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

Crabs of the genus Dotilla are ecologically important members of intertidal sandy shore<br/>communities. Exposed sandy shores represent one of the main habitat types along the coast of the<br/>Laem Son National Park in Thailand, and Dotilla sp. is the dominant macrofaunal species on<br/>these beaches, occurring in immense numbers. Despite their importance as a key member of the<br/>faunal community on these beaches, little is known about the ecology of Dotilla crabs in the<br/>Laem Son. Taxonomic investigations identified the Dotilla crabs present on the exposed oceanic<br/>beaches in the Laem Son to be D. intermedia. This represents the first time that D. intermedia has<br/>been recorded from Thailand. Dotilla intermedia inhabits a very well defined zone on the sandy<br/>beaches, and the factors underlying these zonation patterns were examined. The gradient of the<br/>beach was correlated to the height at which the boundaries of the Dotilla zone occurred, with<br/>physical factors associated with the beach gradient driving the distribution of D. intermedia on<br/>the beach. The upper limit of the Dotilla zone was controlled by the total water content of the<br/>sediment, with D. intermedia absent from areas with less than 15% total water content. Tidal<br/>influences defined the lower boundary of the Dotilla zone, with crabs requiring an area with a<br/>minimum exposure time between tidal immersions of 4-5 hours to feed on the sediment. Within<br/>the Dotilla zone, size segregation was observed; larger crabs occurred higher on the shore, and<br/>small crabs lower down. The sandy shores of the Laem Son were heavily impacted by the<br/>tsunami of 26th December 2004, which effectively destroyed the populations of D. intermedia on<br/>the beaches. However, by April 2005 D. intermedia was present again on the beaches. A<br/>temporal population genetic study was undertaken to investigate the impact of extinction and<br/>recolonisation on the genetic variation of a population. Genetic variation in mtDNA markers was<br/>found to decrease over time, matching the predictions of mathematical models concerning the<br/>effect of bottlenecking events on genetic diversity within populations. The impact of the tsunami<br/>on D. intermedia is discussed further in light of the ecological and molecular data produced in<br/>this thesis.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2010

Author dc:creator

• Allen, Christopher John