Detrital supply suppresses deforestation to maintain healthy kelp forest ecosystems.

Herbivores can reach extraordinary abundances in many ecosystems. When herbivore abundance is high, heavy grazing can severely defoliate primary producers and, in some cases, even drive ecosystem to undergo regime shifts from a high productivity state to a denuded, low productivity state. While the phenomenon of herbivore-driven regime shifts is well documented, we only partially understand the mechanisms underlying these events. Here, we combine herbivory experiments with 21 years of long-term monitoring data of kelp forest ecosystems to test the hypothesis that herbivores drive regime shifts when herbivory exceeds primary production. To test this hypothesis, we quantified how the foraging habits of an important group of marine herbivores-sea urchins-change with increases in sea urchin biomass and trigger regime shifts to a foundation species, giant kelp (Macrocystis pyrifera). Using experiments, we quantified how the grazing capacity of urchins increases as urchin biomass increases, then we combined these estimates of urchin grazing capacity with estimates of kelp production to predict when and where urchin grazing capacity exceeded kelp production. When grazing capacity exceeded kelp production, sea urchins caused a 50-fold reduction in giant kelp biomass. Our findings support the hypothesis that the balance between herbivory and production underlies herbivore-driven regime shifts in Southern California kelp forests and provides insight into when and where urchins are likely to force regime shifts in kelp forest ecosystems.

Piecing together the data of the U.S. marine aquaculture puzzle.

Aquaculture recently became the main source of global seafood production and many countries, including the United States, see potential in marine aquaculture to sustainably fill growing demand. The U.S. supports the majority of its seafood consumption through imports, and therefore identifying bottlenecks to domestic aquaculture growth is a priority at the federal and state level. Yet, one critical aspect that appears not yet addressed is the quality and accessibility of marine aquaculture data. In this study we conducted the first multi-state synthesis and comparison of the most comprehensive suite of species, volume, and value information on U.S. marine aquaculture over time, across the 23 marine coastal states. Using publicly available data sources from the U.S. Department of Agriculture (USDA), state-level solicited data that we aggregated, and data from the National Oceanic and Atmospheric Administration (NOAA), we found strong evidence that marine aquaculture has played an increasingly important role in marine coastal states, but also uncovered numerous data gaps and discrepancies between and within these sources. In particular, we found a dearth of volumetric data and millions in missing value (USD$). We found U.S. marine aquaculture is likely much more diverse, abundant and valuable than is currently reported, but the main sources of error in any given state remain unclear. We recommend U.S. state governments adopt a standardized, digital and annual data collection program, such as the NOAA Fisheries Information Networks. Better strategic aquaculture planning, management, and research depend on accurate data, and existing digital data infrastructures provide strong opportunities for improvement.