The use of cephalopod beaks in ecological and population dynamics studies has allowed major advances of our knowledge on the role of cephalopods in marine ecosystems in the last 60 years. Since the 1960’s, with the pioneering research by Malcolm Clarke and colleagues, cephalopod beaks (also named jaws or mandibles) have been described to species level and their measurements have been shown to be related to cephalopod body size and mass, which permitted important information to be obtained on numerous biological and ecological aspects of cephalopods in marine ecosystems. In the last decade, a range of new techniques has been applied to cephalopod beaks, permitting new kinds of insight into cephalopod biology and ecology. The workshop on cephalopod beaks of the Cephalopod International Advisory Council Conference (Sesimbra, Portugal) in 2022 aimed to review the most recent scientific developments in this field and to identify future challenges, particularly in relation to taxonomy, age, growth, chemical composition (i.e., DNA, proteomics, stable isotopes, trace elements) and physical (i.e., structural) analyses. In terms of taxonomy, new techniques (e.g., 3D geometric morphometrics) for identifying cephalopods from their beaks are being developed with promising results, although the need for experts and reference collections of cephalopod beaks will continue. The use of beak microstructure for age and growth studies has been validated. Stable isotope analyses on beaks have proven to be an excellent technique to get valuable information on the ecology of cephalopods (namely habitat and trophic position). Trace element analyses is also possible using beaks, where concentrations are significantly lower than in other tissues (e.g., muscle, digestive gland, gills). Extracting DNA from beaks was only possible in one study so far. Protein analyses can also be made using cephalopod beaks. Future challenges in research using cephalopod beaks are also discussed.

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The significance of cephalopod beaks as a research tool: An update

Simple Summary Gonatus fabricii is the most abundant cephalopod in the Arctic and northern part of the North Atlantic, which are areas of rapid environmental change. It is very important as a predator of many species of fish and invertebrates and as a prey for larger fish, seabirds, and marine mammals. The life cycle of G. fabricii, in particular ontogenetic changes in diet and habitat, is little known. Ecological modelling is an important method to forecast ecosystems’ dynamics in relation to a changing climate, and it is crucial to assess their present structure and functioning for a viable forecast. Here, the ontogenetic changes in the diet and habitat of large G. fabricii from West Greenland are studied using stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) along trajectories in chitin beaks, which function as archival structures. Using this approach, four stages with clearly distinct ecologies were revealed in the species’ life cycle. This novel ecological periodization is a crucial baseline tool in Arctic marine ecosystem studies and cephalopod biology, and should be used in models to correctly reflect the ecological roles of G. fabricii in marine ecosystems. 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.

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

Deep-sea cephalopods are diverse, abundant, and poorly understood. The Cirrata are gelatinous finned octopods and among the deepest-living cephalopods ever recorded. Their natural feeding behaviour remains undocumented. During deep-sea surveys in the Arctic, we observed Cirroteuthis muelleri. Octopods were encountered with their web spread wide, motionless and drifting in the water column 500–2600 m from the seafloor. Individuals of C. muelleri were also repeatedly observed on the seafloor where they exhibited a repeated, behavioural sequence interpreted as feeding. The sequence (11–21 s) consisted of arm web spreading, enveloping and retreating. Prey capture happened during the enveloping phase and lasted 5–49 s. Numerous traces of feeding activity were also observed on the seafloor. The utilization of the water column for drifting and the deep seafloor for feeding is a novel migration behaviour for cephalopods, but known from gelatinous fishes and holothurians. By benthic feeding, the octopods benefit from the enhanced nutrient availability on the seafloor. Drifting in the water column may be an energetically efficient way of transportation while simultaneously avoiding seafloor-associated predators. In situ observations are indispensable to discover the behaviour of abundant megafauna, and the energetic coupling between the pelagic and benthic deep sea.

Miles down for lunch: deep-sea in situ observations of Arctic finned octopods Cirroteuthis muelleri suggest pelagic–benthic feeding migration

Genome skimming elucidates the evolutionary history of OctopodA.

ABSTRACT The finned octopus Cirroteuthis muelleri is abundant in the far northern hemisphere, yet limited records exist of a possible undescribed southern hemisphere species, Cirroteuthis cf. muelleri. A single specimen of C. cf. muelleri was identified amongst material collected during a 2017 abyssal survey off eastern Australia. The specimen had a dorsal mantle length of about 116 mm when fresh and 56 mm following preservation and was captured at 2338−2581 m depth. Morphological characteristics of this specimen aligned closely with C. cf. muelleri from New Zealand, and differences in these to C. muelleri from the North Atlantic and North Pacific, combined with the disjunct distribution, warrant further investigation of the southern hemisphere specimens as a possible new species. This discovery represents a significant range extension of Cirroteuthis and is the first occurrence of this genus from Australian waters.

Finned octopus Cirroteuthis Eschricht, 1836 (Cephalopoda: Cirrata: Cirroteuthidae) confirmed from Australian waters

Stauroteuthis syrtensis and Cirroteuthis muelleri were studied based on representative material collected in Greenland, Iceland, and the Barents Sea and adjacent deep-sea areas (96 stations and 165 individuals for S. syrtensis, and 82 stations and 215 individuals for C. muelleri). The species occur on the border of the Arctic and the northern North Atlantic; S. syrtensis is a southern species and C. muelleri is a northern species, in the area from the Denmark and Davis Straits and associated underwater ridges. These species were demonstrated to be ecological analogues since they: a) occupy the same depths; b) reach the same abundance density; c) reach virtually the same biomass density when corrected for size differences; and d) their food spectra largely coincide. Temperature, not depth, is a principal factor that prevents these species from crossing the border between the Arctic and the northern North Atlantic, with mean habitat temperatures of 3.5 ± 0.06 °C for S. syrtensis and 0.3 ± 0.06 °C for C. muelleri. This study provides unprecedented density estimates for the North Atlantic and Arctic Cirrata: the highest in the world ocean in terms of biomass and second highest in terms of numerical abundance. Food spectra of the studied species consist of Calanoida (including eurybathic Paraeucheta spp. and Calanus spp., and deep-sea Bradyidius similis), Mysidacea and Isopoda (including deep-sea Eurycopinae) (Crustacea), and in C. muelleri also Cumacea, Amphipoda (Crustacea) and Polychaeta (Polynoidae). Additionally, this study: a) provides specific growth and morphometric equations; b) provides equations to estimate mantle length (ML) and body mass (BM) from beak measurements, and BM of fresh individuals (for modelling purposes or predators diet analyses) from BM of fixed individuals; c) reports maximum sizes for C. muelleri (ML 170 mm, total length 400 mm, BM 781.0 g); and d) reports findings of rarely encountered juvenile cirrates. 

Deep and cold: are Boreal and Arctic finned octopods, Stauroteuthis syrtensis and Cirroteuthis muelleri (Cephalopoda, Octopoda, Cirrata), ecological analogues?

Gudmundur Gudmundsson

Papers

Deep and cold: are Boreal and Arctic finned octopods, Stauroteuthis syrtensis and Cirroteuthis muelleri (Cephalopoda, Octopoda, Cirrata), ecological analogues?