Pacific herring Clupea pallasii and wrack macrophytes subsidize semi-terrestrial detritivores

Abstract

The bi-directional movements of materials, nutrients and energy across the land−sea interface result in a number of ecological consequences. Migratory animals that move across ecosystems drive a number of these spatial subsidies (e.g. anadromous salmon), but many of the world's animal migrations are in decline. The cross-ecosystem reach of Pacific herring Clupea pallasii, a migratory, iteroparous forage fish that spawns along the coastlines of the North Pacific Ocean, has never been studied. Spawn events represent large aggregations of biomass and energy, a portion of which is transferred to intertidal and supratidal zones. Using fatty acids and stable isotopic signatures of carbon and nitrogen, we (1) traced the sources of production and (2) tested the hypothesis that herring subsidizes detritivorous, semi-terrestrial amphipods (Talitridae: Traskorchestia spp.), which are often abundant in intertidal and supratidal zones. Amphipods and likely dietary items (macrophytes and herring eggs) were collected from 5 beaches before and after herring spawned in Quatsino Sound, British Columbia. Combined with the use of mixing models, stable isotopes suggest that herring, in addition to brown algae and seagrass, were major sources of production during the study period. Fatty acid results suggest that brown algae is generally a major dietary resource for amphipods, but herring eggs provide important omega-3 fatty acids that are low in abundance prior to herring spawn events. Taken together, we provide corroborative evidence of a previously unknown cross-ecosystem spatial subsidy by Pacific herring. Further, because amphipods are prey for several terrestrial consumers, we also identify previously unknown marine−terrestrial linkages.KEY WORDS: Pacific herring · Spatial subsidy · Wrack · Amphipoda · Detritivores · Fatty acids · Stable isotope Resale or republication not permitted without written consent of the publisher Editorial responsibility: Omar Defeo,

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