Patterns of pair formation in protandrous anemonefishes,Amphiprion clarkii,A. frenatus andA. perideraion,on coral reefs of Okinawa,Japan

Synopsis At Sesoko Island, stocks of anemonefishes were observed for 2 years in a 350 m × 150 m area where host sea anemones were sparse. About 40% of the pairs separated, mostly due to typhoon attacks or displacement. Widowed mates remained and acquired new mates on the same sea anemone, except for one case. New mates were immigrant adults inAmphiprion clarkii and A.frenatus, but resident juveniles inA. perideraion. A. clarkii andA. frenatus moved between sea anemones and sometimes displaced smaller consexuals, butA. perideraion rarely moved. The difference in mobility among the 3 species was related to the mean difference in standard length between the largest juveniles in breeding groups and the minimum size of breeding males in each species, and that between breeding males and the minimum size of breeding females. InA. perideraion both of these differences were small, so pairs could be formed quickly by residents after mate loss. On the contrary, inA. clarkii andA. frenatus, either or both differences were large and it would take a longer time to form a pair after mate loss. Differences in mobility affected the patterns of pair formation, and then the size composition of members in breeding groups.     

Skeletal structure and progression of growth anomalies in Porites australiensis in Okinawa, Japan

Growth anomalies (GAs), one of the diseases recently reported for scleractinian corals, are characterized by an abnormal skeletal structure and reduced zooxanthella density. The pathological characteristics of GAs were studied in colonies of Porites australiensis on a reef in Kayo, Okinawa, Japan. Corallites in the GA region lost the skeletal architecture characteristic of P. australiensis, and polyp density had decreased in the GAs due to enlargement of both calices and the coenosteum. The gross productivity of isolated GA samples was lower than in healthy samples and decreased to almost 0 within 11 d after isolation. However, when GA samples were brought into contact with healthy-looking samples from the same colony, they fused and both the GA and healthy regions grew. Healthy samples fused with GA samples grew more slowly than those fused with healthy samples. For in situ GAs surrounded by healthy tissue, tissue death usually started at the center of the GA, probably due to a deficiency in the translocated energy supply from the surrounding tissue. The total area of the GA region and the dead area increased at a rate of 5.3 ± 2.9 cm2 yr-1. These results suggest that GA regions are maintained by energy supplies from surrounding healthy tissues and that GAs may have a negative impact on host corals.     

Survival rate and sex ratio in habu,Trimeresurus flavoviridis (Viperidae), on the subtropical Okinawa Island,Japan

We examined the age structure and sex ratio of a viperid snake,Trimeresurus flavoviridis, based on samples collected by hand by local inhabitants, habu hunters and by baited traps in the middle and south of Okinawa Island, Japan. Small individuals had a low possibility of capture in all the collecting methods. The age structure was estimated through summing up the age frequency in each snout-vent length (SVL) class in samples with a similar SVL structure. From the age structures, annual survival rates of adult females and males were estimated to be 0.7 and 0.8, respectively. In most samples the sex ratio was biased towards males, especially in March and August and in large individuals. However, the female proportion increased in June.     

Ocular angiostrongyliasis without meningitis symptoms in Okinawa,Japan

A 62-year-old female farmer presented with retinal detachment in her left eye, and an Angiostrongylus cantonensis worm was recovered by vitreous surgery. The case did not show typical clinical symptoms indicating meningitis, although the patient complained of a mild headache, a low-grade fever, and slight ataxia. The symptoms were treated as influenza before the onset of the retinal detachment. The present case is the first confirmed of ocular angiostrongyliasis in Japan.     

Age,growth, and reproductive biology of blacktail snapper,Lutjanus fulvus,around the Yaeyama Islands,Okinawa, Japan

Age, growth, and reproductive characteristics of blacktail snapper, Lutjanus fulvus, which is a commercial fish species, were investigated using 322 specimens (40–332 mm in fork length) caught around the Yaeyama Islands, Okinawa, Japan. Spawning season was estimated to be from April to October, and spawning was confirmed around the full moon and the last quarter moon. Age determination using sectioned otoliths revealed that ages ranged from 0 to 34 years and the majority was ≥ 3 years. Parameters of the von Bertalanffy growth function were estimated to be L _∞  = 270 mm, k = 0.40, and t ₀  = ?0.48 years for females, and 257 mm, 0.44, and ?0.42 years for males. Initial growth was rapid during the first 3 years, attaining over 200 mm for both sexes, and then females grew larger than males. Sizes (ages) at the first sexual maturity were 225 mm (4 years) for females and 207 mm (3 years) for males. The wide range of age composition in catch with majority of ≥3 years old implied that the current fishing effort to harvest was not sufficiently large enough to collapse the stock immediately.     

Age and growth of Gerres oyena (Forsskål, 1775) on Okinawa Island, Japan

Age and growth were studied for Gerres oyena (Forsskål, 1775) on Okinawa Island, southern Japan from November 2002 to November 2005. A total of 408 samples was collected ranging from 5.85 to 19.65 cm standard length (L_SL). Male fish age was estimated at up to 6⁺ years, whereas females reached 8⁺ years as estimated by sectioned otoliths. The length–weight relationships and the von Bertalanffy growth curve were described for all individuals as: and L_t = 20.54{1 − e^{−0.1807(t+2.8462)}}, respectively. Opaque rings were formed from April to August during the spring–summer seasons.     

Mating behavior and sex change of the anemonefish,Amphiprion clarkii,in the temperate waters of southern Japan

Synopsis In the main habitat of the anemonefishes Amphiprion, their movements between host sea anemones are generally restricted because of the low population density of hosts and high predation pressures. On the contrary, movements of A. clarkii between hosts were usual in the present study area (temperate waters of southern Japan), where host anemones are abundant. The general social unit of the anemonefishes is an isolated group consisting of a monogamous breeding pair and a varying number of nonbreeders. In the present study area, however, monogamous pairs established territories almost contiguous to others and nonbreeders had home ranges on the outskirts of the pairs' territories. The high host population density allows A. clarkii to move between hosts for searching for mates and acquiring additional mates. Most pair bonds lasted for more than 6 months, but 13% of the pairs separated because of migration of a mate to another territory. Bigamy occasionally originated from a penetration into a territory of a breeder by a mated neighbor of the opposite sex after the former's mate loss. Among 18 males who had lost their mates, only 3 changed sex and others re-paired with immigrant females, migrated to unmated females' territories or invaded pairs' territories. In the present study area, sex change to female is not the best way for an unmated male to increase his future reproductive success because of a loss of time spent on sex change and an opportunity to re-pair with new mates larger than himself, but is adaptively maintained as the best of a bad situation for the unmated male.     

Size-dependent sex change can be the ESS without any size advantage of reproduction when mortality is size-dependent

Almost all models of sex change evolution assume that reproductive rate increases with body size. However, size-dependent sex changing plants often show size-independent reproductive success, presumably due to pollen limitation. Can the observed size-dependent sex change pattern be the ESS in this case? To answer this question, we analyze a game model of size-dependent sex expression in plants. We assume: (1) reproductive rate is perfectly independent of size; (2) mortality decreases with size in the same way for both sexes; (3) growth rates decrease at maturity, more for females than males. We show that the ESS is size-dependent sex expression: small individuals are vegetative, intermediate individuals are male, and large individuals are female. These results demonstrate that mortality is important in size-dependent sex allocation even when mortality rate is independent of sex. They also offer an explanation of why we see populations in poor environments to have sex ratios more biased toward the first sex relative to high quality environments.     

Digenetic trematodes of marine fishes of Okinawa, Japan

Between May and September 1985, 348 fishes representing 50 families, 107 genera, and 152 species from the coastal waters of Okinawa were examined for digenetic flukes. Ten families (Lepocreadiidae, Opistholebetidae, Gyliauchenidae, Fellodistomidae, Acanthocolpidae, Opecoelidae, Bucephalidae, Cryptogonimidae, Syncoeliidae, and Hemiuridae), representing 29 genera and 34 species of digenetic flukes were recorded. Seven new geographic locality records and 25 new host records were established. Possibly 2 new species, one being a species of the genus Metadena from Meiacanthus grammistes and the other a species of the genus Mesolecitha from Plectorhynchus chaetodontoides, were detected. Most infections were of a single species, and although prevalence and intensity were low, host specificity was high. Only 3 of the 34 species identified transgressed family bounds in their definitive hosts.     

A new prenylated flavonoid from propolis collected in Okinawa, Japan

The new prenylflavonoid, isonymphaeol-B (1), together with three known compounds, nymphaeol-A (2), nymphaeol-B (3), and nymphaeol-C (4), were isolated from propolis collected in Okinawa, the southern-most prefecture of Japan. The structure of each compound was determined by spectral methods, including mass spectrometry and 2D NMR. Each compound had 1,1-diphenyl-2-picryl-hydrazyl radical-scavenging activity.     

A New Prenylated Flavonoid from Propolis Collected in Okinawa,Japan

The new prenylflavonoid, isonymphaeol-B (1), together with three known compounds, nymphaeol-A (2), nymphaeol-B (3), and nymphaeol-C (4), were isolated from propolis collected in Okinawa, the southern-most prefecture of Japan. The structure of each compound was determined by spectral methods, including mass spectrometry and 2D NMR. Each compound had 1,1-diphenyl-2-picryl-hydrazyl radical-scavenging activity.     

Age, growth, and reproductive biology of the Waigieu seaperch Psammoperca waigiensis (Perciformes: Latidae) around Okinawa Island, Japan

Age, growth, and reproductive biology of the Waigieu seaperch Psammoperca waigiensis were studied using 291 specimens obtained around Okinawa Island, Japan. Otolith opaque zones that formed every year correlated with spawning activity and were thought to be annual rings. Growth of this species was rapid during the first 2 years, reaching 186.2–270.3 mm in standard length (SL). Females (196.6–334.0 mm SL) were larger than males (186.2–288.6 mm SL), caused by differential growth between sexes, which started before 2 years of age. Most of the specimens were 1–11 years old and accounted for 96% in total. Spawning season was estimated to be from April to October by gonadosomatic index (GSI) and histological observation. The smallest mature female and male were 217.0 mm SL (2 years) and 206.0 mm SL (2 years), respectively. After recruitment in rocky areas up to about 200.0 mm SL and 2 years of age, Psammoperca waigiensis were then found to soon mature.     

Intraspecific contact and egg production in the massive coral Goniastrea aspera in Okinawa, subtropical Japan

The effect of intraspecific contact (Contact) on egg production was examined in the massive coral Goniastrea aspera in Okinawa, subtropical Japan. The contact was non-aggressive without damaging soft tissues each other. Within Contact colonies, polyp volume, polyp fertility (%polyps with gonad), and NE/PV (number of eggs per polyp volume) were significantly smaller in marginal (Mg) polyps without direct intraspecific contact than other polyps, but no difference was found between non-marginal and Mg-Contact (marginal with direct intraspecific contact) polyps. Comparisons of non-marginal polyps (non-marginal and Mg-Contact polyps were combined in Contact colonies) between Non-Contact and Contact colonies showed that fertility and NE/PV were significantly larger in Contact colonies than in Non-Contact colonies, but polyp volume were not different significantly. Further analyses dividing colonies at Non-Contact maturation colony size (60 polyps) revealed that fertility and NE/PV were significantly larger in Contact colonies than in Non-Contact colonies only in the small colonies (<60 polyps), indicating that the intraspecific contact promoted sexual maturation at smaller colony size; one polyped Contact coral was also reproductive. The lack of correlation between polyp volume and NE/PV in the small Contact colonies, and the similarity of NE/PV in non-marginal and Mg-Contact polyps within a colony, suggest that the maturation at smaller size in Contact colonies is realized by reproductive integration of polyps at the colony level. The present results show that size-structured populations such as colonial corals may show phenotypic diversity in key demographic parameters, such as reproductive output, dependent on ecological conditions.     

Characterization of fatty acid composition in healthy and bleached corals from Okinawa, Japan

Under bleaching conditions, corals lose their symbiotic zooxanthellae, and thus, the ability to synthesize fatty acids (FAs) from photosynthetically derived carbon. This study investigated the lipid content and FA composition in healthy and bleached corals from the Odo reef flat in Okinawa, southern Japan, following a bleaching event. It was hypothesized that the FA composition and abundance would change as algae are lost or die, and possibly microbial abundance would increase in corals as a consequence of bleaching. The lipid content and FA composition of three healthy coral species (Pavona frondifera, Acropora pulchra, and Goniastrea aspera) and of partially bleached and completely bleached colonies of P. frondifera were examined. The FA composition did not differ among healthy corals, but differed significantly among healthy, partially bleached, and completely bleached specimens of P. frondifera. Completely bleached corals contained significantly lower lipid and total FA content, as well as lower relative amounts of polyunsaturated FAs and higher relative amounts of saturated FAs, than healthy and partially bleached corals. Furthermore, there was a significantly higher relative concentration of monounsaturated FAs and odd-numbered branched FAs in completely bleached corals, indicating an increase in bacterial colonization in the bleached corals.     

Ribosomal DNA haplotype distribution of Bursaphelenchus xylophilus in Kyushu and Okinawa islands, Japan

Ribosomal DNA region sequences (partial 18S, 28S and complete ITS1, 5.8S, and ITS2) of the pinewood nematode (Bursaphelenchus xylophilus) were obtained from DNA extracted directly from wood pieces collected from wilted pine trees throughout the Kyushu and Okinawa islands, Japan. Either a 2569bp or 2573bp sequence was obtained from 88 of 143 samples. Together with the 45 rDNA sequences of pinewood nematode isolates previously reported, there were eight single nucleotide polymorphisms and two indels of two bases. Based on these mutations, nine haplotypes were estimated. The haplotype frequencies differed among regions in Kyushu island (northwest, northeast and center, southeast, and southwest), and the distribution was consistent with the invasion and spreading routes of the pinewood nematode previously estimated from past records of pine wilt and wood importation. There was no significant difference in haplotype frequencies among the collection sites on Okinawa island.     

Socially controlled sex-change in the half-moon grouper,Epinephelus rivulatus,at Ningaloo Reef,Western Australia

The cues controlling sex-change have been elucidated for various species of hermaphroditic fishes that inhabit coral reefs, but not for the epinepheline serranids. A male removal experiment conducted on an assemblage of the half-moon grouper, Epinephelus rivulatus, demonstrated that protogynous sex-change in this species is socially controlled, possibly by the suppressive dominance of males and a threshold sex ratio. The experiment showed that a reproductively ripe female can change sex and become a male with ripening testis within 3 weeks. However, this process can be delayed, slowed, or stopped by the presence of other males in the area.     

Size-fractionated phytoplankton biomass in coral reef waters off Sesoko Island, Okinawa, Japan

The seasonal dynamics of size-fractionated phytoplankton biomassin a coral reef area were investigated off Sesoko Island, Okinawa,Japan. Chlorophyll (Chl) a and nutrient concentrations werelow almost all year round, showing no clear seasonal variabilitywith values similar to those in some other coral reef areas.Picoplankton dominated the phytoplankton community; averagecontributions of pico-, nano- and microplankton to the totalChl a biomass were 52, 34 and 11%, respectively. However, in1998, when the seawater temperature was extremely high and coralbleaching occurred due to the ENSO event, low Chl a coupledwith high nutrient concentrations were observed. This was associatedwith a decrease in the picoplankton size fraction. We suggestthat the high seawater temperature in 1998 decreased the growthrate of the picoplankton; however, the micro- and nanoplanktonmay also be limited by other factors such as low nutrient concentrations.     

New aspects of sex change among reef fishes: recent studies in Japan

New aspects of sex change in reef fishes are reviewed with special emphasis on recent studies in Japan. For protogyny, studies on both monandric and diandric species have been conducted, but the distinction of primary males from prematurational secondary males seems to need further examination. For protandry, detailed field studies on anemonefishes have revealed alternative life-history styles associated with movements between hosts before or after maturation. The most interesting new aspect has been the discovery of 2-way sex change within a species. Conditions for evolution of 2-way sex change are examined in relation to the size-advantage model and social control mechanisms. A fish may change sex when it becomes dominant in a mating group, but a dominant fish may also change sex in the reverse direction when its social status changes to subordinate through inter-group movement. Two-way sex change has hitherto been reported only from basically protogynous fishes (e.g., Gobiidae, Pomacanthidae, Cirrhitidae, Epinephelinae). Possibilities of the reverse sex change in the protandrous anemonefishes are discussed with data from some unpublished studies.