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Tropical Island Ecosystems and Sustainable Development Symposium
Tropical Island Ecosystems and Sustainable Development
Biodiversity Research on Coral Reef and Island Ecosystems: Scientific Cooperation in the Pacific Region
Makoto Tsuchiya, René Galzin, and Neil Davies, 299
Pacific Island Forests: Successionally Impoverished and Now Threatened to Be Overgrown by Aliens?
Dieter Mueller-Dombois, 303
Indigenous forests in remote islands are generally impoverished of secondary successional tree species. After canopy disturbances, the same indigenous tree species seem to resume dominance by a process known as “autosuccession” or “direct succession.” Primary forest tree species are mostly colonizer species. Mature island forests are difficult to categorize as either pioneer, successional, or climax forests by their canopy species composition. Climax forests, which characterize mature forests in less-isolated areas, are typically of distinctly different canopy species composition than the pioneer forests. In central Canada, for example, pioneer pine forests are replaced in succession by mixed hardwood/softwood forests under exclusion of fire. This process is known as “normal replacement succession” or “obligatory succession.” Another well-known ecological concept distinguishes between “primary” and “secondary” forests in the continental tropics. Secondary forests are formed by fast-growing relatively short-lived second-growth species, which quickly assemble after major disturbances. It usually takes a long time for primary tropical rain forest trees to reappear in secondary forests. In contrast, primary island forests rarely include fast-growing indigenous canopy species that form such secondary forests in the continental tropics. Instead, secondary forests in islands are now made up mostly of introduced species. In this paper I attempt to evaluate alien plant invasion in remote islands in view of these concepts of ecological succession.
Differences in Associated Crustacean Fauna and Seasonality of Sexual Reproduction between Two Color Morphs of the Photosymbiotic Ascidian Didemnum molle (Ascidiacea: Didemnidae)
Takumi Fukuda and Euichi Hirose, 309
Photosymbiotic ascidians inhabiting subtropical waters tend to have gonads in spring and summer, whereas those in tropical waters are usually sexually mature year-round. We studied the seasonality of sexual reproduction in two populations of the photosymbiotic ascidian Didemnum molle (Herdman, 1886), sampling monthly for 12 months. Although the two populations were located only about 20 km apart, their color morphs were exclusively distributed: colonies of one population were always dark gray; those of the other population were mostly brown. The seasonality of sexual reproduction differed greatly between the populations (and thus between the color morphs). Sexual reproduction was limited to summer in the population with dark gray colonies, whereas the population with brown colonies possessed embryos with tails almost year-round. Moreover, the resident crustacean fauna in the colonies also differed between the populations. The microenvironment in each habitat may have caused these differences, but there may also be some physiological differences between the color morphs that affect the seasonality of sexual reproduction and the resident crustacean fauna.
Distribution and Possible Impacts of Toxic Organic Pollutants on Coral Reef Ecosystems around Okinawa Island, Japan
S. T. Imo, M. A. Sheikh, K. Sawano, H. Fujimura, and T. Oomori, 317
Organic pollutants have detrimental effects on the environment. In this study we evaluated the current status of contamination with organochlorine pesticides (OCPs), organo-tin compounds (OTCs), and polychlorinated biphenyls (PCBs) in the waters in and around Okinawa Island, Japan. Possible toxicological effects of these pollutants on marine life including corals are also discussed. Concentrations of total OCPs in river water were in the range of 1.02–56.4 ng liter-1. Among the OCPs, α-BHC, β-BHC, and aldrin were common in river water. OTCs detected in 30 samples of seawater were (mean ± SD) monobutyl tin (MBT), 0.44 ± 0.75 ng (Sn) liter-1; dibutyl tin (DBT), 1.32 ± 2.70 ng (Sn) liter-1; tributyl tin (TBT), 0.72 ± 2.90 ng (Sn) liter-1; monophenyl tin (MPhT), 0.04 ± 0.42 ng (Sn) liter-1; diphenyl tin (DPhT), 0.007 ng (Sn) liter-1; and triphenyl tin (TPhT), 0.013 ng (Sn) liter-1. Highest concentrations of TBT, 28.5 ng (Sn) liter-1 for water and 172 ng (Sn) g-1 dry weight for sediment, were detected in samples from Itoman Port. Concentrations of total PCBs were 0.05–0.28 ng liter-1 in open ocean and from 1.59 to 2.48 ng liter-1 in coastal waters. Overall, this study shows that the coral reef ecosystems and their adjacent environments around Okinawa Island are contaminated by toxic organic contaminants (OCPs, OTCs, and PCBs). Levels of these contaminants detected in some sites have exceeded the Environmental Quality Target (EQT), which may pose a risk to health of marine life.
Reproductive Biology and Early Development of Two Species of Sleeper, Eleotris acanthopoma and Eleotris fusca (Teleostei: Eleotridae)
Ken Maeda, Nozomi Yamasaki, Masashi Kondo, and Katsunori Tachihara, 327
Reproductive biology and early development of two species of sleepers, Eleotris acanthopoma Bleeker, 1853, and E. fusca (Forster, 1801), were investigated in streams on Okinawa Island in southern Japan. Gonadal examination and morphology of the genital papillae indicated that E. acanthopoma matured at a smaller body size (ca. 28 mm in standard length) than E. fusca (ca. 50 mm). Mature ovaries were composed of oocytes that could be categorized into two size classes. Larger females of both species had several hundred thousand developed oocytes in the larger size class and may spawn them at one or several consecutive spawning events. Egg masses of both species were found in habitats typically occupied by adults and were deposited, often sparsely, on the underside of objects. Form of the egg masses and morphology of eggs and newly hatched larvae of both species were almost identical. Eggs were a nearly spherical pyriform in shape, with the widest diameters measuring approximately 0.4 mm. Newly hatched larvae were very small (1.0–1.4 mm in notochord length) and undeveloped. The mouth opened and the eyes became pigmented 3 days after hatching, and all of their yolk was consumed 4 days after hatching. Reproductive strategies of both species were characterized by high fecundity through production of small eggs and small newly hatched larvae, with high fecundity likely to mitigate the presumed increased risk associated with widespread larval dispersal.
Flicker Light Effects on Photosynthesis of Symbiotic Algae in the Reef-Building Coral Acropora digitifera (Cnidaria: Anthozoa: Scleractinia)
Takashi Nakamura and Hideo Yamasaki, 341
Reef-building corals inhabit a variety of aquatic habitats with a range of light conditions. Because the coral host depends on photosynthetic products assimilated from endosymbiotic algae, reef-building corals have to cope with irradiance fluctuations on instantaneous to seasonal time scales. Underwater high-frequency light fluctuations resulting from the lens effect on the water surface are prominent in oligotrophic coral reef environments, a phenomenon known as flicker light. Effects of flicker light on endosymbiont photosynthesis of the reef-building coral Acropora digitifera (Dana, 1846) were evaluated with pulse amplitude modulation chlorophyll fluorometry. At supersaturating light intensities, photosynthesis was less inhibited by flicker light than by constant light. Reduction in photoinhibition by flicker light was pronounced at high water temperatures. Flicker light may strongly influence endosymbiont photosynthesis of corals inhabiting shallow reef habitats, especially during periods of strong solar irradiance and high water temperature.
Molecular Phylogeography of the Endemic Five-lined Skink (Plestiodon marginatus) (Reptilia: Scincidae) of the Ryukyu Archipelago, Japan, with Special Reference to the Relationship of a Northern Tokara Population
Masanao Honda, Taku Okamoto, Tsutomu Hikida, and Hidetoshi Ota, 351
Phylogenetic relationships were inferred for populations of the Ryukyu five-lined skink Plestiodon marginatus, a species showing an extraordinary distribution across the Tokara Tectonic Strait. Phylogenetic analyses of 809 base positions of the mitochondrial 12S and 16S rRNA genes supported collective divergence of the southern Tokara and northern Amami populations, which have been classified as P. m. oshimensis. A population from Nakanoshima, an island of the Tokara Group north of the Tokara Tectonic Strait, has the closest affinity with the Okinawajima population of P. m. marginatus rather than with the geographically closer southern Tokara and northern Amami populations. This result is concordant with that of a recent allozyme study and suggests an origin of the Nakanoshima population through long-distance dispersal from the Okinawa Island Group. Also, our results strongly suggest a closer relationship of a population of P. m. oshimensis from Okinoerabujima, a southern island of the Amami Group, with P. m. marginatus from Okinawajima than with the “consubspecific” southern Tokara and northern Amami populations. Both Nakanoshima and Okinoerabujima populations are usually referred to as P. m. oshimensis, and therefore our results indicate nonmonophyly of P. m. oshimensis in the current taxonomic arrangement.
Canopy Multilayering and Woody Species Diversity of a Subtropical Evergreen Broadleaf Forest, Okinawa Island
Akio Hagihara, S. M. Feroz, and Masatsugu Yokota, 363
Woody species diversity and the spatial distribution of trees in a subtropical evergreen broadleaf forest on a silicate substrate, Okinawa Island, were investigated to determine the forest’s architectural stratification. The forest stand consisted of four architectural layers. The values of Shannon’s index Hʹ and Pielou’s index Jʹ tended to increase from the top layer downward, except for the bottom layer. The lower layers contained many species relative to their smaller height ranges. High woody species diversity of the forest depended on small trees. This trend of species diversity was different from that of forest on a limestone substrate on Okinawa Island, where high woody species diversity depended on large trees. Conservation of small trees in the lower layers, especially the bottom layer, is indispensable to maintain diversity in Okinawan evergreen broadleaf forests. Castanopsis sieboldii (Mak.) Hatusima had the highest importance value in all layers, indicating that it is typically a facultative shade species as well as a climax species. The spatial distribution patterns of trees were found to be random in the lower three layers, but in the top layer clumping seemed to occur at three spatial scales. A high degree of overlapping in spatial distributions of trees among the layers suggested that light cannot penetrate easily into the lower layers. As a result, most species in the lower layers must be shade-tolerant. Mean weight index decreased from the top toward the bottom layer, and tree density increased from the top downward. This trend resembled the mean weight-density trajectory of self-thinning plant populations.
Biogeography of the Decapod and Stomatopod Crustacea of the Tropical Pacific: Issues and Prospects
Joseph Poupin, 377
Biogeographic patterns of the Crustacea (Decapoda and Stomatopoda) are given for the tropical Pacific, based on recent taxonomic studies combined with emergence of regional databases. Conclusive results are still difficult to obtain due to incomplete regional inventories and existence of complexes of sibling species with unclear taxonomic status. A time-series graph of the number of new records plotted against time is computed for several central Pacific islands (French Polynesia, Pitcairn, Easter Island, and Clipperton). It demonstrates that the fauna is still insufficiently known in those places. A biodiversity gradient is calculated for several taxa between West and East Pacific. The traditional decrease between Australia and French Polynesia is confirmed for higher taxa (Brachyura, Anomura), but at lower taxonomic levels it is not always verified (e.g., hermit crabs, Calcinus; crabs, Trapezia). A map is presented illustrating the following provisional biogeographic results: (1) cryptic endemic species recognized in the Marquesas Islands; (2) presence of a distinct faunistic province in the South Pacific, along the 25° S parallel, including Rapa and Easter Islands; (3) theoretical position of the border between the Indo-West Pacific (IWP) and East Pacific (EP) faunistic provinces (84 W on the seamounts of Sala y Gómez/Nazca and 110° W on Clipperton); (4) differences between Clipperton, with a mixed IWP-EP fauna (43% IWP versus 57% EP species), and the Galápagos, with obvious EP affinities (10% IWP versus 90% EP species).
Genetic Relationships among Species of Meretrix (Mollusca: Veneridae) in the Western Pacific Ocean
Ayako Yashiki Yamakawa, Masashi Yamaguchi, and Hideyuki Imai, 385
We compared allozymes at 12 loci in 12 populations of six species of Meretrix: M. lusoria (Japan, Korea, and Taiwan), M. petechialis (China and Korea), M. ovum (Thailand and Mozambique), M. lyrata (China), M. lamarckii (Japan), and Meretrix sp. A (Okinawa, Japan). Our allozyme results were generally consistent with the major groupings currently recognized within the genus based on morphological characters. However, we found two cryptic or undescribed species: Meretrix sp. A from Okinawa and M. cf. lusoria from Taiwan. The shell characters of Meretrix sp. A were similar to those of M. lamarckii, but the species was genetically distinct (Nei’s genetic distance D > 0.845) from all other species examined. The Taiwanese Meretrix population was morphologically indistinguishable from Japanese M. lusoria, although the genetic distance between the Taiwanese and Japanese populations showed a high degree of genetic differentiation (D > 0.386). Meretrix lusoria seedlings were introduced into Taiwan from Japan in the 1920s, and Japanese M. lusoria was previously thought to be established as a cultured stock. However, our results suggest that the Taiwanese population may represent a sibling or cryptic species of M. lusoria.
Systematic Review of Late Pleistocene Turtles (Reptilia: Chelonii) from the Ryukyu Archipelago, Japan, with Special Reference to Paleogeographical Implications
Akio Takahashi, Hiroyuki Otsuka, and Hidetoshi Ota, 395
The Quaternary terrestrial turtle fauna of the Ryukyu Archipelago was reviewed on the basis of recently excavated fossils, as well as literature information. As a result, five extinct species (four geoemydids [Cuora sp., Geoemyda amamiensis, Mauremys sp., and another species with undetermined generic and specific status] and one testudinid [Manouria oyamai]) were recognized from Late Pleistocene cave and fissure deposits. Two of the three turtles currently occurring in this archipelago (C. flavomarginata and G. japonica) were also recognized from comparable deposits on islands, including those where they do not occur at present. These records indicate that the terrestrial turtles of the Ryukyus were much more diverse during the Late Pleistocene than at present, and that extinction has occurred during the last few tens of thousands of years not only for those five fossil species but also for some island populations of the extant species. Distributions of three of the extinct species (G. amamiensis, Cuora sp., and the geoemydid [genus and species undetermined]), confined to the central Ryukyus, are concordant with the currently prevailing hypothesis of Ryukyu paleogeography, which assumes a relatively long isolation of this region and much more recent insularization of the southern Ryukyus. In contrast, distributions of the remaining two extinct species (Man. oyamai and Mau. sp.) must be explained by some ad hoc scenario or, otherwise, drastic modification of the current hypothesis.
Low Genetic Diversity of Oval Squid, Sepioteuthis cf. lessoniana (Cephalopoda: Loliginidae), in Japanese Waters Inferred from a Mitochondrial DNA Non-coding Region
Misuzu Aoki, Hideyuki Imai, Tohru Naruse, and Yuzuru Ikeda, 403
Genetic diversity and population structure of Japanese populations of the oval squid, Sepioteuthis cf. lessoniana, were compared with populations from Taiwan and Vietnam using nucleotide sequences of the mitochondrial DNA non-coding region 2. In total, 402 nucleotide sequences representing 242 individuals from Japanese waters (Ishikawa, Japan Sea coast of Honshu; Tokushima, eastern Shikoku; Nagasaki, western Kyushu; and Okinawajima and Ishigakijima Island, in the Ryukyu Archipelago) and the East and South China Seas (Keelung, northern Taiwan; Vietnam, Gulf of Tonkin) were examined. Among the 29 haplotypes recognized, haplotype no. 1 was shared by more than 75% of individuals from Japanese localities, whereas it was found in less than 13% of specimens from the East and South China Seas populations. Conversely, the East and South China Seas populations included more than 30% individuals with haplotype no. 2, whereas less than 10% of haplotype no. 2 individuals were from Japanese localities. The differences of haplotype and nucleotide diversities between pooled Japanese populations (0.2639, 0.23%) and the East and South China Seas populations (0.7900, 1.01%) indicate that S. cf. lessoniana from Japanese waters exhibits lower genetic diversity. An analysis of molecular variance between the Japanese populations and the East and South China Seas populations was highly significant. A minimum spanning tree of 29 haplotypes and an Unweighted Pair Group Method with Arithmetic mean (UPGMA) tree based on pairwise FST comparisons also supported the separation between Japanese and the East and South China Seas populations. We suggest that the Kuroshio Current physically limits gene flow and has thus caused the differences in genetic diversity among the populations examined.
Degree and Pattern of Gene Flow in Several Scleractinian Corals in the Ryukyu Archipelago, Southern Japan
A. Nishikawa, 413
Dispersal distance of planktonic larvae of coral reef organisms is influenced by their ecological characteristics and environmental factors such as current flow and physical structure of reefs. This study reviews the degree and pattern of genetic differentiation in scleractinian corals in the Ryukyu Archipelago, compared with other regions. Small-scale genetic heterogeneity, but broad-scale homogeneity, was detected in some species, including brooders and spawners in the Ryukyus. Comparison with other regions indicated that limited gene flow on a small spatial scale (i.e., self-recruitment) seemed to occur in many regions. However, the degree of gene flow over larger distances was complex and species-dependent. With an implication for conservation in the Ryukyus, the larval source hypothesis, which states that coral larvae were recruited from the Kerama Islands to the Okinawa Islands, was consistent with results illustrating high gene flow in some species. Thus, conservation of corals in the Kerama Islands is high priority. Detection of genetic breaks between the southern and central Ryukyus was not common among species. The genetic structure observed in corals is highly variable and depends on both species and spatial scale in the Ryukyus. In addition, the complex genetic structures of corals may be related to coral-specific destructive events, such as bleaching, outbreaks of crown-of-thorns starfish, and disease. Further studies will provide new insights and a more detailed view of the genetic structure of corals by using different markers (e.g., microsatellites) and approaches (assignment tests and clustering analysis), which will provide useful information for coral reef conservation.
Dietary Habits of the Introduced Cane Toad, Bufo marinus (Amphibia: Bufonidae), on Ishigakijima, Southern Ryukyus, Japan
Noriko Kidera, Nontivich Tandavanitj, Daehyun Oh, Nozomi Nakanishi, Aya Satoh, Tetsuo Denda, Masako Izawa, and Hidetoshi Ota, 423
We examined dietary habits of the introduced cane toad Bufo marinus at three sites representing different types of habitats (pond, forest, and rice paddy) on Ishigakijima Island, southern Ryukyus, Japan. Stomach contents analysis revealed that the toad mostly utilizes terrestrial arthropods, of which hymenopterans (mostly ants), adult coleopterans, hemipterans, and araneans dominated in the frequency of occurrence, hymenopterans in the numerical proportion, and larval lepidopterans, adult coleopterans, and larval dipterans in the volumetric proportion. Comparisons in taxonomic composition of the toad’s stomach contents and pitfall and sweeping net samples suggested ignorance or avoidance of Amphipoda by the toad. Our results suggest the possibility of considerable predation pressure of B. marinus upon the native arthropods, and ants in particular, on Ishigakijima Island.
A Framework for Assessing Impacts of Marine Protected Areas in Moorea (French Polynesia)
Thierry Lison de Loma, Craig W. Osenberg, Jeffrey S. Shima, Yannick Chancerelle, Neil Davies, Andrew J. Brooks, and René Galzin, 431
Marine Protected Areas (MPAs) have been promoted as effective management tools to protect biodiversity at local and global scales, but there remains considerable scientific uncertainty about effects of MPAs on species abundances and biodiversity. Commonly used assessment designs typically fail to provide irrefutable evidence of positive effects. In contrast, Before-After-Control-Impact (BACI) designs potentially remedy many of these problems by explicitly dealing with both spatial and temporal variation. Here, we document the historical context of implementation and the scientific assessment of MPAs recently established at eight sites around the island of Moorea, French Polynesia. In 2004, we designed and implemented a monitoring plan that uses a BACI-Paired Series (BACIPS) design to quantify the effect of the MPAs. Twice per year, we monitor fish, corals, and other benthic invertebrates at 13 sites (eight within MPAs and five outside MPAs) around Moorea, in three distinct reef habitats (fringing, barrier reef, and outer slope). We present statistical analyses of data collected during five surveys (July 2004 to July 2006), before the initiation of enforcement. We also assessed the potential of our program to detect future responses to the established MPA network. Our estimates of biomass for five categories of fishes (Acanthuridae, Chaetodontidae, Serranidae, Scaridae, and fisheries target species) within MPA sites generally track estimates in paired Control sites through time. Estimated statistical power to detect MPA effects (a 192% biomass increase within the MPA) was high at the MPA network scale but varied among taxonomic categories and reef habitats: power was high on the reefouter slope and lower in the lagoon, and generally high for acanthurids and chaetodontids. It did not vary significantly between sites. We discuss limitations of our approach (shared by all MPA assessments to date) and describe solutions and unique opportunities to redress these limitations in French Polynesia.