Academic literature on the topic 'Scylla serrata'

ABSTRAK : Kepiting bakau (Scylla serrata) adalah jenis kepiting yang hidup di perairan pantai, tambak, dan hutan bakau (mangrove). Kepiting bakau (Scylla serrata) merupakan komoditas ekspor bernilai ekonomis tinggi yang sangat potensial untuk dikembangkan dan memiliki nilai ekonomis yang tinggi di Indonesia, terutama kepiting yang sudah dewasa serta gemuk. Tujuan penelitian ini adalah untuk mengetahui karakteristik morfometrik kepiting bakau (Scylla serrata) seperti kelimpahan relatif kepiting bakau (Scylla serrata), distribusi lebar karapas, dan hubungan lebar karapas – berat kepiting bakau (Scylla serrata). Analisis yang digunakan dalam penelitian ini yaitu kelimpahan realatif kepiting dan analisis regresi. Penelitian ini dilaksanakan pada bulan Februari – April 2019 di Kecamatan Wedung, Demak. Materi yang digunakan pada penelitian ini adalah sampel kepiting bakau (Scylla serrata) hasil tangkapan nelayan di daerah tersebut. Kepiting bakau hasil tangkapan nelayan tersebut dihitung jumlahnya, diidentifikasi jenis kelaminnya, diukur lebar karapas dan ditimbang beratnya. Hasil penelitian menunjukkan bahwa Kepiting bakau (Scylla serrata) yang tertangkap pada bulan Februari – April 2019 diperoleh 300 individu yang terdiri dari 202 jantan dan 98 betina. Rata – rata ukuran lebar karapas tertinggi berkisar 9.8 cm pada hasil tangkapan di bulan Februari. Hubungan lebar karapas – berat Kepiting bakau (Scylla serrata) baik jantan maupun betina menunjukkan pola pertumbuhan allometrik negatif. ABSTRACT : Giant mud crab (Scylla serrata) are types of crabs that live in coastal waters, ponds, and mangrove forests. Giant mud crab (Scylla serrata) is a high economic value export commodity that has the potential to be developed and has high economic value in Indonesia, especially crabs that are mature and fat. The purpose of this study was to determine the morphometric characteristics of giant mud crab (Scylla serrata) such as relative abundance of giant mud crab (Scylla serrata), carapace width distribution, and the relationship between carapace width - weight of giant mud crab (Scylla serrata). The analysis used in this study is the relative abundance of giant mud crab and regression analysis. This research was conducted in February - April 2019 in the subdistrict of Wedung, Demak. The material used in this study was a sample of giant mud crab (Scylla serrata) from the fishermen catch in the area. The giant mud crab captured by the fishermen are counted, identified by sex, measured in carapace width and weighed. The results showed that giant mud crab (Scylla serrata) caught in February - April 2019 obtained 300 individuals consisting of 202 males and 98 females. The highest average carapace width ranges from 9.8 cm in catches in February. Relationship between carapace and weight of giant mud crab (Scylla serrata) both male and female showed negative allometric growth patterns.

Peraturan Menteri Kelautan Perikanan RI nomor 1 Tahun 2015 menetapkan ukuran lebar karapas untuk Kepiting Bakau (Scylla serrata) layak tangkap minimal 15 cm. Konstruksi trap yang digunakan untuk menangkap Scylla serrata di perairan Rembang memberikan peluang tertangkapnya stadia juvenille (< 10 cm CW). Trap dengan inovasi celah pelolosan diasumsikan dapat meloloskan Scylla serrata stadia juvenille. Desain celah pelolosan berbentuk segi empat terletak sepanjang bagian sisi bawah trap dengan ukuran tinggi 3 cm, memberikan hasil tangkapan Scylla serrata yang terkecil berukuran lebar karapas rata-rata 8,3 cm dibandingkan tanpa celah pelolosan dengan ukuran terkecil lebar karapas rata-rata 5,3 cm. Tertangkapnya Scylla serrata dengan desain trap bercelah pelolosan < 10 cm CW (stadia juvenille) mengindikasikan bahwa populasi biota tersebut di perairan Rembang berukuran kecil pada saat dilakukannya penelitian pada bulan April sampai dengan Juni 2016. Regulation of the Minister of Marine and Fisheries of the Republic of Indonesia No. 1 / 2015 set the legal size of Mud crab (Scylla serrata) at least 15 cm carapace width. The trap construction used to capture Scylla serrata in Rembang waters provides an opportunity for capturing juvenile stadia (<10 cm carapace width/CW). The innovation of trap with the escape gap is assumed to pass Scylla serrata juvenille stadia. The design escape gap of a rectangular is located along the underside of the trap with a height of 3 cm, giving the smallest Scylla serrata catches the width of an average carapace by 8.3 cm compared with no escape passes with the smallest size of the average carapace width of 5.3 cm. The capture of Scylla serrata with the trap design of a 10 cm CW (juvenile stadia) trap indicates that the biota population in Rembang waters is small in the case of a study in April to June 2016.

Mud crab (Scylla serrata) is a ten-legged crustacean animal from Brachura infraordo, known to have a very short tail (in Greek: brachy = short, ura = tail). Mangrove crab is one of the aquatic biota that has significant economic value and its life is strongly influenced by the existence of mangrove forest. The purpose of this study is to identify and analyze the relationship of weight and growth patterns of mangrove crab (Scylla serrata). Sampling is obtained by catching activities using fishing gear that is bubu (chang). Based on the results of research conducted in the area of Mangrove Forest around Wet Laboratory Faculty of Fisheries and Marine Sciences, Likupang Timur in August - September 2017. Mangrove crab (Scylla serrata) in the can through research obtained as many as 32 individuals.Keywords: Mangrove Crab (Scylla serrata), Long Weight Relation, Growth Pattern, East Likupang ABSTRAKKepiting bakau (Scylla serrata) adalah binatang anggota crustasea berkaki sepuluh dari infraordo Brachura, yang dikenal mempunyai ekor yang sangat pendek (dalam bahasa Yunani : brachy = pendek, ura = ekor). Kepiting bakau adalah salah satu biota perairan yang bernilai ekonomis penting dan kehidupannya sangat dipengaruhi oleh keberadaan hutan mangrove. Adapun tujuan dari penelitian ini yaitu untuk mengidentifikasi dan menganalisis hubungan panjang berat berserta pola pertumbuhan dari kepiting bakau (Scylla serrata). Pengambilan sampel diperoleh dengan melakukan kegiatan penangkapan menggunakan alat tangkap yaitu bubu (chang). Berdasarkan hasil penelitian yang dilakukan di Daerah Hutan Mangrove sekitar Laboratorium Basah Fakultas Perikanan dan Ilmu Kelautan, Likupang Timur pada bulan Agustus – September 2017. Kepiting bakau (Scylla serrata) yang di dapat selama melalukan penelitian diperoleh sebanyak 32 individu. Kata Kunci : Kepiting Bakau (Scylla serrata), Hubungan Panjang Berat, Pola Pertumbuhan, Likupang Timur.

Mangrove crab (Scylla serrata) is one of the prima donna sources of protein caught by fishermen around mangrove forest waters in the waters of the Barumun River Estuary, Labuhanbatu Regency. This study aims to inform about condition factors, growth patterns of crab populations, and reproductive aspects in the form of abundance of Gonad Maturity Level (TKG). Determination of 3 sampling points is done by using purposive random sampling method. Scylla serrata sampling was carried out using Bubu. Data analysis presents information on the abundance of gonadal maturity level, growth pattern, and Fulton condition factor (K), which is presented quantitatively. The results showed that male and female Scylla serrata growth patterns were categorized as negative allometric b < 3, with carapace width growth being faster than weight gain. Fulton condition factor (K) values obtained ranged from 50.14-132.75 for male Scylla serrata, and female ranged from 80.34-123.94. The gonadal maturity level of Scylla serrata was dominated by TKG II crabs, and the lowest abundance of gonad maturity was in TKG IV crabs. This indicates that, in December-February, the condition of the Scylla serrata population around the mangrove forest waters of the Barumun river estuary, is predicted to be in the stage of adult dominance that is ready to reproduce and prepare to spawn.

Research has been carried out on the intensity and prevalence of ectoparasites in mud crabs (Scylla serrata) in the brackish waters of Cadek Village, Baitussalam District, Aceh Besar in November to December 2020. The purpose of this study was to determine the types of types of ectoparasites, prevalence and intensity found in mud crab (Scylla serrata) in Cadek Village, Baitussalam District, Aceh Besar District. Sampling conducted randomly and the data were analyzed descriptively in the form of tables and figures. The results showed that the types of ectoparasites that infect crabs mangroves in the brackish waters of Cadek Village, namely Octolasmis and Zoothamnium sp. Value prevalence of ectoparasites infesting Scylla serrata in the brackish waters of Cadek. Village is Zoothamnium sp. 40% and Octolasmis sp. 90% are included in the category of parasites it almost always infests Scylla serrata. The intensity value of the type of ectoparasites Infesting Scylla serrata in the brackish waters of Cadek Village is Zoothamnium sp. 6.75 parasite/tail and Octolasmis sp. 69 parasites/tails that fall into the category of infestation very heavy.

Labuhan Bahari Belawan Medan merupakan sebuah pulau yang terletak di Selat Malaka, Sumatera Utara. Salah satu sumberdaya perikanan di perairan tersebut adalah kepiting bakau, namun informasi mengenai kepiting bakau pada daerah ini masih kurang terutama jenis spesiesnya. Tujuan dari penelitian yang dilaksanakan pada bulan Januari-Februari 2012 ini adalah untuk mengetahui jenis dan morfologi kepiting bakau, kelimpahan yang mendominasi, dan mengetahui ekonomi kepiting bakau di perairan Labuhan Bahari Belawan Medan. Kepiting yang diteliti adalah kepiting bakau yang tertangkap di wilayah mangrove dan sekitar tambak yang ditumbuhi mangrove. Sampling dilakukan dengan alat tangkap bubu oleh masyarakat sekitar dinamakan bubu planet. Kepiting yang tertangkap diidentifikasi dan dilakukan pengukuran morfometrik kemudian menganalisa data yang didapatkan, dan wawancara nelayan untuk mengetahui nilai ekonomi kepiting bakau tersebut. Jumlah spesies kepiting bakau yang ditemukan adalah 3 spesies yaitu Scylla tranquebarica, Scylla serrata dan Scylla paramamosain, dengan kelimpahan yang mendominasi adalah Scylla tranquebarica sebesar 54,72%, Scylla paramamosain sebesar 33,96%, dan Scylla serrata sebesar 11,32% di stasiun I (di kawasan mangrove), sedangkan di stasiun II (di luar kawasan mangrove) Scylla serrata 45,76%, Scylla tranquebarica sebesar 33,98%, dan Scylla paramamosain sebesar 15,25%. Kepiting bakau yang biasanya dipasarkan adalah kepiting yang memiliki berat ≥200 gram per ekor baik jantan maupun betina.

Kepiting bakau (Scylla serrata) merupakan salah satu spesies kunci dalam ekosistem mangrove yang memegang peranan yang sangat penting. Hutan mangrove yang ada di Kelurahan Belawan Sicanang sudah banyak mengalami konversi lahan seperti tambak dan pemukiman. Kondisi ini menyebabkan terjadinya penurunan kualitas habitat dan penurunan populasi untuk sumberdaya kepiting bakau akibat terjadinya kerusakan daerah asuhan dan mencari makan biota ini. Penelitian ini bertujuan untuk mengetahui kondisi ekologi mangrove, untuk mengetahui kelimpahan kepiting bakau (Scylla serrata), untuk mengetahui pertumbuhan kepiting bakau (Scylla serrata) di Hutan Mangrove Kelurahan Belawan Sicanang Kecamatan Medan Belawan Provinsi Sumatera Utara. Penelitian berlangsung pada Mei - Juni 2016. Metode yang digunakan dalam penentuan lokasi adalah purposive sampling dan dibagi menjadi 3 stasiun berdasarkan aktivitas yang berbeda. Struktur populasi kepiting bakau (Scylla serrata) ditinjau dari kelimpahan kepiting bakau (Scylla serrata), hubungan lebar karapas dengan bobot tubuh, pola pertumbuhan, dan faktor kondisi. Kualitas habitat kepiting bakau (Scylla serrata) dilihat dari kualitas air, tekstur substrat, C-organik, dan pasang surut. Hasil menunjukkan bahwa kelimpahan kepiting bakau (Scylla serrata) 16300 - 17000 ind/ha, dengan pola pertumbuhan allometrik negatif (b<3), faktor kondisi berkisar antara 0 - 1 yang tergolong ke dalam pipih atau tidak gemuk. Kualitas air dan substrat yang dikaji termasuk ke dalam kualitas air yang menunjang kehidupan kepiting bakau (Scylla serrata), tekstur substrat yaitu lempung berpasir dan lempung liat berpasir, serta C-organik < 1% tergolong sangat rendah, dimana tipe pasang surutnya adalah mixed prevailing semidiurnal.Mangrove crab (Scylla serrata) is one of the keystone species in the mangrove ecosystem, which had a very important role. Mangrove forests existed in Village Belawan Sicanang have been many experienced land conversion as embankment and settlements. These conditions led to degradation in habitat quality and population decline for mangrove crab due to the occurrence of the damage to the nursery ground and the feeding ground. The research aimed to determine abundance mangrove crabs and to determine the growth of mangrove crab. The research took place in May - June 2016. The method used in the determination of the location is purposive sampling and divided into 3 stations based on different activities. The mangrove crab population structure in terms of the abundance of mangrove crab, carapace width relation with body weight, growth pattern, and factor condition. The quality habitat mangrove crab viewed the water quality, the substrate texture, C-organic, and tides. The results showed that the growth pattern was negative allometric (b < 3), factor condition ranges between 0 - 1 which classified into flat or not fat. The water quality and substrate were assessed included in the water quality that supported life mangrove crab, the substrate texture was sandy loam and sandy clay loam, C-organic classified < 1% was very low, the type of tides was mixed semidiurnal prevailing.

Penelitian ini bertujuan untuk mengetahui jenis ektoparasit yang menyerang ketiting bakau (Scylla serrata) dan untuk mengetahui tingkat intensitas, prevalensi dan dominasi ektoparasit yang teridentifikasi. Metode yang digunakan dalam penelitian ini adalah metode survei dengan teknik pengambilan sampel yang digunakan untuk menginventarisasi parasit yang ditemukan pada kepiting bakau (Scylla serrata). Metode pengambilan data dilakukan dengan metode observasi lapangan yang dilakukan pada daerah pertambakan masyarakat Desa Segintung. Sampel yang diambil berupa kepiting bakau yang masih hidup sebanyak 100 ekor. Pengamatan ektoparasit dilakukan dengan metode smear dibagian eksternal kepiting bakau (Scylla serrata) yaitu bagian karapaks, kaki jalan, kaki renang dan insang. Penelitiaan ini dilaksanakan pada bulan oktober – november 2018. Parameter yang diamati dalam penelitian ini meliputi prevalensi, intensitas dan dominasi ektoparasit pada kepiting bakau (Scylla serrata) dan data hasil penelitian dianalisa secara deskriftif Hasil penelitian menunjukan bahwa terdapat 4 jenis ektoparasit pada kepiting bakau (Scylla serrata) yaitu Octolasmis sp, Vorticella, Zoothamnium, dan Epistylis sp. Parasit Octolasmis sp. hanya menyerang bagian insang saja. Zoothamnium sp menyerang bagian karapaks dan insang. Vorticella sp dan Epistylis sp menyerang semua bagian mikrobahitat yang diamati pada penelitian ini (kaki jalan, kaki renang, karapaks dan insang). Jumlah parasit terbanyak ditemukan pada bagian karapaks yaitu 658 individu. intensitas serangan parasit tertinggi yang menyerang kepiting bakau adalah parasit Zoothamnium sp dengan intensitas serangan sedang. Prevalensi tertinggi terdapat pada parasit Octolasmis sp dengan nilai prevalensi sebesar 0.62%. Parasit yang menyerang kepiting bakau didominasi oleh parasit Epistylis sp yaitu dengan nilai dominasi sebesar 46.05%

The purpose of this study was to identify the morphometric characters of mangrove crabs Scylla spp. and to grow them on the island of Para Sangihe Islands Regency, North Sulawesi Province. There were 2 types of crabs found during crab’s collection. However, the most abundant one was Scylla serrata while the olivacea is only one tail. The results of this study indicate that mangrove crabs that were kept for 2 weeks feed on trash fish three times a day experience growth. Based on the results of the study, it can be concluded that: the type of crab found on Pulau Para, Tatoareng District, Sangihe Islands Regency, North Sulawesi Province were mostly S. serrata (34 tails) and one tail of S. olivacea. The fattening of mangrove crabs showed results on the body weight and carapace length.Further research on mangrove crabs needs to be done on different aspects such as preferable food and time of the abundancy.Keywords: Crab, Scylla spp., identification, fattening. ABSTRAK Tujuan dari penelitian ini adalah untuk mengidentifikasi karakter morfometrik kepiting bakau Scylla spp dan cara penggemukannya di Pulau Para Kabupaten Kepulauan Sangihe Provinsi Sulawesi Utara. Dua jenis kepiting bakau ditemukan saat pengumpulan data, namun yang ditemukan paling banyak adalah Scylla serrata, sedangkan S. olivacea hanya 1 ekor saja.Hasil penelitian ini menunjukan bahwa kepiting bakau yang dipelihara selama 2 minggu dengan diberi pakan ikan rucah sebanyak tiga kali sehari mengalami pertumbuhan. Berdasarkan hasil penelitian dapat disimpulkan bahwa: jenis kepiting yang ditemukan di Pulau Para Kecamatan Tatoareng Kabupaten Kepulauan Sangihe Provinsi Sulawesi Utara adalah Scylla serrata (34 ekor) dan S. olivacea (1 ekor). Penggemukan kepiting bakau dengan pakan ikan rucah tiga kali sehari menunjukan adanya pertumbuhan berat badan dan panjang lebar karapas. Penelitian lanjutan tentang kepiting bakau perlu dilakukan untuk melihat berbagai aspek seperti makanan kesukaan dan waktu kelimpahanya.Kata kunci : Kepiting, Scylla spp, identifikasi, penggemukan.

The study of population biology of mud crab Scylla serrata is necessary to analyse the population dynamics, such as growth of crabs, size distribution, mortality and exploitation rates of S. serrata. Population biology data collection was carried out from March to June 2016 at estuary and silvofishery areas of three stations (Mayangan, Tanjung Tiga and Blanakan villages). Data were analyzed using analytical methods of FISAT-II (FAO-ICLARM Stock Assessment Toool II)instruments. The results showed the growth of S. serrata male in Subang distric was positive allometric and the female was negative allometric. Growth coefficient (K) ranged from 0.21 to 0.43 in the estuary and from 0.28 to 0.89 in silvofishery area. Exploitation rate in the silvofishery area has been above the maximum exploitation rate. The size distribution of S. serrata in Subang district has the highest frequency at class interval of 106-110 mm (male) and of 101-105 mm. The highest abundance of mature female crabs is in May.Keywords : population biology, Scylla serrata, Subang District

The edible mud crab, genus Scylla, is important to fisheries and aquaculture throughout the Indo Pacific region, but its taxonomic status has been confused for decades and a new classification has only recently been proposed. This project was undertaken to investigate the species status of mud crabs in Southeast Asia, with a view to deciding whether two sympatric morphs of Scylla found in Ban Don Bay, Surat Thani Province, Thailand, are two separate species. A further aim was to elucidate any possible pre-zygotic reproductive isolating mechanisms (RIMs) and ecological features that maintain the apparent sympatry between these two morphs. Mud crabs were collected from a primary site (Surat Thani, Thailand) as well as from six other locations in Thailand, Vietnam, Malaysia and Bangladesh. Crab samples from the latter sites were used selectively to provide a comparison to the primary study site. Descriptive taxonomy, multivariate morphometrics and allozyme electrophoresis were used to a) determine the number of species present within the crab samples collected; b) to ascertain which species they represent; c) to discover any geographical variation between locations sampled; d) to produce a possible phylogeny that summaries the relationship between Scylla species; and e) to look for pre-zygotic RIMs to explain the sympatry of the two morphs in Surat Thani. Findings from the present study reinforce the recent revision of the taxonomy of the genus Scylla into four species, S. serrata, S. olivacea, S. tranquebarica and S. paramamosain and provides new information on two of the four species which are dominant within Southeast Asia, including Ban Don Bay, Surat Thani Province, S. paramamosain and S. olivacea. Population studies showed both genetic and morphological differentiation between conspecific populations of S. paramamosain and S. olivacea, indicating stock structure for each species, although there is some disparity between morphological and genetic distances for S. paramamosain. This is discussed in relation to the effects of larval dispersal mechanisms and the subsequent recruitment of juvenile crabs. Phylogenetic interpretation of both genetic and morphological characters revealed that both S. serrata and S. olivacea are the most diverged of the four Scylla species; however, the direction of evolution is open to interpretation and the evidence for either S. olivacea or S. serrata as the more primitive species are discussed. Reproductive studies on the two mud crab species found in Surat Thani revealed no physical barrier to hybridization. Both species have a protracted breeding season which continues throughout the year. However, the size at first sexual maturity was significantly smaller for S. olivacea when compared to S. paramamosain. This and other potential mechanisms that may maintain these two species sympatrically are discussed. The clarification of four Scylla species, and the establishment of diagnostic genetic and morphological characters that can be used to identify them, means that research can now focus on both the ecology and life history of these closely related species. Such information is needed urgently with respect to fisheries management as well as to understanding the environmental requirements of each species in order to develop their potential for aquaculture.

Mud crabs of the genus Scylla are widely exploited for aquaculture in the Asia- Pacific region. In the current study, a series of in vivo experiments were carried to assess the protein requirement, protein sparing effects of starch and the capacity of Scylla serrata to digest diets that contained different animal and plant-based feed meals and different levels and types of starch. Results from a protein requirement study indicated that juvenile S. serrata fed diets containing 45% or 55% protein demonstrated significantly higher growth responses than those fed the diet containing 25% protein. The subsequent study was carried out to determine if responses to dietary protein could be influenced by using purified wheat, potato, rice or corn starch to manipulate the gross energy level of fishmeal- based diets (18 or 15.5 MJ kg-1), i.e., to see if starch had a protein sparing effect in these animals. Overall, growth responses in this study appeared to be positively correlated with the level of protein in the diet with the highest growth rates achieved using diets containing 45% protein, regardless of the energy level of the diet. In addition, at a dietary protein level of 40% there was no evidence that the source of starch had any significant impact on growth performance or feed utilisation suggesting it had no protein sparing effect. By contrast, it was found that growth of juvenile S. serrata was strongly correlated with the intake of digestible dietary protein. The investigation of the capacity of sub-adult S. serrata to digest different animal and plant- based feed meals showed that apparent dry matter digestibility (ADMD) and apparent gross energy digestibility (AGED) values were not significant different for most selected feed meals (cotton seed, poultry, canola, fishmeal, soybean, and lupin meal). Apparent crude protein digestibility (ACPD) for all test feed meals were relatively high (86-96%). A subsequent study was carried out to determine if purified starch from different sources influenced the digestibility of fishmeal based diets. Overall, most diets containing starch were readily digested by mud crabs. In particular, there were no negative impacts on the digestibility of major nutrients (e.g. protein) observed following the inclusion of wheat, rice or corn starch in formulated feeds. Nevertheless, the apparent starch digestibility (ASD) of wheat starch decreased significantly as the inclusion level was increased from 15% to 60%, although there was no significant effect on ACPD values. At a 30% inclusion level, the ASD of diets containing different starches decreased in the order corn > wheat > potato = rice. Moreover, ACPD values were significantly higher for diets containing corn or rice starch than for those containing wheat or potato starch. The capacity of another species of mud crab commonly exploited for aquaculture in South East Asia, S. paramamosain, to digest the local plant-based ingredients (defatted soybean meal, rice bran, cassava and corn flour) was also conducted in Vietnam. Overall, the findings of this study showed that at a 30% inclusion level diets containing soybean meal or rice bran were well digested by mud crabs. In particular, the ACPD and AGED values for all diets containing soybean meal were not significantly different from the fishmeal based reference diet. Likewise, all digestibility values for the diet containing 30% rice bran were relatively high and not significantly different from the reference diet. By contrast, diets containing cassava flour appeared to be poorly utilised since their digestibility values for all parameters were lower than those from other testingredients. In summary, the apparent digestibility of dry matter, protein and energy was in the following order (from most to least digestible) soybean meal ~ rice bran > corn flour > cassava flour. In the next study the effects of attractants in diets (chicken meal, betaine, tuna oil and bait enhancer), temperature (26.5oC, 28.5oC and 30.5oC), sex (female and male) and size (small, medium and large) on feeding responses of S. serrata were investigated. Significant differences were observed in the behavioral responses of mud crabs to diets containing different attractants. Specifically, consumption of diets with chicken meal or betaine was significantly higher than for other treatments. With the exception of betaine, no significant difference in food consumption was observed when attractant inclusion levels were raised from 2% to 5%. Overall, small crabs consumed significantly more of the ration (as a percentage of body weight) than larger crabs. Temperature showed a significant impact on most behaviour of mud crabs, excepting continuation response and there was some evidence that females were significantly more active than males. Light intensity was considered as a main factor effect to crab response since there were extremely high percentage time of crab spent in half-shaded of the Y –maze which valued at 95.6%, 93.8 and 94.4% (corresponded to small, medium and large size respectively) in comparison to those of crabs spent in the unshaded side. Overall, the findings from these studies demonstrated that mud crabs have a high capacity to digest a range of plant based feed ingredients. In particular, soybean meal appeared to be well digested by both species of mud crabs examined. It was also shown that a range of purified starches were well digested by S. serrata although starch inclusion in diets did not appear to reduce the requirement for protein to promote growth. Subsequent attractant studies demonstrated that chicken meal and betaine produced significantly elevated feeding responses and food consumption when added to diets. Based on these results we propose that these ingredients can be utilised to increase the attractiveness and consumption of artificial mud crab feeds.

Mud crabs of the genus Scylla are widely exploited for aquaculture in the Asia- Pacific region. In the current study, a series of in vivo experiments were carried to assess the protein requirement, protein sparing effects of starch and the capacity of Scylla serrata to digest diets that contained different animal and plant-based feed meals and different levels and types of starch. Results from a protein requirement study indicated that juvenile S. serrata fed diets containing 45% or 55% protein demonstrated significantly higher growth responses than those fed the diet containing 25% protein. The subsequent study was carried out to determine if responses to dietary protein could be influenced by using purified wheat, potato, rice or corn starch to manipulate the gross energy level of fishmeal- based diets (18 or 15.5 MJ kg-1), i.e., to see if starch had a protein sparing effect in these animals. Overall, growth responses in this study appeared to be positively correlated with the level of protein in the diet with the highest growth rates achieved using diets containing 45% protein, regardless of the energy level of the diet. In addition, at a dietary protein level of 40% there was no evidence that the source of starch had any significant impact on growth performance or feed utilisation suggesting it had no protein sparing effect. By contrast, it was found that growth of juvenile S. serrata was strongly correlated with the intake of digestible dietary protein. The investigation of the capacity of sub-adult S. serrata to digest different animal and plant- based feed meals showed that apparent dry matter digestibility (ADMD) and apparent gross energy digestibility (AGED) values were not significant different for most selected feed meals (cotton seed, poultry, canola, fishmeal, soybean, and lupin meal). Apparent crude protein digestibility (ACPD) for all test feed meals were relatively high (86-96%). A subsequent study was carried out to determine if purified starch from different sources influenced the digestibility of fishmeal based diets. Overall, most diets containing starch were readily digested by mud crabs. In particular, there were no negative impacts on the digestibility of major nutrients (e.g. protein) observed following the inclusion of wheat, rice or corn starch in formulated feeds. Nevertheless, the apparent starch digestibility (ASD) of wheat starch decreased significantly as the inclusion level was increased from 15% to 60%, although there was no significant effect on ACPD values. At a 30% inclusion level, the ASD of diets containing different starches decreased in the order corn > wheat > potato = rice. Moreover, ACPD values were significantly higher for diets containing corn or rice starch than for those containing wheat or potato starch. The capacity of another species of mud crab commonly exploited for aquaculture in South East Asia, S. paramamosain, to digest the local plant-based ingredients (defatted soybean meal, rice bran, cassava and corn flour) was also conducted in Vietnam. Overall, the findings of this study showed that at a 30% inclusion level diets containing soybean meal or rice bran were well digested by mud crabs. In particular, the ACPD and AGED values for all diets containing soybean meal were not significantly different from the fishmeal based reference diet. Likewise, all digestibility values for the diet containing 30% rice bran were relatively high and not significantly different from the reference diet. By contrast, diets containing cassava flour appeared to be poorly utilised since their digestibility values for all parameters were lower than those from other testingredients. In summary, the apparent digestibility of dry matter, protein and energy was in the following order (from most to least digestible) soybean meal ~ rice bran > corn flour > cassava flour. In the next study the effects of attractants in diets (chicken meal, betaine, tuna oil and bait enhancer), temperature (26.5oC, 28.5oC and 30.5oC), sex (female and male) and size (small, medium and large) on feeding responses of S. serrata were investigated. Significant differences were observed in the behavioral responses of mud crabs to diets containing different attractants. Specifically, consumption of diets with chicken meal or betaine was significantly higher than for other treatments. With the exception of betaine, no significant difference in food consumption was observed when attractant inclusion levels were raised from 2% to 5%. Overall, small crabs consumed significantly more of the ration (as a percentage of body weight) than larger crabs. Temperature showed a significant impact on most behaviour of mud crabs, excepting continuation response and there was some evidence that females were significantly more active than males. Light intensity was considered as a main factor effect to crab response since there were extremely high percentage time of crab spent in half-shaded of the Y –maze which valued at 95.6%, 93.8 and 94.4% (corresponded to small, medium and large size respectively) in comparison to those of crabs spent in the unshaded side. Overall, the findings from these studies demonstrated that mud crabs have a high capacity to digest a range of plant based feed ingredients. In particular, soybean meal appeared to be well digested by both species of mud crabs examined. It was also shown that a range of purified starches were well digested by S. serrata although starch inclusion in diets did not appear to reduce the requirement for protein to promote growth. Subsequent attractant studies demonstrated that chicken meal and betaine produced significantly elevated feeding responses and food consumption when added to diets. Based on these results we propose that these ingredients can be utilised to increase the attractiveness and consumption of artificial mud crab feeds.

Le crabe de paletuviers scylla serrata f. Est le seul crabe commercialise en nouvelle-caledonie. Son exploitation souleve ainsi frequemment de nombreuses controverses, ce qui a amene le territoire en 1986 a mettre en uvre sur l'ensemble de l'ile une politique de gestion des stocks. Celle-ci supposait d'abord de connaitre la biologie de l'espece et les modalites de son exploitation avant de chiffrer l'etat actuel du stock. Un programme de recherches fut donc mene au centre orstom de noumea de 1986 a 1989. Relevant ainsi principalement d'une etude finalisee vers l'exploitation d'une ressource, il s'est oriente selon deux directions principales: la biologie de l'espece d'une part, les differents aspects de sa pecherie d'autre part. L'etude biologique a permis d'aborder, apres une etude anatomique detaillee, la biometrie, la croissance, l'alimentation, la reproduction et enfin le developpement larvaire de scylla serrata. La pecherie a ete ensuite etudiee: la peche et son evolution ont ete replacees dans le contexte socio-culturel local, deux pecheries ont ete ensuite analysees, permettant l'estimation de biomasses et de rendements; les modalites de la commercialisation et de la distribution entre l'interieur de l'ile et noumea et enfin l'analyse des exportations vers tahiti completent ce volet socio-economique

Commercial farming of mud crab Scylla serrata is a significant industry throughout South East Asia. The limited scientific knowledge of mud crab nutritional requirements and digestive processes, however, is recognised as a major constraint to the future growth of this industry. To better understand the mechanisms of digestion in the mud crab we have analysed the diversity of digestive enzymes from the hepatopancreas. Significant protease, amylase,cellulase and xylanase activities were detected in soluble extracts from this organ. Temperature profiles for all enzymes were basically similar with optimal activities observed at 500C. Examination of pH tolerance revealed optimal activities for protease and amylase at pH 7.0 while optimal activities for cellulase and xylanase were observed at pH 5.5. Under optimum conditions,protease and amylase activities were approximately two orders of magnitude greater than those seen for either cellulase or xylanase. Interestingly, hepatopancreatic extracts were able to liberate glucose from either starch or carboxymethyl (CM)-cellulose suggesting that a range of carbohydrates may be utilised as energy sources. The effects of dietary carbohydrates on feed digestibility, digestive enzyme levels and growth were also studied by inclusion of additional starch or CM-cellulose at the expense of casein in formulated diets. It was shown that amylase, cellulase and xylanase activities in extracts from the hepatopancreas were highest in mud crabs fed diets containing 47% carbohydrate. Based on the findings, we suggest that the ability of the mud crab to modulate digestive enzyme activities may represent a mechanism to maximise access to essential nutrients when the dietary profile changes.

Commercial farming of mud crab Scylla serrata is a significant industry throughout South East Asia. The limited scientific knowledge of mud crab nutritional requirements and digestive processes, however, is recognised as a major constraint to the future growth of this industry. To better understand the mechanisms of digestion in the mud crab we have analysed the diversity of digestive enzymes from the hepatopancreas. Significant protease, amylase,cellulase and xylanase activities were detected in soluble extracts from this organ. Temperature profiles for all enzymes were basically similar with optimal activities observed at 500C. Examination of pH tolerance revealed optimal activities for protease and amylase at pH 7.0 while optimal activities for cellulase and xylanase were observed at pH 5.5. Under optimum conditions,protease and amylase activities were approximately two orders of magnitude greater than those seen for either cellulase or xylanase. Interestingly, hepatopancreatic extracts were able to liberate glucose from either starch or carboxymethyl (CM)-cellulose suggesting that a range of carbohydrates may be utilised as energy sources. The effects of dietary carbohydrates on feed digestibility, digestive enzyme levels and growth were also studied by inclusion of additional starch or CM-cellulose at the expense of casein in formulated diets. It was shown that amylase, cellulase and xylanase activities in extracts from the hepatopancreas were highest in mud crabs fed diets containing 47% carbohydrate. Based on the findings, we suggest that the ability of the mud crab to modulate digestive enzyme activities may represent a mechanism to maximise access to essential nutrients when the dietary profile changes.

The source of a reliable supply of seed is one of the most important factors determining the success of aquaculture. At present mud crab culture is reliant on wild caught juveniles, which limits the expansion of mud crab farming globally. This, coupled with the paucity of knowledge of the spawning and egg characteristics of mud crabs, prompted the investigation into the captive spawning, incubation and egg quality of Scylla serrata in South Africa. A total of 112 mature females were caught from three estuaries in northern KwaZulu Natal and acclimated to captive conditions. Mature females were present in the estuaries throughout the year and ranged from 90 to 200 mm carapace width. Except for 40 crabs all the females spawned in captivity. On average spawning took place 38 ± 23 days after capture but was not dependent on crab size. Fecundity was significantly correlated to crab size (p = 0.026), with larger females producing more eggs. The average fecundity per batch was 5.79 ± 2.07 million eggs. Hatch success rate for all egg batches was high averaging 84 ± 6 %. Egg dropping occurred in all egg batches during incubation. On average 6.5 % of the egg mass was dropped during incubation. At the average temperature of 27⁰C eggs in the incubation system hatched within 292 ± 12 hours after extrusion. In-vitro incubation of eggs proved to be an ineffective means of incubating Scylla serrata eggs with a hatch success rate of only 25 ± 5 %. Egg quality was assessed both directly, using variables such as hatch success rate and hatch synchronicity and retrospectively by using stress tests and comparing survival of larvae from different coloured egg batches. Lipid class composition and fatty acid methyl ester content for 28 batches of eggs and 16 batches of larvae were analyzed. The biochemical composition of the egg was correlated to survival of larvae in the stress tests to ascertain if the lipid content of the eggs determines their quality. Stress tests were used to retrospectively assess egg quality. Four stressors were administered to newly hatched larvae and the LD50 values recorded. An average LD50 of 64 hours was recorded for the starvation tests, 40% for the salinity tests, 37 ppm for the formalin tests and 39.7 mg/l NH3 for the ammonia stress tests was recorded. Egg colour ranged from pale yellow to orange-red. Egg colour was not influenced by female size or the time the females spent in captivity prior to spawning. Egg colour can therefore not be used as an indicator of quality. The lipid profiles of newly extruded eggs had no effect on hatch synchronicity or hatch success rate. However, the stress tests identified female size (p ≤ 0.02), DHA content of the egg (p ≤ 0.02), Σ omega-3 fatty acids of eggs (p ≤ 0.02) and EPA content of eggs (p ≤ 0.007) as possible determinants of egg quality. Larger crabs tended to produce poorer quality eggs. Egg quality also decreased as the amount of DHA, EPA and the Σ omega-3 fatty acids decreased in the eggs. To summarize, the results of this study indicated that the following parameters affect egg quality - crab size, DHA, EPA and Σ omega-3 fatty acid content of eggs.

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
Full Text

Scylla serrata is a portunid crab which can attain a weight of over 2 kg and a carapace width exceeding 250 mm. It is distributed throughout the Indo-West Pacific extending down the east coast of Africa, and both the east and west coasts of Australia. In Australia it is commonly known as the mud crab because it occurs within muddy, mangrove-lined bays and estuaries. Mud crabs are generalist predators eating most small, slow moving animals which they can catch, but they are also vigorous scavengers. Being scavengers, they are readily caught in baited traps set by commercial and recreational fishers, and are the stock for these popular fisheries. Female crabs spawn offshore and larvae spend a period in the plankton where they develop into postlarvae or megalopae...
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment
Science, Environment, Engineering and Technology
Full Text