The Pacific is very big, and is dotted with islands that are small in comparison. The EEZ – Exclusive Economic Zone is very important to them as a significant natural resource.
With rising sea levels some islands are already disappearing beneath the ocean. The loss of one outer island can result in a significant loss in EEZ. Some have argued to freeze the EEZ at the current size, so the loss of an outer island due to rising sea levels does not mean that its associated EEZ is lost too.
Note that the size of the circles is proportional to the size of the EEZ, not the actual shape of the EEZ on the map.