1. Peel the pineapple and cut it into thin circles. Lay the slices down on a non-stick silicone baking mat overnight a closed oven with just the pilot light -- or in an low (150-200° F) oven -- until dry and crispy.
2. To make the gelee with the gelatin sheets, bloom the sheets in cold water until soft and slimy. Take 1/2 of the grapefruit juice and bring to almost a boil; add the gelatin sheets and stir. Mix this in with the remainder of the grapefruit juice. Place on plates and leave in the refrigerator on a flat service so that the gelee may set. You can also pour this into glasses to set in the refrigerator, depending on how you would like it presented. If using powdered gelatin, let sit in 1/2 of grapefruit juice for about 5 minutes, then gently heat to allow it to dissolve. Then pour into or on desired plates, bowls, cups, etc. and let chill in the refrigerator.
3. Bring water to boil in pot large enough to hold the crab. Add the cayenne, fennel, and coriander. Cook the crab(s) in hot water until cooked, approximately 10 minutes. Remove and cool in a bath of ice water until chilled. Once chilled, crack open shells and remove the crabmeat. Be careful of pieces of cartilage that can break -- the color is very similar to the color of the meat itself.
4. Peel the grapefruit with a knife and cut out segments so that there is no skin/membrane. Do the same with the orange. Reserve the juice from both the grapefruit and orange to be used in the vinaigrette.
5. To make the vinaigrette, whisk the reserved grapefruit and orange juice with the olive oil, salt, and pepper, to taste. If the vinaigrette is too tart, whisk in olive oil, a little at a time. Mix the citrus segments, crabmeat, cut romaine hearts, and vinaigrette just enough to season. Season with more salt and pepper. Assemble a small amount of crab salad on the plate (cup, bowl) on top of the gelee. Alternate layers of crab salad and pineapple chips until desired height (2 or 3). Garnish with a chive stick.