Factors affecting seabird distribution in the Humboldt Current upwelling system in northern Chile were studied in January 1999 using ship transect counts. Of 24 species recorded, the Peruvian booby (Sula variegata), the kelp gull (Larus dominicanus) and the Humboldt penguin (Spheniscus humboldti) were the most abundant. Species composition varied among different areas of the system and distribution patterns differed substantially among eight of the more abundant species. Most species showed links to variation in environmental factors (trawler distribution, SST and chlorophyll concentration). Principal component analysis identified a feeding-flock factor as the most important one for explaining observed distribution patterns. One-third of all birds recorded were associated in feeding flocks and 3% of all individuals were directly attending fishing vessels.
Many seaweed species are particularly important for passive marine dispersal, yet relatively little is known about their floating and stranding dynamics. Here, we studied these dynamics for two kelp species over four consecutive years at mid‐latitudes (30°S). Floating kelps were found during all seasons, but Macrocystis pyrifera was always more abundant than Durvillaea incurvata. Highest floating biomasses were reached during summer and fall, whereas considerable stranded biomasses on nearby shores were only observed during summer. The proportion of fragments among the floating kelps was high throughout the entire study period and highest for M. pyrifera during summer. At the same time, blades of M. pyrifera that floated in nearshore waters in summer had a high blade index and thus were intact (i.e., not yet compromised by unfavorable environmental conditions). These results suggest that during summer, floating kelps become quickly resupplied from benthic sources, which compensates their frequent losses due to degradation and stranding. During fall, biomasses of floating kelps remain high because of reduced losses. Interestingly, increased wind speed was a good predictor for the biomass accumulations of the two kelp species, although the floating biomass of M. pyrifera was additionally influenced by oceanographic fronts. Our findings suggest that at mid‐latitudes the dynamics of floating seaweed stocks are dependent on the availability of benthic source populations (continuous throughout the year) and export due to degradation (high in summer/fall) and stranding (high in summer).
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