Description: 31st Annual Conference of IAMSLIC held 10-14 October, 2005 at Rome, Italy

Description: Studies of the pantophysin (Pan I*) locus in Atlantic cod Gadus morhua and other marine gadoids indicate that the locus is under positive selection; in Atlantic cod, genotypic variation at this locus has been linked to differences in growth. Here, we present preliminary data comparing the growth and condition of different Atlantic cod Pan I* genotypes within families held under seminatural mesocosm conditions. Larvae from three full-sibling families carrying Pan I*bb or Pan I*ab genotypes were reared for 10 weeks in two mesocosms. Multivariate analysis of variance indicated that larvae carrying the Pan I*ab genotype exhibited significantly higher standard length, dry weight, and RNA: DNA ratio (condition factor) than did larvae that carried the Pan I*bb genotype, potentially indicating selection. The influence of linked loci cannot be excluded; indeed, the absence of a significant correlation between genotype and growth in one family may substantiate this. The lack of differences in survival among genotypes indicates that moderate selective effects are acting primarily through size-specific mortality and fecundity. The proposed putative fitness effects, together with documented marked geographic differentiation in the wild, have implications for Atlantic cod population structure, effective migration rates, recruitment, and local adaptation, which are of particular relevance in a species threatened by continuing exploitation and rising sea temperatures.

Description: Trimix scuba divers discovered coelacanths in Jesser Canyon at a depth of 104 m on the northern KwaZulu-Natal (KZN) coast (Sodwana Bay) in October 2000. The existence of these animals at such a shallow depth and in the swift and powerful Agulhas Current led to a suggestion that this might be an isolated group swept well away from the main population in the Comoros, where they live at depths of 200-350 m with little current. Subsequent observations from three manned submersible surveys and one remotely operated vehicle expedition together with recreational diver observations indicate that the South African population of coelacanths has at least 26 individuals, mostly occupying the depth range of 104-140 m in canyons. Seventeen CTD sections collected during four cruises in 2002 and 2003 indicate the temperature range in this habitat to be similar to that found in the Comoros Islands (that is, 15-22〈sup〉o〈/sup〉C cf. 15-19〈sup〉o〈/sup〉C in the Comoros). However, a 2.5-month-long time series of hourly data collected by a thermistor array deployed near a known coelacanth cave in Wright Canyon indicated greater variation than anticipated, with temperature changes between 16〈sup〉o〈/sup〉C and 24〈sup〉o〈/sup〉C occurring in a day. Dissolved oxygen levels in this depth zone were found to range between 3.0 ml l〈sup>-1〈/sup> and 4.8 ml l〈sup>-1〈/sup> compared to 3.5 ml l〈sup>-1〈/sup> in the Comoros. The low oxygen values along this coast are a result of the shallow oxygen minimum, which becomes shallower in the southwest Indian Ocean, particularly in the Agulhas Current, than in tropical latitudes. Current velocities measured using a ship-borne ADCP in the depth range 100-140 m at Sodwana were considerably higher than those measured in the Comoros habitat (20-60 cm s〈sup>-1〈/sup> cf. 3-4 cm s〈sup〉-1〈/sup〉) and may be an important factor explaining the coelacanths' occupation of the canyons found along the northern KZN shelf-break.

Description: There is growing concern about the transfer of methane originating from water bodies to the atmosphere. Methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport. This work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere. The bubble model predicts the evolving bubble size, gas composition, and rise distance and is suitable for almost all aquatic environments. The model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep, oxic, saline water with excellent results. Methane bubbles from within the hydrate stability zone (typically below ∼500 m water depth in the ocean) are believed to form an outer hydrate rim. To explain the subsequent slow dissolution, a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone. The calibrated model explains the impressively tall flares (〉1300 m) observed in the hydrate stability zone of the Black Sea. This study suggests that only a small amount of methane reaches the surface at active seep sites in the Black Sea, and this only from very shallow water areas (〈100 m). Clearly, the Black Sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere, although substantial amounts of methane may reach the surface in shallow lakes and reservoirs.

Description: Combined measurements of Mg/Ca and stable oxygen isotopes in tests of the planktonic foraminifer G. bulloides from Ocean Drilling Program (ODP) Site 1172A (East Tasman Plateau) allowed us to reconstruct sea surface temperature (SSTMg/Ca), sea surface salinity (SSS), and hence variations in the Subtropical Convergence (STC) in the southwestern Tasman Sea over the last four major glacial-interglacial changes. During interglacials the commonly enhanced SSTMg/Ca and SSS correspond to a lowered marine productivity and a lowered terrigenous flux, implying that the STC separating cool, high-nutrient Subantarctic Surface Water from warm, saline, oligotrophic Subtropical Surface Water and hence the band of zonal westerlies responsible for the eolian dust flux were located south of East Tasman Plateau. The warm East Australian Current was well established during warm periods and propagated far south. During glacial times, SSTMg/Ca and SSS were lower, while both marine productivity and eolian flux increased. Such conditions prevailed during glacial Marine Isotope Stages MIS 12, MIS 10, and to a lesser degree MIS 6 and implied the extended northward influence of Subantarctic SurfaceWater and a shift of the STC to 〈44�S. The overall climatic signal at Site 1172A appears to be largely attenuated when compared to published climate records from comparable latitudes to the west and to the east. SSTMg/Ca amplitudes were more pronounced in the subantarctic Indian Ocean and at Chatham Rise. They exhibit a consistent pattern suggesting that latitudinal shifts of the STC occurred synchronously in the subantarctic Indian Ocean and at Chatham Rise but were largely damped at East Tasman Plateau due to the influence of the East Australian Current.

Description: Using the manned submersible 〈I〉Jago〈/I〉, the habits, distribution and number of coelacanths within all main submarine canyons of the Greater St Lucia Wetland Park were studied during 47 survey dives, with a total bottom time of 166 hours at depths ranging from 46 to 359 m, between 2002 and 2004. Twenty-four individuals were positively identified from three of the canyons, primarily from inside caves at or close to the canyon edges at depths of 96-133 m with water temperatures between 16 and 22.5〈sup〉o〈/sup〉C. The population size of coelacanths within the canyons is assumed to be relatively small; coelacanths are resident but not widespread nor abundant within the park.