragments accumulate on the seafloor and can be mobilized by water flow. Although natural cementation processes stabilize rubble over time, increased mortality and more intense mobilization events impede recovery, leading to chronically degraded reef areas without intervention. Coir (coconut) husk fiber is a natural, low‐cost material that could be secured over rubble beds as nets to reduce mobilization and facilitate binding. However, its efficacy for coral restoration remains largely untested. We investigated interactions between coir and early coral life stages (larvae and microfragments) and assessed coir biodegradation in saltwater. Twenty‐four‐hour settlement assays examined whether coir fiber influenced coral larval settlement. Coral microfragments were monitored over 15 weeks to assess growth and survival when in direct contact with coir. The tensile strength (TS) of approximately 3.5 mm coir rope maintained in saltwater was measured to quantify biodegradation over time. Coral larvae did not settle directly on coir, but adjacent settlement was not inhibited. Over 15 weeks, direct contact with coir did not reduce microfragment growth or survival. TS declined from 1538 ± 156 (SD) to 0 N cm – 2 within 16 weeks. Laboratory experiments demonstrate the potential for coir netting as a short‐term stabilization material that does not negatively affect early coral life stages and biodegrades naturally in marine conditions.