Individual study: Coral reef rehabilitation through transplantation of staghorn corals Acropora spp. at Tutia Reef, Mafia Island, Tanzania
Lindahl U. (2003) Coral reef rehabilitation through transplantation of staghorn corals: effects of artificial stabilization and mechanical damages. Coral Reefs, 22, 217-223
Tutia Reef (Tanzania) is relatively unaffected by human disturbance. The seabed is covered with a mix of coral rubble, sand, and rhodoliths. The rubble is being colonized by thickets of branching corals Acropora spp.; about 80% of acroporid corals were killed during the 1998 El NiÃ±o event. Although they still dominate the surrounding coral community, it was felt that transplanting Acropora might help to restore the reef, and a new method (the string-grid) was tested. This was designed to avoid coral abrasion, dislodgement and transport due to water movement; the corals were tied to string sections, which were connected on the seabed to form a grid and create stability.
The transplantation site was 3m depth in a sound between two reefs. Branches of A. muricata were collected locally at 24 m depth and of A.vaughani at about 5-6 m depth. The branches were assumed to be clones and had an average length of 34 ± 9 cm. They were transplanted in November 1998, either by (1) placing them loosely on the seabed or (2) attaching 10 coral branches, all belonging to the same clone, to a 1-m section of polythene string at 10-cm intervals and placing these on (but not attached to) the seabed to form a grid. From each clone, two groups of 10 coral branches were randomly assigned to the tied treatment and eight to placement without attachment. In total 28 branches were transplanted from each clone, giving a total of 260 attached branches and 104 unattached branches.
The attached corals suffered less mortality and increased their relative weight of surviving parts at a significantly higher rate than those that were unattached. The average increase in weight of live coral over 1 year was 56%, eight times more than the unattached coral branches. This difference was mainly due to reduced partial mortality of smaller coral fragments on the string-grid. Most corals showed signs of partial mortality one year after transplantation. The proportion of branches without dead tissue was 13% in the attached treatments and 7% among the unattached branches, whereas 3% of the attached branches and 13% of the loose branches were dead or missing.
Most partial mortality on the attached colonies was on parts of the branches that were embedded in, or in contact with, the sediment, but the loose branches also had a lot of mortality on parts that were above the sediment at the time of sampling. Adjacent branches attached to the same string were often fused to each other which added extra stability.
Conclusions: Staghorn coral branches can be successfully transplanted to a moderately wave-exposed habitat using this method. The attachment to strings did not fix the corals entirely, but helped to maintain their orientation. The string-grid method is very simple, and could be carried out by snorkelers down to a depth of 5-10 m after some basic training. It is therefore potentially well suited for community participation projects in developing countries, involving local fishermen and other reef users.
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