Thesis (M.Sc.)--Chulalongkorn University, 2004

Morphology and feeding ecology of gammarid amphipods in coral reef and seagrass communities were compared from amphipods collected from coral reefs in Kang Kao Island, Chonburi Province during April, 2001 and from seagrass bed in Libong Island, Trang Province during December, 2003. It can be concluded that there were four feeding modes in gammarid amphipods in the coral reef and seagrass communities namely filter feeders, filter feeders-predator, grazers and detritus feeders. Gammarid amphipods displayed array of feeding structures, in particular mouthparts mandibles, maxillipeds and two pairs of maxilla, according to different feeding modes. Their associated feeding appendages, antennae and gnathopods also varied accordingly. However the feeding structures in gammarid amphipods which shared the same feeding modes from the two habitats were similar. The feeding behavior and the composition of food items differed according to habitats. Moreover, amphipods from the two habitats also showed different morphological adaptations by those residing in the coral reefs were with thin and slender legs with feather-like setae for swimming. Amphipods in the seagrass beds had stout and short legs with numerous long setae or spines for digging into the sediment. Amphipods of 14 species from 10 families were found in the Kang Kao Island reefs with Ampelisca brevicornis, the benthic filter feeder, as the most dominant species. Benthic microalgae and macroalgae were the major food items for this species. The detritus feeding amphipod, Urothoe simplingnathia, was next in term of abundance. Eriopisa sp. A., grazing amphipod, was also common. Filter feeder-predator amphipods, feeding on phytoplankton, benthic microalgae, zooplankton and benthos, were also found such as Gammaropsis sp. A., Ceradocus sp. A. and Melita appendiculata. Six amphipods in 5 families were found in the seagrass beds in Libong Island. Kamaka sp. A., grazing amphipod, was the dominant species. They feedon benthic micro-and macroalgae. This amphipod species was widely distributed in the sediment and on the seagrass leaves. The filter feeding amphipod, Ampelisca cyclop, was next in term of abundance. Urothoe spinidigitus, the detritus feeding amphipod, was also common. This study revealed that gammarid amphipods in coral reef and seagrass communities play the roles in both the pelagic and benthic food chains.