While ecosystems are often circumscribed for study at habitat boundaries (e.g. land/water or marine/freshwater interface), many if not most important ecological interactions occur across ‘ecotones’ at habitat boundaries. In our systems, we have found that rivers export algae and adult aquatic invertebrates that are tracked by terrestrial consumers, including spiders, lizards, and bats (Power et al. 2004). Sunny, warm, productive mainstems can supply emergence that subsidizes growth of spiders and juvenile spiders residing in less productive tributaries (Power and Uno 2018, Uno 2020). Drift algae, when exported from rivers to the estuary, is devoured by marine isopods and amphipods so rapidly that it disappears—suggesting that these exports represent a hitherto unrecognized trophic subsidy that may matter to estuarine and nearshore food webs (Betts-Ng 2013). Year-to-year variation in the abundance of epiphytic freshwater diatoms to the deep marine canyons off the mouth of the Eel correspond to the interannual abundance patterns of the macroalgal hosts of these diatoms upstream.
The scales of ecosystem exchanges are sometimes surprisingly large, and crucial to keep in mind when we consider repercussions of changes in one part of a connected world. Gabe Rossi is spearheading a study of the Eel River “FoodScape”—expanding his detailed studies of how juvenile steelhead foraging and growth potential respond to seasonal changes in flow and food phenology in tributaries (Rossi et al. 2022). Gabe and his team are now studying the food webs supporting salmonids from tributaries down through mainstems and into the Eel estuary.
In collaboration with colleagues, we are also considering feeding in river floodplains, which are scarce along the canyon-bound Eel, but likely of outsized importance to fish. FoodScape studies investigate the seasonal occurrence of resource pulses down the river network; factors that determine whether fish can track these feeding opportunities; and how we might manage watersheds to increase access of rearing salmonids to seasonally shifting feeding opportunities.