A 1500-year record of mangrove dynamics has been established from palaeoecological analyses on three cores from Salak Phet Bay, Koh Chang island in the eastern Gulf of Thailand. The occurrence of Rhizophora, accompanied by other mangrove species, suggested that Salak Phet Bay supported a mangrove community from at least 1500 cal yr BP. From 1500 cal yr BP the mangrove extent decreased indicating less inundation frequency, possibly in response to a sea-level fall until 1300 cal yr BP. Following this regression, sea-level rise resulted in an increased presence of mangrove taxa until 500 cal yr BP. The study documents that Salak Phet Bay was characterised by relatively low saline conditions based on the occurrence of the moist-loving species (Oncosperma) around 1500-500 cal yr BP. After 500 cal yr BP mangrove taxa gradually decreased and terrestrial herbaceous taxa, mainly grasses, increased suggesting that the frequency of marine inundation was reduced as sea level fell. Drier conditions were also recorded by an increase in terrestrial grasses and a decrease in Oncosperma after 500 cal yr BP. In the uppermost sediments the increased presence of Rhizophora is probably associated with recent global sea-level rise although changes in mangrove composition are possibly related to human activities within Koh Chang. The sedimentation rate and the mangrove migration at Koh Chang have kept pace over the past 1500 years but this may be challenged under predicted future rapid sea-level rise as accommodation space for mangroves to migrate inland is required to maintain viable mangrove forests. Keywords pollen analysis, palaeoecological analysis, the eastern Gulf of Thailand, sealevel change

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A high-resolution multiproxy sedimentary record comprising pollen, charcoal, trace element, stratigraphy and particle size data is used to reveal environmental changes from the mangrove ecosystem at Unguja Ukuu, Zanzibar, Tanzania, over the last 5000 years. Historical human–environment interactions over the last millennia are explored by a comparison of the stratigraphic and archaeological data. The area was characterised by a mixture of mangrove forest and beaches, indicating a low level of tidal inundation to at least 3300 BCE. From 2750 BCE, mangrove forest expanded as the area experienced sea-level rise. Further sea-level rise is recorded between 600 and 1100 CE, indicated by the pollen record, particle size analysis and the presence of shell fragments. After 1100 CE, mangrove forest decreased with back mangrove species increasing, indicating a falling sea level. Cocos nucifera decreased after 1900 CE, which reflects a recent sea-level rise and possibly a phase of exploitation. Cereal pollen shows a high presence at around 1500 CE, which coincided with the arrival of the Portuguese on Zanzibar and the transition to Omani colonisation. The sedimentation rate in the core top indicates that mangroves in Unguja Ukuu cannot keep pace with the current rate of sea-level rise.

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