Takuro Shibuno

Habitat use patterns of fishes across the mangrove-seagrass-coral reef seascape at Ishigaki Island, southern Japan

To clarify seascape-scale habitat use patterns of fishes in the Ryukyu Islands (southern Japan), visual censuses were conducted in the mangrove estuary, sand area, seagrass bed, coral rubble area, branching coral area on the reef flat, and tabular coral area on the outer reef slope at Ishigaki Island in August and November 2004, and May, August and November 2005. During the study period a total of 319 species were observed. Species richness and abundance were highest in the branching and tabular coral areas, followed in order by the seagrass bed and mangrove estuary, and coral rubble and sand areas, in each month. Cluster analysis resulted in a clear grouping of assemblage structures by habitat type rather than by census month. SIMPER analysis showed that fish assemblages in the tabular coral area were mainly characterized by Acanthurus nigrofuscus, Pomacentrus lepidogenys, P. philippinus and P. vaiuli, the branching coral area by Chromis viridis and Pomacentrus moluccensis, the coral rubble area by Amblyeleotris steinitzi and Ctenogobiops pomastictus, the seagrass bed by Cheilio inermis, Lethrinus atkinsoni and Stethojulis strigiventer, the sand area by Valenciennea longipinnis, and the mangrove estuary by Gerres oyena, Lutjanus fulvus and Yongeichthys criniger. Moreover, fishes exhibited two habitat use strategies, inhabiting either a single or several specific habitats throughout their benthic life history stages, or having a possible ontogenetic habitat shift from the mangrove estuary or seagrass bed to coral-dominated habitats (e.g., Lethrinus atkinsoni, Lethrinus obsoletus, Lutjanus fulviflamma, Lutjanus fulvus, Lutjanus gibbus, Lutjanus monostigma and Parupeneus barberinus), suggesting that the mangrove estuary and seagrass bed have a nursery function.

Isolation and characterization of stress-responsive genes from the scleractinian coral Pocillopora damicornis

In order to identify the expression of coral genes induced by stressors such as suspended red soil, mRNA differential display was examined for the coral Pocillopora damicornis. Apparent differences were observed in the gene expression profiles between control colonies and those treated with local red soil, indicating that red soil affects gene expression in P. damicornis. We cloned nine candidate PCR fragments derived from the differentially expressed genes. One of the clones, pPd9-1, showed a high similarity to a member of the heat-shock protein (HSP) 70 family, suggesting that red soil may cause protein denaturation in the coral. Reverse transcription-mediated PCR showed that the expression of pPd9-1 was also increased by elevated temperature, but not by reduced salinity.

Male maturity, number of sperm, and spermatophore size relationships in the coconut crab Birgus latro on Hatoma Island, southern Japan

Abstract To consider effective resource management strategies for the coconut crab, Birgus latro, we determined the size of males at sexual maturity by histological methods and investigated an optimal method to estimate the number of sperm in spermatophores. The size of 50% sexual maturity in male coconut crabs was estimated at 22.2 mm thoracic length (TL) on the Hatoma Island, Japan. We established a procedure to soak spermatophores for more than 120 min in a 20% NaOH solution before mixing, and to count the sperm within 24 h after mixing, thereby enabling us to assess the number of sperm per individual and estimate male reproductive potential. Using this method, we investigated the relationship between male size and number of sperm retained by males. Larger male coconut crabs have a higher number of sperm in both the vasa deferentia and testis. The relationships between male size and spermatophore volume also increased with increasing male size, and the sperm quantity packed in a spermatophore increased with increasing spermatophore volume. Thus, male coconut crabs display a size-dependent reproductive output, as is reported for other species of anomurans.

The relationship between habitat physical complexity and recruitment of the coral reef damselfish, Pomacentrus amboinensis: an experimental study using small-scale artificial reefs

Abstract A manipulative experiment using small-scale artificial reefs was conducted to quantify the relationship between habitat physical complexity and recruitment of the coral reef damselfish, Pomacentrus amboinensis, at Urasoko Bay, Ishigaki Island (Ryukyu Islands, Japan), from January to July 2000. Four types of small-scale, structurally different artificial reefs, including (1) vertical bars with three layers of horizontal bars (type A), (2) vertical bars with a single layer of horizontal bars (type B), (3) vertical bars only (type C), and (4) no bars (type D), were employed for the experiment. Although the peak numbers of P. amboinensis recruits on most of the artificial reefs were recorded on 9 June, the mean number of recruits per replicate varied depending on the reef types. The mean number of recruits on type A was significantly greater than those on the other types, whereas no difference between types B and C were found, and only a few juveniles were observed on type D at one observation time. The experiment demonstrated that the degree of habitat structural complexity had a significant impact on the number of P. amboinensis recruits.

Habitat use and coexistence of three territorial herbivorous damselfish on different-size patch reefs

In local reef fish communities, species richness increases with increasing reef area. At Ishigaki Island, Japan, species richness is much lower on large reefs in the shallow back reef than that expected from random placement model simulations (RPMS). As three aggressive territorial herbivorous damselfish, Stegastes nigricans , Stegastes lividus and Hemiglyphidodon plagiometopon , coexist only on such large reefs, we focused on these species and examined patterns of their distribution and abundance on 84 patch reefs of various sizes (area and height). We also examined their aggressive intra- and interspecific behavioural interactions and habitat use on the two large reefs (the largest complex patch reef and the large flat patch reef) among the 84 patch reefs. While the abundance of both S. lividus and H. plagiometopon was highly correlated with patch reef area, that of S. nigricans was closely correlated with patch reef height. For S. nigricans and S. lividus , interspecific interactions occurred significantly more frequently than intraspecific interactions on the large flat patch reef. However, there was no significant difference in frequencies of the two interaction types on the largest complex patch reef, where they three-dimensionally segregated conspecific territories. This study suggested that reef height as well as reef area influence the distribution and abundance of these territorial herbivorous damselfish in the shallow back reef. As large patch reefs cannot be tall allometrically in shallow back reefs, relatively flat patch reefs may not have the high species richness expected from RPMS based on reef area.

Sessile Organisms on PVC Panels in the Waters around a Coral Reef of Ishigaki Island, Yaeyama Islands, Japan, Immediately after the Catastrophic Coral Bleaching in 1998

Sessile organisms on PVC panels suspended inside and outside coral reef at Ishigaki Island, Yaeyama Islands, Japan, was monitored for 20 days just after the wide-spread incident of coral bleaching in September, 1998. The settlement of a total of 16 species of algae and invertebrates was recorded. Generally, Enteromorpha sp. (Chlorophyceae) dominated the panels. The percentage area cover, number of species, biomass and algal growth were significantly greater in waters outside the reef.