Summary of observations and possible interpretations of microbial and macro-organism data collected from the Northern Line Island survey.

Two hypotheses are considered: Hydrology/regional hypothesis-Larger islands are associated with more upwelling and algae. Different levels of bleaching on the various islands are the explanation of historical changes (i.e., loss of corals cause fish to leave). For example, the lagoons of Kiritimati and Tabuaeran may have served as sources of hot water during a warming period in the region. Human-driven food web shift hypothesis-Overfishing increases macroalgae, which increases amount of labile dissolved organic carbon (DOC). In turn the DOC increases heterotrophic/pathogenic microbes, which kill corals. These two hypotheses are not mutually exclusive. For example, algal-microbial dominated system may represent an alternate stable state initiated by a bleaching event. Where multiple interpretations are given, they are ranked in order of possible importance. Some questions for consideration are highlighted in red.
*Decreased grazing leads to higher concentrations of turf algae [18], [94]. These turfs contain cyanobacteria that fix nitrogen.