From earth and ocean: investigating the importance of cross‐ecosystem resource linkages to a mobile estuarine consumer

Abstract

Abstract. Externally derived resources often contribute to the structuring of ecological communities.Estuaries are one of the most productive ecosystems in the world and provide an ideal system to test how communities may be shaped by resource subsidies because they occur at the intersection of marine, freshwater and terrestrial habitats. Here we tested the effects of both terrestrial-and salmon-derived subsidies, in addition to other factors such as habitat area, on the diet (inferred from stable isotopes), abundance and size of a mobile estuarine consumer, the Dungeness crab (Metacarcinus magister). Crab trap surveys encompassed 19 watersheds over two seasons in the central coast of British Columbia, Canada, which spanned natural gradients in estuary size, watershed size, riparian tree composition, and Pacific salmon spawning density. Stable isotope ratios of crab tissue confirmed the predictions that estuarine nutrient regimes can be strongly affected by upstream watershed size, salmon density, and the dominance of nitrogen-fixing red alder (Alnus rubra). There were more crabs in larger estuaries and the largest crabs were found in estuaries below the largest watersheds. The proportional contributions of terrestrial-and salmon-derived subsidies to the diet of Dungeness crabs increased with watershed size and salmon density, respectively. These results confirmed that resource subsidies can constitute large proportions of the Dungeness crab's diet, that crab abundance is determined by habitat size, but that crab size is affected by the magnitude of terrestrial resource influx.

Landscape Structure and Species Interactions Drive the Distribution of Salmon Carcasses in Coastal Watersheds

“…Salmon carcasses deposited in riparian forests by these consumers can increase soil organic content (Bartz and Naiman, 2005;Gende et al, 2007), elevate nutrient concentration, shift the diversity of riparian plant communities (Bilby et al, 2003;Hocking and Reynolds, 2011), and provide substantial resources to terrestrial invertebrate communities (Hocking et al, 2009(Hocking et al, , 2013. Although salmon play important roles in stream ecosystems as a source of nutrients and disturbance to stream beds through the action of digging redds (Janetski et al, 2009;Tiegs et al, 2009;Harding et al, 2014), considerable proportions of carcasses are also exported to estuaries (Gende et al, 2004b), which can elevate dissolved nutrient concentrations and provide substantial resource inputs into estuarine food webs (Cak et al, 2008;Harding and Reynolds, 2014a;Harding et al, 2015). However, differences in salmon nutrient input to estuaries likely vary as a function of spawner distributions and stream size as carcasses are usually transported limited distances downstream and are often retained within pools and organic debris within streams (Cederholm and Peterson, 1985;Minakawa and Gara, 2005;Strobel et al, 2009).…”

Salmon nutrients are associated with the phylogenetic dispersion of riparian flowering‐plant assemblages

“…Riparian areas in larger watersheds are wider, more productive and often support early seral species such as the nitrogen fixing red alder ( A. rubra ; Shaftel et al. , Harding and Reynolds ).…”

“…The size of a watershed can also influence the nitrogen enrichment of riparian habitat (Hocking and Reimchen 2009). Riparian areas in larger watersheds are wider, more productive and often support early seral species such as the nitrogen fixing red alder (A. rubra; Shaftel et al 2012, Harding andReynolds 2014).…”

“…We predicted that locations further from the stream edge and with steeper slopes would have phylogenetically clustered assemblages due to decreased access to nutrients and higher nutrient runoff. We also predicted that larger watersheds would have more phylogenetically dispersed assemblages because the riparian areas are wider and more productive (e.g., Harding and Reynolds 2014). All predictions were tested in a model comparison framework using habitat variables, measures of salmon subsidy, and a metric of phylogenetic dispersion (Kembel et al 2010) based on an assembled phylogenetic tree of 60 flowering plant species and their percent cover in each plot.…”

Subsidies from anadromous sea lamprey (Petromyzon marinus) carcasses function as a reciprocal nutrient exchange between marine and freshwaters

“…For example, islands and coastal lands are subsidized by nutrient exchanges from surrounding oceans via sea wrack, birds, and mammals (Anderson & Polis, ; Farina, Salazar, Wallem, Witman, & Ellis, ; Polis & Hurd, ), and reciprocal exchanges occur between temperate forests and headwater streams by leaf litter and riparian insects (Fisher & Likens, ; Richardson, Zhang, & Marczak, ). Migratory animals, such as fish, also serve as an important link between ecosystems separated by great distances and exemplify cross‐boundary exchanges of nutrients and material (Flecker et al, ; Harding & Reynolds, ; Lamberti, Chaloner, & Hershey, ).…”