ECOLOGICAL ENGINEERING CONSIDERATIONS FOR CORAL REEFS IN THE DESIGN OF MULTIFUNCTIONAL COASTAL STRUCTURES

摘要

A multifunctional structure is being designed for the Kahului Harbor, Maui, Hawaia€?i, to mitigate operational problems caused by wave energy while also providing coral reef habitat. There is limited information on how the design of a coastal structure can be manipulated to enhance the ecology of targeted coral communities. To inform the ecological engineering of an artificial coral reef, the relationship between substrate characteristics and coral colonization was investigated through coral recruitment experiments and study of field conditions. Three concrete compositions that differed by the use of basalt, limestone, or recycled aggregates were tested in field and laboratory experiments to determine the impact of each substrate on the recruitment of juvenile hermatypic corals. The concrete test plates were deployed in three environments for a period of about one year, after which the coral recruits on each plate were identified and counted. No significant difference was found in the average number of coral recruits on the concrete mixed with basalt, limestone and recycled aggregate (60 ?± 9, 83 ?± 17 and 77 ?± 14, respectively). Significant differences in coral recruitment were found due to the laboratory tanks, deep water, and shallow water field tests environments (86 ?± 11, 135 ?± 15 and 4 ?± 1, respectively). These results highlight the importance of environmental site conditions for the development of coral reef habitat. A field study was conducted in the vicinity of purposed artificial reef site to relate the topographic features of the surrounding environment to the levels of live coral coverage. The benthic zone was surveyed using a drop camera system and by divers who recorded in-situ observations. Of the area surveyed, the highest density of coral coverage (90% cover on 60% of the area) was found on an adjacent natural reef area that was characterized by spur and groove geomorphology with a high degree of macro- and microtopographic complexity. In contrast, sparse coral cover was discovered on the concrete armor units of the existing east breakwater structure, while no live coral cover was observed on the sand and carbonate rubble substrate at the proposed artificial reef location. The high degree of coral coverage on the adjacent natural reef suggests that the artificial coral reef design should emulate the natural spur and groove structure with regards to topographic complexity on multiple scales, orientation with wave direction, and water depth.