Growth assessment of Acropora cervicornis and Acropora palmata fragments using in-situ coral nurseries, Saba – Dutch Caribbean
As part of the program for the Restoration of Ecosystem Services and Coral Reef Quality (RESCQ), this study aims at contributing to the development of active restoration tools, for, on a global scale, denuding coral reefs. Initiated by Wageningen Marine Research (WMR) and in collaboration with local partners, the program assesses growth and survival of coral fragments, suspended in coral Ladder and -tree nurseries© on Saba and other Netherlands Antilles.
Protagonists of the research are two scleractinian coral species of the genus Acropora, staghorn- (Acropora cervicornis) and elkhorn coral (Acropora palmata). Both take the roles of reef ecosystem key species due to their high growth rates and branching complexity. That way, the species used to contribute essentially to Caribbean reef structure accretion. However, the populations of both species declined drastically during the last three decades. In the Caribbean where they fulfilled an ecosystem function presumably irreplaceable by other hermatypic corals, the decline of locally >95%, undermines reef function and pauperizes associated ecosystem services.
As coral cover declines globally, active coral reef restoration tools such as the coral nurseries operated by the Saba Conservation Foundation have become a key management tool to restore denuded reefs. To develop the ‘coral gardening’ method in a biologically and ecologically sound way, this study aims to ascertain the effect of contributing factors on growth and -survival of A. cervicornis and A. palmata fragments. Therefore, two different in-situ nurseries around Saba were monitored and maintained on a regular basis, while analyzing fragment growth and -survival (A. cervicornis, n = 47; A palmata, n = 25) based on initial fragment size (at time of recruitment), fragment depth as well as assumed fragment genotype.
Results for A. cervicornis indicate that neither the depth, nor the initial fragment size had an effect on the monthly growth rate of the fragments. However, the genotype and the interaction between the genotype and the initial fragment size affected the growth rates of A. cervicornis fragments significantly.
Depth did also not have an effect on the monthly growth rates of A. palmata fragments, but the initial fragment size (cm2) did have a significant influence. The larger the fragment was at the beginning of the grow-out period, the faster it grew. Good survival of both species (>96%) as well as average tip growth rates of A. cervicornis- (2.62 ± 0.15 mm/month) and surface growth of A. palmata (23.65 ± 5.6 mm2/month) fragments, are comparable with similar studies of Caribbean coral nurseries.
This research gives information on how to optimize A. cervicornis and A. palmata mariculture in the Caribbean and eventually how to develop effective active restoration tools such as coral nurseries to a point where they can aid direct reef restoration. Only long-term data however can reveal the effectiveness of gardening programs such as this one, therefore we recommend the further development of a method of best practice to produce meaningful data.