Masami Hamaguchi

MICROSATELLITE MARKERS REVEAL POPULATION GENETIC STRUCTURE OF THE TOXIC DINOFLAGELLATE ALEXANDRIUM TAMARENSE (DINOPHYCEAE) IN JAPANESE COASTAL WATERS1

This is the first report to explore the fine‐scale diversity, population genetic structure, and biogeography of a typical planktonic microbe in Japanese and Korean coastal waters and also to try to detect the impact of natural and human‐assisted dispersals on the genetic structure and gene flow in a toxic dinoflagellate species. Here we present the genetic analysis of Alexandrium tamarense (Lebour) Balech populations from 10 sites along the Japanese and Korean coasts. We used nine microsatellite loci, which varied widely in number of alleles and gene diversity across populations. The analysis revealed that Neis genetic distance correlated significantly with geographic distance in pair‐wise comparisons, and that there was genetic differentiation in about half of 45 pair‐wise populations. These results clearly indicate genetic isolation among populations according to geographic distance and restricted gene flow via natural dispersal through tidal currents among the populations. On the other hand, high P‐values in Fishers combined test were detected in five pair‐wise populations, suggesting similar genetic structure and a close genetic relationship between the populations. These findings suggest that the genetic structure of Japanese A. tamarense populations has been disturbed, possibly by human‐assisted dispersal, which has resulted in gene flow between geographically separated populations.

Gene flow of Acanthaster planci (L.) in relation to ocean currents revealed by microsatellite analysis

Population outbreaks of the coral‐eating starfish, Acanthaster planci, are hypothesized to spread to many localities in the Indo‐Pacific Ocean through dispersal of planktonic larvae. To elucidate the gene flow of A. planci across the Indo‐Pacific in relation to ocean currents and to test the larval dispersal hypothesis, the genetic structure among 23 samples over the Indo‐Pacific was analysed using seven highly polymorphic microsatellite loci. The F‐statistics and genetic admixture analysis detected genetically distinct groups in accordance with ocean current systems, that is, the Southeast African group (Kenya and Mayotte), the Northwestern Pacific group (the Philippines and Japan), Palau, the North Central Pacific group (Majuro and Pohnpei), the Great Barrier Reef, Fiji, and French Polynesia, with a large genetic break between the Indian and Pacific Oceans. A pattern of significant isolation by distance was observed among all samples (P = 0.001, r = 0.88, n = 253, Mantel test), indicating restricted gene flow among the samples in accordance with geographical distances. The data also indicated strong gene flow within the Southeast African, Northwestern Pacific, and Great Barrier Reef groups. These results suggest that the western boundary currents have strong influence on gene flow of this species and may trigger secondary outbreaks.

Geographic variability in organic carbon stock and accumulation rate in sediments of East and Southeast Asian seagrass meadows

Organic carbon (OC) stored in the sediments of seagrass meadows has been considered a globally significant OC reservoir. However, the sparsity and regional bias of studies on long-term OC accumulation in coastal sediments have limited reliable estimation of the capacity of seagrass meadows as a global OC sink. We evaluated the amount and accumulation rate of OC in sediment of seagrass meadows and adjacent areas in East and Southeast Asia. In temperate sites, the average OC concentration in the top 30u2009cm of sediment was higher in seagrass meadows (780–1080u2009μmolu2009g−1) than in sediments without seagrass cover (52–430u2009μmolu2009g−1). The average OC in the top 30u2009cm of subtropical and tropical seagrass meadow sediments ranged from 140 to 440u2009μmolu2009g−1. Carbon isotope mass balancing suggested that the contribution of seagrass-derived carbon to OC stored in sediments was often relatively minor (temperate: 10–40%; subtropical: 35–82%; tropical: 4–34%) and correlated to the habitat type, being particularly low in estuarine habitats. Stock of OC in the top meter of sediment of all the studied meadows ranged from 38 to 120u2009Mgu2009ha−1. The sediment accumulation rates were estimated by radiocarbon dating of six selected cores (0.32–1.34u2009mmu2009yr−1). The long-term OC accumulation rates calculated from the sediment accumulation rate and the top 30u2009cm average OC concentration for the seagrass meadows (24–101u2009kgu2009ha−1u2009yr−1) were considerably lower than the OC accumulation rates previously reported for Mediterranean Posidonia oceanica meadows (580u2009kgu2009ha−1u2009yr−1 on average). Current estimates for the global carbon sink capacity of seagrass meadows, which rely largely on Mediterranean studies, may be considerable overestimations.

Complete mitochondrial genome sequences for Crown-of-thorns starfish Acanthaster planci and Acanthaster brevispinus

BackgroundThe crown-of-thorns starfish, Acanthaster planci (L.), has been blamed for coral mortality in a large number of coral reef systems situated in the Indo-Pacific region. Because of its high fecundity and the long duration of the pelagic larval stage, the mechanism of outbreaks may be related to its meta-population dynamics, which should be examined by larval sampling and population genetic analysis. However, A. planci larvae have undistinguished morphological features compared with other asteroid larvae, hence it has been difficult to discriminate A. planci larvae in plankton samples without species-specific markers. Also, no tools are available to reveal the dispersal pathway of A. planci larvae. Therefore the development of highly polymorphic genetic markers has the potential to overcome these difficulties. To obtain genomic information for these purposes, the complete nucleotide sequences of the mitochondrial genome of A. planci and its putative sibling species, A. brevispinus were determined and their characteristics discussed.ResultsThe complete mtDNA of A. planci and A. brevispinus are 16,234 bp and 16,254 bp in size, respectively. These values fall within the length variation range reported for other metazoan mitochondrial genomes. They contain 13 proteins, 2 rRNA, and 22 tRNA genes and the putative control region in the same order as the asteroid, Asterina pectinifera. The A + T contents of A. planci and A. brevispinus on their L strands that encode the majority of protein-coding genes are 56.3% and 56.4% respectively and are lower than that of A. pectinifera (61.2%). The percent similarity of nucleotide sequences between A. planci and A. brevispinus is found to be highest in the CO2 and CO3 regions (both 90.6%) and lowest in ND2 gene (84.2%) among the 13 protein-coding genes. In the deduced putative amino acid sequences, CO1 is highly conserved (99.2%), and ATP8 apparently evolves faster any of the other protein-coding gene (85.2%).ConclusionThe gene arrangement, base composition, codon usage and tRNA structure of A. planci are similar to those of A. brevispinus. However, there are significant variations between A. planci and A. brevispinus. Complete mtDNA sequences are useful for the study of phylogeny, larval detection and population genetics.

Identification and characterization of microsatellite loci in the blue coral Heliopora coerulea (Alcynonaria: Coenothecalia)

We isolated 11 polymorphic microsatellites from blue coral (Heliopora coerulea), whose conservation and management are of great concern. The number of alleles ranged from 3 to 20 with an average of 5.5, and the observed and expected heterozygosities ranged from 0.115 to 0.833 and from 0.371 to 0.915, respectively. These loci are useful for conservation genetics in H.xa0coerulea populations.

Application of the coastal ecosystem complex concept toward integrated management for sustainable coastal fisheries under oligotrophication

Harmonizing coastal fisheries with water-quality improvement has become an essential factor for the sustainable use of coastal ecosystem services. Here, we present the scope of our study based on an interdisciplinary approach including ecological actions, socio-economic actions and socio-psychological actions. We chose to focus on the interaction between oyster aquaculture and seagrass vegetation as a typical ecological action using the coastal ecosystem complex (CEC) concept. Coastal organisms have adapted their traits to the environment over a long period of time, so that restoration of the CEC represents reconstruction of the original process of coastal production. Subtidal seagrass vegetation with intertidal oyster reefs is the original CEC in Japan, which would be expected to enhance coastal production by improving the production efficiency without adding nutrients. A simple field experiment examining carbon and nitrogen contents and stable isotope ratios revealed that oyster spats cultivated on a tidal flat adjacent to seagrass beds had higher nitrogen contents and higher δ13C ratios than spats cultivated in an offshore area using only pelagic production. This result suggests that utilization of the CEC, which enables oysters to use both pelagic and benthic production, has potential to sustain a food provisioning service for humans, even in oligotrophic conditions.

Carbon Sequestration in Sediment as an Ecosystem Function of Seagrass Meadows

Seagrass meadows have the potential to sequester large amounts of organic carbon (OC) in underlying sediments as detrital OC. This ecosystem function of seagrass meadows depends not only on the high primary productivity of seagrasses and associated algae, but also on the physical and hydrological properties of seagrass meadows that accumulate fine-grained mineral sediment and allochthonous organic matter and stabilize the sediment. The burial efficiency of OC in marine sediment is constrained principally by (i) structural recalcitrance of accumulated organic matter, (ii) enhancement of OC preservation through organic–mineral interactions, and (iii) the length of the oxygen exposure time in the reactive layer of sediment. We discuss how these mechanisms contribute to and constrain OC sequestration in seagrass sediments. From the sediment source–sink perspective, long-term carbon sequestration capacity can be viewed as an emergent property of coastal vegetated ecosystems such as seagrass meadows. Sequestration of OC also depends on the nature of the OC supplied, which is largely determined by the origin of the OC. The major sources of OC to seagrass meadow sediments are reviewed and classified in terms of their mode of transport and degradability in the early diagenetic process. The available methods of evaluating various OC sources, including recently developed environmental DNA techniques, are also critically reviewed. Finally, available data are compiled on the concentration and burial rate of OC in seagrass meadow sediments and a tentative global estimate of the long-term (~1000 years) OC sequestration rate in seagrass meadows as 1.6–9.4 Tg C year−1 is provided. This is lower than previous estimates of the global OC burial rate in seagrass meadows.

A New Record of Sargassum Alternato-pinnatum Yamada (Fucales, Phaeophyceae) from Taiwan

This report describes Sargassum alternato-pinnatum Yamada as a newly recorded species in Taiwan. The specimens for this study were collected from a shallow tidepool in Lan-yu, Taiwan. This species is characterized by the following features: (1) small discoid holdfast, (2) terete primary branches, (3) sharp spines arising from surface of branches, (4) leaves that furcate 1-3 times, (5) spherical vesicles around the apex, (6) pseudozygocarpic receptacles with leaves or vesicle-like tissues, and (7) male and female conceptacles scattered within the receptacles. In this report, we also present a line drawing and photographs for the identification of S. alternato-pinnatum.