Linking Aquatic-Terrestrial Habitats through Resource and Process Subsidies: Insights from Too Few Salmon and Too Many Carp

Resource subsidies are the input of energy, nutrients, and organisms that directly alter pools of resources within a recipient habitat. In contrast, process subsidies arise when the feeding or behaviors of a mobile organism affect process rates within the recipient habitat. Using salmon carcasses as a model resource subsidy and Asian carp as model process subsidy, two experiments were conducted to explore the complex direct and indirect pathways through which these subsidy classifications influence linkages between aquatic and terrestrial environments. Salmon carcasses increased resident trout production through multiple pathways including bottom-up (algae, insects), direct consumption, and reciprocal inputs of adult and larval carrion flies. These subsidized predators cropped benthic insect larvae, reducing their emergence as adults, and indirectly reduced riparian insectivores, indicating strong subsidy effects can spillover to other habitats, however responses are not always positive. Strong consumptive effects of bighead carp reduced filamentous algae and zooplankton within pelagic habitats. Consequently, egested materials shunted organic matter from pelagic to benthic habitats, where Chironimidae emergence increased, resulting in a greater flux of organic matter from aquatic to terrestrial habitats. In each study, the effects these mobile fishes reverberated through aquatic-terrestrial habitats, highlighting the importance fishes in linked ecosystems.