Add ground turmeric, ground coriander, garam masala and red chili powder. Saute, stirring, for 1 minute or until the raw smell disappears. add tomatoes. Cook, stirring occasionally, for 3-4 minutes or until they turn mushy. Add coconut paste, coriander leaves, soaked coccum with water, cleaned crab pieces and 1 cup water. Season with salt. Stir to combine. Cook, covered, for 6-8 minutes.