Image analysis of typhoon impacts on soft coral community at Munseom in Jeju, Korea

Abstract

Impacts of Typhoon Maemi on a soft-coral community located on subtidal cliff at Munseom, Jeju were investigated in this study using underwater photography. Typhoon Maemi hit Jeju Island in late September 2003 and its impact was strong enough to destruct most shallow water sessile benthos including soft corals. To estimate numbers and size of soft-coral colonies, a line transect was installed on the cliff at depth from 3 to 9 m and photographs were taken serially by every 1 m. From each 1 × 1 m underwater photograph, species and size of soft-coral colony was determined. Number of soft-coral colony and its percent coverage (PC) in each 1 m2 quadrat was calculated. Soft corals Scleronephthya gracillimum, Dendronephthya gigantea, D. putteri, D. spinulosa and D. castanea were identified from the photographs. Dendronephthya sp. was mainly distributed at 3-6 m while S. gracillimum was mostly occurred at 6∼9 m. A survey conducted before the typhoon showed that number of the soft-coral colonies at 3∼4 m, 4∼5 m, 5∼6 m, 6∼7 m, 7∼8 m and 8∼9 m was 17, 24, 20, 23, 18 and 30 colonies/m2 or 21, 48, 36, 28, 24 and 43%, respectively. After the typhoon, number of soft-coral colonies in the transect increased, 31, 35, 27, 10, 21 and 50 colonies/m2 while PC was remarkably decreased as 21, 23, 21, 5, 9 and 13%, respectively. Our data suggested that the impact was limited in larger colonies; larger soft coral colonies were selectively destroyed and removed while the small colonies underneath the larger colonies remained undestroyed.