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Abstract: This work examined diet data from studies of top pelagic predators from three large regions of the equatorial and South Pacific Ocean. Food webs of each of these three systems were found to have relatively high species diversity, but in contrast to other marine systems, relatively low connectance. Food webs were examined using graph-theoretic methods, which included aggregating species based on food-web relationships and identification of potentially influential species. Species aggregations were used to construct simplified qualitative models from each region’s food web. Models from each region were then analyzed to make predictions of response to climate change for six commercially important species: mahi mahi, skipjack tuna, albacore tuna, yellowfin tuna, bigeye tuna, and swordfish. We found little commonality in the structure of the three food webs, although the two regions in the equatorial Pacific had food webs composed of four predation tiers, as defined by network levels of predation, whereas the south-western region had only three predation tiers. We also found no consistent pattern in the predicted outcomes of the perturbations, which underlines the need for detailed trophic databases to adequately describe regional pelagic ecosystems. This work demonstrates that food-web structure will be central to understanding and predicting how top pelagic predators, and the ecosystems in which they are embedded, will respond to climate change. [Copyright &y& Elsevier]

Abstract: Ten-day sea level anomalies (SLA) charts, based on the TOPEX/Poseidon (T/P) altimetry data for 1992–2003, as well as corresponding charts of sea surface dynamic heights constructed by the superposition of SLA distributions over the climatic dynamic topography, were used to study main oceanic currents in the region 45°S–20°S, 110°W–70°W. Spatial and seasonal variability of the South Pacific Current has been investigated based on the maps of dynamic topography (DT) gradients. Also maps of the temperature gradients at the ocean surface were used to study the mesoscale variability related to the Subtropical Front (STF) in the Southeastern Pacific. The analysis allowed to distinguish the zones with different degree of variability in the current and front positions. The variability is minimal at 99°W, where the current is most intensive. Westward of 105°W, the RMS of the STF position may reach 3° of latitude. This is accompanied by a pronounced spectral peak with a period of 350 days in its temporal variability. Eastward of 105°W, there is no dominant peak in the frequency spectra describing the variability of the current and front. Comparison of the satellite derived front and current positions with in situ data acquired during R/V “Atlantida” expedition in November–December 2002 shows a good correspondence. Zones of high dynamic topography gradients and sea surface temperatures gradients coincide within the physical errors of the method. The analysis of pelagic fish distribution patterns in the Southeastern Pacific Ocean based on acoustic survey data and synoptic variability of the dynamic topography reveals that most dense fish concentrations relate to dynamic heterogeneities, which are located at the northern periphery of the Subtropical Front. [Copyright &y& Elsevier]