Prey dominance shapes trophic structure of the northern California Current pelagic food web: evidence from stable isotopes and diet analysis

Abstract

Eastern boundary current (EBC) upwelling zones are among the most productive of marine ecosystems globally and have been generalized in terms of their food web structure. Little empirically based evidence exists to suggest that there is any one form of trophic control of EBC systems and, because of logistical constraints, knowledge of food web structure is limited in these large marine ecosystems. To determine principal trophic links within the pelagic food web, we combined stable isotope and diet analysis of 21 dominant species of nekton found within the northern California Current, a highly productive EBC upwelling ecosystem. Samples of nekton and zooplankton were collected in June and August 2000 and 2002 from the shelf-slope waters of northern California to Washington. Results showed most nekton consumed mixed diets of zooplankton and larval-juvenile or adult fishes, indicating the importance of omnivory in this system. Euphausiids were overwhelmingly the most prevalent zooplankton taxa in the diets of nekton across multiple trophic levels, accounting for > 50% of the index of relative importance in 10 of 21 nekton species analyzed. Nitrogen stable isotopes (δ 15 N) reflected trophic patterns observed in the diets, with most nekton species (~62%) falling between trophic levels (TL) of full zooplanktivores (TL = 3) and full piscivores (TL = 4). The prevalence of omnivory observed here is probably due to high primary production that supports an abundance of large zooplankton prey, such as euphausiids, which may be a more available prey resource for a broad range of predators. A modification of this form of bottom-up control, termed bottom-up omnivory, is presented.

Seasonal variability of δ13C and δ15N of fish and squid in the Cabo Frio upwelling system of the southwestern Atlantic

“…The fish data from the Bay of Biscay in the northeast Atlantic showed signals from coastal, oceanic and deep-sea areas, where river discharges appeared to be the primary factor in terms of influencing the δ Our study indicated that fish and squids function as the tertiary (TL4) and quaternary (TL5) consumers. Miller et al (2010) found 5 TLs (including sea lion species) in the Northern California Current pelagic food web, where fish had values ranging from 2.7 to 3.8, which were lower than our results. Ranges lower than our observations were also registered in a tropical estuary off the coast of Senegal (2.6−4.7; Faye et al 2011), and for the Bay of Banyuls-sur-Mer (France), where the benthic food web was composed of 4 TLs, with fish distributed between TL3 and TL4 (Carlier et al 2007).…”

“…These results suggest mixed diets and TL omnivory. Similar results were reported for pelagic food webs of the California Current upwelling (Miller et al 2010) and the Southern California Current upwelling (Madigan et al 2012).…”

“…Due to the number of species (41) analysed, we used the accepted TEF (δ 15 N = 3.4 ‰) of Minagawa & Wada (1984), which is considered to be robust and valid (Søreide et al 2006) for estimating the TL. Additionally, we used this factor to make comparisons with other ecosystems described in published papers (Carlier et al 2007, Miller et al 2010, Faye et al 2011. (Miller et al 2010, Madigan et al 2012.…”

“…Additionally, we used this factor to make comparisons with other ecosystems described in published papers (Carlier et al 2007, Miller et al 2010, Faye et al 2011. (Miller et al 2010, Madigan et al 2012. The range of values is also similar to those of the Newfoundland and Labrador continental shelves (Sherwood & Rose 2005).…”

Are dominant plant species more susceptible to leaf‐mining insects? A case study at Saihanwula Nature Reserve, China

“…Dominant species are the small number of species that significantly affect other species (McNaughton & Wolf, 1970; Whittaker, 1965). Due to their high biomass, large size, high productivity, and other traits (Bouchenak‐Khelladi, Slingsby, Verboom, & Bond, 2014; Collins & Duffy, 2016), they can change environmental conditions and resource availability and thus shape community structure (Frieswyk, Johnston, & Zedler, 2007; Okullo, Greve, & Moe, 2013), community diversity (Kunte, 2008; Okullo et al., 2013), community phylogeny (Chalmandrier, Münkemüller, Lavergne, & Thuiller, 2015), trophic structure (Miller, Brodeur, Rau, & Omori, 2010), and ecosystem functions (Behera et al., 2017; Furey, Tecco, Perez‐Harguindeguy, Giorgis, & Grossi, 2014; Grime, 1998; Mokany, Ash, & Roxburgh, 2008; Seabloom et al., 2015). Both dominant species and keystone species are functionally important, but keystone species are much less abundant (Christianou & Ebenman, 2005; Hurlbert, 1997; Mouquet, Gravel, Massol, & Calcagno, 2013; Power et al., 1996).…”