Trophic relationships of a subtidal fish assemblage in the Francisco Coloane Coastal Marine Protected Area, southern Chilean Patagonia

Abstract

A combination of stomach content and nitrogen (δ 15 N) and carbon (δ 13 C) stable-isotope analysis was used to assess the trophic interactions and feeding habits of three notothenioid coastal fish (Champsocephalus esox, Patagonotothen tessellata and Patagonotothen cornucola) and one exotic salmon species (Oncorhynchus tschawytscha) with diverse life habits (benthic and benthopelagic) in the Francisco Coloane Coastal Marine Protected Area, southern Chile. The stomach contents of C. esox were mainly fish; those of P. cornucola and O. tschawytscha were crustacean decapods, Munida gregaria. A cluster analysis on isotope data and stable-isotope Bayesian ellipses detected two different predator groups, one with benthopelagic habits (C. esox and O. tshawytscha) and one with benthic habits (P. cornucola and P. tessellata). These results were supported with similar isotopic trophic level of each group. We suggest that the exotic salmon O. tschawytscha is a generalist predator with a broad trophic niche that may compete with the native notothenioid C. esox, as both have equivalent trophic levels with substantial overlap. This preliminary study is the first on trophic relationships of a subtidal fish assemblage within a remote ecosystem of fjords and channels in Chile's southern Patagonia.

Shape, condition and diet of the pike icefish Champsocephalus esox (Teleostei: Channichthyidae): evidence of phenotypic plasticity?

“…There was a relatively low FI in the specimens collected, which has been a frequent feature in previous studies of this species (50–60%; Isla 1993, Hüne et al 2018), as well as in other Channichthyidae. In Chaenocephalus aceratus from the South Shetland Islands, most of the stomachs (76–85%) were empty (Flores et al 2004).…”

“…These results do not support an increase in intraspecific specialization in C. esox , as seen in the polymorphic populations of C. lavaretus from subarctic lakes. Nevertheless, these results for C. esox should be taken as referential, because Hüne et al (2018) did not perform a morphological analysis and the environmental conditions were dissimilar to those of our study area (lower salinity and higher turbidity than in the Barbara Channel). According to Skúlason et al (2019), plasticity can produce phenotypic variation due to environmental changes (e.g.…”

“…However, we cannot discard potential selective feeding among morphs, as differences in diet could be masked by the low FI, as well as the degree of prey digestion in the stomach contents from the specimens analysed. The trophic niche breadth reported for C. esox was smaller than for other coastal fish in the Barbara Channel, close to the Strait of Magellan (Hüne et al 2018). These results do not support an increase in intraspecific specialization in C. esox , as seen in the polymorphic populations of C. lavaretus from subarctic lakes.…”

“…The latter has been considered a common factor in morphological diversification, allowing niche expansion thanks to the absence of competition (Robinson & Wilson 1994, Eastman & DeVries 1997). However, the introduction of exotic salmon species ( O. tshawytscha ) during the 1970s–1990s could have changed the low-level interspecific competition scenario, as O. tshawytscha may compete for food resources with C. esox owing to their similar trophic levels and niche overlap (Hüne et al 2018).…”

“…This species is a carnivorous predator, preying upon fishes (nototheniids) and crustaceans (mysids, squat lobsters, copepods; Isla 1993). Recent studies using stable isotopes indicate that pike icefish are a top predator that may compete with the invasive salmon species Oncorhynchus tshawytscha in southern Patagonia (Hüne et al 2018).…”