ALBERT

Description: We examine the diffusive behavior of the flow field in an eddy-resolving, primitive equation circulation model. Analysis of fluid particle trajectories illustrates the transport mechanisms, which are leading to uniform tracer and potential vorticity distributions in the interior of the subtropical thermocline. In contrast to the assumption of weak mixing in recent analytical theories, the numerical model indicates the alternative of tracer and potential vorticity homogenization on isopycnal surfaces taking place in a nonideal fluid with strong, along-isopycnal eddy mixing. The eastern, ventilated portion of the gyre appears to be sufficiently homogeneous to allow the concept of an eddy diffusivity to apply. A break in a random walk behavior of particle statistics occurs after about 100 days when along-flow dispersion sharply increases, indicative of mean shear effects. During the first months of particle spreading, eddy dispersal and mean advection are of similar magnitude. Eddy kinetic energy is of O(60–80 cm2 s−2) in the model thermocline, comparable to the pool of weak eddy intensity found in the eastern parts of the subtropical oceans. Eddy diffusivity in the model thermocline (Kxx = 8 × 107, Kyy = 3 × 107 cm2 s−1) seems to be higher by a factor of about 3 than oceanic values estimated for these area. Below the thermocline, model diffusivity decreases substantially and becomes much more anisotropic, with particle dispersal preferentially in the zonal direction. The strong nonisotropic behavior, prominent also in all other areas of water eddy intensity, appears as the major discrepancy when compared with the observed behavior of SOFAR floats and surface drifters in the ocean.

Description: This investigation contribute to our knowledge of the pigment content of certain previously described Cyanophycea found in symbiotic association with sponges and ascidians (Duclaux, 1977; Lafargue and Duclaux, 1979). It is opportunity to test the hypothesis of a single symbiont Synechocystis trididemni Lafargue and Duclaux associated both with Trididemnum cyanophorum Lafargue and Duclaux and T. tegulum. Phycoerythrin characteristics suggest that T. cyanophorum contains a cyanophyte symbiont which is different from the cyanophyte symbiont of T. tegulum.

Description: This is the first report of Prochlorophyta in association with the genus Polysyncraton, a Didemnid Ascidian (Tunicata). The species P. bilobatum Lafargue, 1968 is common near Galapagos islands as well on the European and the West-African coasts. It is a key species in the evolutive line of the Didemnidae in the French coast and probably in the world.

Description: A coupled ocean-atmosphere general circulation model has been developed for TOGA related problems. The coupled model consists of an ocean model of the tropical Pacific and a global low-order spectral atmosphere model. The two models interact via wind stress and sea surface temperature. In order to avoid a climate drift within the coupled model, a flux correction method is applied.Experiments were performed by introducing a westerly wind stress burst over the western equatorial Pacific for one month. Thereafter, the wind burst is turned off and the response of the coupled model to the initial disturbance is investigated. The results are compared with the response of the ocean model run with the same disturbance in an uncoupled mode.It is shown that the coupling leads to a significant increase of the duration of anomalous conditions in the ocean. SST anomalies persist for about 12 months in the coupled run, while they have already disappeared after 4 months in the uncoupled case. The increase in persistence is due to the feedback of the atmosphere, which responds with an eastward shift of the ascending branch of the Walker Circulation.In a second experiment with the coupled model the initial disturbance was introduced within another season. The results show no basic differences to the results of the first experiment.An interesting result of the coupled model runs is the occurrence of spontaneous westerly wind bursts over the western Pacific, which developed by internal dynamics. Location and duration of these spontaneous wind bursts show some correspondence with the time-space structure of observed westerly wind stress episodes over the western Pacific.

Description: Long-term temperature and current-meter records from moorings in the northern Canary Basin display strong current events with time scales between one and three months and large vertical scales of several thousand meters. The data are compared to hydrographic surveys in the area that show a meandering subtropical front. The strong current events are found to be related to the passage of the front through the mooring positions. An analysis of composite time series, for selected depths, indicates cases of westward and of eastward propagation of frontal meanders. The frontal pattern is also found in geopotential anomalies inferred from historical XBT data sets, suggesting that the front is a persistent feature of the density field. In two cases strong current events appear to be related to a Mediterranean Water lens.

Description: Thirty seven juvenile specimens and one adult specimen of the cranchiid squid Mesonychoteuthis hamiltoni were captured by the opening and closing RMT8 net during RRS ‘Discovery’ cruise 100 (1979) in the Southern Ocean. The collection extends the size ränge of juveniles of this species previously described and illustrated. The small specimens resemble small juveniles of Galiteuthis glacialis, which also occur in most hauls, but are separated on the following characters : (a) M. hamiltoni lacks paired tubercles at the nuchal mantle fusion, (b) M. hamiltoni possesses a more capacious and thicker mantle, which is freer at the nuchal fusion and less constricted posterior to the opening; (c) juvenile M. hamiltoni up to a size of 26.5 mm (the largest in the present collection) have very small fins, while in G. glacialis of this size the posterior portion of the mantle has begun to extend into a tail and prominent fins appears; (d) M. hamiltoni has longer tentacles until it reaches a dorsal mantle length of approximately 25 mm. All specimens of M. hamiltoni were captured to the south of the Antarctic Convergence, and most were captured at depths between 20 m and 500 m apparently concentrated in the upper zone of ‘Warm Deep Water’ beneath the surface layer. Four newly hatched specimens were captured at 55°35’S between 20 and 500 m. The adult specimen was captured in a haul which had sampled a depth horizon from 2 000 m to 2 200 m.

Description: Seventeen advanced macrotritopus “larvae” from 7 to 15 mm mantle length were attracted to underwater lights in St. Croix, U.S. Virgin Islands. Their behavior was observed in situ, then seven were captured alive and one female was reared to an adult Octopus defilippi. The characteristic long arms of the planktonic young appear to function in flotation, feeding, crawling and defense. There is evidence that larger macrotritopus may be planktonic by night and benthic by day; thus the transition from a planktonic to benthic life may be controlled to ensure widespread distribution on to a suitable habitat. Morphological examination of 106 specimens from the Atlantic indicate that all macrotritopus “larvae” from this ocean are O. defilippi.

Description: A methodology is presented for obtaining egg masses from captive populations of the ommastrephid squid Illex illecebrosus and for incubating them intact under controlled conditions. Survival of rhynchoteuthion larvae for 9 days after hatching is the best reported to date, though it has not yet been possible to induce feeding. Factors critical to rearing success are discussed, e.g. tank size, stocking density, turbulence, light levels and photoperiod, as well as food type and concentration.

Description: The unique rhynchoteuthions of the ommastrephid squids are the smallest decapodan cephalopod hatchlings and have never been successfully reared. Based on anatomical and behavioural observations a mechanism of suspension feeding is proposed which depends on direct interception and inertial impaction on the mucus coated body surface. Mucus is transferred to the mouth area by ciliary motion and by observed cleaning behaviours. Suspension feeding is suggested to be a supplement to raptorial feeding but may be a critical "bridge" between small yolk reserves and the minimum development required for effective predation. Loss of ciliature through contact with vessel walls may prevent feeding in culture.

Description: Rhynchoteuthion larvae of three species of ommastrephid squids from Hawaiian waters were identified, and aspects of their ecology examined. Important taxonomic characters for field Identification include the number and location of photophores, length of the proboscis (fused tentacles), size at which the proboscis completely divides and the relative sizes of the suckers on the proboscis tip. Other taxonomic characters include sucker structure and chromatophore patterns. Variation among species were found in both temporal and vertical distributions.

Description: While carrying out a systematic revision of the pelagic squid genus Octopoteuthis, the author examined 146 “larval” specimens of the genus from museum sources worldwide. Individuals could not be separated into species but morphometric and meristic characters were examined giving information on ontogenetic development. Specimens ranged in size from 1.3 to 27.0 mm dorsal mantle length (DML) and represented locations in the Atlantic, Pacific and Indian Oceans and also the Mediterranean Sea. Captures were made with a variety of trawls and plankton nets. The deepest record from a closing net was 1 200 m using a MOCNESS system. The largest group examined totalling 105 individuals was collected in the North Atlantic. In the Atlantic the highest larval occurence was found to be in March, April, and June (which may reflect higher sampling pressure in those months) but specimens were obtained in all months except January and December. Low numbers in each of the other oceans prohibited an evaluation of yearly larval distribution.

Description: Larval squid were sampled in three surveys off the eastern Australian coast in January, March and May 1983. Ommastrephid larvae were abundant and occurred at over 90 % of stations. Although Identification to species level has not so far been possible for the majority of specimens, general patterns of distribution with respect to latitude and bottom depth are presented.