Marine bird distribution and abundance off southern California: Pattern and process at multiple scales.

摘要

This research investigates how marine birds reflect oceanographic variability in a pelagic environment. This dissertation addresses a broad range of temporal (hours–years) and spatial (10's–1000's km) scales, and combines three distinct perspectives of seabird dispersion: Individual foragers, regional scales, and oceanic domains.; The study of satellite-tracked albatross movements (Chapter 3) and vessel-based seabird surveys (Chapter 5) support the notion that water mass distributions and ocean productivity patterns influence seabird dispersion and community structure over macro-mega (1000's km) scales. Satellite telemetry revealed that North Pacific albatrosses commuted to highly productive subarctic (Laysan Albatross, Phoebastria immutabilis) and California Current (Black-footed Albatross, P. nigripes) waters, thousands of kilometers from their breeding colony in Tern Island, Hawaii. Long-term (1987–1998) seabird surveys off southern California documented pervasive changes in marine bird feeding guilds, biogeographic assemblages, and warm-water and coldwater species groups within the CalCOFI study area, concurrent with a pronounced warming of near-surface (10m) and thermocline (100m) ocean temperatures.; The foraging movements of satellite-tracked North Pacific albatrosses (Chapter 3) and the long-term (1987–1998) changes in seabird communities documented off southern California (Chapter 4), also suggest that marine birds respond to environmental variability over smaller coarse—meso scales (10's–100's km). Satellite telemetry revealed that breeding albatrosses focused their foraging on highly-productive regions of prey aggregation, such as continental shelves and oceanic fronts. Moreover, vessel-based surveys of marine bird populations documented temporal shifts in the composition of coastal seabird assemblages off southern California, associated with a long-term decline in macro-zooplankton abundance and aggregation in onshore waters. Additionally, behavioral observations of seabird vessel-attraction onboard CalCOFI cruises (Chapter 2) illustrated that survey vessels influence albatross dispersion over tens of kilometers.; This dissertation underscores the notion that distinct processes structure pelagic communities at diverse spatial and temporal scales. This research suggests that seabird assemblages are influenced by prey dispersion over coarse-meso scales (10's–100's km), and by ocean productivity and water mass distributions over larger macro-mega scales (1000's km). These results have important implications for our understanding of the ecology of far-ranging marine species, and the biotic consequences of climatic change in pelagic ecosystems.