Pacific herring spawn events influence nearshore subtidal and intertidal species

Abstract

As intermediaries between the bottom and top of food webs, forage fish fuel a diversity of coastal consumers and are of socioecological importance throughout the world's oceans. Many forage fish are migratory, but despite their recognized importance, relatively little is known about their role in providing spatial subsidies, which are the movements of energy, material, and organisms across ecosystems. Until recently, spatial subsidies associated with Pacific herring Clupea pallasii, a dominant migratory forage fish that spawns in subtidal and intertidal zones, received little scrutiny. Building on research that traced links between herring spawns and coastal ecosystems, we used stable isotopes of carbon ( 13 C) and nitrogen ( 15 N) to assess whether herring spawning events influenced isotopic signatures of 10 macrophyte and invertebrate species across beaches where spawning did or did not occur. Overall, species collected from spawning beaches had significantly greater 15 N levels (general linear mixed model parameter estimate = 1.58 0.17 SE, F 1, 370 = 83.77, p < 0.001); no significant effects were detected for 13 C (parameter estimate = 0.03 0.23 SE, F 1, 343 = 0.01, p = 0.914). In terms of total nitrogen, macrophytes from spawning beaches had significantly elevated concentrations (parameter estimate = 5.03 0.94 SE, F 1,180 = 28.71, p < 0.001). Using directional statistics, mean angles of isotopic change differed significantly between species collected from spawning and non-spawning beaches (Watson-Williams F-test; F 1, 48 = 10.44, p = 0.002). Our study identifies multiple species as recipients of herring-derived nutrients at spawning events, providing additional evidence of the broad ecological influence of Pacific herring.