Biological Sunglasses in a Deep-Sea Squid: Pigment Migration in the Retina of Gonatus onyx.

The outward migration of ommin pigment granules from the bases to the tips of the photoreceptors in response to light has been reported in the retina of several (mostly coastal) squid species. Following exposure to light and then dark conditions, we collected and processed retinal tissue from juvenile specimens of a deep-sea oegopsid squid, Gonatus onyx. We aimed to determine whether the ommin pigment returns to baseline, and to investigate the presence of glutamate neurotransmitter signaling under both dark and light conditions. We confirmed the presence of ommin granules but observed variability in the return of pigment to the basal layer in dark conditions, as well as changes in glutamate distribution. These findings provide support for the migration of retinal ommin pigment granules as a mechanism for regulating incoming light.

Metal composition of arrow squid (Nototodarus sloanii [Gray 1849]) from the Chatham Rise, New Zealand: implications for human consumption.

Cephalopods are important in the diets of humans and many other apex predators, and can play an important role in the bioaccumulation of metals. In this study, metal concentrations were analysed in the commercially and ecologically important southern arrow squid, Nototodarus sloanii (Gray 1849), from a heavily targeted fisheries area on New Zealand's Chatham Rise. A variety of tissue types were compared in order to assess the bioaccumulation in edible tissues (mantle and arms) and other organs (digestive gland, kidney, and hearts). Although metal concentrations varied among tissue types, the highest concentrations were found in the digestive gland (for Cd, Cu, Fe, Ni, Zn) and branchial hearts (for Cr, U). We report the first Cd concentrations for N. sloanii from the Chatham Rise, with mean values of 3.11 µg. g-1 in the mantle and 102.53 µg. g-1 in the digestive gland. Our data suggest that concentrations observed in the mantle tissue (which forms the majority of the muscle tissue) and digestive gland (the primary organ for metal accumulation) can be used to estimate the animal's total body burden for all metals analysed. The toxicological and dietary consequences for predators (including humans) feeding on arrow squid can be inferred from measurements of mass and metal concentration in these tissues. Arrow squid represent an important vector for Cd transfer within the pelagic Chatham Rise food web. These are the first recorded baseline data for metal concentrations for any squid in this oceanic region.

The study of deep-sea cephalopods.

"Deep-sea" cephalopods are here defined as cephalopods that spend a significant part of their life cycles outside the euphotic zone. In this chapter, the state of knowledge in several aspects of deep-sea cephalopod research are summarized, including information sources for these animals, diversity and general biogeography and life cycles, including reproduction. Recommendations are made for addressing some of the remaining knowledge deficiencies using a variety of traditional and more recently developed methods. The types of oceanic gear that are suitable for collecting cephalopod specimens and images are reviewed. Many groups of deep-sea cephalopods require taxonomic reviews, ideally based on both morphological and molecular characters. Museum collections play a vital role in these revisions, and novel (molecular) techniques may facilitate new use of old museum specimens. Fundamental life-cycle parameters remain unknown for many species; techniques developed for neritic species that could potentially be applied to deep-sea cephalopods are discussed. Reproductive tactics and strategies in deep-sea cephalopods are very diverse and call for comparative evolutionary and experimental studies, but even in the twenty-first century, mature individuals are still unknown for many species. New insights into diet and trophic position have begun to reveal a more diverse range of feeding strategies than the typically voracious predatory lifestyle known for many cephalopods. Regular standardized deep-sea cephalopod surveys are necessary to provide insight into temporal changes in oceanic cephalopod populations and to forecast, verify and monitor the impacts of global marine changes and human impacts on these populations.