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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/4884

Title: The ecology and biology of amphioxus in Hong Kong
Other Titles: Xianggang wen chang yu de sheng tai ji sheng wu xue yan jiu
香港文昌魚的生態及生物學研究
Authors: Chen, Yan (陳彥)
Department: Dept. of Biology and Chemistry
Degree: Doctor of Philosophy
Issue Date: 2007
Publisher: City University of Hong Kong
Subjects: Amphioxus -- China -- Hong Kong
Notes: CityU Call Number: QL611.C45 2007
Includes bibliographical references (leaves 236-266)
Thesis (Ph.D.)--City University of Hong Kong, 2007
xxvi, 294 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Amphioxus is regarded as a link from the evolution of marine invertebrates to vertebrates. The present study focused on some aspects of the ecology and biology of amphioxus in Hong Kong, including 1) distribution and abundance; 2) habitat requirements; 3) taxonomy and molecular comparison; 4) growth and reproduction; and 5) food source. Amphioxus was recorded in eastern waters of Hong Kong according to previous benthic surveys, especially close to the Sai Kung Peninsula. In the present study, further surveys were undertaken along the coast of Sai Kung at 34 sites in four bays (Nam She Wan, Tai Long Wan, Long Ke Wan, and Pak Lap Wan) in the winter of 2003 and summer of 2004, to determine the extent of distribution of amphioxus as well as their abundance, habitat preference and community structure. Results showed that amphioxi are present in shallow water depth between 5 and 23 m in all the four bays. High abundance was found at some specific locations in Tai Long Wan and Pak Lap Wan, with a maximum of 460 and 290 ind/m2, respectively. Sediment analysis indicated that amphioxus was only confined to sediments containing a high percentage of sand and granule (73-99%), with a median diameter (Mdφ) varying between -0.75 and 3.18φ, low organic content (< 4%) and low moisture content (17-37%). Further research on the habitat requirements of amphioxus was conducted by monitoring the sediment and water quality at one site in Tai Long Wan and another in Pak Lap Wan from November 2003 to October 2004. Results indicated that seawater at amphioxus habitats had two essential characters: firstly, oceanic (32-36‰); secondly, low content of suspended solids (<13 mg/L). Such findings were consistent with results obtained from laboratory observations: B. belcheri could not survive at low salinity (LC50 at 17.5‰); and high suspended solids in the water could induce physical damages on the oral cirri of B. belcheri. Thus, it can be concluded that clear oceanic water combined with sand sediment with low organic content are the most important habitat requirements for amphioxus. The benthic community associated with amphioxus in the sampling areas of Nam She Wan, Tai Long Wan, Long Ke Wan and Pak Lap Wan was largely dominated by polychaetes, crustaceans (primarily amphipods), bivalve molluscs and echinoderms (mostly brittle starfish). A total of 139 species were recorded. Apart from amphioxus, the dominant species (> 10 ind/ 0.1 m2) included the polychaetes Onuphis eremita, Magelona crenulifrons, Prionospio malmgreni, Eunice indica and Ophelina acuminata, crustaceans (amphipods) Ampelisca brevicornis and Urothoe grmaldii, and the echinoderm (brittle starfish) Amphiodia obtecta. Onuphis eremita and the amphipods Ampelisca brevicornis and Urothoe grmaldii were typical inhabitants of sandy sediments in shallow water depths. While there were spatial groupings of sampling sites based on species composition, seasonal difference was not so pronounced as compared to spatial distribution, especially at the one-year sampling sites in Tai Long Wan and Pak Lap Wan. Sediment analysis showed that the Tai Long Wan sampling site had coarser sediments (Mdφ: -0.35-0.42φ) as compared with that in Pak Lap Wan (Mdφ: 0.38-1.20φ), and both sites were characterized by high portions of granule and sand (> 98%), and low content of organic matter (< 4%). The fluctuations of sediment parameters were relatively minimal throughout the year. Five amphioxus species have been identified in Hong Kong waters, comprising three Branchiostoma species (B. belcheri, B. japonicum and B. malayanum) and two Epigonichthys species (E. culltellus and E. lucayanus). Except for B. belcheri, the other four species have never been reported in Hong Kong before. In order to determine the genomic fingerprint of amphioxus species / populations, six populations comprising B. belcheri from Hong Kong and Xiamen, B. japonicum from Hong Kong, Xiamen and Qingdao, and B. malayanum from Hong Kong were studied. Phylogenetic separations among the species and geographic populations were evaluated by the analysis of 12S ribosomal RNA gene sequences and amplified fragment length polymorphism (AFLP) markers. The phylogenetic affinities indicated by both the 12S rRNA gene and AFLP analyses revealed a more recent phylogenetic splitting of B. belcheri and B. malayanum than that of B. belcheri and B. japonicum. The AFLP data demonstrated a high genetic diversity within each of the amphioxus populations. The within-population genetic diversity of the three B. japonicum populations was the highest in Hong Kong, followed by Xiamen and Qingdao populations. The within-population genetic diversity of B. belcheri in Hong Kong was also higher than that in Xiamen. These results suggested that genetic diversity of the Branchiostoma populations decreased from low (e.g., Hong Kong) to high (e.g., Qingdao) latitudes. In the AFLP similarity tree, the three geographic populations of B. japonicum from Hong Kong, Xiamen and Qingdao were clustered into separate clades, indicating that they were genetic-differentiated geographic populations. Analysis of Molecular Variance (AMOVA) showed that the genetic differentiation was significant among / between the geographic populations. However, genetic differences among the three B. japonicum populations of Hong Kong, Xiamen and Qingdao were not significantly correlated with the geographic distances. In order to investigate the population dynamics, growth, secondary production and reproduction cycle of B. belcheri and B. malayanum populations, a monthly investigation was conducted in Pak Lap Wan from June 2005 to June 2006. Based on the size incremental data obtained in the annual investigation, von Bertalanffy growth models of B. belcheri and B. malayanum were established. The size ranges of one, two and three-year-old B. belcheri were estimated to be 5-28, 28-38 and 38-45 mm BL, respectively, and the secondary production was calculated at 1.15 g/m2/yr DW or 0.63 g/m2/yr AFDW with the P/B at 1.13. The one and two-year-old B. malayanum were estimated to be 7-30 and 30-35 mm BL, respectively, and the secondary production was calculated at 0.51 g/m2/yr DW or 0.40 g/m2/yr AFDW with the P/B at 0.98. For the reproduction cycle, gonads of B. belcheri were measured with the maximum size in June and July, which was identified as the peak breeding season of B. belcheri. However, the larval settlement of B. belcheri was recorded from June to January of the next year, mostly in September in the present study, implying that the spawning of B. belcheri continued from May to December. Gonads of B. malayanum were measured with the maximum size in August and April, which thus can be identified as the peak spawning periods of B. malayanum in Hong Kong waters. This is the first comprehensive report on the growth, reproduction and recruitment patterns of B. belcheri and B. malayanum populations in Hong Kong. Similar research on B. malayanum has never been reported in literature. In order to identify the diet of amphioxus in Hong Kong waters, and evaluate the trophic relationship between these co-occurring B. belcheri and B. malayanum populations, fatty acid profile and carbon / nitrogen stable isotope markers (δ13C and δ15N) were analyzed on B. belcheri and B. malayanum specimens and the total particulate matter (TPM) from water. Results showed that TPM was the main food supply for amphioxus in Hong Kong waters, and the diet of amphioxus can be traced from microbes to microplankton. Results of fatty acid profile analysis revealed contributions from dinoflagellates (22:6n3), zooplankton (22:6n3), detritus (16:0 and 18:0) and bacteria (17:0), and minor contribution from diatoms (20:5n3, 14:0 and 16:1n7) and fungi (18:1n9 and 18:2n6) in the diet of amphioxus in Hong Kong waters. Amphioxus may play an important trophic role in marine food webs by transferring microbial production to higher trophic levels through utilizing microbes in seawater as food. Both fatty acid and stable isotope (δ13C and δ15N) trophic markers determined in the present study, were strongly similar between B. belcheri and B. malayanum. This indicated that the B. belcheri and B. malayanum populations in Hong Kong waters were highly overlapped not only in their spatial but also their trophic niches. The present study provided comprehensive information on the ecology and biology of amphioxus in Hong Kong, which can form a basis for implementing future conservation activities.
Online Catalog Link: http://lib.cityu.edu.hk/record=b2217889
Appears in Collections:BCH - Doctor of Philosophy

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