Ecological Values of Shallow-Water Habitats: Implications for the Restoration of Disturbed Ecosystems |
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Authors: | Cary B Lopez James E Cloern Tara S Schraga Amy J Little Lisa V Lucas Janet K Thompson Jon R Burau |
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Institution: | (1) US Geological Survey, 345 Middlefield Road MS 496, Menlo Park, California 94025, USA;(2) US Geological Survey, Placer Hall, 6000 J Street, Sacramento, California 95819, USA |
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Abstract: | A presumed value of shallow-habitat enhanced pelagic productivity derives from the principle that in nutrient-rich aquatic
systems phytoplankton growth rate is controlled by light availability, which varies inversely with habitat depth. We measured
a set of biological indicators across the gradient of habitat depth within the Sacramento–San Joaquin River Delta (California)
to test the hypothesis that plankton biomass, production, and pelagic energy flow also vary systematically with habitat depth.
Results showed that phytoplankton biomass and production were only weakly related to phytoplankton growth rates whereas other
processes (transport, consumption) were important controls. Distribution of the invasive clam Corbicula fluminea was patchy, and heavily colonized habitats all supported low phytoplankton biomass and production and functioned as food
sinks. Surplus primary production in shallow, uncolonized habitats provided potential subsidies to neighboring recipient habitats.
Zooplankton in deeper habitats, where grazing exceeded phytoplankton production, were likely supported by significant fluxes
of phytoplankton biomass from connected donor habitats. Our results provide three important lessons for ecosystem science:
(a) in the absence of process measurements, derived indices provide valuable information to improve our mechanistic understanding
of ecosystem function and to benefit adaptive management strategies; (b) the benefits of some ecosystem functions are displaced
by water movements, so the value of individual habitat types can only be revealed through a regional perspective that includes
connectedness among habitats; and (c) invasive species can act as overriding controls of habitat function, adding to the uncertainty
of management outcomes. |
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Keywords: | restoration shallow-water habitat pelagic production food web freshwater ecosystems |
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