Published kelp forest food webs are poorly resolved for small mobile invertebrates that are prey for many predators. Kelp forest ecosystem stability and functional redundancy measured from these webs might depend on the level of aggregation in the network. Our objective was to provide a high-resolution topological kelp forest food web suitable for network analysis.
We defined the study system as rocky reef that supports giant kelp (Macrocystis pyrifera) in the Santa Barbara Channel. We constrained the food web to those species regularly using the water column and benthic zones within kelp forests. The node list was assembled using information from primary literature, monitoring group species lists and surveys, technical reports, direct sampling (plankton tows, benthic algae and kelp holdfast collection), expert opinion, crowd sourced observations (in the case of birds, pinnipeds, and cetaceans), and inference. Very rare species (<1% frequency of detection in surveys) were only included if species were cryptic and/ or unlikely to be detected by monitoring method), or high trophic level and transient, so naturally would be rare in the system. Diet links were assigned based on direct observation, literature, and, where data were sparse, logical inference.
Results/Conclusions
Increasing taxonomic resolution more than doubled the number of nodes in the web (relative to previously published webs) and dramatically increased the number of links. This affected structural metrics. In addition to increasing richness and connectance, functional redundancy declined and nestedness increased among middle trophic levels. Trophic levels increased from large bony fishes to sharks, birds, pinnipeds, and cetaceans. Modules (communities of densely interacting nodes) were identified within the overall network, revealing functional subunits of the system.