Ecology of the intertidal crab Dotilla intermedia from tsunami-impacted beaches in Thailand

摘要

Crabs of the genus Dotilla are ecologically important members of intertidal sandy shorecommunities. Exposed sandy shores represent one of the main habitat types along the coast of theLaem Son National Park in Thailand, and Dotilla sp. is the dominant macrofaunal species onthese beaches, occurring in immense numbers. Despite their importance as a key member of thefaunal community on these beaches, little is known about the ecology of Dotilla crabs in theLaem Son. Taxonomic investigations identified the Dotilla crabs present on the exposed oceanicbeaches in the Laem Son to be D. intermedia. This represents the first time that D. intermedia hasbeen recorded from Thailand. Dotilla intermedia inhabits a very well defined zone on the sandybeaches, and the factors underlying these zonation patterns were examined. The gradient of thebeach was correlated to the height at which the boundaries of the Dotilla zone occurred, withphysical factors associated with the beach gradient driving the distribution of D. intermedia onthe beach. The upper limit of the Dotilla zone was controlled by the total water content of thesediment, with D. intermedia absent from areas with less than 15% total water content. Tidalinfluences defined the lower boundary of the Dotilla zone, with crabs requiring an area with aminimum exposure time between tidal immersions of 4-5 hours to feed on the sediment. Withinthe Dotilla zone, size segregation was observed; larger crabs occurred higher on the shore, andsmall crabs lower down. The sandy shores of the Laem Son were heavily impacted by thetsunami of 26th December 2004, which effectively destroyed the populations of D. intermedia onthe beaches. However, by April 2005 D. intermedia was present again on the beaches. Atemporal population genetic study was undertaken to investigate the impact of extinction andrecolonisation on the genetic variation of a population. Genetic variation in mtDNA markers wasfound to decrease over time, matching the predictions of mathematical models concerning theeffect of bottlenecking events on genetic diversity within populations. The impact of the tsunamion D. intermedia is discussed further in light of the ecological and molecular data produced inthis thesis.