Atoll islands are unique in several ways. For example, there is no rock other than coral limestone composed of calcium carbonate. This means that plants needing other minerals, such as silica, cannot be cultivated without using fertilisers or another outside source of rock from a larger island composed of volcanic or other igneous rock.
Palm trees grow on atoll islands because they thrive on brackish water and their seeds, or nuts, are distributed by floating from one island to another.
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