Some economic implications of continental drift

Concepts of the way in which the Earth's surface has evolved have changed drastically during the last ten years. The implications of these ideas on the formation and preservation of metal ores and fossil fuels is examined in order to indicate areas where further exploration may be justified and to enable a better assessment of the world's decreasing reserves of these geological deposits.     

Comparison of methods for determining key marine areas from tracking data

There is an urgent need to identify key marine areas for conservation, particularly in the high seas. A range of techniques have been applied to tracking data from higher predators, particularly seabirds and pinnipeds, to determine the areas of greatest use. This study compared three commonly used methods—kernel, first-passage time and state-space modelling—and a new approach, minimum displacement rate, for the analysis of data from the wandering albatross Diomedea exulans of Bird Island, South Georgia, tracked during the chick-rearing period. Applied to a single track, these four models identified similar marine areas as important. The greatest similarity in areas identified occurred when model assumptions were shared (such as slow speed indicating spatial preference) even when methods modelled these assumptions differently (e.g. Bayesian inference versus cumulative density surface). A gridded overlap approach applied to all tracks revealed core areas not apparent from results of any single analysis. The gridded approach also revealed spatial overlap between methods based on different assumptions (e.g. minimum displacement rate and kernel analysis) and between individuals. Although areas identified as important by kernel and first-passage time analysis of a single track were biased towards resting locations during darkness, this does not negate the requirement for their protection. Using the gridded overlap approach, two distinct core regions were identified for the wandering albatross; one close to the breeding colony and another 800 km to the North–West in the high seas. This convenient and pragmatic approach could be applied to large data sets and across species for the identification of a network of candidate marine protected areas in coastal and pelagic waters.     

Buchbesprechungen

The Science of Nature -     

On the timing of moulting processes in reproductively active Northern krill Meganyctiphanes norvegica

The interactions between moult phasing, growth and environmental cues in Northern krill (Meganyctiphanes norvegica) were examined through analysing populations at seasonal, weekly, and daily timescales. The analyses were carried out on resident populations of krill found in three different neritic locations that experience similar environmental signals (the Clyde Sea, Scotland; the Kattegat, Denmark; Gullmarsfjord, Sweden). Seasonal analyses were carried out on the Clyde Sea population and showed that moulting frequency increased significantly moving from winter to summer. The proportion of moulting females in summer samples was often more than double the proportion of moulting males, suggesting that females had a comparatively shorter intermoult period (IMP). Weekly samples taken from the Kattegat showed a similar pattern. However, although the difference between the proportion of female and male moulters was significant in one week, it was not another, mainly because of the variability in the proportion of female moulters. Such variability in females was equally evident in the daily samples taken at Gullmarsfjord. It suggests that females have a shorter IMP (12.5 days) than males (18.4 days) and are more likely to moult in synchrony. Nevertheless, the daily samples revealed that males are also capable of moult synchronisation, although less frequently than females. Shortened IMPs in females were not a result of the abbreviation of specific moult stages. Accordingly, reproductive activity did not alter the course of the normal moult cycle. There was no significant difference between the total body lengths of males and females indicating that females achieve the same levels of growth despite moulting more frequently and having to provision the energy-rich ovaries. This is in contrast to most other crustaceans where the energy costs of reproduction reduce female growth. The fact that females were less abundant than males, probably by suffering a greater level of mortality, suggests that different behavioural strategies, particularly vertical migration regimes, were adopted by each sex to maximise growth and reproduction.     

Metabolic properties of Northern krill, Meganyctiphanes norvegica, from different climatic zones. I. Respiration and excretion

Adaptive processes linked to overall metabolism were studied in terms of oxygen consumption and ammonia excretion in each of three self-contained krill populations along a climatic gradient. In the Danish Kattegat, krill were exposed to temperatures which ranged from 4°C to 16°C between seasons and a vertical temperature gradient of up to 10°C during summer. In the Scottish Clyde Sea, water temperatures varied less between seasons and the vertical temperature gradient in summer was only 3°C. Temperatures in the Ligurian Sea, off Nice, were relatively constant around 12-13°C throughout the year, with a thin surface layer (20-30 m) of warm water developing during summer. The trophic conditions were rich in the Kattegat and, particularly, in the Clyde, but comparatively poor in the Ligurian Sea. Oxygen consumption increased exponentially with increasing experimental temperature, which ranged from 4°C to 16°C. Overall respiration rates were between 19.9 and 89.9 µmol O₂ g^-1 dry wt h^-1. Krill from the Kattegat, the Clyde Sea, and the Ligurian Sea all exhibited approximately the same level of oxygen consumption (30-35 µmol O₂ g^-1 dry wt h^-1) when incubated at the ambient temperatures found in their respective environments (9°C, 5°C, and 12°C). This indicates that krill adjust their overall metabolic rates to the prevailing thermal conditions. The exception to this were the respiration rates of Ligurian krill from winter/spring, which were about twice as high as the rates from summer krill despite the fact that the thermal conditions were the same. This effect appears to result from enhanced somatic activity during a short period of increased food availability and reproduction. Accordingly, krill appears to be capable of adapting to both changing thermal and trophic conditions, especially when nutrition is a limiting factor in physiological processes.     

Can a key boreal Calanus copepod species now complete its life-cycle in the Arctic? Evidence and implications for Arctic food-webs

The changing Arctic environment is affecting zooplankton that support its abundant wildlife. We examined how these changes are influencing a key zooplankton species, Calanus finmarchicus, principally found in the North Atlantic but expatriated to the Arctic. Close to the ice-edge in the Fram Strait, we identified areas that, since the 1980s, are increasingly favourable to C. finmarchicus. Field-sampling revealed part of the population there to be capable of amassing enough reserves to overwinter. Early developmental stages were also present in early summer, suggesting successful local recruitment. This extension to suitable C. finmarchicus habitat is most likely facilitated by the long-term retreat of the ice-edge, allowing phytoplankton to bloom earlier and for longer and through higher temperatures increasing copepod developmental rates. The increased capacity for this species to complete its life-cycle and prosper in the Fram Strait can change community structure, with large consequences to regional food-webs.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01667-y.