Environmental heterogeneity and plankton community structure in the central North Pacific

Spatial and temporal patterns of heterogeneity in nutrients (PO4, NO3), integrated water column chlorophyll, integrated water column primary production, and macrozooplankton biomass in the central North Pacific are described on spatial scales ranging from less than one to several thousand kilometers and on temporal scales from one day to 12 years. Fluctuations in these properties represent an index of the biological response of the ecosystem to physical forcing on various scales. These patterns are an important aspect of ecosystem structure because environmental perturbations may affect the outcome of biological interactions between populations. Heterogeneity in each property was low on all scales. Diel changes were evident only in macrozooplankton biomass, and no seasonal cycles were detected. This is consistent with a low overall level of physical forcing, little advection from outside the system into it, and lack of seasonal changes in nutrient flux to the euphotic zone. The central North Pacific shows relatively low heterogeneity, especially on mesoscales (tens to hundreds of kilometers), when compared to other pelagic ecosystems, suggesting that environmental disturbances do not have a major effect upon macrozooplankton and nekton populations.