Productivity and Sustainable Management of the Humboldt Current Large Marine Ecosystem under climate change
Introduction
The Humboldt Current Large Marine Ecosystem (HCLME) covers the area within 55° of latitude off Peru and Chile (3°23.57′ to 58°21.02′) and over 200 nautical miles offshore (Fig. 1). 65% of the HCLME extension corresponds to the Humboldt Current System (HCS), which is under the influence of seasonal or permanent coastal upwelling, from approximately 4 to 40° south.
Several features characterize the HCLME among similar ecosystems associated with Eastern Boundary Currents (EBCs: California, Canarias, Humboldt and Benguela). First, it extends closest to the equatorial line among the four systems. Second, it is the most exposed EBC system to the El Niño Southern Oscillation, which is the largest source of interannual climatic variability on the Earth. Third, it exhibits the highest fish productivity among the four EBC systems, notwithstanding primary productivity is in the same range as the primary productivity of the other systems. Fourth, it is associated with the presence of a shallow intense subsurface oxygen minimum layer that compresses the oxygenated epipelagic habitat to a few dozen meters.
Global warming is likely to alter the atmosphere–ocean–continent energy and matter exchanges, modifying the pressure gradients and alongshore and cross-shore wind fields along with marine currents, sea surface temperature (SST) and the thermal stratification, in addition to the intensity and spatio-temporal distribution of coastal upwelling. Global models predict the decrease of marine primary productivity and a significant loss of marine biodiversity, especially at the tropic and polar latitudes. On the other hand, the influx of anthropogenic CO2 to the ocean and large-scale stratification are causing acidification and deoxygenation, which might trigger a cascade of biogeochemical and ecological changes in marine ecosystems. It is uncertain how these multiple stressors will impact on the productivity and biodiversity of the HCLME. A debate about the response of EBC upwelling ecosystems to global warming is ongoing with contradictory future scenarios (upwelling intensification vs weakening). In any case, physical and biogeochemical changes will likely affect the phenology, spatial distributions and species compositions of primary and secondary producers. Improving resiliency by reducing non-climatic hazards is the current challenge to ensure the adaptive sustainable management of this large marine ecosystem.
Section snippets
Setting the scene
The Humboldt Current (HC) or Peru Current is the large-scale offshore surface current that derives from the West Wind Drift (WWD) at around 40°S and flows northwards along the Pacific eastern seaboard as part of the Coriolis force induced South Pacific gyre (Fig. 1). The WWD also originates as a coastal poleward flow south at 45°S, the Cape Horn Current, which mixes the more saline waters with the fresher waters from the Chilean fjords. Off Central Chile the HC attains high speeds and it is
Biogeochemistry: a system close to the edge
Lack of ventilation and low-oxygen content of source waters, long residence times of waters due to the weak to moderate winds in the Tropical South Eastern Pacific, and decay of the intense biological production in surface waters explains the existence of the oxygen minimum zone (OMZ) in the HCLME region (Pennington et al., 2006). The South Eastern Pacific OMZ accounts for 11% of the global volume of OMZ waters, and it is the fourth largest area among regional OMZs. Its upper boundary is
Primary productivity and channeling to the upper trophic levels
Fig. 4 shows the spatial and temporal changes of the primary productivity in the HCLME. At least four provinces can be described along the HCLME, based on the primary productivity of the marine coastal zone and the fjords (Table 1). The most productive area is located off the Peruvian coast, in which the offshore extension of the coastal productive belt ranges between 100 and 200 km, with an average annual primary production rate (PPR) of 1.2 kg C m−2 y−1. Next in productivity is the area off the
Current features of the main resource landings in the HCLME
The 2.5 million km2 HCLME area currently accounts for 12% of the world's marine fish landings and includes the largest single species fishery in the world: the Peruvian anchovy. Fig. 6 presents the composition of marine fish landings for the two countries for the period 2009–2013, reflecting the dominance of anchovy catch in the total fishing activity of which 25,146,910 and 4,609,166 t of anchovy were landed during this period in Peru and Chile, respectively. Of the other three main pelagic
Sensitivity to climate variability
Proxy climatic and oceanographic records show the sensitivity of the HCLME to climate variability at multiple time-scales. Millennial and centennial time-scale variability of the earth climate affects the intensity of the Walker circulation, the mean position of the Intertropical Convergence zone and the size and position of the Hadley cell. In consequence, the circulation, productivity and oxygenation patterns in the HCLME also vary with the climatic conditions (De Pol-Holz et al., 2007;
Recent trends and climate change scenarios: implications for the biological productivity
As mentioned above, an exceptional pelagic fish productivity characterizes the HCLME and a major part of it is concentrated in the Peru upwelling subsystem. Despite primary productivity being within the same range of other EBUSs, the fish production (mostly anchovy) here is one order of magnitude higher. Several mechanisms have been postulated to explain this paradox: (1) a moderate alongshore wind intensity off Peru which results in strong upwelling, low turbulence and longer residence times
A transboundary diagnostic analysis of the HCLME
Peru and Chile add up to approximately 6950 km-long coastal belt, which currently is fished by close to 135,000 artisanal fisherfolk with 39,000 fishing vessels. In total, coastal fisheries support upwards of one million livelihoods in the region. As mentioned above, marine fish landings have decreased in both countries in the past decade. Even though it is early to predict if this trend will continue or not, better governance and management for the HCLME ecosystem services, from which fish
The valuation of the HCLME goods and services
In order to protect the delivery of goods and services derived from the HCLME area it is obviously important to know the major threats to this LME as identified above, both natural and anthropogenic, while also being aware of the annual total economic value derived from the area. Economic valuations of ecosystem goods and services have been carried out worldwide and are summarized in Table 4. The wide variations in value reflect three factors: (1) the absence of an accepted standard LME goods
Sustainable management under climate change: a challenge for adaptation
It is expected that climate change will impact on the biodiversity, habitat quality, carrying capacities and life cycles of marine ecosystems and organisms, as well as on socio-economic services, such as fish catch potential, fishing efforts and fishers incomes, increasing the vulnerability of the ecosystem and the human local communities. Other anthropic stressors, such as by-catch, discard practices and pollution can further amplify climate change impacts through effects on ecological
Conclusions
The very large productivity of the HCLME is supported by a set of environmental factors that are highly sensitive to climate variability and climate change. Expected changes in atmosphere and ocean circulation patterns will likely affect coastal wind intensities, water mass distribution and upwelling productivity, influencing on recruitment success, biomass and spatial distribution of fishery resources. In addition, increasing extreme climatic events such as El Niño will likely increase the
Acknowledgments
We gratefully acknowledge the GEF-UNDP Humboldt project team and the leading institutions from Peru (IMARPE) and Chile (IFOP), for all their help and collaboration. In particular, we acknowledge Alexis Chaigneau, Carlos Y. Romero and Noel Domínguez for their contributions to the preparation of figures in the physical oceanography section of this document. Finally, we express our gratitude to Dr. Ken Sherman of NOAA, and Dr. Hashali Hamukuaya of the Benguela Current Commission (BCC) for their
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