The critically endangered species Acropora cervicornis, commonly known as staghorn coral, has been successfully reared in coral tree nurseries by the Reef Rescue Network in The Bahamas. Last October, we joined a research expedition aboard Shedd Aquarium’s R/V Coral Reef II, where staghorn coral fragments were moved between nurseries throughout the islands of Bimini, New Providence, Eleuthera, Cat Island and the Exumas. In each location, fragments from coral nurseries and wild colonies were collected and new coral tree nurseries were installed with genotypes from different places. In doing so, the goal was to increase genetic diversity at each site.
Four months after the expedition, all the translocated coral fragments survived and are healthy. Growth was observed in all fragments and some of them have already doubled or tripled their original size. As shown in the graphs below, genotypes 94, 95 & 96 from New Providence seem to grow faster than genotypes 133 & 134 from Bimini. At the same time, they are developing more secondary and tertiary branches than their counterparts.
Growth rates in terms of total linear extension (tle) of staghorn fragments at four nursery sites. The measurements are from October 2019 – April 2020 at Bimini (BIM) and Cat Island (CAT) and October 2019 – March 2020 at Cape Eleuthera Institute (CEI) and Nassau (NAS). Colors represent different genotypes with their respective tag number.
We observed the lowest growth rates in genotypes from wild populations. However, all these fragments recovered after manual fragmentation, and new tissue has grown over the crimp sleeves. It is important to note that fragments collected from wild populations were the smallest in size. They were cut and monofilament was added to hang them in the nursery. With that being said, some genotypes just recently healed and didn’t increase in size more than 2 cm (wild colonies from Eleuthera). Other genotypes grew twice their original size and covered the entire crimp sleeve.
Genotypes from wild colonies at Cape Eleuthera Institute (CEI) nursery site. The growth is reflected on the difference in size between October 2019 and February 2020 of each fragment. The red number represent the genotype of the selected pictures.
Fragments that were collected from nurseries kept growing in their new locations, but genotypes from Nassau developed more branches and seem to grow faster than the others, both in Nassau and in Eleuthera.
Increasing genetic diversity within populations is one of the key factors to ensure the persistence of the species. This collaborative project between Shedd Aquarium and the Perry Institute for Marine Science has already garnered excellent results. We are looking forward to going back into the field to continue measuring and photographing our staghorn fragments.