Cost-effective coral settlement substrates for restoration, exports and research

Abstract The sexual production of corals in aquaculture could increase the sustainability of coral restoration and export industries, particularly in developing countries where these industries predominantly rely on wild coral collections. Development of low-cost aquaculture facilities and coral settlement substrates is essential to encourage the uptake of these methods. Clay is widely available, easy and safe to use, and provides a low-cost option for coral settlement. The inclusion of non-toxic waste materials as additives in substrates to reduce costs may also promote coral settlement, given their combustion during firing creates pores and some coral taxa prefer to settle in crevices. Additives may also indirectly influence settlement via changes to the development of settlement-inducing biofilms during substrate conditioning. Here, we demonstrated the successful settlement of Acropora millepora larvae to substrates handmade from local clay (Kalimantan, Indonesia), to which three widely available cheap or free waste products were added [(1) coconut charcoal, (2) grog (fired clay ground into a granular form), and (3) breadcrumbs] at three concentrations (5, 15, and 25%). No differences in coral settlement to substrates containing the three additives were detected, nor were there differences among substrates with different additive concentrations. Also, crustose coralline algae cover, a common coral settlement inducer, did not vary among substrates containing different additives or additive concentrations after 28 days conditioning. Further testing of these and other additives across a broader suite of coral species should be explored, given their potential to reduce substrate costs while maintaining coral settlement.