Life History of the Arctic Squid Gonatus fabricii (Cephalopoda: Oegopsida) Reconstructed by Analysis of Individual Ontogenetic Stable Isotopic Trajectories

Abstract

Cephalopods are important in Arctic marine ecosystems as predators and prey, but knowledge of their life cycles is poor. Consequently, they are under-represented in the Arctic ecosystems assessment models. One important parameter is the change in ecological role (habitat and diet) associated with individual ontogenies. Here, the life history of Gonatus fabricii, the most abundant Arctic cephalopod, is reconstructed by the analysis of individual ontogenetic trajectories of stable isotopes (δ13C and δ15N) in archival hard body structures. This approach allows the prediction of the exact mantle length (ML) and mass when the species changes its ecological role. Our results show that the life history of G. fabricii is divided into four stages, each having a distinct ecology: (1) epipelagic squid (ML < 20 mm), preying mostly on copepods; (2) epi- and occasionally mesopelagic squid (ML 20–50 mm), preying on larger crustaceans, fish, and cephalopods; (3) meso- and bathypelagic squid (ML > 50 mm), preying mainly on fish and cephalopods; and (4) non-feeding bathypelagic gelatinous females (ML > 200 mm). Existing Arctic ecosystem models do not reflect the different ecological roles of G. fabricii correctly, and the novel data provided here are a necessary baseline for Arctic ecosystem modelling and forecasting.

High Arctic “hotspots” for sperm whales (Physeter macrocephalus) off western and northern Svalbard, Norway, revealed by multi-year Passive Acoustic Monitoring (PAM)

“…It may be that sperm whales adjust their foraging behavior to diel movements of potential prey species. For example, the Boreoatlantic armhook squid performs diurnal vertical migrations 69 . It has been shown that sperm whales adjust their foraging strategy to optimize the relationship between prey energetic value and the foraging energy cost at different depths or prey layers 48 .…”

Insights on long-term ecosystem changes from stable isotopes in historical squid beaks

“…Main time series are ‘1900s’, ‘1930s’, ‘1970s’, ‘2000s’ and ‘2010s’, while ‘late XIX th century’ with n = 2 were only used in some analyses (see below). Stable isotope data on ‘contemporary’ G. fabricii beaks, sampled in 2016, 2017 and 2019 in the Baffin Bay and Davis Strait were previously analysed in Ref [ 54 ]. We did not pool these beaks with the ‘2010s’ from this study (sampled in 2014) because the ‘2010s’ were from the Nordic Seas and δ 13 C values in G. fabricii were significantly different between the Nordic Seas and Baffin Bay [ 57 ].…”

“…Cephalopods have chitinous jaws (= beak) to cut their prey into smaller pieces [ 50 , 51 ]. The beaks were successfully used as archival tissue for detailed SIA life history reconstructions of contemporary cephalopods in the Arctic and Antarctic [ 52 – 54 ]. However, there is only a single study from the Atlantic that involves historical squid, where the sample size ( n = 4) is too small to assess potential ecosystem implications [ 55 ].…”

“…It was chosen as an abundant species of North Atlantic squid fauna, which occasionally enters low latitude Arctic ecosystems [ 60 , 61 ]. Both species show ontogenetic dietary shifts from small to large crustaceans, and then to fishes and cephalopods, including cannibalism [ 54 , 58 , 60 – 62 ]. Early paralarvae of T. sagittatus are detritivorous [ 63 ].…”

Cephalopod ontogeny and life cycle patterns

“…Oegopsid data must be pieced together from a variety of indirect methods, including stable isotopes and other elemental analyses of beaks and gladii. These methods have been essential in understanding how deep-sea species occupy different water masses or localities their life cycles (e.g., Cherel and Hobson, 2005;Semmens et al, 2007;Zumholz et al, 2007;Lukeneder et al, 2008;Staudinger et al, 2013;Golikov et al, 2018;Golikov et al, 2022b).…”