Ecosystem dynamics at a productivity gradient: A study of the lower trophic dynamics around the northern atolls in the Hawaiian Archipelago

Application of a lower trophic ecosystem model coupled with an ocean circulation model allows us to derive a time series of estimated plankton biomass for waters around Kure Atoll, Pearl & Hermes Atoll and Midway Islands, over the period 1964-2006. This time series shows considerable interannual and decadal variation in productivity, and changes in recent years that are coherent with observed changes at higher trophic levels. Further the model results show that the change in productivity can be viewed from the perspective that the atolls, at the northern edge of the subtropical gyre, are situated at a strong physical, chemical and biological gradient. The gradient moves north and south seasonally and interannually resulting in changes in lower trophic level productivity around the atolls fixed in position. Variation in biome boundaries or gradients may be a key factor in ecosystem dynamics in many ecosystems located near such boundaries.