Interrelationships of fish communities in coral reef and seagrass bed at Ko Phangan, Changwat Surat Thani

Abstract

Interrelationships of fish communities in coral reef and seagrass bed at Ko Phangan, Changwat Surat Thani was investigated from August 1991 to April 1992 using the fish visual census and beam trawl techniques of ASEAN-Australia : Coastal Living Resources Project for study the fish in coral reef and seagrass bed, and gillnets to catch the fishes migrating between coral reef and seagrass bed. In coral reef, a total of 76 species were recorded. Target species was dominated by Lutjanidae. The indicator species found to be Chaetodon octofasciatus and the most abundant major families was Pomacentridae. Species richness and abundance found to be low in January andhigher in April, and species composition recorded from January and April did not show any differences. In seagrass bed, a total of 22 species were collected and 13 species were also found in coral reef. It was dominated by small size and less commercial value such as Teraponidae, Blenniidae and Monocanthidae, and the juvenile of high commercial value fishes from the adjacent coral reef such as Lutjanidae and Lethrinidae. The night sample found to have more organisms than the day sample and the collection showed the differences in species composition of fish between the day and night samples. The seasonal variation of seagrass fish community showed that more abundance of fishes were found in January to April than in August and October. A total of 47 species of migrated fishes were collected which 30 species were also found in coral reef. It was dominated by Labridae, Pomcentridae, Holocentridae and Apogonidae. Differences in species of fishes collected between day and night were significantly found. The stomach content analysis showed that most of all fishes collected migrated to feed in the seagrass bed. The variation in species composition and abundance of fishes in coral reef, seagrass and migrated species were observed which the factors deyermining these variations were and wind action, salinity, behavior of fishes and the availability of habitats. Migration of fishes between coral reef and seagrass bed revealed that they migrated to use the seagrass bed as nursery and/or feeding grounds such as Lethrinidae, Lutjanidae, Serranidae, Labridae, Holocentridae, and Apogonidae. The similarity of fish species composition in coral reef and seagrass bed, and migration of fishes between habitats demonstrated the interrelationships of fish communities between these two types of habitats and showed the biologicaldeterminant of the interconnection between coral reef and seagrass bed.