Shellfish subsidies along the Pacific coast of North America

Abstract

Spatial subsidies are associated with pronounced ecosystem responses, as nutrients cross ecological boundaries and cascade through food webs. While the importance of subsidies is known, the role of shellfish, specifically molluscs, as a marine subsidy has not been formally described. Focusing primarily on the Pacific coast of North America, we identify vectors that transport shellfish-derived nutrients into coastal terrestrial environments, including birds, mammals, and over 13 000 yr of marine resource use by people. Evidence from recipient ecosystems suggests shellfish drastically influence soil chemistry, forest productivity and the diversity of primary producers at the regional and landscape level. Responses in higher trophic levels have not yet been investigated, but given documented responses in lower trophic levels, this may be due to a lack of examination. To determine if the processes we describe within the northeast Pacific are pertinent to coastal environments worldwide, we also explore shellfish subsidies globally, with a specific focus on temperate and tropical islands. As shellfish are not as spatially or temporally constrained as other subsidies, our examination suggests our findings are applicable to many other geographical regions along the marine-terrestrial interface. Marine subsidiesMarine subsidies occur when nutrients are transferred from marine to terrestrial ecosystems, anywhere along the 594 000 km of global coastline (Hammond 1990). These subsidies can take the form of seabird guano (Sánchez-Piñero and Polis 2000), marine mammal carcasses (Polis and Hurd 1996), spawning fishes (Fox et al. 2015, Reimchen 2018 or macroalgae deposition (Spiller et al. 2010). While all of these subsidies play important roles in shaping terrestrial productivity, their effect sizes vary over space and time. For example, relatively brief, intense pulses of marine nutrients are deposited in riparian forests during annual Pacific salmon Oncorhynchus spp. autumn spawning (Gende et al.

Ancestral and contemporary intertidal mariculture practices support marine biodiversity in the northeast Pacific

“…Scientific evidence that the robust and dynamic history of human-ecosystem interactions structures ecological communities is mounting 9,17,19,49 . A fact well-known by many coastal First Peoples, these interactions are not limited to the ecological communities and cultivation methods described here, as fish weirs, root gardens, forest gardens, landscape terracing, and shellfish cultivation are spatially and temporally abundant throughout the northeast Pacific 9,11,14,29 .…”

Legacy of salmon-derived nutrients on riparian soil chemistry and soil fertility on the Central Coast of British Columbia, Canada

“…This process is also consistent with the relatively steady CEC observations in this and other studies, and may thus represent a long-term "calcium pump" where potassium, magnesium, and other cations are slowly displaced by calcium in the soil profile over time. This could have mixed effects on site fertility depending on context, but here is likely positively correlated with fertility since high calcium is associated with greater tree biomass in nearby areas due to anthropological soil amendments from shellfish harvesting (Trant et al, 2016;Cox et al, 2020), particularly large old-growth redcedar trees (D' Amore et al, 2009).…”

The diet of osprey Pandion haliaetus on Marawah Island (Abu Dhabi Emirate, United Arab Emirates) and its implications for the study of archaeological assemblages

“…It has been shown that salmon subsidies (eggs and fish carcasses) annually affect the stream-riparian food web, in particular by fertilizing the vegetation and feeding arthropod larvae (Collins & Baxter, 2014). Mollusc shells also contribute to terrestrial ecosystems by improving the soil chemistry (by calcium and phosphorus intakes), drainage, and stability (Cox et al, 2020). Shell remains in archaeological shell middens can also assist the preservation of human and terrestrial faunal osteological remains by increasing the alkaline pH thereby aiding their preservation.…”