A first endeavour in restoring denuded, post-bleached reefs in Tanzania

The worldwide decline in coral reefs has prompted a search for effective restoration protocols. We transplanted 6912 and 7110 corals (Acropora muricata, Acropora nasuta, Acropora hemprichi, Pocillopora verrucosa, Porites cylindrica, Millepora sp.) in Changuu, Zanzibar and Kitutia, Mafia, Tanzanian reefs that suffered in 1998 from a massive coral bleaching incident, causing a wide spread coral death. No sign for natural recovery has been recorded thereafter. In each site, we randomly set up 12 plots (36m² each), of which three were transplanted with a mix of three Acropora spp. (Treatment 1, T1), three with a mix of all six scleractinian species (T2), and six served as controls. Within one month of transplantation, an outbreak of Acanthaster planci in Changuu caused mortality at 50%. One year survival of transplants in T1 and T2 at Kitutia reached 66.4% and 62.5% respectively, significantly higher than at Changuu; an outcome recorded through species-by-species comparisons on four species only (P.verrucosa, P. cylindrica, A.muricata, A. nasuta). After one year no significant difference was documented in ecological volumes (EV) between T1 and T2 in stark contrast to the among species comparisons in T1, at each site. A within treatment one-way ANOSIM comparison for fish assemblage structures performed between the first and last three months of the transplantation year (Kitutia reef) revealed strong separation (T1, Global R=0.743, P<0.001; T2, R=0.445, P<0.001 and T3, R=0.694, P<0.001) while the same treatment revealed weak separation at Changuu site T1 (R=0.035, P>0.262) and T2 plots (R=0.119, P<0.043). Similarly, one-way ANOSIM done on the initial and last 3-month periods on invertebrates' community composition (at all sites, except T1 of Changuu reef), showed no significant difference between community composition at both ends of the sampling period. Altogether, transplantation cost (US$0.19/colony) suggested that large scale transplantation is economically viable. Cumulatively, field results and economic evaluations showed that transplantation of nursery-grown colonies might uphold critical ecosystem functions while used in reversing phase shift states in coral reefs.