Growth of the critically endangered Acropora cervicornis and A. palmata in the coral nurseries of Saba, Dutch Caribbean
Previously dominant, reef-building Acropora cervicornis and A. palmata abundance decreased dramatically in the Caribbean in the 1970s, mainly due to the white band disease. They have been on the IUCN Red List as ‘critically endangered’ species since 2008, but restoration efforts already date back to the year 2000. Of these methods, fragmentation used in coral gardening seems to be the most productive method for these species, but there is a need for optimisation of this process. This research filled up the nurseries of Saba, Dutch Caribbean, with Acropora, measured growth of both species and of the two staghorn mother colonies. Furthermore, some staghorn fragments were outplanted on an outplanting structure. Growth rates of staghorn differed between some trees, with the highest growth rates in the cut fragments that were ready for outplanting and therefore have lived in the nursery for the longest time. The outplants themselves showed a lower growth rate, which might have to do with the structure itself. There was generally no correlation between initial primary branch length and growth rates of staghorn found except for one tree. Furthermore, branching corals grew faster than non-branching corals, independent of the amount of side branches. Side branches tend to appear from about 10 cm length, but half of the fragments without side branches did not branch at all in the maximum of 79 days. Side branching over time seems to follow an exponential model, but prolonged measurements are needed to prove this. Elkhorn growth in surface area and perimeter was found already in a short period of time, but the method used must be further improved. The results of this research can be used to improve coral gardening of Acropora spp.