Methane hydrate is an icelike substance that is stable at high pressure and low temperature in continental margin sediments. Since the discovery of a large number of gas flares at the landward termination of the gas hydrate stability zone off Svalbard, there has been concern that warming bottom waters have started to dissociate large amounts of gas hydrate and that the resulting methane release may possibly accelerate global warming. Here, we corroborate that hydrates play a role in the observed seepage of gas, but we present evidence that seepage off Svalbard has been ongoing for at least 3000 years and that seasonal fluctuations of 1° to 2°C in the bottom-water temperature cause periodic gas hydrate formation and dissociation, which focus seepage at the observed sites.

The Stjernsund, located in subpolar setting at 70.5°N off northern Norway, hosts a thriving cold-water coral reef community on a morainic sill. Dives with manned submersible JAGO identified the different reef zones and sedimentary facies on top and on the slopes of the sill. Hydrographic investigations indicate different water mass distribution east and west of the sill. Winter Mode Water and Norwegian Coastal Water variability depends on the runoff and freshwater discharge into the fjord. Atlantic Water dynamics are almost entirely tidally driven. High-resolution CTD time series covering a full tidal cycle demonstrate mixing processes occurring east of the sill. Additionally, the different bathymetric distribution of living corals on the western and eastern slope of the sill portrays the dependence on these tidal dynamics. The living corals thrive just below the isopycnal of 27.5 kg m − 3 , which marks the boundary between Norwegian Coastal Water and Atlantic Water.

1. Members of a field population cd Cryflus campestris L. vaned in their walking and calling activity. In both sexes, some individuals occupied burrows whereas others walked around in the observation area. Males at burrows could be either silent cbr calling.2. In the course of one summer, population density decreased and the initial balanced sex ratio changed to a large surplus of males.3. At high population density, there were equal numbers of noncalling males at burrows, calling males at burrows and walking males, while walking females predominated over females at burrows. Noncalling males at burrows achieved more encounters with females than did calling and walking males. Females met males by walking through the population and by waiting at burrows. Thus, calling and phonotaxis were not essential for mate finding and calling was less effective than previously thought. 4. At low population density calling males predominated. Calling males at burrows achieved the most encounters with females. Females met males only by walking around in the population area. Calling was thus more important in mate finding than at high population density. 5 . Changes in sex ratio and population density may cause the flexibility in mate finding behaviour of individual crickets.

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SynopsisLocomotion and fin coordination of the only living crossopterygian fish Latimeria chalumnae were studied with submersibles in the fish's natural habitat at around 200 m depth off Grand Comoro, western Indian Ocean. Latimeria is a highly specialized predatory fish adapted for nocturnal drift hunting with good fast start capability. Twelve different forward movements and manoeuvres were found and described. The movements of the paired and unpaired fins were analysed. Propulsion was accomplished with downstrokes of the pectoral fins and right-left or left-right strokes of the unpaired lobed fins. The paired fins were not used for walking on the bottom. Swimming velocity, stroke amplitudes and stroke duration were analysed from films and videos taken in the wild. Stroke duration of the paired and unpaired lobed fins was similar and varies between 1.0 to 5.8sec. Paired fins alternated synchronously. The coordination at approximately 0 = 180" between opposite paired fins is stable and independent of locomotory pattern and velocity. A phase deviation of about 90"-100" exists between paired and unpaired fins. A model is developed that describes the functional implication of this deviation as a method of producing a steady swimming performance which smooths recoil movements and prevents rotation of the body. The novel slow and fast swimming mode of Latimeria i!j named in accordance with Breder's (1926) descriptive nomenclature as 'coelacanthiform'. This study indicates a primary swimming function for the primitive sarcopterygian fin and confirms earlier evolutionary assumptions of a more open-water life style of coelacanth fishes. Paleoethological models of the walking habits of Latimeria have to be rejected. Synchronous alternation of paired fins originating from hydrodynamic demands could be a pre-adaptation and a shared derived character in sarcopterygian fishes that facilitated the fish-tetrapod transition.

Coelacanths were discovered in the Comoros archipelago to the northwest of Madagascar in 1952. Since then, these rare, ancient fish have been found to the south off Mozambique, Madagascar and South Africa, and to the north off Kenya and Tanzania -- but it was unclear whether these are separate populations or even subspecies. Here we show that the genetic variation between individuals from these different locations is unexpectedly low. Combined with earlier results from submersible and oceanographic observations, our findings indicate that a separate African metapopulation is unlikely to have existed and that locations distant from the Comoros were probably inhabited relatively recently by either dead-end drifters or founders that originated in the Comoros.

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