Impacts of plastic-free materials on coral-associated bacterial communities during reef restoration.

Coral propagation and out-planting based restoration approaches are increasingly being applied to assist natural recovery of coral reefs. However, many restoration methods rely on plastic zip-ties to secure coral material which is potentially problematic for the marine environment. Plastic-free biodegradable alternatives may however pose unique risks to coral-associated bacterial communities integral to coral health. Therefore, to identify whether biodegradable materials differentially impact coral-associated bacterial communities we examined Acropora millepora coral-associated bacterial communities during propagation in two experiments on the Great Barrier Reef. Coral fragments were secured to coral nurseries with conventional plastic, metal, or biodegradable (polyester and polycaprolactone) ties. Tie failure and coral-associated bacterial communities were then characterized over six months. Minimal coral mortality was observed (3.6%-8%) and all ties had low failure rates (0%-4.2%) except for biodegradable polyester ties (29.2% failure). No differences were observed between coral-associated bacterial communities of fragments secured with different ties, and no proliferation of putatively pathogenic bacteria was recorded. Overall, our findings suggest that reducing reliance on conventional plastic is feasible through transitions to biodegradable materials, without any notable impacts on coral-associated bacterial communities. However, we caution the need to examine more coral taxa of different morphologies and new plastic-free materials prior to application.