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

Abstract

Ecological 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.

The evolution of marine dwelling in Diptera

“…Stress from the environment, as abiotic factors, could be in the form of UV radiation, wind, variable temperatures, fluctuating tides, humidity, and water surface tension from the nearby sea (Dionisio‐Sese et al., 2001 ; Ikawa et al., 2012 ; Peace, 2020 ). Biotic factors that may be shaping marine fly populations include predation by birds, fish, and other beach fauna, competition from other marine organisms, the degree of kelp, algae, and other forms of vegetation, as well as the pathogens and endosymbionts inhabiting the beach (Rechsteiner et al., 2018 ; Wickham et al., 2020 ). In addition, human activity has influenced the state of both terrestrial and marine environments, possibly disrupting natural processes of nutrient cycling and vegetation growth (Nielsen et al., 2004 ).…”

The ghost of a giant – Six hypotheses for how an extinct megaherbivore structured kelp forests across the North Pacific Rim

“…Finally, Steller often observed birds perching on the exposed backs of sea cows, apparently feeding on a marine parasite that infested their skin (Domning, 1978; Steller, 1751), much like the oxpecker (Buphagidae) on large mammals of southern Africa (Galetti et al., 2018; Plantan et al., 2013). Diverse linkages between kelp forests and bird communities have been previously described (e.g., Anthony et al., 2008; Irons et al 1986; Rechsteiner et al., 2018); however, the mutualistic (or perhaps parasitic) relationship between seabirds and sea cows is another intriguing relationship that would have disappeared along with the sea cow.…”

Cascading social-ecological costs and benefits triggered by a recovering keystone predator

“…More importantly, the increased biomass of kelps and other lower trophic species not explicitly consumed in the model (Fig. 2 and table S8) can yield benefits through deep-ocean carbon storage (27) or as a nutritional subsidy to other parts of the ecosystem (28,29). We estimated the value of this subsidy based on a predicted increase in higher trophic species (i.e., commercial finfish), to be worth 9.4 [2.0, 30.4] million CA$/year (table S6).…”

“…3) because the fate of the surplus production, the trophic transfer efficiencies, and the future landed values are not well known. The estimated value of this service does not include the contribution from increased biomass of subcanopy algal species (28), other economic benefits (e.g., recreational fishing, kelp harvesting), or the benefits of the nutritional subsidy to the broader food web.…”