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Tongatapu, like Tahiti, was visited by many early European navigators and was one of the first of the South Pacific islands to be charted in any detail. Though it was discovered (and named Amsterdam Island) by Tasman in January 1643 (Sharp 1968, 152-158), the first comments on the sand cays of the surrounding reefs were made by Cook during his second voyage, with the Resolution and Adventure, in October 1773. On this occasion Cook spent less than a week at Tongatapu, anchored in the northwest, and commented that "it would have taken up more time than I could spare to have surveyed these parts Minutely as there are a number of small Islots and reefs of rocks extending to the NE even further than we could see" (1961, 261). His naturalists, the Forsters, did not describe the cays, though Georg Forster remarked on the emersion of reef limestones on Tongatapu and its similarity to the continuing emergence of the land in Scandinavia (1777, I, 453). Cook returned on his last voyage in 1777, with the Resolution and Discovery, and stayed for a month. He anchored near modern Nuku'alofa and landed on Pangaimotu and possibly other islands (1967, 124-125, 155, 890). He charted the area but gave no description of the cays.

On the 21 small islands located within the northern bays and reef systems of Tongatapu, Tonga, species of terrestrial flora present were identified, and vegetation units and gemorphological features surveyed on 12 that were previously unmapped. A species/ area plot of the data shows that rock islands are consistently more diverse than sand islands. Size of flora is also a function of frequency of human use of islands, which increases with area, and proximity to the mainland. Floristic composition varies from east to west across the group, with increasing shelter provided by the mainland from prevailing winds.