Macroalgae contribute to nested mosaics of pH variability in a subarctic fjord

The Arctic Ocean is considered the most vulnerable ecosystem to ocean acidification, and large-scale assessments of pH and the saturation state for aragonite (O_arag) have led to the notion that the Arctic Ocean is already close to a corrosive state. In high-latitude coastal waters the regulation of pH and O_arag is, however, far more complex than offshore because increased biological activity and input of glacial meltwater affect pH. Effects of ocean acidification on calcifiers and non-calcifying phototrophs occupying coastal habitats cannot be derived from extrapolation of current and forecasted offshore conditions, but they require an understanding of the regimes of pH and O_arag in their coastal habitats. To increase knowledge of the natural variability in pH in the Arctic coastal zone and specifically to test the influence of benthic vegetated habitats, we quantified pH variability in a Greenland fjord in a nested-scale approach. A sensor array logging pH, O₂, PAR, temperature and salinity was applied on spatial scales ranging from kilometre scale across the horizontal extension of the fjord; to 100 m scale vertically in the fjord, 10–100 m scale between subtidal habitats with and without kelp forests and between vegetated tidal pools and adjacent vegetated shores; and to centimetre to metre scale within kelp forests and millimetre scale across diffusive boundary layers of macrophyte tissue. In addition, we assessed the temporal variability in pH on diurnal and seasonal scales. Based on pH measurements combined with point samples of total alkalinity, dissolved inorganic carbon and relationships to salinity, we also estimated variability in O_arag. Results show variability in pH and O_arag of up to 0.2–0.3 units at several scales, i.e. along the horizontal and vertical extension of the fjord, between seasons and on a diel basis in benthic habitats and within 1 m³ of kelp forest. Vegetated intertidal pools exhibited extreme diel pH variability of > 1.5 units and macrophyte diffusive boundary layers a pH range of up to 0.8 units. Overall, pelagic and benthic metabolism was an important driver of pH and O_arag producing mosaics of variability from low levels in the dark to peak levels at high irradiance generally appearing favourable for calcification. We suggest that productive coastal environments may form niches of high pH in a future acidified Arctic Ocean

Actual fecundity of the Arctic squid Gonatus fabricii (Cephalopoda) based on the examination of a rarely encountered spent female

Gonatus fabricii (Lichtenstein, 1818) is an ecologically important squid that spends its entire life cycle within the Arctic where it is the most abundant cephalopod. Due to the rarity of mature and reproducing females, it is unknown how many eggs females spawn (actual fecundity). Among 47,000 specimens studied between 2005 and 2019 one spent, degenerated and gelatinous female with a mantle length of 230 mm was caught in West Greenland in 2019. Examination allowed the first detailed description of fecundity and spawning pattern in the species. Oocyte development shows that the most considerable maturation of mid-vitellogenic oocytes to late vitellogenic and then to ripe stages occurs immediately after the first ripe oocytes appear in the ovary. There were no ripe oocytes in the ovary or oviducts. The ovary contained an estimated 6561 oocytes and 2551 post-ovulatory follicles and hence the total fecundity was 9112. This specimen of G. fabricii realised 28.0% of its potential fecundity which is comparable to Berryteuthis magister, which also belongs to Gonatidae, and lower than in the majority of studied deep-sea squids (including other gonatids). Spent females may provide clues as to where the major spawning areas of this abundant but poorly known squid are located

Flapjack devilfish in the northern North Atlantic: morphology, biology and ecology of Opisthoteuthis borealis (Cephalopoda, Octopoda, Cirrata)

© 2020, Senckenberg Gesellschaft für Naturforschung. Deep-sea cephalopods are important in the bathyal ecosystems in terms of both abundance and diversity, but are seriously understudied. One of the most intriguing groups among the deep-sea cephalopods are Cirrata, relatively primitive octopods. Opisthoteuthis is the largest genus among the Cirrata. The least studied species of Opisthoteuthis in the Atlantic, Opisthoteuthis borealis Collins, 2005 was known from nine specimens only prior to our study, and nothing was described about its biology. Four males, all larger than the previously known maximum size (mantle length 78–96 mm cf. 75 mm), are described and COI sequence of the species provided to ease the identification of the Atlantic Opisthoteuthis. Our findings expand the known geographical (North Atlantic from 60° N northward and up to the Davis and Denmark Straits and the Iceland–Faroe Ridge), depth (878–1321 m) and temperature (3.0–3.6 °C) ranges of O. borealis. Arm bifurcation is reported in Cirrata for the first time, suggesting well-developed regeneration is present even in this ancient taxon of cephalopods. Ontogenetic increase of spermatophore length, i.e., when the spermatophores produced later during ontogenesis are larger than those produced earlier, is reported in Cirrata for the first time. The stomachs in all the studied specimens were at least one-third full, suggesting that O. borealis continues to feed and grow after reaching maturity. Polychaetes dominated over crustaceans in the stomach contents. Contrary to the assumption that Cirrata feed on relatively small prey only, large mature males of O. borealis consume polychaetes reaching 41.5–45.9% ML of the specimens

Ontogenetic changes in stable isotope (δ13C and δ15N) values in squid Gonatus fabricii (Cephalopoda) reveal its important ecological role in the Arctic

Gonatus fabricii is the most abundant cephalopod species in Arctic waters, and the only squid that completes its entire life cycle there. In order to understand its ecological role in the Arctic, we conducted stable isotope analyses of beaks from all ontogenetic groups from west and east Greenland waters and the Barents Sea, complemented with morphological data. The values of both delta C-13 and delta N-15 of G. fabricii were not related to sex. Values of delta C-13 showed a small ontogenetic increase, and these values were geographically distinct, with highest levels found in the western part of the study area. Values of delta N-15 showed a dramatic ontogenetic increase (i.e. 10.0 parts per thousand delta N-15; 2.6 trophic levels), from epipelagic juvenile forms to large bathypelagic adults, without significant geographical variation. The observed maximum value of delta N-15 (14.9 parts per thousand) is the highest ever recorded in cephalopod beaks. The estimated trophic level (up to 5.1) compares only to top vertebrate predators in the Arctic: large piscivorous fishes, seals and toothed whales or large benthic scavenging fishes. Thus, G. fabricii is a top invertebrate predator in the Arctic, with the widest isotopic niche observed to date for any species there. Among cephalopods its trophic level is only exceeded by its Antarctic congener, G. antarcticus, and by the Antarctic colossal squid Mesonychoteuthis hamiltoni. Thus, polar squids occupy higher trophic positions than do squids living in warmer regions. Finally, our study shows that G. fabricii descends to bathypelagic layers during ontogenesis, continuously increasing its trophic level by changing prey types and sizes, and avoiding predation pressure

Diet and life history reduce interspecific and intraspecific competition among three sympatric Arctic cephalopods

© 2020, The Author(s). Trophic niche and diet comparisons among closely sympatric marine species are important to understand complex food webs, particularly in regions most affected by climate change. Using stable isotope analyses, all ontogenetic stages of three sympatric species of Arctic cephalopods (genus Rossia) were studied to assess inter- and intraspecific competition with niche and diet overlap and partitioning in West Greenland and the Barents Sea. Seven traits related to resource and habitat utilization were identified in Rossia: no trait was shared by all three species. High boreal R. megaptera and Arctic endemic R. moelleri shared three traits with each other, while both R. megaptera and R. moelleri shared only two unique traits each with widespread boreal-Arctic R. palpebrosa. Thus all traits formed fully uncrossing pattern with each species having unique strategy of resource and habitat utilization. Predicted climate changes in the Arctic would have an impact on competition among Rossia with one potential ‘winner’ (R. megaptera in the Barents Sea) but no potential ‘losers’