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Notes: Abstract This study compares the small-scale (100's to 1000's of meters) horizontal spatial distribution of zooplankton from stations in the California Current (29°N; 118°W) and in the North Pacific Central Gyre (31°N; 155°W). Patterns were inferred from the spacing of vertical tows and the variability in abundance of 15 taxonomic categories caught in these tows. In the California Current, 4 tows were taken at random positions within 2000 m of a drogue or fixed geographic position and 4 replicate tows were taken at the drougue or the fixed point. Four series of these 8 tows were taken around noon and midnight during two days. At the Central Gyre station, two similar series (one day and one night) were taken while following a drogue. Estimates of the scale of structure based on comparisons of replicate and random tow variability suggest that aggregated patterns in the Central Gyre are larger than a few hundred meters, while the California Current structures may be less than 100 m in size. Day-night changes in patch size were not apparent in either area. Evidence for multispecies patches was found only for the Central Gyre station. Replication samples in both areas gave more consistent measures of community structure (relative proportions of species) than the random tows. Similarity of community structure decreased with increasing distance between tows being compared. The decrease was much greater for the California Current station, a further indication of smaller patch size in this area. Diurnal changes in community structure occurred in both areas.

Notes: Abstract The small-scale vertical (10′s of meters) and horizontal (100′s to 1000′s of meters) distribution of zooplankton in the California Current near Guadalupe Island, Baja California, Mexico was studied. Vertical distributions were sampled using a vertically-towed Longhurst-Hardy Plankton Recorder (LHPR) which gave a sequence of samples, each integrated over about 5 m, from 250 m to the surface. Because of the sampling biases of the LHPR, details in vertical structure of less than 15 to 20 m were not considered. The pattern of the vertical tows and the variability of the integrated counts of species were used to infer horizontal distribution. Four series of 8 tows each were taken around noon and midnight over a 2-day period. Four of the 8 tows in each series were randomly positioned within 2000 m of a parachute drogue (first day) or a fixed geographic position (second day); four were replicate tows taken at the drogue or the fixed position. Sixty-seven taxonomic categories were counted. The replicate tows, separated by no more than a few hundred meters, gave more similar vertical profiles for species than did the random tows, with separations of 100′s to 1000′s of meters. The night replicate tows showed less variability in depth distribution than did either the night random or any of the day tows, leading to the hypothesis that the vertical distributions observed were generated by interactions of the organisms' diel behavior with internal waves. Variability of abundance estimates using the integrated counts was the same for both replicate and random tows, indicating that horizontal patches may be smaller than 100 m. No evidence was found for a day-night change in patch size, or for a consistent overlapping of patches of different species. Replicate tows gave more similar estimates of community structure (relative proportions of species) than did random tows. Overall day community structure was more similar between tows than night structure. Similarities in species' proportions of any random tow to the replicate tows or to other random tows of a series decreased with increasing distance between the tows being compared. This decrease was greater for the night samples, suggesting that community structure is more heterogeneous at night.

Notes: Abstract During June 1991, we studied sea birds at a mid-ocean seamount (Fieberling Guyot) in the eastern North Pacific Ocean. Avifaunal composition changed from small Procellariiformes [a storm-petrel; Oceanodroma leucorhoa (Vieillot)] away from the seamount to an assemblage dominated by larger tubenoses [mostly black-footed albatross Diomedea nigripes Audubon and Cook's petrel Pterodroma cookii (Gray)]. Compared to adjacent waters, sea-bird density and biomass within a 30-km radius centered on the seamount summit were 2.4 and 8 times higher, respectively. Individual sea-bird taxa were 2 to 40 times more abundant at the seamount relative to values reported previously from large-scale surveys of deep-ocean regions in the central North Pacific. In September 1991 we studied potential prey of sea birds in the upper water column using a neuston net and multiple opening-closing net system (MOCNESS) tows. Most potential prey types in the neuston exhibited no significant enhancement over the seamount. MOCNESS samples at 10 m depth, however, showed several prey types to be more abundant over the seamount, and the dominant size class of fish was slightly larger. We attribute the sea-bird aggregation observed at this seamount to changes in the abundance and/or behavior of pelagic organisms in the deep scattering layer (not adequately sampled in this study), perhaps augmented by migrations of seamount residents into the surface layers. Processes on and in the vicinity of seamounts may provide spatially-predictable prey to wide-ranging aerial sea birds foraging in this relatively austere environment.

Notes: Abstract In mid-summer 1975 throughout the Western Slope Water of the North Atlantic Ocean, massive numbers ofSalpa aspera performed a diel vertical migration of at least 800 m. This resulted in a movement of 85 to 90% of the total zooplankton biomass out of the upper 500 m during the day. Fecal pellet production and losses from this salp population were estimated to contribute approximately 12 mg C m-2 day-1 to the deep planktonic and benthic populations. If all this organic matter reached the deep-sea floor, it would represent over 100% of the daily deep-sea benthic infauna energy requirements.