Recent changes in coral assemblages of a South African coral reef, with recommendations for long-term monitoring

Two-mile reef, Sodwana, South Africa is an unusual coral reef, being situated on a submerged fossilized sand dune and being very southerly (27 degrees 54'). It is a popular Scuba diving venue receiving about 100 000 dives year(-1). The line-intercept transect method, as recommended by the global coral reef monitoring network (GCRMN), was used to determine soft coral, hard coral and other benthos percentage cover. Physical coral damage, disease and bleaching were also recorded. Results were compared with those of B. Riegl (1993 - unpublished PhD thesis) 5 to 7 years earlier. The reef appears to be ecologically and highly dynamic. In the interim, there has been an increase in living benthos cover of 22.3% but also an increase in coral bleaching from 0% in 1993 to 1% in 1998. Physical damage, despite the large number of dives on the reef was minimal (1.52%), although it appears as if coral diseases may be increasing. The 20-m transects recommended by GCRMN are too long for this highly rugose reef with its distinct ridges and gullies. It is recommended that benthos cover, coral damage, bleaching and disease should be monitored annually using 40 5-m transects on the reef ridges and 40 5-m transects on the reef slopes.