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Intertidal habitats provide numerous ecosystem services, including the sequestration and storage of carbon, a topic of great recent interest owing to land-cover transitions and climate change. Mangrove forests and seagrass meadows form a continuum of intertidal habitats, alongside unvegetated mudflats and sandbars, however, studies that consider carbon stocks across these spatially-linked, threatened ecosystems are limited world-wide. This paper presents the results of a field-based carbon stock assessment of aboveground, belowground and sediment organic carbon stock to a depth of 1 m at Chek Jawa, Singapore. It is the first study of ecosystem carbon stocks of both vegetated and unvegetated intertidal habitats in the tropics. Ecosystem carbon stocks were 497 Mg C ha -1 in the mangrove forest and 138 Mg C ha -1 in the seagrass meadow. Sediment organic carbon stock dominated the total storage in both habitats, constituting 62% and >99% in the mangrove forest and seagrass meadow, respectively. In the adjacent mudflat and sandbars, which had no vegetative components, sediment organic carbon stock ranged from 124-143 Mg C ha -1 , suggesting that unvegetated habitats have a carbon storage role on the same order of importance as seagrass meadows. This study reinforces the importance of sediment in carbon storage within the intertidal ecosystem, and demonstrates the need to consider unvegetated habitats in intertidal 'blue carbon' stock assessments.

This study used random amplified polymorphic DNA (RAPD) fingerprinting for estimating genetic variation and species differentiation in three species of tilapia. A 16-mer random primer generated RAPD markers ranging from 250 to 2400 base pairs (bp). Genetic similarity estimates obtained by pairwise comparisons based on the method of Nei and Li (1979) indicated high genetic similarity (mean genetic similarity (--_ SD), 0.73 (_ 0.15) for Nile tilapia; 0.78 (_+ 0.12) for Mozambique tilapia; and 0.87 (___ 0.07) for Aureus tilapia) within each of the tilapia species. The average interspecies genetic similarities obtained among the three species were 0.59 (+-0.07) for Mozambique/Nile tilapia, 0.46 (+_ 0.09) for Aureus/Nile tilapia and 0.38 (---0.07) for Aureus/Mozambique tilapia pair. DNA profiles generated in each species of tilapia were unique. A total of 13 RAPD markers differentiating the three species of tilapia were detected. Our study presented RAPD markers as a new class of useful genetic markers for assessment of genetic diversity and species differentiation in tilapia.

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