Approaches to resolving cephalopod movement and migration patterns

Cephalopod movement occurs during all phases of the life history, with the abundance and location of cephalopod populations strongly influenced by the prevalence and scale of their movements. Environmental parameters, such as sea temperature and oceanographic processes, have a large influence on movement at the various life cycle stages, particularly those of oceanic squid. Tag recapture studies are the most common way of directly examining cephalopod movement, particularly in species which are heavily fished. Electronic tags, however, are being more commonly used to track cephalopods, providing detailed small- and large-scale movement information. Chemical tagging of paralarvae through maternal transfer may prove to be a viable technique for tracking this little understood cephalopod life stage, as large numbers of individuals could be tagged at once. Numerous indirect methods can also be used to examine cephalopod movement, such as chemical analyses of the elemental and/or isotopic signatures of cephalopod hard parts, with growing interest in utilising these techniques for elucidating migration pathways, as is commonly done for fish. Geographic differences in parasite fauna have also been used to indirectly provide movement information, however, explicit movement studies require detailed information on parasite-host specificity and parasite geographic distribution, which is yet to be determined for cephalopods. Molecular genetics offers a powerful approach to estimating realised effective migration rates among populations, and continuing developments in markers and analytical techniques hold the promise of more detailed identification of migrants. To date genetic studies indicate that migration in squids is extensive but can be blocked by major oceanographic features, and in cuttlefish and octopus migration is more locally restricted than predictions from life history parameters would suggest. Satellite data showing the location of fishing lights have been increasingly used to examine the movement of squid fishing vessels, as a proxy for monitoring the movement of the squid populations themselves, allowing for the remote monitoring of oceanic species.     

Effect of Nitrate and Sulfate on Dechlorination by a Mixed Hydrogen-Fed Culture

A novel hollow-fiber membrane remediation technology developed in our laboratory for hydrogen delivery to the subsurface was shown to support the dechlorination of perchloroethene (PCE) to cis-dichloroethene. In previous research, the presence of nitrate or sulfate has been observed to inhibit biological reductive dechlorination. In this study hollow-fiber membranes were used to supply hydrogen to a mixed culture to investigate whether adequate hydrogen could be added to support dechlorination in the presence of alternative electron acceptors. By continuously supplying hydrogen through the membrane, the hydrogen concentrations within the reactor were maintained well above the hydrogen thresholds reported to sustain reductive dechlorination. It was hypothesized that by preventing nitrate and sulfate reducers from decreasing hydrogen concentrations to below the dehalorespirer threshold, the inhibition of PCE dechlorination by nitrate and sulfate might be avoided and dechlorination could be stimulated more effectively. Enough membrane-fed hydrogen was supplied to completely degrade the alternative electron acceptors present and initiate dechlorination. Nevertheless, nitrate and sulfate inhibited dechlorinating activity even when hydrogen was not limiting. This suggests that competition for hydrogen was not responsible for the observed inhibition. Subsequent microcosm experiments demonstrated that the denitrification intermediate nitrous oxide was inhibitory at 13 µM.     

An examination of the role of the digestive gland of two loliginid squids,with respect to lipid: storage or excretion?

The role of the digestive gland, with respect to non-structural lipid, was examined using proximal analysis, histochemistry and quantitative histological techniques in the tropical loliginid squids Sepioteuthis lessoniana (Lesson) and Photololigo sp. The digestive gland of both species was characterized by large and numerous lipid droplets in the apical portion of the digestive cells and very few in the basal portion. The apical lipid droplets were released into the lumen of the gland and subsequently rapidly removed. Despite the numerous large apical lipid droplets, the lipid concentration in the digestive glands of S. lessoniana and Photololigo sp. was lower than that reported for most squid species. There was no relationship between lipid concentration and stage of digestion, suggesting that lipid is not stored in the gland after a meal. There was also no relationship between lipid concentration and the sex of an individual or stage of reproductive maturity, suggesting that these squids are not storing lipid in the digestive gland for use in fuelling reproductive maturation or providing an energy source for oocytes. I believe this study is the first to combine proximal analysis and quantitative histological techniques to examine the role of the squid digestive gland with respect to non-structural lipids. The results indicate that the digestive gland of these tropical loliginid squids is excreting, not storing, excess dietary lipid.