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Declines of Steller sea lion (Eumetopias jubatus) populations in the Aleutian Islands and Gulf of Alaska could be a consequence of physical oceanographic changes associated with the 1976-77 climate regime shift. Changes in ocean climate are hypothesized to have affected the quantity, quality, and accessibility of prey, which in turn may have affected the rates of birth and death of sea lions. Recent studies of the spatial and temporal variations in the ocean climate system of the North Pacific support this hypothesis. Ocean climate changes appear to have created adaptive opportunities for various species that are preyed upon by Steller sea lions at mid-trophic levels. The east-west asymmetry of the oceanic response to climate forcing after 1976-77 is consistent with both the temporal aspect (populations decreased after the late 1970s) and the spatial aspect of the decline (western, but not eastern, sea lion populations decreased). These broad-scale climate variations appear to be modulated by regionally sensitive biogeographic structures along the Aleutian Islands and Gulf of Alaska, which include a transition point from coastal to open-ocean conditions at Samalga Pass westward along the Aleutian Islands. These transition points delineate distinct clusterings of different combinations of prey species, which are in turn correlated with differential population sizes and trajectories of Steller sea lions. Archaeological records spanning 4000 yr further indicate that sea lion populations have experienced major shifts in abundance in the past. Shifts in ocean climate are the most parsimonious underlying explanation for the broad suite of ecosystem changes that have been observed in the North Pacific Ocean in recent decades.

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Interdecadal sea surface temperature (SST) anoma-1 We use the term "interdecadal" to loosely refer to timescales that are longer than interannual (ENSO) and shorter than centennial (greenhouse gas forcing).lies show a "canonical" structure (e.g., Tanimoto et al. 1993;Zhang et al. 1997), with central North Pacific SSTs near the subtropical front bracketed to the east, north, and south by oppositely signed SSTs. A second SST pattern is centered around the subpolar front in the Kuroshio-Oyashio Extension region (Deser and Blackmon 1995;Nakamura et al. 1997) and tends to lag the subpolar front SST anomalies by a few years on interdecadal timescales (Miller and Schneider

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The temporal and depth variability of stimulated bioluminescence at 59øN, 21øW in the North Atlantic during 1991 was measured by two bathyphotometers (BP's). A moored BP (MOORDEX) obtained a 106-day time series of bioluminescence at 50 m between May 1 and August 15. A profiling BP (high-intake, defined excitation, HIDEX) measured bioluminescence in the upper water column during cruises in May and August. MOORDEX-measured bioluminescence intensity cycled with an approximate 20-day periodicity. In May, bioluminescence was correlated with chlorophyll fluorescence with similar vertical distributions in the water column. From May to August, the mean intensity and duration of individual flash events increased, and integrated water column bioluminescence increased by a factor of 4, to 1.2 x 1015 quantam -2. In August, chlorophyll fluorescence distributions and mixed layer depths were shallower than in May. Despite this, the vertical distribution of bioluminescence remained unchanged from May. The following results, potentially caused by typical seasonal changes superimposed upon short-term high variability during each cruise, suggest a change in organism assemblage between May and August: (1) increase in the intensity of flash events, (2) shift to a broader distribution of flash kinetics, and (3) loss of correlation between fluorescence and bioluminescence. Introduction The dynamics of biological communities in the ocean are driven by physical, optical, and chemical processes, with changes in biological communities correlated with temporal and spatial variability in these bulk processes. For example, the spring bloom phenomenon in the North Atlantic is correlated with increased solar insolation and shallowing of the mixed layer [Ducklow and Harris, 1993]. Bioluminescence is a ubiquitous feature of the world's oceans and originates from organisms representing all trophic levels. Because background levels of in situ bioluminescence are low [Baguet et al., 1983; Widder et al., 1989], profiling, moored, and ship-mounted bathyphotometers [e.g., Losee et al., 1985; Swift et al., 1985; Ondercin, 1989; Widder et al., 1993] are used to measure levels of stimulated bioluminescence in situ. Although on scales larger than 100 km, bioluminescence may be correlated with hydrographic features [e.g., Swift et al., 1985; Losee et al., 1989], on smaller scales there are few correlations of bioluminescence with other bulk properties [e.g., Ondercin, 1989]. Bioluminescence has been correlated with beam attenuation [Lapota et al., 1989], the chlorophyll to temperature ratio [Losee et al., 1989], and zooplankton biomass [Buskey, 1992].

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