Eastern boundary current systems are among the world's most productive large marine ecosystems. Because upwelling currents transport nutrient-rich but oxygen-depleted water onto shallow seas, large expanses of productive continental shelves can be vulnerable to the risk of extreme low-oxygen events. Here, we report the novel rise of water-column shelf anoxia in the northern California Current system, a large marine ecosystem with no previous record of such extreme oxygen deficits. The expansion of anoxia highlights the potential for rapid and discontinuous ecosystem change in productive coastal systems that sustain a major portion of the world's fisheries.

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Seasonal development of dissolved-oxygen deficits (hypoxia) represents an acute system-level perturbation to ecological dynamics and fishery sustainability in coastal ecosystems around the globe. Whereas anthropogenic nutrient loading has increased the frequency and severity of hypoxia in estuaries and semi-enclosed seas, the occurrence of hypoxia in open-coast upwelling systems reflects ocean conditions that control the delivery of oxygen-poor and nutrient-rich deep water onto continental shelves. Upwelling systems support a large proportion of the world's fisheries, therefore understanding the links between changes in ocean climate, upwelling-driven hypoxia and ecological perturbations is critical. Here we report on the unprecedented development of severe inner-shelf (<70 m) hypoxia and resultant mass die-offs of fish and invertebrates within the California Current System. In 2002, cross-shelf transects revealed the development of abnormally low dissolved-oxygen levels as a response to anomalously strong flow of subarctic water into the California Current System. Our findings highlight the sensitivity of inner-shelf ecosystems to variation in ocean conditions, and the potential impacts of climate change on marine communities.

A long-standing issue in marine biology is identifying spatial scales at which populations of sessile adults are connected by planktonic offspring. We examined the genetic continuity of the acorn barnacle Balanus glandula, an abundant member of rocky intertidal communities of the northeastern Pacific Ocean, and compared these genetic patterns to the nearshore oceanography described by trajectories of surface drifters. Consistent with its broad dispersal potential, barnacle populations are genetically similar at both mitochondrial (cytochrome oxidase I) and nuclear (elongation factor 1-alpha) loci across broad swaths of the species' range. In central California, however, there is a striking genetic cline across 475 km of coastline between northern and southern populations. These patterns indicate that gene flow within central California is far more restricted spatially than among other populations. Possible reasons for the steep cline include the slow secondary introgression of historically separated populations, a balance between diversifying selection and dispersal, or some mix of both. Geographic trajectories of oceanic drifters closely parallel geographical patterns of gene flow. Drifters placed to the north (Oregon; approximately 44 degrees N) and south (Santa Barbara, California; approximately 34 degrees N) of the cline disperse hundreds of kilometers within 40 days, yet over the long-term their trajectories never overlapped. The lack of communication between waters originating in Oregon and southern California probably helps to maintain strong genetic differentiation between these regions. More broadly, the geographical variation in gene flow implies that focusing on species-level averages of gene flow can mask biologically important variance within species which reflects local environmental conditions and historical events.

Wind-driven coastal ocean upwelling supplies nutrients to the euphotic zone near the coast. Nutrients fuel the growth of phytoplankton, the base of a very productive coastal marine ecosystem [Pauly D, Christensen V (1995) Nature 374:255-257]. Because nutrient supply and phytoplankton biomass in shelf waters are highly sensitive to variation in upwelling-driven circulation, shifts in the timing and strength of upwelling may alter basic nutrient and carbon fluxes through marine food webs. We show how a 1-month delay in the 2005 spring transition to upwelling-favorable wind stress in the northern California Current Large Marine Ecosystem resulted in numerous anomalies: warm water, low nutrient levels, low primary productivity, and an unprecedented low recruitment of rocky intertidal organisms. The delay was associated with 20-to 40-day wind oscillations accompanying a southward shift of the jet stream. Early in the upwelling season (May-July) off Oregon, the cumulative upwelling-favorable wind stress was the lowest in 20 years, nearshore surface waters averaged 2°C warmer than normal, surf-zone chlorophyll-a and nutrients were 50% and 30% less than normal, respectively, and densities of recruits of mussels and barnacles were reduced by 83% and 66%, respectively. Delayed early-season upwelling and stronger late-season upwelling are consistent with predictions of the influence of global warming on coastal upwelling regions.climate variability ͉ coastal marine ecosystems ͉ coastal ocean upwelling ͉ marine ecology E quatorward winds along the eastern boundaries of the world's oceans drive offshore surface Ekman transport and the upwelling of cold, nutrient-rich water into the euphotic zone near the coast. These nutrient pulses stimulate high phytoplankton production, which, in turn, supports a rich coastal marine ecosystem and productive fisheries (1). Examples of such dynamics include the California Current, the Humboldt Current, the Benguela Current, and the Canary Current (2).The strength and extent of the seasonal cycle in upwellingfavorable winds varies along the U.S. west coast. In the northern California Current Large Marine Ecosystem (CCLME), there is a strong seasonal cycle with upwelling-favorable winds, the appearance of cold, saline, nutrient-rich water near the coast, and equatorward currents over the shelf occurring after a spring transition (3). Alongshore winds in the northern CCLME are more variable than those farther south because they are more frequently influenced by eastward-traveling Gulf of Alaska low-pressure systems. The intermittent cessation of upwelling-favorable winds is called relaxation and plays an important role in coastal circulation and the recruitment of marine organisms † † . The timing of the spring transition and the total amount of upwelling-favorable winds during the spring-summer upwelling season have a considerable impact on coastal ecosystem responses. Farther south in the CCLME, winds are more persistently upwelling-favorable and the transition to a more productive spring-su...

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The near-term progression of ocean acidification (OA) is projected to bring about sharp changes in the chemistry of coastal upwelling ecosystems. The distribution of OA exposure across these early-impact systems, however, is highly uncertain and limits our understanding of whether and how spatial management actions can be deployed to ameliorate future impacts. Through a novel coastal OA observing network, we have uncovered a remarkably persistent spatial mosaic in the penetration of acidified waters into ecologically-important nearshore habitats across 1,000 km of the California Current Large Marine Ecosystem. In the most severe exposure hotspots, suboptimal conditions for calcifying organisms encompassed up to 56% of the summer season, and were accompanied by some of the lowest and most variable pH environments known for the surface ocean. Persistent refuge areas were also found, highlighting new opportunities for local adaptation to address the global challenge of OA in productive coastal systems.

a b s t r a c tA central challenge for natural resource management is developing rigorous yet practical approaches for balancing the costs and benefits of diverse human uses of ecosystems. Economic theory has a long history of evaluating tradeoffs in returns from different assets to identify optimal investment strategies. There has been recent progress applying this framework to the delivery of ecosystem services in land use planning. However, despite growing national and international interest in marine spatial planning, there is a lack of parallel frameworks in the marine realm. This paper reviews an ecosystem service tradeoff analysis framework and provides a more comprehensive synthesis for how it can be applied to marine spatial planning and marine ecosystem-based management. A tradeoff analysis approach can reveal inferior management options, demonstrate the benefits of comprehensive planning for multiple, interacting services over managing single services, and identify 'compatible' services that provide winwin management options.