While they were on land, the plant energy that he could absorb while fighting and growing plants was enough to replenish his energy loss, which was why he could continue using his powers without having to rely on absorbing zombie crystals.
Now that they were on the sea, plant energy was scarce, so he had to keep absorbing zombie crystals to replenish the energy that he was using.
Nathan could only nod as they could feel the shaking again, aside from the waves that were pulling them. The aftershocks had obviously begun, and the shaking was still very strong.
After the aftershock, they could feel that the waves that were pulling them back to the sea began moving to the shore again.
Their box was slammed again and again by the waves and the water currents, so he still did what he did before and kept growing more vines when some parts of the box were torn off.
