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Three species of large crab are found in Western Australian waters, namely the champagne crab Hypothalassia acerba, the crystal crab Chaceon bicolor and the giant crab Pseudocarcinus gigas, all of which are fished commercially in these waters. This thesis reports the results of studies carried out on the biology of the first two species, for which there were previously very little information. The results increase our knowledge of the benthic fauna in deeper waters off the southwestern Australian coast and provide data that can be used by fisheries managers to develop plans for conserving the stocks of H. acerba and C. bicolor. The champagne crab Hypothalassia acerba is found southwards of Kalbarri at ~ 27„aS, 114„aE on the west coast and eastwards to Eucla at ~ 32„aS, 129„aE on the south coast. There is a small commercial trap fishery for H. acerba on both the lower west and south coasts of Western Australia. However, on the west coast, H. acerba is managed as a single species fishery, whereas on the south coast it is a component of a multi-species fishery, which also includes the southern rock lobster Jasus edwardsii and P. gigas. On the west coast, the commercial catches of H. acerba increased sharply from ~ 1,500 kg in 1989 to reach maximum levels of 30-46,000 kg in 1997-99, reflecting a marked increase in fishing effort. However, it subsequently declined to essentially zero after 2000 due to effort shifting towards fishing for C. bicolor. Catches of H. acerba on the south coast peaked at 26-27,000 kg in 1997-98 but, in contrast to those on the west coast, remained relatively high in 2001 to 2003. The crystal crab Chaceon bicolor occurs in water depths of ~ 450 to 1220 m around Australia and New Zealand. However the commercial fishery is almost entirely located between Carnarvon on the north-west coast at ~ 25„aS, 113„aE to approximately Windy Harbor at ~ 35„aS, 116„aE on the south coast. Commercial catches of C. bicolor in southwestern Australia, which came almost entirely from the lower west coast, rose from very low levels in 1997 to ~ 222,000 kg in 2001 and then remained close to this level in 2002 and 2003. These trends largely reflect an increase in fishing effort. Hypothalassia acerba was sampled seasonally by setting traps at depths of 35, 90, 145, 200, 255, 310 and 365 m on the west and south coasts of Western Australia. Catch rates on the west and south coasts peaked sharply at depths of 200 and 145 m, respectively, but at similar temperatures of 16 - 17¢XC. The catches on those coasts contained 69 and 84% males, respectively. The carapace length of H. acerba declined significantly by 4 mm for each 100 m increase in depth. Males attained a greater maximum carapace length than females on both the west coast, i.e. 135 vs 113 mm, and south coast, i.e. 138 vs 120 mm. Furthermore, after adjustment to a common depth of 200 m, the mean carapace length of males was greater than females on both the west coast (96.6 vs 94.6 mm) and south coast (101.5 and 91.4 mm) and the latter difference was significant (p < 0.001). These results thus show that, for H. acerba, (1) the distribution is related to depth and temperature, (2) body size is inversely related to water depth and (3) males grow to a larger size and are more prevalent in catches than females. There was also evidence that the distribution of H. acerba changed slightly with season and that there was spatial partitioning by this species and other large deep water invertebrate predators. The trends exhibited by reproductive variables demonstrate that H. acerba reproduces seasonally on the lower west coast, with ovaries maturing progressively between July and December and oviposition occurring between January and March. The characteristics of H. acerba on the south coast differed in the following ways from those on the lower west coast. (i) No ovigerous females and only two females with egg remnants were caught. (ii) Ovaries did not develop late yolk granule oocytes until females had reached a larger size. (iii) Investment in gonadal development was less. These results strongly suggest that conditions on the south coast are not as conducive for ovarian development and reproduction and indicate that females migrate from the south to lower west coast for spawning. In contrast to H. acerba, C. bicolor reproduces throughout much or all of the year on the lower west coast, presumably reflecting its occupancy of far deeper waters where environmental conditions vary less during the year. Although the mean weights of ovigerous females of H. acerba and C. bicolor were not significantly different (p > 0.05), the mean fecundity of the former species (356,210) was significantly greater (p < 0.001) than that of the latter species (192,070). The relatively high fecundity of H. acerba may reflect adaptations by this species to optimise egg production during its relatively short breeding season. The size at onset of sexual maturity (SOM) of the females of crustacean species, which is often used by fisheries managers for developing management plans for such species, is typically estimated using logistic regression analysis of the proportions of mature females in sequential size classes. The validity of this approach depends on the composition of the samples reflecting accurately that present in the environment. However, catches obtained by traps, a passive fishing method, typically contain disproportionately greater numbers of large crabs, whereas those obtained using active fishing methods, such as seine netting and otter trawling, will presumably represent far better the size composition of the population. Since H. acerba and C. bicolor could be caught in numbers only by using traps, comparisons between the influence of passive and active fishing methods were explored using the extensive data previously collected for Portunus pelagicus employing different sampling methods (de Lestang et al. 2003a,b). These data are analysed in order to demonstrate that the females of P. pelagicus caught by trapping were predominantly mature, whereas those obtained by seining and trawling contained numerous immature as well as mature females. The samples of females collected by trap are, therefore, clearly biased towards mature crabs. Consequently, for any size class, it would be predicted that the proportion of mature females in trap catches will be overestimated, thus shifting the logistic curve fitted to the proportions of mature crabs at each size to the left, and thereby yielding an underestimate of the SOM. This conclusion is substantiated by the fact that the carapace width of female P. pelagicus, at which 50% of individuals reach maturity (SOM50), was estimated to be markedly greater when using the proportion of mature females obtained by seine-netting and otter trawling collectively, i.e. 101.1 mm, than by trapping, i.e. 86.1 mm. From the above data for P. pelagicus, it is considered likely that, through a greater vulnerability of mature females of these species to capture by traps, the respective SOM50s derived for female H. acerba and C. bicolor from trap samples (i.e. carapace lengths of 69.7 and 90.5 mm) will represent considerable underestimates of the true SOM50s. Many workers have assumed that the chelae of male crabs undergo a change in allometry at the pubertal moult and that this could thus be used as the basis for determining the size of those crabs at morphometric maturity. Since initial plots of the logarithms of propodus length and carapace width (CW) of the males of P. pelagicus and carapace length (CL) of the males of H. acerba and C. bicolor revealed no conspicuous change in allometry, the question of whether the chelae of these species undergo such an allometric change was explored statistically. The Akaike and Bayesian Information Criteria were thus used to ascertain whether a linear, quadratic, broken stick or overlapping-lines model best represented the above logarithmic size data. Since the broken stick model provided the best fit for P. pelagicus, the chelae of this species does undergo allometric change. This occurred at 80.0 mm CW, which is ~ 8 mm less than the CW at physiological maturity. In contrast, my analyses provided no evidence that the chelae of either H. acerba or C. bicolor exhibited an inflection and thus morphometric maturity could not be determined for these two species from chela length. Thus, mangers will have to use the SOM50 for physiological maturity, which was estimated to be 68.1 and 94.3 mm CL for H. acerba and C. bicolor, respectively.

A blowout is an uncontrolled flow of reservoir fluids into the wellbore to the surface, causing serious, sometimes catastrophic, problems in different types of petroleum engineering operations. If the formation's strength is low and the pore pressure is high, bridging can be a very effective method for blowout containment. In this method, the formation caves into the open hole or onto the casing and stops the flow of the formation's fluid, either naturally or intentionally. This method can be effective in deepwater blowouts where the formation has high pore pressure and considerable shale intervals with low strength. In this research, wellbore stability and fluid flow performance subroutines have been developed with Visual Basic for Applications (VBA) programming. By integrating the subroutines together, we made a simulation tool to predict wellbore stability during blowouts and, consequently, predict wellbore bridging during normal and blowout situations. Then we used a real case in the country of Brunei to investigate a field case of a bridged wellbore to validate the simulator. In addition to the field case, we used GMI SFIB 5.02, a wellbore stability software, to provide validation. In the final part of this research we studied the effect of water depth in bridging tendency during blowout for the deepwater Gulf of Mexico (GOM). Since we could not find any real data in this area, we used general trends and correlations related to the GOM. The results of our study showed that water depth delays the occurrences of breakout in the wellbore during blowouts (i.e. for greater depth of water, wellbore collapse occurs farther below the mudline). However, the depth in which collapse occurs is different for different maximum horizontal stress amounts.

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Abstract Methane (CH4) and nitrous oxide (N2O) are not only important but also long-lived greenhouse gases. Unfortunately, in Taiwan, although there are some data on CH4 emission from rivers and lakes there is no data about N2O emission from rivers, lakes and coasts. So this study investigated CH4 and N2O distribution in natural waters around Taiwan. In Taiwan, the average CH4 concentration in rivers is about 3082¡Ó12399nM (n=152). The average CH4 concentration in mountain lakes is about 2899¡Ó7291nM (n=51). The average CH4 concentration in lower elevation lakes and reservoirs is about 1825¡Ó2755nM ppmv (n=95). The average CH4 concentration in near-shore waters is about 36.7¡Ó285nM (n=476). The CH4 distribution is rivers> mountain lakes>low-elevation lakes and reservoirs >seawater. In southeastern China, the average CH4 concentration in rivers is about 1029¡Ó2487nM ppmv (n=36). The average CH4 concentration of samples taken from rivers in southeastern China is lower than Taiwan rivers. But the highest CH4 concentration of all samples is in Chih-Kan river of southeastern China (14914nM), due to uneven population distribution as well as different levels of development among cities and suburbs. In Taiwan, the average N2O concentration in rivers is about 32.8¡Ó69.1nM (n=58). In southeastern China, the average N2O concentration in rivers is about 29.7¡Ó9.05nM (n=36). The average N2O concentration in Taiwanese rivers is higher than found in southeastern China. This is likely because farmers in Taiwan use more synthetic fertilizers so the soil becomes full of N element, and then rivers and rains rinse the soil. This process has increased the concentration of N and N2O in rivers. In summer, the average CH4 and N2O concentrations in northern Taiwan Strait are about 3.27¡Ó2.42nM and 7.22¡Ó0.62nM (n=7), respectively; and the average CH4 and N2O fluxes are about 0.17¡Ó0.43£gmol/m2/h and 0.14¡Ó0.26 £gmol/m2/h, respectively. The average CH4 and N2O concentrations in southern Taiwan Strait are about 3.35¡Ó1.97nM and10.31¡Ó2.51nM (n=30), respectively; and the average CH4 and N2O fluxes are about 0.04¡Ó0.09£gmol/m2/h and 0.19¡Ó0.22 £gmol/m2/h, respectively. In winter, the average CH4 and N2O concentrations in northern Taiwan Strait are about 4.74¡Ó1.43nM and 8.41¡Ó0.46nM (n=9), respectively; and the average CH4 and N2O fluxes are about 0.10¡Ó0.14£gmol/m2/h and 0.008¡Ó0.033 £gmol/m2/h, respectively. The average CH4 and N2O concentrations in southern Taiwan Strait are about 4.70¡Ó2.42nM and 8.36¡Ó0.97nM (n=17), respectively; and the average CH4 and N2O fluxes are about 0.17¡Ó0.46£gmol/m2/h and 0.11¡Ó0.12 £gmol/m2/h, respectively. Taiwan Strait is a source of CH4 and N2O regardless of whether it is summer or winter. In summer, the average CH4 and N2O concentrations in the South China Sea are about 4.34¡Ó2.33nM and 8.23¡Ó1.5nM (n=55), respectively; and the average CH4 and N2O fluxes are about 0.33¡Ó0.35£gmol/m2/h and 0.20¡Ó0.24 £gmol/m2/h, respectively. It is a source of CH4 and N2O to the atmosphere. In summer, the average CH4 and N2O concentrations in the West Philippines Sea are about 3.18¡Ó1.57nM and 4.64¡Ó0.39nM (n=60), respectively; and the average CH4 and N2O fluxes are about 0.23¡Ó0.33£gmol/m2/h and -0.28¡Ó0.30 £gmol/m2/h, respectively. It is a source of CH4 but a sink of N2O to the atmosphere.

This thesis examined the reproductive biology of the poorly-known deep-water gorgonian Acanella arbuscula from the Northwest Atlantic. Colonies were collected from The Gully in 2007 and 2010 between 914 and 1860 m depth, and the Flemish Cap in 2009 between 671 and 1264 m. Mean polyp fecundity was relatively high for both females and males, and the large oocyte size suggests that A. arbuscula produces lecithotrophic larvae. This species may have overlapping periodic or seasonal cycles of gametogenesis, and the absence of planulae suggests that A. arbuscula is a broadcast spawner. No spatial variation in the reproductive characteristics of this species was found, suggesting that environmental conditions are similar between the two sites. Female polyp fecundity decreased with increasing depth, which may be due to the high cost of producing oocytes versus sperm. The relatively high mean polyp fecundity, probable lecithotrophic larval development, and broadcast spawning may allow for the wide dispersal and settlement of A. arbuscula across the North Atlantic.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / This thesis explores the diversity, spatial patterns and community structure for the sponges (Porifera) along the west and south coasts of South Africa. Species collected were identified to the lowest level of lowest taxonomic unit possible (either species or genus). The study site was divided into areas and in each of these we documented the spatial diversity and in so doing were able to assess the variation of sponge communities between the west and south coasts. The total number of species recorded for this deep-water region was eighty-three of which nineteen are described. The south coast was more diverse than the west coast and eleven species were found to be common to both coasts. The analysis based on location and depth showed that both coasts are significantly different to each other. We determined that these areas are biogeographically separated. Species contributing toward the dissimilarity between both coasts include Suberites carnosus, Myxilla (Burtonanchora) sp 1, Rossella antarctica, Tetilla capillosa and Haliclona sp. Patterns of species richness showed an increase in diversity from the west to south. It was found that species richness increases with depth for both coasts but only up to 350 m for the west coast and 200 m for the south coast. However, the sampling effort was determined to possibly have not been enough to gain a full understanding of species richness for the entire study area as the number of species was correlated with sampling effort. Estimated richness found that higher richness of sponges could still be found within most of the best bins and for each coast. An estimate of samples needed both each depth bin per coast showed that more samples would be needed on the south coast and this is possibly due to the greater variety and variability of the species found on the coast. The sponge community on the south coast was found to have no significant difference in pattern with some of the depth bins, whereas depth plays a role in sponge community on the west coast. Species of Suberites were dominant at depths lower than 200 m while Hamacantha (Vomerula) esperioides was dominant between 200 and 350 m with Tetilla capillosa dominated depths lower than 350 m. The thesis is concluded with an overview of what is now known and what still needs to be discovered and determined to further enhance biodiversity knowledge in the country.