Gotowa bibliografia na temat „Mudcrab”

The study was conducted to assess the existing supply chain for mudcrab in Region 10 and to identify areas for improvement. The study covered major mudcrab producing areas in Region 10. Reconnaissance survey, courtesy calls and visits to the Local Government Units, Bureau of Fisheries and Aquatic Resources, and Department of Agriculture Offices in the mudcrab producing areas were done to identify the study sites. Results revealed that almost half (49.42%) of the mudcrab production in the country is from Region 10 which were majority caught/sourced from Panguil Bay. There are four specific supply chains traced. Computation of the marketing cost and margin for each key player revealed that the profit margin is higher towards downstream key players (traders). Also, the shorter the supply chain the more equitable distribution of income is observed. There is no face to face interaction between the local traders and the metro manila traders which resulted to information asymmetry. Some of the issues included mortality of mudcrabs during transport, price fluctuation, opportunistic behavior of the fisherman, and political intervention. Finally, common perception of the interviewed respondents pointed out that mudcrab supply is decreasing in Region 10. Therefore, the need for further intervention project on the production technology/ reinforcement of mudcrab industry should be done.

<p>ABSTRACT<br />Mudcrab is one of the fishery commodity with high economic value in Indonesia. High market and price stimulated the development of the mudcrabs business in this country. The aim of this research was to evaluate interaction between habitat characteristics and the mudcrabs (Scylla spp.) species. The research was conducted in silvofishery ponds of Eretan village, Indramayu, West Java from September-November 2013 and August-September 2014. Sampling was conducted at five stations. They were BDR (Brackishwater dominated Rhizophora sp.), BDA (Brackishwater dominated Avicennia sp.), BCDR (Brackishwater cannal dominated Rhizopora sp.), BCDA (Brackishwater cannal dominated Avicennia sp.) and SMF (Side of the mangrove forest). The result showed there were two species of the mudcrabs Scylla paramamosain and Scylla olivacea. S. paramamosain was dominated than S. olivacea at all stations. Total number of the S. paramamosain was 107 ind (consisted of 67 male and 40 female), while total number of the S. olivacea was 28 ind (consisted of 17 male and 11 female). Composition of the mudcrabs species in each station was 91% S. paramamosain and 9% S. olivacea at BDR, 89% S. paramamosain and 11% S. olivacea at BDA, 86% S. paramamosain and 14% S. olivacea at BCDR, 68% S. paramamosain and 32% S. olivacea at BCDA, 73% S. paramamosain and 27% S. olivacea at SMF. Differences between kinds of mudcrab in each stations showed there are interaction between kinds of mudcrabs with habitat characteristics.</p><p><br />Keywords: Indramayu, mangrove, mudcrabs, substrate,</p><p>-------</p><p>ABSTRAK</p><p>Kepiting bakau (Scylla spp.) merupakan salah satu komoditas perikanan di Indonesia yang bernilai ekonomis tinggi. Luasnya pemasaran dan tingginya nilai jual kepiting bakau membuat bisnis tersebut semakin berkembang. Penelitian ini bertujuan untuk mengetahui hubungan keberadaan jenis kepiting bakau dengan karakteristik habitatnya. Penelitian ini dilakukan dari Agustus-November 2013 dan Agustus-September 2014 pada kawasan tambak silvofishery Desa Eretan, Indramayu, Jawa Barat. Pengambilan sampel dilakukan pada lima stasiun pengamatan diantaranya TSDR (Tambak silvofishery dominan Rhizopora sp.), TSDA (Tambak silvofishery dominan Avicennia sp.), KDR (Kanal dominan Rhizopora sp.), KDA (Kanal dominan Avicennia sp.) dan PHM (Pinggiran hutan mangrove). Hasil penelitian ini menunjukkan bahwa terdapat dua jenis kepiting bakau yaitu Scylla paramamosain dan S. olivacea. Di lokasi penelitian jumlah Scylla paramamosain yang tertangkap sebanyak 107 individu yang terdiri dari 67 jantan dan 40 betina, sedangkan jumlah S. olivacea yang tertangkap sebanyak 28 individu yang terdiri atas 17 jantan dan 11 betina. Hasil penelitian menunjukkan pada umumnya jumlah S. paramamosain yang tertangkap melebihi S. olivacea. Persentase kepiting bakau yang tertangkap pada tiap stasiun pengamatan yaitu 91% S. paramamosain dan 9% S. olivacea pada TSDR, 89% S. paramamosain dan 11% S. olivacea pada TSDA, 86% S. paramamosain dan 14% S. olivacea pada KDR, 68% S. paramamosain dan 32% S. olivacea pada KDA, 73% S. paramamosain dan 27% S. olivacea pada PHM. Perbedaan jumlah jenis kepiting bakau yang diperoleh pada tiap stasiun penangkapan menunjukan bahwa terdapat hubungan antara jenis kepiting bakau dengan habitat hidupnya.</p><p><br />Kata kunci: Indramayu, mangrove, kepiting bakau, substrat,</p>

<p><strong>ABSTRACT</strong></p><p>Molting phase is one of many factors that can inhibit mudcrab growth. Recirculation system in culturing mudcrab has a weakness which is the decreasing of ions. Calcium and magnesium in the water can affect the molting phase. The aim of this study was to evaluate the best additional frequency of calcium and magnesium in recirculation system. This research used mudcrab seeds that have weight of 54.856±2.195 gram. This research used completely randomized design with four treatments and three replicates. The treatments were additional frequency of Ca and Mg, comprised of four levels, without additional Ca and Mg (A), additional 30 mg/L Ca and 30 mg/L Mg in every five days (B), additional 30 mg/L Ca, and 30 mg/L Mg in every 10 days (C), and additional 30 mg/L Ca and 30 mg/L Mg in every 15 days (D). The result showed that total of biomass in every treatments were A (379.99±86.16 gram), B (517.65±103.94 gram), C (808.68±59.29 gram), and D (1,054.41±73.54 gram). The highest final biomass was the D treatment (1,054,41±73.54), which was significantly different to others (P&lt;0.05).</p><p>Keywords: mudcrab, resirculation, calcium, magnesium, molting, production</p><p> </p><p> </p><p><strong>ABSTRAK</strong></p><p>Salah satu faktor penghambat pertumbuhan kepiting bakau adalah fase molting. Sistem resirkulasi budidaya kepiting bakau memiliki kelemahan yaitu berkurangnya ion-ion. Fase moting pada kepiting bakau sangat dipengaruhi oleh keberadaan ion kalsium dan magnesium dalam air. Penelitian ini bertujuan untuk menentukan frekuensi waktu penambahan kalsium dan magnesium terbaik dalam sistem resirkulasi. Penelitian ini menggunakan benih kepiting bakau dengan berat rata-rata 54,856±2,195 gram. Penelitian ini menggunakan rancangan acak lengkap (RAL) dengan empat perlakuan dan tiga ulangan. Perlakuan penambahan Ca dan Mg sebanyak 30 mg/L terdiri atas empat macam frekuensi, yaitu tanpa penambahan Ca dan Mg (A), frekuensi lima hari sekali (B), frekuensi 10 hari sekali (C), dan frekuensi 15 hari sekali (D). Hasil penelitian menunjukkan jumlah biomassa masing-masing perlakuan adalah A (379,99±86,16 gram), B (517,65±103,94 gram), C (808,68±59,29 gram), dan D (1.054,41±73,54 gram). Perlakuan terbaik diperoleh pada perlakuan D dengan jumlah biomassa sebesar (1.054,41±73,54 gram) ini berbeda nyata (P&lt;0,05) dengan perlakuan lainnya.<br /> <br />Kata kunci: kepiting bakau, resirkulasi, kalsium, magnesium, molting, produksi</p>

<p>ABSTRACT</p><p>Molting phase is one of many factors that can inhibit mudcrab growth. Recirculation system in culturing mudcrab has a weakness which is the decreasing of ions. Calcium and magnesium in the water can affect the molting phase. The aim of this study was to evaluate the best additional frequency of calcium and magnesium in recirculation system. This research used mudcrab seeds that have weight of 54.856±2.195 gram. This research used completely randomized design with four treatments and three replicates. The treatments were additional frequency of Ca and Mg, comprised of four levels, without additional Ca and Mg (A), additional 30 mg/L Ca and 30 mg/L Mg in every five days (B), additional 30 mg/L Ca, and 30 mg/L Mg in every 10 days (C), and additional 30 mg/L Ca and 30 mg/L Mg in every 15 days (D). The result showed that total of biomass in every treatments were A (379.99±86.16 gram), B (517.65±103.94 gram), C (808.68±59.29 gram), and D (1,054.41±73.54 gram). The highest final biomass was the D treatment (1,054,41±73.54), which was significantly different to others (P&lt;0.05).</p><p>Keywords: mudcrab, resirculation, calcium, magnesium, molting, production</p><p>ABSTRAK</p><p>Salah satu faktor penghambat pertumbuhan kepiting bakau adalah fase molting. Sistem resirkulasi budidaya kepiting bakau memiliki kelemahan yaitu berkurangnya ion-ion. Fase moting pada kepiting bakau sangat dipengaruhi oleh keberadaan ion kalsium dan magnesium dalam air. Penelitian ini bertujuan untuk menentukan frekuensi waktu penambahan kalsium dan magnesium terbaik dalam sistem resirkulasi. Penelitian ini menggunakan benih kepiting bakau dengan berat rata-rata 54,856±2,195 gram. Penelitian ini menggunakan rancangan acak lengkap (RAL) dengan empat perlakuan dan tiga ulangan. Perlakuan penambahan Ca dan Mg sebanyak 30 mg/L terdiri atas empat macam frekuensi, yaitu tanpa penambahan Ca dan Mg (A), frekuensi lima hari sekali (B), frekuensi 10 hari sekali (C), dan frekuensi 15 hari sekali (D). Hasil penelitian menunjukkan jumlah biomassa masing-masing perlakuan adalah A (379,99±86,16 gram), B (517,65±103,94 gram), C (808,68±59,29 gram), dan D (1.054,41±73,54 gram). Perlakuan terbaik diperoleh pada perlakuan D dengan jumlah biomassa sebesar (1.054,41±73,54 gram) ini berbeda nyata (P&lt;0,05) dengan perlakuan lainnya.<br /> <br />Kata kunci: kepiting bakau, resirkulasi, kalsium, magnesium, molting, produksi</p>

Kegiatan pembesaran kepiting bakau hasil pembenihan di tambak masih terbatas dan pada umumnya masih merupakan kegiatan penelitian. Tujuan penelitian ini adalah untuk mengetahui pertumbuhan, sintasan, produksi, dan membuat analisis usaha pembesaran krablet kepiting bakau hasil pembenihan pada beberapa lokasi tambak tradisional. Penelitian dilakukan di tiga lokasi tambak yaitu Maros, Pangkep, dan Polewali Mandar (Polman). Tambak yang digunakan pada setiap lokasi merupakan tambak tradisional berkonstruksi tanah dengan sistem penggantian air berdasarkan pasang surut. Krablet kepiting bakau dengan kisaran bobot 0,05-0,1 g/ekor ditebar dengan kepadatan 0,24 ekor/m2 dan 0,27 ekor/m2 untuk Kabupaten Pangkep dan Polman secara berurutan sedangkan pada Kabupaten Maros dengan kepadatan 0,53 ekor/m2. Jenis pakan yang diberikan yaitu ikan rucah atau ikan liar yang ada di sekitar lokasi tambak dengan dosis 5%-10% dari biomassa dan diberikan dua atau tiga hari sekali. Hasil penelitian menunjukkan bahwa pertumbuhan kepiting bakau di tiga lokasi pada bulan ketiga diperoleh bobot akhir rata-rata dengan kisaran 131,05-199,50 g/ekor (163,17 ± 34,42); sintasan 22%-36,94% (30,41 ± 7,65); dan produksi 79,25-272,12 kg/ha (176,07 ± 96,43). Keuntungan tertinggi diperoleh pada lokasi Maros yaitu Rp5.454.750,00/ha/siklus dan terendah di lokasi Polman yaitu Rp317.150,00/ha/siklus. Nilai R/C rasio untuk semua lokasi menunjukkan lebih besar dari satu yang berarti bahwa usaha pembesaran kepiting bakau di tambak menggunakan krablet asal hatchery merupakan usaha yang layak. Ketersediaan pakan yang cukup, keberadaan shelter, pergantian air secara rutin dan kondisi kualitas air yang optimal merupakan faktor penting yang perlu diperhatikan untuk meningkatkan produksi pada ketiga lokasi di samping meningkatkan kepadatan sampai 1 ekor/m2.The grow-out cultures of hatchery-produced mudcrab seed in pond are rare and mostly part of research activities. The purpose of this study was to determine the performance of growth, survival rate, production, and develop a business analysis of mudcrab (S. tranquebarica) grow-out culture in different pond locations using hatchery-reared seed. The study was conducted in three pond areas in Maros, Pangkep, and Polewali Mandar (Polman). The ponds used in each location were traditional soil ponds with sufficient tidal system for water exchange. Crablets with a weight range of 0.05-0.1 g were reared in the ponds located in Pangkep, Polman and Maros with stocking densities of 0.24, 0.27 and 0.53 ind./m2, respectively. The feed used was trash fish or locally caught wild fish and given 5%-10% of the total crab biomass once every two or three days. The results showed that the average final weight of mudcrab in the three locations during three months rearing period was 131.05-199.50 g/ind. (163.17 ± 34.42) with survival rates of 22%-36.94% (30.41 ± 7.65), and crab production of 79.25-272.12 kg/ha (176.07 ± 96.43). The highest profit was obtained by grow-out culture in Maros location (IDR 5,454,750/ha/cycle) followed by Pangkep location (IDR 4,624,400/ha/cycle) and the lowest at Polman location (IDR 317,150/ha/cycle). The R/C ratio for all locations was greater than one which means that mudcrab culture in pond using seed from hatchery is economically feasibility.

The present study aimed to identify the Octolasmis spp. ectoparasite’s intensity and prevalence in mud crab in Pohuwato Regency. It employed survey and site observation methods with sampling technique of mud crabs in Pohuwato Regency. The research was carried out in three different sites: site 1 (Pohuwato Timur Village), site II (Bulili Village), and site III (Mootilango Village). The results showed that the parasites infesting mud crab in the three separate locations are Octolasmis angulata and Octolasmis cor. The highest intensity rate was at site III, which was dominated by Octolasmis cor. The prevalence of the parasite in sites I, II, and III was 60%, 40%, and 60% in consecutive order. Moreover, the parasite has a 100% and 46% prevalence in female and male crabs, respectively. The water quality indicator (involving temperature, pH level, and soluble oxygen) was at the appropriate rate for mud crab farming.

Mating activity in a southern Queensland population of S. serrata was at a maximum level in mid-spring and late summer-early autumn. Spawning activity, as indicated by the incidence of spent females, began early in spring and ended in early autumn while water temperatures exceeded approximately 22�C. Nevertheless, ovary condition was apparently held constant during the colder non-spawning half of the year. Ovary condition was not correlated with either ovary coloui or crab size.

Mudcrab Scylla serrata (Crustacea: Decapoda) in an ecologically and economically important species of Sundarbans Biosphere Reserve was studied for its behaviour under the exposure of toxic arsenic - a common xenobiotic of this area. The behavioural profile of aquatic animals exposed to diverse toxicants are considered as an index to estimate the degree and nature of stress experienced by the animals both in nature and in experimental conditions. Present investigation involved study of selected behavioural shift of S. serrata under the sublethalconcentrations of 1, 2 and 3 ppm of sodium arsenite for 1, 2, 3 and 4 days in controlled laboratory condition. Exposure to arsenic resulted an appearance of selected abnormal behavioural manifestation including tendency of avoidance, hypersecretion of mucoid element and release of excess excretory products. Toxin induced alteration of studied behaviour is indicative to possible shift in the overall physiological functions and biological activities of this important species in its natural habitat. Chronic exposure to 3 ppm of sodium arsenite for 30 days may lead to decline this economically important species in Sundarbans Biosphere Reserve.

It is often hypothesised that marine species with mobile planktonic phases are capable of widespread dispersal and may therefore be genetically homogenous throughout their distribution. Studies that have demonstrated positive correlation between duration of plankton phase and levels of gene flow reinforce the prediction that life history characteristics of marine species determine the potential extent of genetic and demographic connectivity throughout their distributions. This prediction has however been challenged by studies that have employed genetic markers highly sensitive to both historical and contemporary demographic changes. Disparities between dispersal potential and measured levels of gene flow have been demonstrated both among historically disconnected ocean basins and within semi-enclosed areas of strong hydraulic connectivity. These studies and others highlight a need for greater focus on factors that may influence population structure and distribution for marine species. In this thesis, I have examined genetic structure within and among populations of an estuarine species of mud crab Scylla serrata (Forskal, 1775) using a number of genetic markers and methods. The species is widely distributed throughout mangrove and estuarine habitats of the Indo - West Pacific (IWP); it is generally assumed that life-history characteristics of S. serrata promote high levels of population admixture and gene flow throughout its distribution. Alternatively, factors that have promoted population genetic structure for a variety of IWP marine species may also have affected S. serrata populations. By investigating genetic structure at several spatial scales of sampling, I was able to address a variety of hypotheses concerning the species distribution, dispersal, and genetic structure. Episodic changes to marine habitat and conditions experienced within the IWP during the Pleistocene may have affected genetic structure for a broad variety of marine taxa. The relative strength of this hypothesis may be assayed by comparative genetic studies of widespread IWP taxa with high dispersal capacity. In order to ascertain levels of historical and contemporary gene flow for S. serrata, I investigated the phylogeographic distribution of mitochondrial DNA haplotypes sampled throughout the species range. Adults were sampled from three west Indian ocean locations (N=21), six west Pacific sites (N=68), and two sites from northern eastern Australia (N=35). Temperature gradient gel electrophoresis and sequencing of 549 base pairs of the mitochondrial cytochrome oxidase I (COI) coding gene identified 18 distinct haplotypes. Apart from that seen in northern Australia, haplotype diversity was low (h < 0.36) at each of the locations. Total nucleotide diversity in the entire sample (excluding northern Australian locations) was also low (p = 0.09). Haplotypes clustered into two clades separated by approximately 2% sequence divergence. One clade was widespread throughout the IWP (clade 1) whereas the other was strictly confined to northern Australia (clade 2). Genealogical assessment of sequenced haplotypes relative to their distributions suggested that a historical radiation of clade 1 S. serrata throughout the IWP occurred rapidly and recently (<1Myr bp) from a west Pacific origin. The evidence of fixed unique haplotypes at the majority of locations suggested that contemporary maternal gene flow between trans-oceanic sites was limited. Contrary to reports for other widespread species of IWP taxa, there was no evidence of lengthy periods of regional separation between Indian from Pacific Ocean populations. However, results may indicate a separation of northern Australian crabs from other locations before and during the IWP radiation. I speculated that this isolation might have resulted in the formation of a new species of Scylla. Additional sampling of mud crabs from the Australian coastline allowed an examination of the diversity and distribution of clade 1 and 2 haplotypes among recently formed shelf-connected coastal locations, and across a historical bio-geographic barrier. Over 300 individuals were sampled from multiple locations within coastal regions (western, northern and eastern) of Australia and analysed for mutational differences at the COI gene. Analysis of molecular variance partitioned by sampling scale (Among regions, within regions, and within all locations) indicated mitochondrial haplotypes were structured regionally (P < 0.001), which contrasted with evidence of genetic panmixia within regions. Regional genetic structure broadly correlated with hydrological circulation, supporting the contention that release and transport of propagules away from the estuary may allow genetic connectivity among widespread shelf-connected S. serrata populations. That similar patterns of maternal gene flow were absent among trans-oceanic populations may indicate that the spatial scale of effective dispersal for this species is generally limited to areas of coastal shelf. The two clades of haplotypes were geographically separated either side of the Torres Strait, a narrow sea channel connecting the northern and eastern regions of coastal Australia. This pattern of historical genetic separation was concordant with a number of other marine species across northern Australia, and might indicate a shared history of vicariance induced by eustasy. Alternatively, differences in diversity and distribution of the clades may be evidence of two independent expansions of clade 1 and 2 crab populations into Australian regions following post-glacial estuary formation. Overall, despite evidence of genetic panmixia within extensive sections of the Australian distribution, there was also evidence of significant barriers to maternal gene flow with both shallow and deep regional phylogeographic assortment of mtDNA haplotypes. The presence of these barriers indicated both historical and contemporary factors have imposed limits to effective dispersal by this species among coastal habitats. A subset of the Australian sample (8 locations, N = 188) was also examined for variation at five microsatellite loci developed specifically here for S. serrata. I examined variation among samples at each of the loci to: a) independently verify regional structure among crab populations previously detected using the mtDNA analysis; b) test for evidence of co-distributed non-interbreeding stocks of S. serrata within Australian waters by examining samples for segregation of alleles within microsatellite loci concordant with the two mtDNA clades. The frequency and distribution of alleles for each of the highly polymorphic microsatellites were homogenous at all levels of sample partitioning and contrasted sharply with the instances of both weak and strong regional phylogeographic assortment of mtDNA haplotypes. These contrasting results between different genomic markers were examined in relation to the species life history, and to differences in mutational rate and inheritance of the genetic markers. Several hypotheses may explain the disparity, however it is most likely that rampant homoplasy and high rates of mutation at the microsatellite in conjunction with large Ne at locations may be concerted to delay equilibrium between genetic drift and migration among populations at these highly polymorphic nuclear markers. There was also no evidence that alleles at microsatellite loci were co-segregated with mtDNA clades and therefore no evidence of segregated breeding between the clades of crabs. Whether or not this result was also driven by homoplasy at the microsatellites remains unknown. Recently established mud crab populations (~ 3-4 years old) observed in a number of southwest Australian estuaries are almost 1000 kilometres south of their previously recorded distribution on the Western Australian coast. Colonisation of the southwest region may have occurred either by a natural range expansion from northwest Australian mud crab populations or by means of translocation from any number of mud crab sources within the Indo - West Pacific. I used mtDNA analysis to verify the species and determine the potential source population(s) of the colonists, by comparing sampled genetic material from the southwest (N = 32) against that previously described for the genus. I also compared levels of diversity at mtDNA and two microsatellite loci between the colonist and suspected source population(s) to qualitatively determine if the southwest populations experienced reductions in genetic diversity as a result of the colonisation process. All colonist samples had S. serrata mtDNA COI sequences identical to one previously described as both prevalent and endemic to northwest Australia. High levels of genetic diversity among source and colonist populations at two microsatellite loci contrasted to the mitochondrial locus which displayed an absence of variation among colonists compared to moderately diverse source populations. I argued that the southwest was recently colonised by large numbers of S. serrata propagules derived from the northwest of Australia, possibly due to an enhanced recruitment event coinciding with the reported strengthening of the Leeuwin Current during 1999. Contrasting levels of diversity among nuclear and mitochondrial loci may be attributed to a difference in response by the two genomes to the colonisation process. I predict that such differences may be generally prevalent among plankton-dispersed species. Finally, I discuss aspects of the species distribution and biogeography obtained as a composite of the various results and ideas expressed in this thesis. I propose that S. serrata populations in the IWP may have experienced several cycles of extinction and population retraction from temperate areas followed by subsequent periods of colonisation and rapid coastal expansion in response to the effects of glacial episodes on coastal habitats in the IWP. I propose that persistence of this species as remnant populations of clade 1 and 2 crabs at equatorial locations during low sea level stands provided source populations for later expansions by the species into a variety of coastal areas throughout the IWP. Further analysis is required to determine if mtDNA clade 1 and 2 crabs are non-interbreeding species of mud crab.

It is often hypothesised that marine species with mobile planktonic phases are capable of widespread dispersal and may therefore be genetically homogenous throughout their distribution. Studies that have demonstrated positive correlation between duration of plankton phase and levels of gene flow reinforce the prediction that life history characteristics of marine species determine the potential extent of genetic and demographic connectivity throughout their distributions. This prediction has however been challenged by studies that have employed genetic markers highly sensitive to both historical and contemporary demographic changes. Disparities between dispersal potential and measured levels of gene flow have been demonstrated both among historically disconnected ocean basins and within semi-enclosed areas of strong hydraulic connectivity. These studies and others highlight a need for greater focus on factors that may influence population structure and distribution for marine species. In this thesis, I have examined genetic structure within and among populations of an estuarine species of mud crab Scylla serrata (Forskal, 1775) using a number of genetic markers and methods. The species is widely distributed throughout mangrove and estuarine habitats of the Indo - West Pacific (IWP); it is generally assumed that life-history characteristics of S. serrata promote high levels of population admixture and gene flow throughout its distribution. Alternatively, factors that have promoted population genetic structure for a variety of IWP marine species may also have affected S. serrata populations. By investigating genetic structure at several spatial scales of sampling, I was able to address a variety of hypotheses concerning the species distribution, dispersal, and genetic structure. Episodic changes to marine habitat and conditions experienced within the IWP during the Pleistocene may have affected genetic structure for a broad variety of marine taxa. The relative strength of this hypothesis may be assayed by comparative genetic studies of widespread IWP taxa with high dispersal capacity. In order to ascertain levels of historical and contemporary gene flow for S. serrata, I investigated the phylogeographic distribution of mitochondrial DNA haplotypes sampled throughout the species range. Adults were sampled from three west Indian ocean locations (N=21), six west Pacific sites (N=68), and two sites from northern eastern Australia (N=35). Temperature gradient gel electrophoresis and sequencing of 549 base pairs of the mitochondrial cytochrome oxidase I (COI) coding gene identified 18 distinct haplotypes. Apart from that seen in northern Australia, haplotype diversity was low (h < 0.36) at each of the locations. Total nucleotide diversity in the entire sample (excluding northern Australian locations) was also low (p = 0.09). Haplotypes clustered into two clades separated by approximately 2% sequence divergence. One clade was widespread throughout the IWP (clade 1) whereas the other was strictly confined to northern Australia (clade 2). Genealogical assessment of sequenced haplotypes relative to their distributions suggested that a historical radiation of clade 1 S. serrata throughout the IWP occurred rapidly and recently (<1Myr bp) from a west Pacific origin. The evidence of fixed unique haplotypes at the majority of locations suggested that contemporary maternal gene flow between trans-oceanic sites was limited. Contrary to reports for other widespread species of IWP taxa, there was no evidence of lengthy periods of regional separation between Indian from Pacific Ocean populations. However, results may indicate a separation of northern Australian crabs from other locations before and during the IWP radiation. I speculated that this isolation might have resulted in the formation of a new species of Scylla. Additional sampling of mud crabs from the Australian coastline allowed an examination of the diversity and distribution of clade 1 and 2 haplotypes among recently formed shelf-connected coastal locations, and across a historical bio-geographic barrier. Over 300 individuals were sampled from multiple locations within coastal regions (western, northern and eastern) of Australia and analysed for mutational differences at the COI gene. Analysis of molecular variance partitioned by sampling scale (Among regions, within regions, and within all locations) indicated mitochondrial haplotypes were structured regionally (P < 0.001), which contrasted with evidence of genetic panmixia within regions. Regional genetic structure broadly correlated with hydrological circulation, supporting the contention that release and transport of propagules away from the estuary may allow genetic connectivity among widespread shelf-connected S. serrata populations. That similar patterns of maternal gene flow were absent among trans-oceanic populations may indicate that the spatial scale of effective dispersal for this species is generally limited to areas of coastal shelf. The two clades of haplotypes were geographically separated either side of the Torres Strait, a narrow sea channel connecting the northern and eastern regions of coastal Australia. This pattern of historical genetic separation was concordant with a number of other marine species across northern Australia, and might indicate a shared history of vicariance induced by eustasy. Alternatively, differences in diversity and distribution of the clades may be evidence of two independent expansions of clade 1 and 2 crab populations into Australian regions following post-glacial estuary formation. Overall, despite evidence of genetic panmixia within extensive sections of the Australian distribution, there was also evidence of significant barriers to maternal gene flow with both shallow and deep regional phylogeographic assortment of mtDNA haplotypes. The presence of these barriers indicated both historical and contemporary factors have imposed limits to effective dispersal by this species among coastal habitats. A subset of the Australian sample (8 locations, N = 188) was also examined for variation at five microsatellite loci developed specifically here for S. serrata. I examined variation among samples at each of the loci to: a) independently verify regional structure among crab populations previously detected using the mtDNA analysis; b) test for evidence of co-distributed non-interbreeding stocks of S. serrata within Australian waters by examining samples for segregation of alleles within microsatellite loci concordant with the two mtDNA clades. The frequency and distribution of alleles for each of the highly polymorphic microsatellites were homogenous at all levels of sample partitioning and contrasted sharply with the instances of both weak and strong regional phylogeographic assortment of mtDNA haplotypes. These contrasting results between different genomic markers were examined in relation to the species life history, and to differences in mutational rate and inheritance of the genetic markers. Several hypotheses may explain the disparity, however it is most likely that rampant homoplasy and high rates of mutation at the microsatellite in conjunction with large Ne at locations may be concerted to delay equilibrium between genetic drift and migration among populations at these highly polymorphic nuclear markers. There was also no evidence that alleles at microsatellite loci were co-segregated with mtDNA clades and therefore no evidence of segregated breeding between the clades of crabs. Whether or not this result was also driven by homoplasy at the microsatellites remains unknown. Recently established mud crab populations (~ 3-4 years old) observed in a number of southwest Australian estuaries are almost 1000 kilometres south of their previously recorded distribution on the Western Australian coast. Colonisation of the southwest region may have occurred either by a natural range expansion from northwest Australian mud crab populations or by means of translocation from any number of mud crab sources within the Indo - West Pacific. I used mtDNA analysis to verify the species and determine the potential source population(s) of the colonists, by comparing sampled genetic material from the southwest (N = 32) against that previously described for the genus. I also compared levels of diversity at mtDNA and two microsatellite loci between the colonist and suspected source population(s) to qualitatively determine if the southwest populations experienced reductions in genetic diversity as a result of the colonisation process. All colonist samples had S. serrata mtDNA COI sequences identical to one previously described as both prevalent and endemic to northwest Australia. High levels of genetic diversity among source and colonist populations at two microsatellite loci contrasted to the mitochondrial locus which displayed an absence of variation among colonists compared to moderately diverse source populations. I argued that the southwest was recently colonised by large numbers of S. serrata propagules derived from the northwest of Australia, possibly due to an enhanced recruitment event coinciding with the reported strengthening of the Leeuwin Current during 1999. Contrasting levels of diversity among nuclear and mitochondrial loci may be attributed to a difference in response by the two genomes to the colonisation process. I predict that such differences may be generally prevalent among plankton-dispersed species. Finally, I discuss aspects of the species distribution and biogeography obtained as a composite of the various results and ideas expressed in this thesis. I propose that S. serrata populations in the IWP may have experienced several cycles of extinction and population retraction from temperate areas followed by subsequent periods of colonisation and rapid coastal expansion in response to the effects of glacial episodes on coastal habitats in the IWP. I propose that persistence of this species as remnant populations of clade 1 and 2 crabs at equatorial locations during low sea level stands provided source populations for later expansions by the species into a variety of coastal areas throughout the IWP. Further analysis is required to determine if mtDNA clade 1 and 2 crabs are non-interbreeding species of mud crab.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies
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Managed Pressure Drilling now at the pinnacle of the 'Oil Well Drilling' evolution tree, has itself been coined in 2003. It is an umbrella term for a few new drilling techniques and some preexisting drilling techniques, all of them aiming to solve several drilling problems, including non-productive time and/or drilling flat time issues. These techniques, now sub-classifications of Managed Pressure Drilling, are referred to as 'Variations' and 'Methods' of Managed Pressure Drilling. Although using Managed Pressure Drilling for drilling wells has several benefits, not all wells that seem a potential candidate for Managed Pressure Drilling, need Managed Pressure Drilling. The drilling industry has numerous simulators and software models to perform drilling hydraulics calculations and simulations. Most of them are designed for conventional well hydraulics, while some can perform Underbalanced Drilling calculations, and a select few can perform Managed Pressure Drilling calculations. Most of the few available Managed Pressure Drilling models are modified Underbalanced Drilling versions that fit Managed Pressure Drilling needs. However, none of them focus on Managed Pressure Drilling and its candidate selection alone. An 'Managed Pressure Drilling Candidate Selection Model and software' that can act as a preliminary screen to determine the utility of Managed Pressure Drilling for potential candidate wells are developed as a part of this research dissertation. The model and a flow diagram identify the key steps in candidate selection. The software performs the basic hydraulic calculations and provides useful results in the form of tables, plots and graphs that would help in making better engineering decisions. An additional Managed Pressure Drilling worldwide wells database with basic information on a few Managed Pressure Drilling projects has also been compiled that can act as a basic guide on the Managed Pressure Drilling variation and project frequencies and aid in Managed Pressure Drilling candidate selection.

Abstract Managed Pressure Drilling (MPD) has been used on multiple projects by several operators in different regions of North America to drill through formations that had ultra-narrow (or conventionally undrillable) pressure windows. As illustrated by the case studies discussed here, a combination of Constant Bottomhole Pressure (CBHP) MPD, Anchor Point MPD, and Pressurized MudCap Drilling (PMCD) MPD variations helped drill through several of these formations, trip in and out safely, log and core hole-sections, and run liner or casing to the target depth and cement it in place. Thus, MPD successfully enabled the operators to tap into these otherwise unattainable reserves. Typical challenges include formation/wellbore instability, shallow-water flows, over-pressured formations, low FIT/LOT, fracture pressure/wellbore strength regression, and moderate to severe losses. A few anomalous formations with uncertain pressure regimes resulted in severe to total losses on one well, while an adjacent well drilled at similar depths resulted in high-pressure influxes with ensuing well-control consequences. A detailed evaluation of historical data, comprehensive hydraulic analysis, appropriate MPD design and planning, and use of technologically advanced, reliable, efficient, and well-maintained equipment were critical factors that led to the success of these MPD projects. Above all, utilizing knowledgeable, experienced, and well-trained MPD personnel helped integrate MPD with the existing rig systems and teams and consistently solve the seemingly insurmountable drilling challenges safely and reliably.

Abstract Drilling for oil and gas wells is considered as a risk factor that is perceived as tolerable. As drilling companies expand into harsh environments and farther depth, the probability of a potential failure increases. An unexpected influx to or from the wellbore might be disastrous if not handled properly. Drilling-related issues such as jammed pipes, lost circulation, and high mud costs demonstrate the need for improved drilling technologies. The goal is to limit annular frictional pressure losses, especially in fields where the pore pressure and fracture pressure gradient are too close together. If these issues can be resolved, the economics of drilling wells would increase, allowing the industry to drill previously uneconomical wells. Managed Pressure Drilling (MPD) is a unique approach that allows the control of annular frictional pressure losses and can solve these types of drilling challenges. The industry is still mostly unaware of the entire range of advantages. Prompt detecting and handling of an influx of formation fluids can have the possibility to reduce the magnitude and extent of a kick by operating on a faster time scale with greater precision. Constant Bottomhole Pressure (CBHP), Pressurised Mudcap Drilling (PMCD), and Dual Gradient Drilling (DGD) are a few MPD variants. MPD reduces drilling issues and increases the economics of drilling wells. This research focuses on strategies employed in MPD, with the goal of uncovering some of the less well-known and thus underappreciated possibilities.

Abstract Drilling the Point Pleasant-Utica formation in the Appalachian Basin has posed challenges to most operators, especially in Western Pennsylvania. A recent well drilled in this region demonstrated that with proper buy-in from the Operator, Constant Bottomhole Pressure (CBHP) Managed Pressure Drilling (MPD) could be the answer when planned and executed correctly. This paper drives the point that MPD is more than simply dropping chokes on location. Prior to drilling the well, the Operator initiated the communication very early with the MPD service provider and created an avenue to reduce the projected mud weight and develop a detailed CBHP MPD plan with a Pressurized Mudcap Drilling (PMCD) contingency. The anticipated challenges on this well were: High-pressure gas fractures, formation instability/shale breakout, severe/total loss of returns, inability to reach Target Depth, and casing/cementing issues. The Operator took time and worked with the new MPD service provider to carefully design and plan a new well (referred to as ‘Y1’ in this document), which helped execute the MPD part of the project within 30 days. In contrast, the MPD execution on a previous well (referred to as ‘X2’ in this document) with the older MPD service provider took more than 90 days. MPD execution on the new MPD well included dynamic influx management and loss mitigation, and understanding of the petro-physical conditions to reach the target. The significant factors that helped drill this well safely with a low Non-Productive Time (NPT) are excellent safety culture, communication, high quality and well-maintained MPD equipment, and a very knowledgeable and highly experienced MPD team. This project was finished within half of the budgeted Authorization for Expenditure (AFE), setting milestones in this region for this Operator.