Objectives and background to the 1994 Franco-Australian expedition to Taiaro Atoll (Tuamotu Archipelago, French Polynesia)

 The 9 km² uplifted lagoon of Taiaro Atoll (15°45′S, 144°38′W) is hypersaline due to its isolation from the ocean, yet it contains a high diversity of fish. The question unifying our expedition was to discover whether these assemblages could be self-sustaining despite very limited contact with the ocean. Although we were constrained by time, collections of fish larvae showed that some species can complete their life-cycle within the lagoon, while others differed genetically between the lagoon and the ocean, consistent with restricted gene flow. The lagoon contained few oceanic species of zooplankton, confirming its general isolation, but nevertheless some fish species may depend upon infrequent colonisation from the ocean (when large waves drive water over the normally dry reef crest). Isotopic signatures in fish otoliths suggest the basis for a more definitive and inclusive test of the sources of the lagoonal assemblage. Accepted: 28 August 1997     

Replenishment of fish populations in the enclosed lagoon of Taiaro Atoll: (Tuamotu Archipelago, French Polynesia) evidence from eggs and larvae

 Taiaro Atoll Lagoon is normally isolated from the ocean, but at least 125 marine fish species of 31 families are present there. We sampled fish larvae in Taiaro Lagoon and the nearby ocean in February 1994 with plankton net, neuston net and light trap to investigate which taxa were completing their life cycles in the lagoon. Concentrations of fish eggs and larvae were very high in the lagoon indicating intense spawning, but larvae of only 18 taxa of 10 families were present. Only six, a callionymid, gobiids, a hemiramphid, a microdesmid, and two pomacentrids, were present across a full range of pelagic sizes, and were clearly completing their pelagic stage in the lagoon. Four other taxa, an apogonid, two labrids and a scarid, were common, but the largest individuals were small (<5 mm) postflexion larvae. These may have been completing their pelagic stage in the lagoon. The remaining lagoonal larvae (eight taxa) were rare and at the preflexion stage, so we could only conclude that they hatched from eggs spawned in the lagoon. Nineteen taxa of 15 families found as adults in the lagoon were present outside the lagoon as larvae, but not inside, suggesting that they may not normally complete their life cycles in the lagoon. Horizontal distributions of larvae in the lagoon are apparently due to the interaction of larval vertical distribution behaviour with a wind-driven countercurrent system. Accepted: 16 October 1996     

Tropical zooplankton in the highly-enclosed lagoon of Taiaro Atoll (Tuamotu Archipelago, French Polynesia)

 Nocturnal zooplankton assemblages around Taiaro Atoll were sampled over six nights during February 1994. Replicate zooplankton samples were collected at windward and leeward locations in the enclosed lagoon and adjacent ocean with a metered net (85 cm diameter, 500 μm mesh) towed for 15 min at 5 m depth. The zooplankton community in the lagoon was very different from that in the ocean. Oceanic samples contained 50 mostly holoplanktonic taxa (diversity index, H′=2.62; evenness index, J′=0.67). Lagoonal samples contained 19 mostly meroplanktonic taxa (H′=1.54, J′=0.52) with three taxa (decapod larvae; an ostracod, Cypridina sp.; a copepod, Acartia fossae) contributing >90% of the individuals. Unlike the ocean, zooplankton distributions in the lagoon were not homogenous; instead spatial patterns were apparently formed by the interaction between hydrodynamic processes and species-specific behaviour. Accepted: 28 August 1997     

Genetic evidence of closed life-cycles for some coral reef fishes within Taiaro Lagoon (Tuamotu Archipelago, French Polynesia)

 Taiaro Lagoon has no permanent or regular connection with the ocean (ingress is restricted to episodes of high sea-level and/or strong wave action) raising the question of how fish populations with normally dispersive larvae are maintained inside this lagoon. We compared the genetic population structures of two coral reef fishes, Acanthurus triostegus and Chaetodon ulietensis, present on both sides of the atoll rim to determine whether there is evidence of reproductive isolation. Genetic surveys showed that the lagoonal and oceanic populations were statistically different at five loci (AAT ^* -3, GDA ^*, HPD ^*, MDH ^* and SDH ^*) in A. triostegus and three loci (PGI-2^*, IDH ^* and PGD ^*) in C. ulietensis, producing high F _st values of 0.055 and 0.021, respectively. Our genetic and demographic data on these species suggest that both may be completing their life-cycles inside the lagoon, which leads us to question the common assumption that coral reef fishes require oceanic conditions for larval development. Accepted: 28 August 1997     

Trophic structure and productivity of the lagoonal communities of Tikehau atoll (Tuamotu Archipelago,French Polynesia)

Carbon standing stocks and fluxes were studied in the lagoon of Tikehau atoll (Tuamotu archipelago, French Polynesia), from 1983 to 1988.The average POC concentration (0.7–2000 µm) was 203 mg C m^–3. The suspended living carbon (31.6 mg C m^–3) was made up of bacteria (53%), phytoplankton < 5 µm (14.2%), phytoplankton > 5 µm (14.2%), nanozooplankton 5–35 µm (5.7%), microzooplankton 35–200 µm (4.7%) and mesozooplankton 200–2000 µm (7.9%). The microphytobenthos biomass was 480 mg C m^–2.Suspended detritus (84.4% of the total POC) did not originate from the reef flat but from lagoonal primary productions. Their sedimentation exceeded phytobenthos production.It was estimated that 50% of bacterial biomass was adsorbed on particles. the bacterial biomass dominance was explained by the utilisation of 1) DOC excreted by phytoplankton (44–175 mg C m^–2 day ^–1) and zooplankton (50 mg Cm^–2 day^–1)2) organic compounds produced by solar-induced photochemical reactions 3) coral mucus.50% of the phytoplankton biomass belongs to the < 5 µm fraction. This production (440 mg C m^–2 day^–1) exceeded phytobenthos production (250 mg C m^–2 day^–1) when the whole lagoon was considered.The zooplankton > 35 µm ingested 315 mg C m^–2 day^–1, made up of phytoplankton, nanozooplankton and detritus. Its production was 132 mg C m^–2 day^–1.     

Short Term Bioturbation Activity in the Lagoonal Sediments of Tikehau Atoll (Tuamotu Archipelago,French Polynesia)

To quantify bioturbation activity in Tikehau lagoon, a tracer made of black basaltic sand was poured over the natural white calcareous sediment surface. Three stations respectively located on the inner flat (-3m), the inner slope (-9m), and the lagoon floor (-19m), were studied for short periods of time (48 hours). Bioturbation by macrofauna was quantified by volume of sediment ejected onto the experimental surface and by volume of tracer incorporated into sediment. The results showed a rapid incorporation of sedimented particles at the interface by way of the funnels and burrows of surface deposit feeders and carnivores. Expelled quantities varied with respect to site location: 213 cm³ · m⁻² · 24 h⁻¹ in the inner flat; 98.9 cm³ · m⁻² · 24 h⁻¹ in the inner slope; 7.9 m³ · m⁻² · 24 h⁻¹ in the lagoon floor. Bioturbation by decapod megafauna appeared to be important in the dynamics of the sediments in the deepest areas of the lagoon. In these areas, with almost no hydrodynamical impacts on sediments, bioturbating events were responsible for sediment mixing (despite lower absolute rates than in shallow area). Hydrodynamics controlled the spatial distribution of macroinvertebrate trophic groups by its effects on sedimentation.     

Assessment of deep water stocks of pearl oysters at Takapoto Atoll (Tuamotu Archipelago, French Polynesia)

An assessment of natural stocks of the commercially important black pearl oyster, Pinctada margaritifera, was conducted in the lagoon of Takapoto Atoll, French Polynesia. The sampling methodology combined estimates of reef area from remote sensing, depth profiles across the lagoon, and in situ sampling using scuba. Confidence limits around estimates of mean oyster density began to stabilize after ten dives, and did not decrease further after 30. Densities of oysters increased steadily with depth, ranging from a mean of 1 per 100 m² at 0–10 m to 8/100 m² at 30–40 m. More than half of the stock occurred at depths greater than 30 m. The total stock was estimated to be 4.3 ± 0.67 million, equivalent to 834 metric tonnes (including shells). Accepted: 15 June 1999     

Small-scale spatial variation in the elemental composition of otoliths of Stegastes nigricans (Pomacentridae) in French Polynesia

Solution-based inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine if Stegastes nigricans collected from 15 sites in French Polynesia could be distinguished by the trace element composition of their otoliths. A total of 293 adults were collected by spearing and their otoliths were analysed. We found that elemental signatures differed significantly among sites within and between the islands of Tahiti and Moorea (p<0.001), primarily due to variation in concentrations of the elements Ba, Ca, Li, Mg, Mn, Na, Sr and Y. The otoliths of fish collected within Papeete Harbour in Tahiti had distinctive elemental signatures characterised by relatively high concentrations of Mn. Otoliths of these fish could be distinguished from others that were collected only a small distance (200 m) from the harbour. This is the first time that differences in chemical composition of otoliths have been reported at such small spatial scales and this trait may prove useful for the studies of connectivity of populations at within reef scales.     

Isotopic composition of the delta-18O--delta-13C from the otoliths of reef fish from Taiaro (Tuamotu, French Polynesia): isotopic and biological implications

Nuclei (larval stage) and outer parts (adult stage) of fish otoliths from the Taiaro closed lagoon (French Polynesia) and adjacent ocean have been analysed for the C-O isotopic compositions. delta 18O values of the nuclei of both populations indicate that isotopic equilibrium is reached. This implies that the lagoonal fish population has done its complete biological cycle in the lagoon and represents an adaptation in a closed system. delta 18O values of the outer parts show a slight isotopic disequilibrium (< 0.2@1000) interpreted in term of vital effect. All the delta 13C values exhibit a strong isotopic disequilibrium related to metabolic activity.     

Direct measurements of carbon and carbonate export from a coral reef ecosystem (Moorea Island , French Polynesia)

The export of carbon and carbonate from coral reefs was investigated through a multidisciplinary investigation of the hydrological, geochemical, sedimentological and biological features of Tiahura reef on the northwestern coast of Moorea Island (French Polynesia). The hydrology of the fore-reef is characterised by prevailing longshore western currents and a strong thermocline. As revealed by turbidity structures (benthic and intermediate nepheloid layers) and by the amount of particles collected by near-bottom sediment traps, horizontal and downslope advections of particles dominate over offshore vertical transport. The exported material is rich in carbonate (ca. 80%) and poor in organic matter (ca. 4%). Sedimentation rates at 430 m depth, i.e. definitive export, reached 209.6 mg m^-2 d^-1 (dry weight). Estimates of carbon and carbonates export for Tiahura reef also reported here represent respectively 47% and 21% of the organic and inorganic carbon produced within the reef.     

Relationship between benthic foraminiferal assemblages and environmental factors in atoll lagoons of the central Tuamotu Archipelago (French Polynesia)

Foraminiferal assemblages were studied in ten atoll lagoons in the central Tuamotu Archipelago, French Polynesia, in order to determine which environmental factors influence their distribution. Among geomorphological conditions, the degree of aperture has a major influence on lagoonal communities. Cluster and factor analyses reveal a clear contrast between the foraminiferal associations located in the peripheral and central areas of the lagoons, showing the effect of the vicinity of coral reef, and a limited post-mortem transport of species from the periphery toward the center of the lagoons. The rarity of planktonic species indicates limited penetration of the lagoon by planktonic forms, including planktonic stages of benthic colonizers. Colonization of these remote lagoons, even those with a high degree of aperture, may thus require long periods. Therefore, the Holocene transgression that flooded the deeper lagoons before the shallower ones, allowing a longer colonization period, may have contributed to the higher species richness of foraminifera within them.     

Growth and reproduction in Canthigaster valentini (Pisces,Tetraodontidae): a comparison of a toxic reef fish with other reef fishes

Synopsis The growth and reproduction of Cantigaster valentini were studied in two sites at Lizard Island, Australia. C. valentini was found to be a gonochore, with a sex ratio very close to 1:1; sexes could be distinguished externally. The growth (in length) of known individuals from both sites was measured at least every two months over two years. Growth rates of males and females decrease as their sizes increase. Growth rates differ between sexes and between sites: males generally grow faster than females and individuals at Mermaid Cove generally grow faster than individuals at Palfrey Island. Spawning is demersal, it occurs daily between 0800 and 1600h, and continues year-round. For females the interval between successive spawnings varies from about 4 days in the warm-water season to about 10 days in the cool-water season. From a comparison of local reproductive output and local recruitment survivorship of larvae in the plankton was estimated to be much higher than in another species (Pomacentrus wardi) for which a similar estimate was available. We suggest that some aspects of the reproductive strategy of C. valentini differ from other, non-toxic reef fishes in ways consistent with a reduced threat of predation upon adults, eggs, and larvae: courtship and spawning are unhurried and occur throughout most of the day; spawning is unrelated to lunar cycles; there is no parental care or defense of fertilized eggs; and embryos often hatch on rising tides.Centre for Environmental and Urban StudiesSenior author's present address: School of Biological Sciences F07, University of Sydney, Sydney 2006, N.S.W., Australia     

Population size and structure of giant clams at Rose Atoll, an important refuge in the Samoan Archipelago

Rose Atoll is an important refuge for giant clams (Tridacna maxima) that have been heavily exploited elsewhere in Samoa. During an extensive survey of six islands in the archipelago (50.5?ha surveyed in 420 transects), 97% of a total of 2853 clams were recorded at the atoll (42% of area surveyed). Clam densities were highest in the atoll lagoon, especially around the bases of the pinnacles (mean density=8870?ha^-1). Estimated population size for the small atoll (615?ha) was approximately 27800 clams. Twenty four percent of the population consisted of mature clams (?12?cm), 70% of which occupied the pinnacles and shallow lagoon habitat. Estimated mortality was low (Z=0.3) and primarily due to natural mortality (M=0.3). Maximum recorded size (L _max ) and asymptotic mean size (L _∞) were 25.0?cm and 27.8?cm respectively.     

Spatial, temporal and habitat-related variation in the abundance of large predatory fish at One Tree Reef, Australia

 Patterns of abundance of large piscivorous fish (>200 mm TL) were documented at two spatial and four temporal scales within the main lagoon of One Tree Reef on Australia’s Great Barrier Reef. Grouper (Serranidae), snapper (Lutjanidae) and wrasses (Labridae) were the most abundant large piscivores. On a large scale (hundreds of metres), patterns of predator abundance were consistently greater on the inner edge than centre of the lagoon over a range of temporal scales: days, weeks, months and years. On a small spatial scale (tens of metres), the abundance of large predatory fish was patchy. At both spatial scales, fish were consistently aggregated in particular areas and associated with specific structural features of the reef habitat. Predator abundance was high where live corals were predominant and the topography was more complex. Hence, predation pressure and its potential effects on the distribution and abundance of prey populations, both in time and space, may vary greatly within lagoonal environments. Accepted: 25 May 1997     

Lek-like spawning,parental care and mating periodicity of the triggerfishPseudobalistes flavimarginatus (Balistidae)

Synopsis The triggerfishPseudobalistes flavimarginatus has a lek-like spawning system at Yonge Reef, Great Barrier Reef. Males migrate to a traditional mating ground where they establish territories enclosing nest sites and egg chambers. Females arrive several days later and choose a male for mating. There is biparental care of the fertilized eggs and a strict division of labour. Females appeared to be confined to the nest site by the male. Mating was semi-lunar: eggs were observed in nests several days before the new and full moons on days when high tide occurred near sunset. Differences were observed in the spawning system of another triggerfish (P. fuscus) between the Great Barrier Reef and the Red Sea. Observations of another triggerfish (Balistoides viridescens) are also reported.     

The diversity of nuclear cycle in microcyclic rust fungi (Uredinales) and its ecological and evolutionary implications

 Nine types with 11 variations of nuclear cycle and associated metabasidium development were distinguished in microcyclic rust fungi. An additional type was recognized in rust fungi with an expanded life cycle. A significant proportion of rust fungi with a reduced life cycle is assumed to have lost a sexual genetic recombination process, being either apomictic or asexual in reproduction. Most species that retain a sexual process in the microcyclic life cycle seem to have become homothallic. During life cycle evolution by the omission of spore stages, these traits might have had a selective advantage for those species that had less opportunity to encounter a genetically different but sexually compatible mate because of isolated patchy distribution or a short growing season. The findings that different populations of a morphologically identifiable species exhibit two or more distinct patterns of nuclear cycle and different metabasidium development indicate that microcyclic lineages might have evolved independently and repeatedly from a macrocyclic parental species. Those lineages are morphologically the same but would differ from each other in their genetics and biology. Received: July 5, 2002 / Accepted: August 5, 2002 Acknowledgment This work was supported in part by a Grant-in-Aid for Scientific Research (no. 09640744) from the Ministry of Education, Science and Culture (now the Ministry of Education, Culture, Sports, Science and Technology), Japan. Correspondence to:Y. Ono     

Nuclear DNA contents of all species of Helleborus (Ranunculaceae) discriminate between species and sectional divisions

 Genome size (C-values) and pollen viability staining were applied as new criteria to investigate the species of the genus Helleborus Linnaeus (Ranunculaceae). All species have the same chromosome number (2n=32). However, the nuclear DNA content, as measured by flow cytometry with propidium iodide, could be demonstrated to range between 19 pg to 35.7 pg. The different genome sizes of the species coincided to a large extent with earlier determined section boundaries based on morphology. Flow cytometry can be a convenient method to discriminate between some species. Received April 17, 2001 Accepted May 7, 2001     

Development of the musculature in the limpet Patella (Mollusca, Patellogastropoda)

 Whole-mount technique using fluorescent-labelled phalloidin for actin staining and confocal laser scanning microscopy as well as semi-thin serial sectioning, scanning and transmission electron microscopy were applied to investigate the ontogeny of the various muscular systems during larval development in the limpets Patella vulgata L. and P. caerulea L. In contrast to earlier studies, which described a single or two larval shell muscles, the pretorsional trochophore-like larva shows no less than four different muscle systems, namely the asymmetrical main head/foot larval retractor muscle, an accessory larval retractor with distinct insertion area, a circular prototroch/velar system, and a plexus-like pedal muscle system. In both Patella species only posttorsional larvae are able to retract into the shell and to close the aperture by means of the operculum. Shortly after torsion the two adult shell muscles originate independently in lateral positions, starting with two fine muscle fibres which insert at the operculum and laterally at the shell. During late larval development the main larval retractor and the accessory larval retractor become reduced and the velar muscle system is shed. In contrast, the paired adult shell muscles and the pedal muscle plexus increase in volume, and a new mantle musculature, the tentacular muscle system, and the buccal musculature arise. Because the adult shell muscles are entirely independent from the various larval muscular systems, several current hypotheses on the ontogeny and phylogeny of the early gastropod muscle system have to be reconsidered. Received: 23 June 1998 / Accepted: 25 November 1998     

Significance of new records of Tridacna squamosa Lamarck, 1819, in the Tuamotu and Gambier Archipelagos (French Polynesia)

The giant clam subfamily Tridacninae (family Cardiidae) is an important group of bivalve molluscs found throughout the Red Sea and Indo-Pacific, from East Africa to the Eastern Pacific biogeographic region. The Tridacna genus is currently revised with numerous cryptic species identified with molecular markers. New Tridacna records from the fringe of the known distribution areas are extremely useful to identify genetically unique species, geographic ranges, and to examine processes associated with species differentiation. While Tridacna maxima is abundant in French Polynesia (Central South Pacific Ocean) the larger fluted giant clam Tridacna squamosa was formerly reported only in the Austral Islands in the south. Following a recent survey that spanned 23 islands and atolls of the Society, Tuamotu and Gambier Archipelagos, the presence of T. squamosa between the Cook Islands and Pitcairn Islands is confirmed using both morphological and molecular information, suggesting a relic distribution across the Central Pacific Ocean. Tridacna squamosa is rare, but present throughout Tuamotu and Gambier. However, it remained undetected from the Society Islands, probably due to historical over-fishing. This species is valued by local inhabitants, and is sought after mainly as gifts and also for a limited local shell trade. The rarity of T. squamosa may call for conservation measures in the near future.     

Corals in a non-reef setting in the southern Arabian Gulf (Dubai, UAE): fauna and community structure in response to recurring mass mortality

 Reef coral communities in a non-reef setting on shallow, flat hardgrounds were quantitatively sampled in Dubai Emirate (UAE, Southern Arabian Gulf) before and after a coral mass mortality in 1996. The coral fauna consisted of 34 scleractinian species before and 27 after the event, which removed virtually all Acropora. No alcyonacea were recorded. Five community types were identified and characterized by the dominant species: (A) a sparse Porites lutea community in sandy areas, (B) a dense Acropora clathrata community in areas with little sand, (C) a faviid community in muddy areas, (D) a Siderastrea savignyana community in sandy areas, and (E) a Porites compressa community, which built a framework in sandy areas. These communities are comparable to those described from other areas of the Gulf, where a stable pattern of community differentiation appears to exist. The spatial distribution and dynamics of the coral communities appears to be strongly influenced by mass mortality events recurring every 15 to 20 y. A combination of extreme water temperatures and high sedimentation/turbidity appear to be the major cause of mortality. Accepted: 13 June 1998