Body size‐based trophic structure of a deep marine ecosystem

Abstract

. Nitrogen stable isotope ratios (δ 15 N) and body size were used to describe the size-based trophic structure of a deep-sea ecosystem, the Avilés submarine Canyon (Cantabrian Sea, Southern Bay of Biscay). We analyzed δ 15 N of specimens collected on a seasonal basis (March 2012, October 2012, and May 2013, from a variety of zones (benthic, pelagic), taxa (from zooplankton through invertebrates and fi shes to giant squids and cetaceans), or depths (from surface to 4700 m) that spanned nine orders of magnitude in body mass. Our data reveal a strong linear dependence of trophic level on body size when data were considered either individually, aggregated into taxonomical categories, or binned into size classes. The three approaches render similar results that were not signifi cantly different and yielded predator : prey body mass ratios ( PPMR ) of 1156:1, 3792:1 and 2718:1, respectively. Thus, our data represent unequivocal evidence of interspecifi c, size-based trophic structure of a whole ecosystem based on taxonomic/functional categories. We studied the variability in δ 15 N not explained by body mass ( W ) using linear mixed modeling and found that the δ 15 N vs. log 10 W relationship holds for both pelagic and benthic systems, with benthic organisms isotopically enriched relative to pelagic organisms of the same size. However there is a marked seasonal variation potentially related to the recycling state of the system.

Trophic ecology of Humboldt squid, Dosidicus gigas, in conjunction with body size and climatic variability in the Gulf of California, Mexico

“…Each sample was examined with a binocular dissecting microscope (8×–40×) under both dark‐field and bright‐field illumination. Prey items much smaller than the expected prey size for squid of the sizes sampled (<0.01 g, Fernandez Araoz ; Barnes et al ; Romero‐Romero et al ) and commonly consumed by myctophids, including ostracods, copepods, and amphipods (Dalpadado and Gjøsæter ; Van Noord et al ), were considered to have been prey of consumed fishes and excluded from the analyses.…”

Seasonal and vertical dynamics in the trophic structure of a temperate zooplankton assemblage

“…Assuming a constant trophic fractionation of 3.4‰ (Minagawa and Wada ), the predator : prey body mass ratio (PPMR) in size‐structured food webs can be calculated from b as PPMR = 10 (3.4/ b ) (Jennings et al ), yielding a value of 27 : 1. This PPMR calculated for zooplankton is two orders of magnitude lower than mean estimates for the entire ecosystem from copepods to top predators (~ 10 3 : 1; Romero‐Romero et al ). This might be explained by the fact that PPMR increases with predator size (Barnes et al ) and that our analysis was focused only on a narrow size range not including larger organisms.…”

“…The BIOCANT cruises are representative of three different environmental conditions, which were previously described in Romero‐Romero et al () (Table ; Supporting Information Fig. S1).…”

“…For instance, predators are usually larger than their prey (Sheldon et al ), which explains why the body size of organisms accounts for more variation in their trophic position than their taxonomic identity (Jennings et al ). Previous studies have quantified the relationship between body size and trophic level in marine ecosystems using analyses of stable isotopes, and most assumed that the dependence of trophic level on body size is constant through time (e.g., Jennings et al ; Al‐Habsi et al ), although there are few investigations where temporal variations were considered (e.g., Jennings et al ; Nakazawa et al ; Romero‐Romero et al ). This relationship is expected to be stronger in marine food webs which are based on phytoplankton than those dependent on detritus (Layman et al ; Al‐Habsi et al ).…”

Understanding the role of parasites in food webs using the group model

“…For example, concomitant predation creates loops that violate the cascade model, and allometric patterns which hold for free‐living species (e.g. Brose, Williams, & Martinez, ), such as predator:prey body mass ratios, are inverted for parasitic interactions (Romero‐Romero, Molina‐Ramrez, Höfer, & Acuña, ). Models such as Allometric Diet Breadth Model (Petchey et al., ) and the Allometric Trophic Network (Berlow et al., ), which are based on body size data, are unlikely to capture parasites successfully.…”