Award: OCE-1041454

Forests of giant kelp (Macrocystis pyrifera) occur on shallow rocky reefs along the western coast of North America and other temperate regions of the world. Among the most productive ecosystems on Earth, these forests create habitat and primary production that support species rich communities. Culturally and economically important commercial and recreational fisheries target many species of finfishes and invertebrates (e.g., sea urchins, spiny lobster, abalone) within kelp forests. Recent establishment of marine protected areas (MPAs) throughout the coast of California and elsewhere holds the potential for increasing size and abundance of fished species, particularly those higher in the food chain. These changes may have consequences that amplify throughout forest foodwebs and are difficult to predict. Moreover, in kelp forests off southern California, important fisheries for spiny lobster, California sheephead, and red urchin are likely to be significantly impacted if populations of the federally listed southern sea otter (Enhydra lutris nereis), a voracious predator considered to be a "keystone" species, continue to grow and expand southward to their historical geographic limits. In order to understand and proactively address these potential changes to kelp forest ecosystems along the coast of California, we developed analytical tools that facilitate ecosystem-based decision making and management. These tools will allow us to forecast how marine reserves and the impending re-colonization of sea otters will affect both the ecosystems in the region and the valued fisheries they support. Using large-scale and long-term monitoring data from central and southern California kelp forests we characterized the composition and dynamics of these communities in order to inform and calibrate ecosystem-based models such as Ecopath with Ecosim, loop analysis, and allometric models. These ecological models required an unprecedented collection of quantitative information about life-history traits, demography, and interactions of kelp forest species. To accomplish this we constructed an online interactive database (http://kelpforest.ucsc.edu/) and enlisted dozens of researchers doing kelp forest related work at several research institutions from Mexico to Alaksa to collect and enter thousands of observations from the scientific literature. This database will be maintained in perpetuity, and can be expanded for application to other ecosystems and fields of research. Key findings of the modeling and empirical analyses conducted for this project include the following results: Fishing of one or more species of finfish has impacts on abundance (biomass) of organisms at all levels within kelp forest food webs. Our models show these effects are greater when particular species of fish and ecological roles (e.g., plankton eaters) are targeted. Species showing strong indirect responses to fishing are therefore the most important to monitor for the impacts of fishing or the establishment of MPAs As expected, models show the abundance of the foundation species, giant kelp, has important effects on biomass levels higher in the food web, however, the amount of year-to-year variability in kelp abundance, which is predicted to increase under changing climate conditions, can have equally important consequences. Models that incorporate species body size in food web networks perform better at predicting the behavior of the foodweb than those that do not, and this benefit actually increases as these networks become more complex. Giant kelp and urchin populations show dramatic phase shifts in southern California kelp forests. We tested a suite of potential early warning indicators to identify tipping points between algae and urchin-dominated periods within a 31 year record of monitoring data. None of the indicators tested were effective predictors suggesting that the phase shifts are complex and likely governed by multiple and external interact...