UC Santa Barbara

This dissertation describes and analyzes the Palmyra Atoll sand flat food web. This food web is unique in measuring the body sizes, densities, and feeding links for all life stages of free-living and parasitic metazoans. Chapter 1 puts the research in context by reviewing the roles of parasites in marine food webs. Chapter 2 starts by describing the physical attributes (sediment particle size, water depth, temperature) of the 35 random sampling sites. It then lists the 22 sampling methods used to estimate the body size and abundance of 670 life stages comprising 275 species. The resulting free-living community contains represents 195 free-living species across 18 phyla, and 389 separate life stages. Chapter 2 then describes how parasites were measured from >2500 hosts collected and dissected to reveal a parasite community with 80 species across 9 phyla, and 281 separate life stages. Chapter 3 then uses stomach contents, field observations, literature, and natural history to estimate 24,575 trophic interactions, ontogenetic development and parasite transmission pathways among the 670 nodes in Chapter 2. Chapter 4 compares the Palmyra sand flat food web with the only published food web described in similar detail, the west coast estuary food web. In both systems, parasites make contributions to richness, abundance, and biomass comparable to free-living consumer groups, such as birds. Further, in both systems parasites dominate network structure in ways that free-living consumers cannot. These results suggest that parasites make general and important contributions to ecosystem structure. Our understanding of food webs is incomplete without them.