Predator effects link ecological communities: kelp created by sea otters provides an unexpected subsidy to bald eagles

Abstract

AbstractEcological communities are best studied at the landscape level, where linkages among communities are considered. Such linkages are often driven by increases in primary production caused by apex predators limiting herbivores. In this note, we describe a novel linkage among sea otters (Enhydra lutris), the long‐lived woody kelp (Pterygophora californica), and bald eagles (Haliaeetus leucocephalus). While counting sea otters in an isolated group of rocky islets on the Central Coast of British Columbia, we found an eagle nest composed of mostly Pterygophora stalks. Pterygophora recruits rapidly after sea otters arrive in an area and limit sea urchins; the subsequent pulsed Pterygophora recruitment results in narrow age‐class cohorts that senesce en masse after about 20 yr. When the woody stipes wash ashore, they degrade slowly and persist as beach wrack for years. These windrows of woody kelp are common on the BC coast where sea otters have re‐established. We demonstrate how this subsidy can be used by bald eagles, and predict that as sea otters recover across their range in BC, further effects of Pterygophora to intertidal, supralittoral, and terrestrial communities will be observed.