Tridacna Maxima Research Articles

Early mid‐Holocene SST variability and surface‐ocean water balance in the southwest Pacific

We present early mid‐Holocene records of Sr/Ca,δ18O and δ18Osw from marine archives collected in Vanuatu: two Porites sp. corals (6.7–6.5 ka BP) and a Tridacna maxima giant clam (6.2–6.0 ka BP). Sr/Ca, δ18O, and δ18Osw were used as proxies for sea surface temperature (SST) and sea surface salinity (SSS). The fossil geochemical records were compared to modern Porites sp. and T. maxima records. Reconstructed mean SSTs from the two fossil Porites sp.and from the modern coral are similar, implying that the Western Pacific Warm Pool (WPWP)' southern edge had reached its modern location by 6.7–6.5 ka BP. The post‐glacial SST rise in the Southwest Pacific was thus completed by the early mid‐Holocene. The two early mid‐Holocene corals and the giant clam recorded saltier conditions than modern related to 1) a decoupling between the precipitation regime and the SPCZ due to a northerly position of this climatic feature and 2) an increase of the moisture transport to the extra‐tropics, driven by a strengthened or extended Hadley cell. The longestδ18O coral profile displays an El Niño Southern Oscillation (ENSO) signal reduced by 20–30% compared to the period 1928–1992, in concordance with the reduced ENSO variability observed in the Pacific area during the first half of the Holocene. However, the decoupling between the SPCZ and the precipitation regime may have also contributed to the weak ENSO signal recorded in the early mid‐Holocene coralδ18O profile.

Four-Stranded Coiled-Coil Elastic Protein in the Byssus of the Giant Clam, Tridacna maxima

An elastic protein with a secondary structure distinct from all well-known load-bearing proteins is found in the byssus of the giant clam, Tridacna maxima . The byssus consists of a bundle of hundreds of individual threads, each measuring about about 100 μm in diameter, which exhibit a tendon-like mechanical response. The amino acid composition of Tridacna byssus, however, is unlike tendon collagen, lacking high glycine, proline, and hydroxyproline. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) measurements suggest that the constituent nanofibrils of the byssal threads are distinct from known secondary structure motifs previously reported for elastic proteins including the collagen triple-helix, the β-sheet nanocrystalline domains of silks, or the double-stranded coiled-coil regions of intermediate filaments. Instead, X-ray diffraction data indicate a structural organization in which four coiled-coil α-helices form a stable rope-like structure, which then further pack in a pseudohexagonal lattice to form nanofibrils. Amino acid composition analysis shows unusually high concentrations of acidic as well as basic residues, suggesting that the four-helix structure is stabilized by strong ionic interactions between oppositely charged residues in neighboring strands. The composition also suggests additional stabilization by disulfide cross-linking. On a larger scale, scanning and conventional transmission electron microscope (STEM and TEM) observations indicate that the nanofibrils exhibit an alternating periodicity of about 500 nm along the axial direction. A molecular model that combines the mechanical properties with the structural characteristics of the Tridacna byssal threads is proposed.

Studies on the Indo-Pacific Tridacnidae (<i>Tridacna maxima</i>) from the Northern Red Sea, Egypt

In Egypt, Tridacna Maxima are found in Gulf of Suez, Gulf of Aqaba and Red Sea. Tridacna Maxima are very important ecological species as seafood source and as a substrate for reef-associated organisms; therefore we should protect it from extinction. Recently, these species are exposed for many factors of pollution (human activities, tourism and natural resources) that affect the distribution and abundance of it. The main objective of this research is to shed some light on the origin, stratigraphic position, systematic palaeontology and geographic distribution of Tridacna Maxima. In addition to their ecologic and environmental conditions were discussed. Finally, a proposed rules for protection these species from extinction were listed. Individuals of Tridacna Maxima were collected from different sites along the red Sea coast.

Preliminary study on the preservation of giant clam (Tridacnidae) shells from the Balobok Rockshelter archaeological site, south Philippines

AbstractTridacnidae shells, a valuable archive of past environments, are common in the Balobok Rockshelter archaeological site on Sanga‐Sanga Island in the south Philippines. This site was occupied during the mid‐Holocene (ca. 5000–8800 14C yr B.P.), a period of Neolithic cultural expansion in the Philippines. This paper focuses on the preservation of two shell specimens, Hippopus hippopus and Tridacna maxima, unearthed from two mid‐Holocene layers within the rockshelter. The shells' mineralogy and microstructure (prismatic and crossed‐lamellar) were studied using micro‐Fourier transform infrared spectroscopy and scanning electron microscopy to determine if the samples were suitable as paleoenvironmental records. Both shells are still aragonitic but aragonite crystals of both microstructure types are partly dissolved. This dissolution, characteristic of meteoric water alteration, precludes their utility in paleoenvironmental geochemical studies. Nevertheless, these shells are abundant in archaeological sites in the region and may be better preserved in other depositional contexts; more studies on Philippine Tridacnidae shell diagenesis are needed. © 2011 Wiley Periodicals, Inc.

Isolation and characterisation of nine microsatellite markers in the boring giant clam (Tridacna crocea) and cross-amplification in five other tridacnid species

Nine novel polymorphic microsatellite markers were isolated in the boring giant clam (Tridacna crocea). The number of alleles ranged from 7 to 21. The observed and expected heterozygosity varied from 0.400 to 1.000 and 0.727 to 0.932, respectively. No significant linkage disequilibrium between pairs of loci was found and eight of nine loci were in Hardy-Weinberg proportions. Cross-amplification in other tridacnid species showed that all loci could be successfully amplified in Tridacna maxima, five in T. squamosa, three in T. derasa, three in T. gigas, and three in T. costata. These markers are therefore potentially useful for studies on the genetic diversity and connectivity of giant clam populations in order to facilitate the spatial arrangement of marine protected areas (MPAs) and fisheries management for these species.

Growth of cultured giant clams (Tridacnaspp.) in low pH, high-nutrient seawater: species-specific effects of substrate and supplemental feeding under acidification

Four species of giant clams,Tridacna maxima, T. squamosa, T. derasaandT. crocea, were cultured in outdoor raceways for 364 days at the Waikīkī Aquarium and the Oceanic Institute on the island of O‘ahu, Hawai‘i, USA. Growth of each species was compared among individuals grown with and without supplemental phytoplankton feeding, and directly on the substrate or mounted on concrete plugs in low pH, high nutrient seawater. Among clams cultured with and without supplemental phytoplankton (Chaetocerosspp.), feeding resulted in significantly lower mortality in all species butT. deresa, whereas growth was significantly higher among fed clams for all species exceptT. squamosa. Tridacna derasashowed roughly a three-fold increase in growth when fed (88.5 g ± 4.4 SD) than when unfed (26.0 g ± 2.1 SD), whereasT. maximagrowth was substantially lower, but nearly 10-fold greater in response to feeding (9.0 g ± 1.9 SD). The overall mortality rate of juvenile clams was significantly lower in the fed (44.4 ± 10.0%) than the unfed (71.8 ± 9.6%) trials, with the greatest effect observed in mortality ofT. maxima(fed 15% versus unfed 80%) andT. squamosa(fed 65% versus unfed 95%). None of theT. squamosaremained on concrete plugs for the duration of the experiment. Among the remaining three species, there was no difference in either wet weight or shell length forT. maximaand for wet weight only inT. derasaon (186.5 g ± 16.1 SD) and off (147.0 g ± 6.0 SD) the concrete plugs. In contrast,T. croceahad significantly greater shell growth off the plugs (14.3 mm ± 1.0 SD versus 8.5 mm ± 1.7 SD) but significantly greater gain in wet weight on the concrete plugs (26.3 g ± 1.5 SD versus 58.5 g ± 2.5 SD). The seawater wells used for this study are well characterized with elevated levels of inorganic nutrients and higher pCO2relative to tropical ocean waters, roughly approximating predictions for future oceanic conditions under IPCC IS92a emission scenarios. In comparison to previous studies in natural seawater,T. derasahad a significantly higher shell growth rate in the high-nutrient, low-pH well water. In contrast,T. maximaandT. squamosahad significantly lower growth rates in low pH, whereas growth ofT. croceawas not significantly different between low pH and ambient seawater. These experiments demonstrate species-specific differences with each treatment, which cautions against making broad generalizations regarding the effects of substrate type, feeding effects, nutrient enrichment, and ocean acidification on tridacnid culture and survival.

Evidence of large, local variations in recruitment and mortality in the small giant clam, Tridacna maxima, at Ningaloo Marine Park, Western Australia

Understanding variability of recruitment and mortality is essential for attempts to conserve populations or assessing changes resulting from perceived disturbances. In the absence of long-term studies, we examined population density and size-frequency distributions of the small giant clam, Tridacna maxima, at 20 sites in Ningaloo Marine Park, Western Australia, where the clams are abundant on discontinuous, intertidal rocky platforms attached to the shoreline. Density ranged over two orders of magnitude (0.04–8.27 m–2), and size ranged from 1.5 to 31.0 cm. The shapes of the size-frequency distributions varied substantially, indicating variability in recruitment and mortality, including failures of cohorts to recruit and catastrophic events of mortality. Consistency of recruitment, as indexed by the coefficient of variation of the size-frequency distribution, was greater towards the north of the Park, on intertidal platforms with greater complexity across their widths, and with smoother surfaces in the part of the platform occupied by the clams. The average turnover time was estimated at 5.4 years, giving a median age of 13 years. However, variation among sites was large, highlighting the importance of variability of the dynamics of local populations and the need for long-term studies to understand any particular population.

Ecological determinants and stochastic fluctuations of Tridacna maxima survival rate in Lakshadweep Archipelago

Compounding effects of slow life-history traits and adult-specific overharvesting have caused a range-wide decline of several giant clam populations. Erratic changes in these populations reported at isolated reefs, are attributable to stochastic fluctuations in recruitment and survival rates. These population rate parameters may be adversely influenced by the considerable and increasing human–reef economic interactions in tropical waters. The unsubstantiated knowledge on such influences hinders conservation management of species-habitat linkages particularly for species like the small giant clam (Tridacna maxima). Our study reports small giant clam survival rate, its ecological determinants and stochastic fluctuations from shallow lagoon waters of Lakshadweep Archipelago; a natural habitat not subjected to commercial giant clam harvesting. Survival rate was estimated by monitoring the status of identified individuals in belt-transects through successive years 2005–2009. The role of different factors in explaining the variation in survival rates was investigated at relevant scales: anthropogenic pressure at the population level in the reef, clam density at sub-population level in the belt-transects, and variables related to clams at the individual level. Effects were quantified through univariate regression techniques and Kaplan–Meier estimator coupled with generalized linear (logit link) models. Small giant clam survival rate in the reef decreased and its spatio-temporal fluctuations increased along the increasing gradient of human populations. Survival was density-independent. Size/age specific survival followed Siler distribution characterized by very low early-age survival, increased adult-age survival, and low older-age survival. Anchorage in coral substrate exerted a curvilinear effect, where survival of moderately anchored clams > loosely anchored clams >> deeply embedded clams. Our study recommends regular population monitoring in densely inhabited islands to detect incipient changes, which can subsequently be confronted by scientific lagoon bed management.

ChemInform Abstract: Arsenic Compounds from the Kidney of the Giant Clam Tridacna maxima: Isolation and Identification of an Arsenic-Containing Nucleoside.

The kidney of the giant clam Tridacna maxima contains algal arsenic compounds, probably as a consequence of the clam's symbiotic relationship with unicellular algae (zooxanthallae). Extraction of Tridacna kidneys yielded three novel arsenic compounds, N-(5′-deoxy-5′-dimethylarsinoyl-β-D-ribosyloxycarbonyl)glycine 5, (2S)-3-(5′-deoxy-5′-dimethylarsinoyl-β-D-ribosyloxy)-2-hydroxypropanoic acid 4a, and (2R)-3-(5′-deoxy-5′-dimethylarsinoyl-β-D-ribosyloxy)-2-hydroxypropanoic acid 4b, in addition to four previously reported dimethylarsinoylribosides. The structures of the three new Compounds were assigned chiefly from NMR data, and those for compounds 4a and 4b were confirmed by synthesis. Extraction of a second batch of Tridacna kidneys gave, in addition to compounds identified in the first extraction, (2S)-3-[(5′-deoxy-5′-trimethylarsonio-β-D-ribosyloxy)-2-hydroxypropyl]sulfate 18 and two novel compounds: an arsenic-containing nucleoside, 9-(5′-deoxy-5′-dimethylarsinoyl)-9H-adenosine 16 and N-[4-(dimethylarsinoyl)butanoyl]taurine 21. Syntheses of compounds 16 and 21 are reported. The presence of the nucleoside 16 in Tridacna, as a consequence of algal metabolism, supports a proposed pathway for the biogenesis of arsenic-containing ribosides by algae involving methylation and adenosylation by S-adenosylmethionine. A biogenetic pathway for compound 21 involving donation of the 3-amino-3-carboxypropyl moiety of S-adenosylmethionine is also proposed. The presence of both compounds 16 and 21 in Tridacna may represent the first example of donation, by S-adenosylmethionine, of all three of its alkyl groups to a single acceptor (arsenic) within one organism.

Monitoring densities of the giant clam Tridacna maxima in the Lakshadweep Archipelago

Giant clams are endangered in many parts of their Indo-Pacific range owing to adult specific overharvesting that threatens recruitment, a demographic parameter exhibiting high sensitivity to environmental disturbances and adult densities among tridacnids. Lakshadweep reefs are not subjected to commercial giant clam fishery, and population assessment has not been carried out in these waters so far. We monitored the small giant clam Tridacna maxima populations in confined waters of 12 reefs in Lakshadweep Archipelago during 2005–2007 using a systematic line transect based distance sampling framework. Overall T. maxima density in the Archipelago was estimated at 141.2/ha (95% CL 118.2–168.7) in 2005 and 122.7/ha (103.60–145.37) in 2006. Populations showed wide variation in densities and relative proportions of different age-classes between reefs. While Agatti, Bitra and Chetlat lagoons harboured high clam densities, Amini harboured the most impoverished population. Data simulation showed that total clam count along transects of 100 m length × 2–5 m strip width, in a minimum of 140 replicates, stratified by area among lagoons, would provide a viable monitoring index for rapid assessments of T. maxima in Lakshadweep. Compared to unbiased absolute abundance estimates, this monitoring index could be achieved more easily, without much compromise on accuracy and precision, necessary for meaningful spatio-temporal comparisons.

The Lagoon at Caroline/Millennium Atoll, Republic of Kiribati: Natural History of a Nearly Pristine Ecosystem

A series of surveys were carried out to characterize the physical and biological parameters of the Millennium Atoll lagoon during a research expedition in April of 2009. Millennium is a remote coral atoll in the Central Pacific belonging to the Republic of Kiribati, and a member of the Southern Line Islands chain. The atoll is among the few remaining coral reef ecosystems that are relatively pristine. The lagoon is highly enclosed, and was characterized by reticulate patch and line reefs throughout the center of the lagoon as well as perimeter reefs around the rim of the atoll. The depth reached a maximum of 33.3 m in the central region of the lagoon, and averaged between 8.8 and 13.7 m in most of the pools. The deepest areas were found to harbor large platforms of Favia matthaii, which presumably provided a base upon which the dominant corals (Acropora spp.) grew to form the reticulate reef structure. The benthic algal communities consisted mainly of crustose coralline algae (CCA), microfilamentous turf algae and isolated patches of Halimeda spp. and Caulerpa spp. Fish species richness in the lagoon was half of that observed on the adjacent fore reef. The lagoon is likely an important nursery habitat for a number of important fisheries species including the blacktip reef shark and Napoleon wrasse, which are heavily exploited elsewhere around the world but were common in the lagoon at Millennium. The lagoon also supports an abundance of giant clams (Tridacna maxima). Millennium lagoon provides an excellent reference of a relatively undisturbed coral atoll. As with most coral reefs around the world, the lagoon communities of Millennium may be threatened by climate change and associated warming, acidification and sea level rise, as well as sporadic local resource exploitation which is difficult to monitor and enforce because of the atoll's remote location. While the remote nature of Millennium has allowed it to remain one of the few nearly pristine coral reef ecosystems in the world, it is imperative that this ecosystem receives protection so that it may survive for future generations.

Studies on Glycosaminoglycans Isolated from Bivalves Molluscs Tridacna maxima and Perna viridis

The glycosaminoglycans (GAGs) in two marine invertebrate molluscs such as Tridacna maxima and Perna viridis were analyzed. Both the species was found to contain variable amounts of GAGs in the form of heparin biomolecules as identified by metachromatic activity and agarose gel electrophoresis analysis. Anticoagulant property of the biomolecules was assessed by anti factor Xa activity. Their molecular weight was estimated as 15000 and 9000 Daltons through GPC-HPLC. The 1HNMR analysis of heparin was used to predict binding sites of the heparin. Structural characterization studies clearly demonstrated that heparin is the major GAGs constituents in the test animals. Key words: Anticoagulant, Bivalves molluscs, Glycosaminoglycans, Heparin, InvertebratesDOI: 10.3126/on.v7i1.2548Our Nature (2009) 7:10-17

First identification of the neurotoxin homoanatoxin-a from mats of Hydrocoleum lyngbyaceum (marine cyanobacterium) possibly linked to giant clam poisoning in New Caledonia

We report the first identification of homoanatoxin-a from benthic marine cyanobacteria ( Hydrocoleum lyngbyaceum) samples collected in Lifou (Loyalty Islands, New Caledonia), where cases of giant clams ( Tridacna maxima) intoxications were recorded during a severe ciguatera fish poisoning outbreak. Homoanatoxin-a was also detected in extracts of giant clams harvested in the surroundings of the contaminated area suggesting the possible link between these poisoning events and the occurrence of potentially neurotoxic Hydrocoleum.

A comparison of two surveys of invertebrates at Pacific Ocean islands: the giant clam at Raivavae Island, Australes Archipelago, French Polynesia

Abstract Andréfouët, S., Friedman, K., Gilbert, A., and Remoissenet, G. 2009. A comparison of two surveys of invertebrates at Pacific Ocean islands: the giant clam at Raivavae Island, Australes Archipelago, French Polynesia. – ICES Journal of Marine Science, 66: 1825–1836. An assessment of invertebrate fisheries is currently taking place at several Pacific Ocean islands. The objectives are to obtain either detailed information on certain stocks at limited sites or to assess more broadly a variety of benthic resources across different islands. In French Polynesia, giant clam (Tridacna maxima) populations were surveyed by Service de la Pêche and Institut de Recherche pour le Développement (SPE/IRD). Sampling was optimized to determine stock abundance as a tool to enhance management of the clam fishery. Currently, the Secretariat of the Pacific Community (SPC) is investigating throughout the Pacific the status of invertebrate resources; a large-scale study not necessarily establishing a precise stock estimate for resources such as clams, but comparing resource status for several target species using coverage, density, and size measures. Raivavae Island (French Polynesia) was investigated by both programmes and offered an opportunity to verify whether the different sampling schedules provided consistent perspectives of the status of the T. maxima resource. The different strategies that SPE/IRD and SPC adopted resulted in no direct spatial overlap between the locations investigated: nevertheless, the ranges of densities and clam sizes recorded were generally consistent between surveys, and both programmes described similar spatial variation in clam presence at an island scale. SPE/IRD provided a detailed map of clam densities per habitat using a high-resolution satellite image, which yielded an estimated standing stock of 8.16 ± 0.91 million clams, representing a flesh biomass of 354 ± 41 t. SPC's study delivered coverage, density, and clam length, but no stock estimate. Unavailable from SPE/IRD, SPC also described the status of a variety of important invertebrate species targeted by fishers in the Pacific. Both programmes independently made similar fishery management recommendations. The relative merits and complementarities of the two approaches in the context of Pacific Ocean Island resource management are discussed.

Antiproliferative heparin (glycosaminoglycans) isolated from giant clam ( Tridacna maxima ) and green mussel ( Perna viridis )

Heparin was isolated from two bivalve mollusks, Tridacna maxima (giant clam) and Perna viridis (green mussel). The isolated heparin was quantified in crude as well as purified samples and they were estimated as 2.72 and 2.2 g/kg (in crude) and 260 and 248 mg/g (in purified samples) in T. maxima and P. viridis, respectively. The antiproliferative activity of both the samples performed with pulmonary artery smooth muscle cells (PASMC) indicate a dose dependent manner. Among these two clams, P. viridis heparin showed higher antiproliferative activity than that of T. maxima.

Antiproliferative heparin (glycosaminoglycans) isolated from giant clam ( Tridacna maxima ) and green mussel ( Perna viridis )

Heparin was isolated from two bivalve mollusks, Tridacna maxima (giant clam) and Perna viridis (green mussel). The isolated heparin was quantified in crude as well as purified samples and they were estimated as 2.72 and 2.2 g/kg (in crude) and 260 and 248 mg/g (in purified samples) in T. maxima and P. viridis, respectively. The antiproliferative activity of both the samples performed with pulmonary artery smooth muscle cells (PASMC) indicate a dose dependent manner. Among these two clams, P. viridis heparin showed higher antiproliferative activity than that of T. maxima.

Photosynthetic performance of giant clams, Tridacna maxima and T. squamosa, Red Sea

Two species of giant clams, Tridacna maxima and T. squamosa, coexist in the Red Sea, but exhibit dis- tinctly different depth distributions: T. maxima mostly occurs in shallow waters (reef flat and edge), while T. squamosa may occur down to the lower fore-reef slope. Giant clams have been described as mixotrophic, capable of both filter-feeding and photosynthesis due to algal symbionts (zooxanthellae), therefore, observed depth preferences were investigated in relation to possible differences in autotrophy vs. heterotrophy. This study was conducted from April to June 2004, at the reef near the Marine Science Station, Aq- aba, Gulf of Aqaba, Red Sea, and in May 2007, at a reef near Dahab, Sinai Peninsula, Egypt. In situ measurements using a submersible pulse amplitude modulated fluorometer (Diving PAM), revealed no significant differences in effective PSII quantum yield (DF/Fm 0 ) and relative electron transport rates (ETR) between the two species; but rapid light curves (ETR vs. light, photosynthetically active irradiance, PAR) showed significant differences in maximum photosynthetic rates (ETRmax), with 20% higher values in T. maxima. Chamber incubations displayed higher net and gross oxygen produc- tion by T. maxima (88.0 and 120.3 lmol O2 cm -2 mantle area day -1 ) than T. squamosa (56.7 and 84.8 lmol O2 cm -2 mantle area day -1 ); even under shading conditions (simu- lated depth of 20 m) T. maxima still achieved 93% of the surface gross O2 production, whereas T. squamosa reached only 44%. A correlation was found between ETR and net photosynthesis measured as oxygen production (T. maxima: R 2 = 0.53; T. squamosa: R 2 = 0.61). Calculated compen- sation depth (CD) (gross photosynthesis equals respiration) in T. maxima (16 m) matches the maximum depth of occurrence in this study (17 m). By contrast, the CD of T. squamosa (9 m) was much shallower than the maximum vertical range (42 m). Findings suggest T. maxima is a strict functional photoautotroph limited by light, whereas T. squamosa is a mixotroph whose photoautotrophic range is extended by heterotrophy.

Pasua and the politics of environmental management, Tongareva, Cook Islands

This article presents a summary of findings from an exploration of the politics and practices of environmental management concerning a species of giant clam, pasua (Tridacna maxima) on the island of Tongareva, an atoll in the northern Cook Islands, Eastern South Pacific. The discussion focuses on the variations in what the Tongarevan people see as the ‘problem with pasua’ and the interplay between their conceptions and the acceptance or not of a proposed customary closure on pasua harvest known as rahui. The paper suggests that environmental problems which appear ‘local’ are never about what happens in any one location but are, rather, complex, multiple and situated in networks of competing relations. The article concludes that the ‘problem with pasua’ is in a sense not locatable, because pasua is revealed in this study to be relational, networked and deeply socialised.

The significance of the giant clam Tridacna squamosa at Tubuai, Austral Islands, French Polynesia

Gilbert et al. (2007) report Tridacna squamosa at »20 m depth oV Tubuai (23°20 S, 145°20 W) an Indo-west PaciWc species previously unknown in French Polynesia. They go on to propose that the discovery corroborates a peripheral dispersal hypothesis of Randall (1995): e.g., some species colonized remote islands of the eastern Polynesia from the west via high latitude islands such as the Australs before they dispersed to the more central, tropical reaches. T. squamosa, however, had already been recorded as a questionable fossil from the Tuamotus, and as extant in easternmost Polynesia (Pitcairn 25°04 S 130°65 W; Paulay 1989), and Newman and Gomez 2003 had proposed a reliction hypothesis to account for the apparent longitudinal disjunction between the Marshall and/or Cook Islands to Pitcairn (»160°E to 130°W). Furthermore, they noted that similar disjunctions can be found in Veron (2000) for as many as 31 species of otherwise widely distributed zooxanthellate corals. The Tridacninae completely died out in the tropical Atlantic, evidently due to restriction of the tropics in general. Therefore, reliction to the Indo-west PaciWc was at the subfamilial level. Like Tridacna maxima, T. squamosa ranges throughout the tropics from East Africa to the Marshall and Cook Islands, but it has a greater depth range (0–25.5 m; Juinio et al 1989). Of the living species, only the SW PaciWc relic, Tridacna mbalavuana, is found at greater depths. Where found in eastern Polynesia, T. squamosa is also restricted to deep water, and this is interpreted as a sign of reliction rather than some ecological complication such as lack of appropriate habitat or dispersal limitations. Thus, a reliction rather than a peripheral dispersal hypothesis seems to apply. But whatever the case may be, why T. squamosa is so restricted would remain puzzling even if it turned out simply to be very patchy rather than completely absent from the central reaches of western French Polynesia.

Benthic community associated with coral reefs in the coastal area of Gulf of Aqaba, Red Scs, Egypt

Benthic community associated with coral reefs was investigated at four sites along the coastline of Gulf of Aqaba, Red Sea Egypt. The four sites (Taba, Nuweiba, Dahab and Shann El-Sheikh) are important popular spots for recreational activities and the reefs of these sites are of fringing type. Drupella cornus and Trochus maculatus were the most important gastropods associated with coral reefs. Taba and Sharm El-Sheikh showed high occurrence of worm shells (Gastropoda) Dendropdma maximum (up to 30 individuals / colony). Concerning the abundance of bivalves (Mollusca), Taba showed greater abundance of Spondylus varium and Pteria penguin ^ whereas Sharm El-Sheikh had the greatest abundance of Tridacna maxima (up to 40 individuals/lOm). The studied sites exhibited high density of Echinoderms, particularly the sea urchins Diadema setosvm, Tripneitstes gratilla and Heterocentrotus mammillatus. The study revealed selective associations between mollusc species and coral growth forms. The bivalve Pteriapenguin was found to be attached with plate-like coral Mellipora platyphylla and the branching coral Millepora dichotoma. The vennetid gastropod Dendropoma maximum was also found to be inserted into the Melliporid coral colonies. Aggregates of Drupella cornus were observed attached with branching corals, especially Acropora spp. and Stylophora spp. In contrast to the Drupella cornus, the corallivore gastropod CoralUphila neritoidea and the bivalve Tridacna maxima were predominantly preying on the massive corals of Poriies spp. The distribution of coral growth forms was compared. In general, massive, branched and plate-like colonies were the dominant growth forms of corals in the area of study. Massive colonies were dominant in the reef flat area, reef margin and the deep parts of the outer reef slope. Branching coral colonies were flourishing on the fringing reef flat, the barrier reef flat and the outer reef slope until 10m depth (upper layers of outer reef slope), their importance declined with depth. All plate-like coral colonies in the area of study belong to Hydrocorals (Milleporidae); Millepora platyphyla. They are abundant in the reef edge and upper zone of outer reef slope (the reef zone exposed to high wave action). The considerable abundance of macroalgae in the coral communities of the sampling sites were probably resulting from increased levels of nutrients caused by enhanced terrestrial runoff of sewage and sediments concomitant with increased human pressure in the area and coastal