Seawater is highly concentrated in salt, and with that being said, it has a low concentration of water molecules.
Hypertonic means the solution has a lower water concentration than the other side (cell), vice versa for hypotonic, a high water concentration than the other side of the solution, and for isotonic, it means that both sides of the solution have the same water concentration.
So, the answer should be 1, hypertonic.
In addition, when your cells are exposed to hypertonic solution, the water molecules in your cells will start flowing out of the cells, to the outside, due to the difference in water concentration leading to osmosis. Your cells will lose so much water that they may even shrink!
The fallen tree would have let in more sunlight as it was blocking sunlight from getting in most of the time. Since the tree fell more sunlight will be able to get in. The only problem would the fact that there will be less space depending on the size of the tree and how it fell over.
The solution is hypertonic because the amount of solute(s) is higher outside of the cell than it is inside the cell, so the solvent (e.g. water) would move from the cell to the solution in order to obtain equilibrium between the two.
