2002-2003 Science Planning Summary

Biology & Medicine

Dr. Polly Penhale
Program Manager


NSF/OPP 02-34570 (SGER)
Station: Not based at a station
Research Site(s): Reunion Island, Indian Ocean

Food web structure across a large-scale ocean productivity gradient: Top predator assemblages in the southern Indian Ocean
Dr. George L. Hunt
Ecological and Evolutionary Biology
Dr. K. David Hyrenbach
Duke University

Deploying Team Members: George Hunt . K D Hyrenbach
Research Objectives: During an Océan Indien Service d’Observation cruise, this group will test the hypothesis that the dispersion and community of top predators vary with large-scale differences in physical structure and ocean productivity by conducting an interdisciplinary survey of marine bird and mammal use of distinct domains in the southern Indian Ocean. French team members will sample physical oceanography and ocean productivity while USAP participants survey top predator distributions across a 35º latitudinal gradient from subtropical to subantarctic waters.

Project team members will address the primary hypothesis that top predator assemblages are structured by spatial gradients in hydrographic properties and ocean productivity patterns known to influence the distribution and patchiness of their zooplankton, fish, and squid prey. The researchers hypothesize that the overall abundance of marine top predators within a specific domain is largely determined by ocean productivity. They also hypothesize that the energetic costs of foraging determine which types of marine top predators inhabit specific domains. Species with high foraging costs must exploit dense prey aggregations within highly productive areas. Conversely, taxa with low foraging costs are able to inhabit areas of low productivity, where they exploit more dispersed prey.

To test these hypotheses, researchers will quantify the spatial association of top predator assemblages with specific water masses and the aggregate response of top predators at hydrographic and bathymetric domains. Because top predators respond to oceanographic variability at multiple scales of time and space, project team members will assess their responses to habitat variability at two specific scales, mega-macro and coarse. At the mega-macro scale (thousands of kilometers), faunal associations with specific water masses and ocean productivity domains will be characterized. At the coarse scale (tens of kilometers), top predator aggregations at frontal systems and continental shelf margins will be quantified.

The analytical methods used will include compositional analysis of coarse-scale habitat preferences, generalized additive models, recurrent group analysis, ordination of hydrographic data and top predator assemblages, and measurement of top predator aggregation using Lloyd’s index of dispersion and autocorrelation statistics.

More specifically, project team members will study how overall top predator abundance and the distributions of distinct assemblages and feeding guilds change across spatial gradients in physical and biological properties. This interdisciplinary perspective will enhance the current understanding of the way physical and biological processes structure pelagic communities in the southern Indian Ocean.

Field Season Overview:
Working from the bridge of the French research vessel Marion Dufresne, project team members will observe the distribution and abundance of marine birds and mammals in the research area.