This page of the Coral Island guide focuses on turtles. Sooner or later you will encounter these nice creatures under water. They will block you from further underwater exploration. As a result, you will not be able to activate Solar orbs.
Solar orbs and diving
Ling will contact you after making enough progress in the sotry. You'll have to meet her at the pier. Go there. You will be asked to go under the water and activate strange machinery (Solar orbs). From now on, you will be able to dive here.
After diving, you have to clear the bottom of rubbish to discover special "transmitters". They look like little yellow-gray cones. You have to be careful, because they are easy to miss. If you interact with them, they will activate machines called Solar orbs.
They will shoot an energy beam. You have to clear its path of rubbish. This will activate a machine that will remove the oil from the area.
However, during this quest, sooner or later you will encounter turtles. These friendly creatures will block your path. They will want different things from you for removing yourself from the path. It will always be some product from your farm - plants (e.g. cucumber) or animal products (e.g. milk). You will know what a given creature wants from the picture floating above it.
However, note that they will never ask for anything of the regular quality - turtles always want a minimum of "brown stars". Remember that you will increase the quality of plants with fertilizer, and the animals must be regularly fed and petted.