Normal sudoku rules apply. Along green lines, adjacent digits must have a difference of 5 or greater. Some cells are coral and others are water. The high digits and 5 {5,6,7,8,9} are all part of the coral. All coral cells are orthogonally connected. The low digits {1,2,3,4} are all part of the water. There may be multiple bodies of water, and all bodies of water are orthogonally connected to the edge of the grid. No 2x2 area is entirely coral or entirely water.