Naoko Isomura

Possible natural hybridization of two morphologically distinct species of Acropora (Cnidaria, Scleractinia) in the Pacific: fertilization and larval survival rates.

Natural hybridization of corals in the Indo-Pacific has been considered rather rare. However, field studies have observed many corals with intermediate interspecific or unusual morphologies. Given that the existence of F1 hybrids with intermediate interspecific morphologies has been proven in the Caribbean, hybrids may also inhabit the Indo-Pacific and occur more frequently than expected. In this study, we focused on two morphologically different species, Acropora florida and A. intermedia, and performed crossing experiments at Akajima Island, Japan. Results showed that these species could hybridize in both directions via eggs and sperm, but that fertilization rates significantly differed according to which species provided eggs. These results are similar to those reported from the Caribbean. Although all embryos developed normally to the planular larval stage, the developmental processes of some hybrid embryos were delayed by approximately 1 h compared with conspecific embryos, suggesting that fertilization occurred 1 h later in interspecific crosses than in intraspecific crosses. More successful hybridization could occur under conditions with low numbers of conspecific colonies. Additionally, a comparison of survival rates between hybrid and intraspecific larvae revealed that intra- and interspecific larvae produced from eggs of A. florida survived for significantly longer than those produced from eggs of A. intermedia. Considering these data, under specific conditions, hybrids can be expected to be produced and survive in nature in the Pacific. Furthermore, we identified one colony with intermediate morphology between A. florida and A. intermedia in the field. This colony was fertilized only by eggs of A. florida, with high fertilization rates, suggesting that this colony would be a hybrid of these two species and might be backcrossed.

Genetic connectivity in the broadcast-spawning coral Acropora digitifera analyzed by microsatellite markers on the Sekisei Reef, southwestern Japan.

Worldwide decline has been observed in coral populations due to environmental changes at both regional and global levels. Since corals have a typical metapopulation structure, the recovery of severely disturbed local populations depends on larval recruitment from outside the disturbed region. Therefore, the connectivity among local populations may play a key role in the disturbance/ recovery dynamics of coral populations. On the basis of the simulation of surface currents, derived from ocean currents, we hypothesized that the genetic connectivity of coral populations is weak between the northern and southern regions of Sekisei Reef, Japan. To test this hypothesis, the connectivity of the population of the broadcast-spawning coral Acropora digitifera, one of the dominant corals in the Sekisei Reef, was analyzed at six sampling sites that were 5–25 km apart by using six microsatellite markers. The degree of genetic differentiation of A. digitifera was very low among all the sites (FST from -0.006 to 0.015), and no evidence was found in support of our hypothesis. The relative lack of genetic differentiation of A. digitifera among the sites may be attributable to the large effect of wind-driven surface currents, which highly vary on an annual basis, on coral larvae or to the time gap between simulation based on ocean current patterns and accumulation of genetic differences. Considering the pattern of the genetic connectivity of A. digitifera in the Sekisei Reef, the sites that are located within less-disturbed areas may act as larval sources and should, therefore, be preserved.

Development of Underwater Monitoring Wireless Sensor Network to Support Coral Reef Observation

We have been developing a wireless sensor network system to support coral ecological system survey activities. This paper studies the required functions of a wireless sensor node for gathering information on underwater environmental conditions. For this purpose, a prototype sensor node is developed to clarify necessary functions through a practical experiment. In this paper, the hardware configuration of a latest prototype of wireless sensor node is described. The design of this prototype was based on our previous experiments and the comments of coral reef researchers. We conducted practical field experiments to observe the coral reefs along the Okinawa coast in Japan by using the prototype. Moreover, a browsing system of gathered information by the sensor network is described. Finally, we discuss the experimental results and the required functions of the sensor node for the future research.

Underwater Image Gathering by Utilizing Stationary and Movable Sensor Nodes: Towards Observation of Symbiosis System in the Coral Reef of Okinawa

This paper describes the underwater data collection utilizing stationary sensor node and movable sensor node. We consider applying the system to investigate the conditions of marine ecosystem around the coral reef at Okinawa, Japan. The framework and fundamental design of our proposed underwater information gathering system under development are introduced. It is also reported the development of the prototypes of the sensory node and movable sensor node. Basic examinations utilizing such prototype at underwater environment are also described. This paper also describes experimental results of image gathering from via wireless local area network communication. Our future trials based on the current developmental situation are also discussed.

Possible Self-Fertilization in the Brooding Coral Acropora (Isopora) brueggemanni

Abstract We examined gametogenesis and the periodicity of planula release in the brooding coral Acropora (Isopora) brueggemanni (Brook, 1893) on Akajima Island, Okinawa, Japan. We captured the moment when A. brueggemanni would be in the process of self-fertilization. Whole colonies of this species were cultured separately or together with other colonies in plastic containers. We observed no apparent periodicity of planula release in the collected colonies. A few planulae were released intermittently during the observation period, regardless of whether the colonies were cultured individually or with other colonies. Serial paraffin sections of A. brueggemanni showed follicle-like cells surrounding the oocyte during vitellogenesis. In September and October, some spermaries looked half-broken and some ova were surrounded by sperm or spermaries instead of follicle-like cells. Such ova were heart-shaped and may have been cells at the first cleavage stage. These observations suggest that the migration of spermaries and/or oocytes resulted in the close proximity of oocytes and sperm, which would allow self-fertilization. This possibility, together with the production of planula larvae by isolated colonies, suggests that this brooding coral engages in self-fertilization.

Does dopamine block the spawning of the acroporid coral Acropora tenuis

Most corals undergo spawning after a particular moon phase, but how moon-related spawning is endogenously regulated in corals remains unknown. The objective of the present study was to evaluate whether dopamine (DA) affects spawning in Acropora tenuis. When pieces of four A. tenuis colonies were reared under a natural photoperiod and water temperature, spawning was observed after the predicted moon phase. After exposure to water containing DA at 0.1 μM, pieces of the same colonies only released 5 to 10 bundles. Co-treatment with DA and pimozide (D1 and D2 receptors antagonist), but not domperidone (D2 receptor antagonist), induced mass release of bundles from the colonies. A cross-experiment revealed high fertilization rates between the control colonies (95%) and between the control and DA-treated colonies (90%), suggesting that gametes developed normally in coral tissue. Therefore, DA appears to have an inhibitory effect on the spawning of A. tenuis.

Spawning and fertility of F1 hybrids of the coral genus Acropora in the Indo-Pacific

The role of hybridization through multi-specific synchronous spawning in the evolution of reef-building corals has been discussed since the 1990s, particularly for the genus Acropora. However, F1 hybrids have been reported as common in only one case in the Caribbean, with no evidence of mechanisms that would allow continuous reproduction of the hybrids. In this study, we report for the first time the fecundity of two F1 hybrid colonies produced experimentally from two Indo-Pacific species, A. intermedia and A. florida. These F1 hybrids spawned at the same time as the parental corals. Backcrossing and F1 hybrid crossing were successful in both directions. Furthermore, more than 90% self-fertilization was achieved in an F1 hybrid, although it was negligible in the parental corals. While it is possible that the F1 hybrid was a chimera, these results suggest that some products of interspecific hybridization may persist as the offspring of self-fertilizing F1 hybrids.

Bloom of the cyanobacterium Moorea bouillonii on the gorgonian coral Annella reticulata in Japan

Coral populations are in decline due to environmental changes and biological attacks by predators and infectious diseases. Here, we report a localized bloom of the benthic filamentous cyanobacterium Moorea bouillonii (formerly Lyngbya bouillonii) observed exclusively on the gorgonian (sea fan) coral Annella reticulata at around 20 m depth in Japan. The degree of infection has reached 26% among different sizes of Annella colonies. Thick and continuous growth of Moorea may be sustained partly by symbiotic alpheid shrimp, which affix Moorea filaments to gorgonian corals for use as food and shelter. Most filaments get entangled on the coral colony, some penetrate into the stem of the coral with a swollen end like a root hair, which appears to function as an anchor in Annella. In addition to the cyanobacterium–shrimp interaction, the new trait of anchoring by the cyanobacterium into gorgonian coral may contribute to persistence of this bloom.

The relationship between genetic similarity and reproductive success in the branching coral Acropora intermedia

Abstract Reproductive success via sexual reproduction is a key factor in restoring and maintaining populations of branching corals. It is crucial to consider the relationship between genetic similarity and reproductive success when restoring branching acroporids because these corals have characteristics such as fragmentation and localized recruitment. In this study, we examined the relationship between genetic similarity (as measured by amplified fragment length polymorphisms) and reproductive success of Acropora intermedia in 2009 and 2010, at Okinawa, southern Japan. There was a significant negative relationship between fertilization rate and genetic similarity. However, there was no significant relationship between genetic similarity and planula survivorship. Based on these findings and the characteristics of A. intermedia, asexual reproduction may decrease genetic diversity and promote inbreeding in the population.

Microsatellite loci isolated from the scleractinian coral, Acropora nobilis

We report the isolation and characterization of eight microsatellite loci from the scleractinian coral, Acropora nobilis. The microsatellite loci were obtained using compound SSR primers or an enrichment protocol. All the loci were polymorphic with four to eight alleles per locus and observed heterozygosities ranging from 0.22 to 0.76. Some of the primers developed for the two congeners, Acropora palmata and Acropora millepora were applicable to A. nobilis. These loci are useful for studying the connectivity among A. nobilis populations in Okinawa, southern Japan.