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It has been suggested that production in offshore waters of the subarctic Pacific is limited by availability of dissolved Fe. Although that is not yet adequately established, the functional consequences of the limitation (if it exists) can be characterized from the results of the Subarctic Pacific Ecosystem Research (SUPER) program. Fe limitation, or something like it, establishes a phytoplankton community dominated by very small cells. These plants are not limited by Fe availability. Rather, their production is limited by their stock and available illumination. Stock is set by microzooplankton grazers with rapid population growth rates and, thus, rapid response to increases in phytoplankton abundance. Micrograzers provide efficient recycling of nitrogen as NH,, and the ready availability of NH, sharply limits the annual utilization of NO,. Persistently high NO, concentrations result. Other possibly Fe-limited, oceanic ecosystems with persistently high, near-surface nutrients require similar, detailed analysis of ecosystem function.

Calanus finmarchicus (Gunnerus) stratify nariowly near 500 m depth dunng their fifth copepodite resting phase in North Atlantic Slope Water off southern New England USA They probably a c h~e v e this by migration to a specific, daytime isolume Photoperiod information provided by light intensity at depth could serve as a cue for termination of the resting phase Population data on tooth formation and gonad growth show that the reshng stock prepares foi termination in late winter and matures in February-March Photopel~ods are lengthening throughout that seasonal interval, and might cue arousal An endogenous, long-range timer that cues arousal after an interval of rest is another possible mechamsm