Marine Subsidies

Ecosystems are closely linked through the exchange of resources. Marine subsidies refer to the cross-ecosystem flows of ocean-derived resources, including organisms, nutrients, and detritus. These subsidies occur in two forms: passive, resulting from deposition by abiotic forces such as gravity, wind, and waves, and active, through animal-mediated resource transport. These transfers often enrich recipient habitats with otherwise limiting nutrients, leading to enhanced productivity and causing a wide range of ecological impacts. The influence of marine subsidies extends across terrestrial, freshwater, and marine environments. On arid desert islands in Baja California, Mexico, the influence of marine subsidies to terrestrial ecosystems is particularly evident; here, the energy gained from passively donated marine detritus outweighs islands’ terrestrial productivity. Seabird guano, on the other hand, is an example of an actively deposited marine input in terrestrial ecosystems. This resource has been studied for decades, likely due to its high commercial value in the fertilizer industry. Meanwhile, Pacific salmon provide a classical example of marine subsidies to both freshwater and terrestrial systems. These fish feed and gain mass in the ocean before they spawn and die in their natal freshwater streams, facilitating the fertilization of both nutrient-limited streams and riparian terrestrial habitats. Finally, marine subsidies can also refer to cross-ecosystem movements between different types of marine habitats. For example, zooplankton feed on phytoplankton, which remove vast amounts of carbon dioxide from the atmosphere. Fecal pellets from upper-pelagic zooplankton slowly drift downward in the water column through gravity and passively subsidize deep ocean ecological communities. Marine animals, including whales, can move nutrients back upwards in the water column against the pull of gravity as they feed in the deep ocean and return to the sea surface to breathe, excreting feces and urine on the way. Through a process called upwelling, this upward movement of nutrients can also happen passively. Upwelling is a wind-driven phenomenon by which cold, nutrient-rich waters are forced up toward the sea surface, resulting in increased productivity in surface waters. Overall, marine subsidies link various ecosystems through the movement of marine-derived resources, and greatly impact the ecologies of recipient habitat flora and fauna. From fertilizing nutrient-limited streams to subsidizing deep ocean benthic communities, marine subsidies have significant ecological impacts across the globe.