Tridacnid Clams Research Articles

Improving the quality of tridacnid clam juveniles through crossbreeding broodstock from different zones across the Spermonde Archipelago

Tridacnid clam populations have declined, and they are considered as endangered. There is increasing concern over their status in the Spermonde archipelago, South Sulawesi, where some species can no longer be found, including larger species such as Tridacna gigas and T. derasa as well as the shallow-water clam Hippopus hippopus. This research aimed to produce high-quality juvenile tridacnid clams by crossbreeding distantly related broodstock from different zones as a contribution to the effective conservation of endangered species. The research was conducted in the Spermonde archipelago and at the Hasanuddin University Marine Station Hatchery in Barrang Lompo Island. Broodstock of T derasa and T. squamosa were collected from zones III and IV of the Spermonde Archipelago. Juvenile clam production followed established methods for inducing spawning and larval rearing through trocophore, veliger, and pediveliger stages to produce juveniles that were reared in land-based and ocean nurseries. Parameters measured were the juvenile survival rate and the quality of zooxanthellae (density, chlorophyll content, and mitotic index). Data were analyzed descriptively. The mean density of zooxanthellae in juvenile clams was 3.17 x 106 cells/ind (range 3.15x106 - 5.27x106 cells/in). The mean chlorophyll-a content of these zooxanthellae was 2.7 mg/m3 (range 1.1 mg/m3 - 4.1 mg/m3), which is consistent with the mean phaeopigment concentration of 5.5 mg/m3 (range 4.2 mg/m3 - 6.2 mg/m). The mitotic index peaked at 8.5% between 09:00 and 12:00.

Quality of giant clam (Tridacna derasa) juveniles as non–target organisms after exposure to clove oil in concentrations suitable for anaesthetising ornamental fish

The use of clove oil as an alternative to cyanide has proven effective for catching several types of ornamental fish on coral reefs. However, it is very important to evaluate the post-exposure condition of non-target organisms in coral reef ecosystems where ornamental fishing occurs, such as juvenile tridacnid clams. The aim of this study was to analyse the condition of juvenile clams (Tridacna derasa juveniles, size class 3-4 cm shell width) after exposure to clove oil at the concentrations found effective for ornamental fish capture. A factorial experimental design was used with 7 clove oil concentrations (control, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm) and 5 post-exposure times (1,5,9,13 and 17 days) with 3 replicates per treatment. The juvenile clams were acclimatized for a week before being exposed to clove oil for 5 minutes, then transferred to a recovery aquarium for 60 seconds before being placed in holding aquaria. The density and mitotic index of the zooxanthellae in the clam mantles were measured for each treatment and time. There was no significant difference (p> 0.05) between control clams and those exposed to clove oil with concentrations from 20 - 70 ppm in either the density or the mitotic index of zooxanthellae present. These results indicate that juveniles of the clam Tridacna derasa did not experience a significant decline in quality (condition) after a short exposure to clove oil, such as might typically occur if clove oil was used in ornamental fishing on coral reefs.

Geometric Design of Scalable Forward Scatterers for Optimally Efficient Solar Transformers.

It will be ideal to deliver equal, optimally efficient "doses" of sunlight to all cells in a photobioreactor system, while simultaneously utilizing the entire solar resource. Backed by the numerical scattering simulation and optimization, here, the design, synthesis, and characterization of the synthetic iridocytes that recapitulated the salient forward-scattering behavior of the Tridacnid clam system are reported, which presents the first geometric solution to allow narrow, precise forward redistribution of flux, utilizing the solar resource at the maximum quantum efficiency possible in living cells. The synthetic iridocytes are composed of silica nanoparticles in microspheres embedded in gelatin, both are low refractive index materials and inexpensive. They show wavelength selectivity, have little loss (the back-scattering intensity is reduced to less than ≈0.01% of the forward-scattered intensity), and narrow forward scattering cone similar to giant clams. Moreover, by comparing experiments and theoretical calculation, it is confirmed that the nonuniformity of the scatter sizes is a "feature not a bug" of the design, allowing for efficient, forward redistribution of solar flux in a micrometer-scaled paradigm. This method is environmentally benign, inexpensive, and scalable to produce optical components that will find uses in efficiency-limited solar conversion technologies, heat sinks, and biofuel production.

Photosymbiotic giant clams are transformers of solar flux.

'Giant' tridacnid clams have evolved a three-dimensional, spatially efficient, photodamage-preventing system for photosymbiosis. We discovered that the mantle tissue of giant clams, which harbours symbiotic nutrition-providing microalgae, contains a layer of iridescent cells called iridocytes that serve to distribute photosynthetically productive wavelengths by lateral and forward-scattering of light into the tissue while back-reflecting non-productive wavelengths with a Bragg mirror. The wavelength- and angle-dependent scattering from the iridocytes is geometrically coupled to the vertically pillared microalgae, resulting in an even re-distribution of the incoming light along the sides of the pillars, thus enabling photosynthesis deep in the tissue. There is a physical analogy between the evolved function of the clam system and an electric transformer, which changes energy flux per area in a system while conserving total energy. At incident light levels found on shallow coral reefs, this arrangement may allow algae within the clam system to both efficiently use all incident solar energy and avoid the photodamage and efficiency losses due to non-photochemical quenching that occur in the reef-building coral photosymbiosis. Both intra-tissue radiometry and multiscale optical modelling support our interpretation of the system's photophysics. This highly evolved 'three-dimensional' biophotonic system suggests a strategy for more efficient, damage-resistant photovoltaic materials and more spatially efficient solar production of algal biofuels, foods and chemicals.

Early development, survival and growth rates of the giant clam Tridacna crocea (Bivalvia: Tridacnidae)

Tridacnid clams are conspicuous inhabitants of Indo-Pacific coral reefs and are traded and cultivated for the aquarium and food industries. In the present study, daily growth rates of larvae of the giant clam Tridacna crocea were determined in the laboratory during the first week of life. Adults were induced to spawn via intra-gonadal serotonin injection through the byssal orifice. After spawning oocytes were collected, fertilized and kept in 3 L glass beakers and raceways treated with antibiotics to avoid culture contamination. Larvae were fed twice with the microalga Isochrysis galbana and zooxanthellae were also offered twice during the veliger stage (days 4 and 6). Larval length was measured using a digitizing tablet coupled to a microcomputer. Larval mortality was exponential during the first 48 hours of life declining significantly afterwards. Mean growth rate was 11.3 μm day-1, increasing after addition of symbionts to 18.0 μm day-1. Survival increased to ca. 75% after the addition of zooxanthellae. The results describe the growth curve for T. crocea larvae and suggest that the acquisition of symbionts by larvae may be useful for larval growth and survival even before larvae have attained metamorphosis.

Carotenoids in Marine Invertebrates Living along the Kuroshio Current Coast

Carotenoids of the corals Acropora japonica, A. secale, and A. hyacinthus, the tridacnid clam Tridacna squamosa, the crown-of-thorns starfish Acanthaster planci, and the small sea snail Drupella fragum were investigated. The corals and the tridacnid clam are filter feeders and are associated with symbiotic zooxanthellae. Peridinin and pyrrhoxanthin, which originated from symbiotic zooxanthellae, were found to be major carotenoids in corals and the tridacnid clam. The crown-of-thorns starfish and the sea snail D. fragum are carnivorous and mainly feed on corals. Peridinin-3-acyl esters were major carotenoids in the sea snail D. fragum. On the other hand, ketocarotenoids such as 7,8-didehydroastaxanthin and astaxanthin were major carotenoids in the crown-of-thorns starfish. Carotenoids found in these marine animals closely reflected not only their metabolism but also their food chains.

Growth and survival of hatchery-bred giant clams (Tridacna gigas) in an ocean nursery in Sagay Marine Reserve, Philippines

To restore the diminishing population of the giant clam Tridacna gigas in Sagay Marine Reserve (SMR), Negros Occidental, central Philippines, two size classes [8- and 10-cm shell length (SL)] of hatchery-bred T. gigas were reared in an adjacent ocean nursery for restocking to Carbin Reef later upon reaching grow-out size of ≥20 cm SL. Growth rates did not significantly differ for both sizes and were on average 0.67 cm month−1. However, survival after 382 days of rearing T. gigas was significantly higher in the 10-cm SL clams than the 8-cm SL clams (96 and 83%, respectively). For future restocking projects, the use of 8-cm SL clams is recommended because the lower survival of this size class is compensated by its cheaper price. While rearing the clams to attain grow-out size, the population of wild clams (Family Tridacnidae) in Carbin Reef was assessed using ten 50 × 2-m belt transects. Four species of tridacnid clams have been recorded: Hippopus hippopus, Tridacna crocea, T. maxima, and T. squamosa. T. crocea comprised 12.5–93.9% of all the clams observed in all ten transects. There was a significant difference in clam density between species (ANOVA, F = 6.94, P < 0.001), with T. crocea having the highest density. Living T. gigas were absent, but presence of dead shells was indicative of its presence in the reef in the past. It can be expected that the release of hatchery-bred T. gigas juveniles in Carbin Reef could provide future breeders that will repopulate this reef and the adjacent reef communities.

Dimethylsulfoniopropionate in six species of giant clams and the evolution of dimethylsulfide after death

Substantial accumulation of dimethylsulfoniopropionate (DMSP) is documented in tissues of all six of the common species of giant clams (Tridacnidae). Results include measures of DMSP concentrations in siphonal mantle, byssal mantle, adductor muscle, and gill tissues obtained by gas chromatography of alkalized extracts plus evidence of DMSP from mass spectrometry. Formation of dimethylsulfide (DMS) by tissues after death is documented. The tridacnid clams maintain symbiotic associations with populations of dinoflagellates, which live within the enlarged siphonal mantle. We postulated that because of their association with dinoflagellates, the clams would chronically accumulate DMSP to high concentrations. Our results show that DMSP occurs at over 30 mmol·kg–1 in many tissues of tridacnid clams (sometimes 50–60 mmol·kg–1), meaning that these clams accumulate DMSP to the highest documented tissue concentrations in the animal kingdom. DMSP at such concentrations could affect multiple properties and functions. Our particular interest for this research was to assess whether postmortem breakdown of DMSP is responsible for the rapid development of potent off-odors and off-tastes that have blocked the commercial success of giant clam aquaculture. High concentrations of DMS produced in the day after death probably account for the peculiar perishability of giant clam tissues.

Dimethylsulfoniopropionate in giant clams (Tridacnidae).

The tridacnid clams maintain symbiotic associations with certain dinoflagellates (termed zooxanthellae). Tridacnids are thus candidates to have high tissue concentrations of dimethylsulfoniopropionate (DMSP), a tertiary sulfonium compound that is not synthesized by animals but is commonly produced by dinoflagellates. This study establishes that DMSP is about an order of magnitude more concentrated in the light-exposed and shaded mantle and gills of Tridacna maxima and T. squamosa than in any other known animal tissues. The DMSP concentration in the light-exposed, siphonal mantle--the location of most zooxanthellae--is an inverse function of body size, paralleling an inverse relation between apparent density of zooxanthellae (measured as pheophytin concentration) and body size. The shaded mantle and gills are high in DMSP despite having low densities of zooxanthellae, indicating that high DMSP concentrations occur in molluscan tissue, not just in algal cells. DMSP is almost an order of magnitude less concentrated in the adductor muscle than in other tissues. The high DMSP concentrations found in tridacnids, by providing abundant substrate for formation of volatile dimethylsulfide, probably explain the peculiar tendency of tridacnids to rapidly develop offensive odors and tastes after death: a serious problem for their exploitation as food. Tridacnids are the one group of animals in which DMSP concentrations are high enough in some tissues to be in the range capable of perturbing enzyme function at high physiological temperatures. Thus, tridacnids may require enzyme forms adapted to DMSP.

Effect of Perkinsus olseni (Protozoa, Apicomplexa) on the weight of Tridacna crocea (Mollusca, Bivalvia) from Lizard Island, Great Barrier Reef

Protozoan parasites in the genus Perkinsus infect American oysters causing loss of condition and death of the host in heavy infections. Length-to-weight relationship was used to assess the effect of Perkinsus olseni on wild tridacnid clams, Tridacna crocea, from around Lizard Island on the Great Barrier Reef. Perkinsus olseni infection intensity increased with increasing length of clams but did not induce a change in the length-to-weight relationship in 120 clams up to 100 mm shell length. Therefore, infection by Perkinsus parasites is unlikely to affect culture of tridacnid clams in this size range.

Carbon isotopic analysis of the free fatty acids in a tridacnid―algal symbiosis: interpretation and implications for the symbiotic association

The transfer of photosynthates from zooxanthellae symbiotic with tridacnid clams contributes to the clam's survival. We used compound-specific isotope analysis to examine the contribution that zooxanthellar lipids make to the fatty acid pool of the host. Bulk tissue $\delta ^{13}$C values for zooxanthellae from two Tridacna gigas do not appear to exhibit typical values expected for algae utilizing a sole C3 fixation pathway. Rather they are indicative of reduced isotope discrimination levels due to the high photosynthetic rates which result in depletion of the inorganic carbon source. Fatty acids extracted from zooxanthellae are only minimally $^{13}$C-depleted or slightly $^{13}$C-enriched when compared to bulk tissue. We interpret this as evidence for the synthesis of acids from acetate, short-cutting the usual pathway via pyruvate. Palmitic and 16:1$\omega $7 acids in host tissues had similar $\delta ^{13}$C values to their respective zooxanthellae, suggesting direct translocation of these acids to the host. Other fatty acids in the host were $^{13}$C-depleted when compared to the corresponding acids in the zooxanthellae, indicating multiple sources for these acids.

Conjoint Valuation of Product Attributes

The demand for tridacnid clams in the aquarium industry is expected to increase. Conjoint analysis was used in this paper to estimate the value of size and color enhancement for Tridacnu derasa to aquarium distributors in Hawaii. The preferences of the 26 distributors fell into three different groups. Nine preferred larger, enhanced clams, six preferred smaller, enhanced clams and eleven distributors preferred enhanced clams with no regard for size. The distributor's size, type of product and marketing influenced his or her preferences. Conjoint analysis can be used to determine the value of a product's characteristics to various market segments, but careful attention must be paid to the design of the experiment used to elicit the stated preferences of participants.

Cymatium muricinum and other ranellid gastropods: major predators of cultured tridacnid clams

xii 1 . Introduction: Giant Clam Mariculture and Ranellid Gastropods 1.1 Giant Clams (Bivalvia: Tridacnidae) 1 Anatomy and Biology of the Tridacnidae 1 1.2 Mariculture of Giant Clams 3 The History of Giant Clam Mariculture 3 Giant Clam Culture Technology 3 Ocean-Nursery Culture of Tridacnid Clams 5 Predation in Tridacnid Mariculture 6 . 1 3 Ranellidae 8 Habitat Preferences of Ranellid Predators of Tridacnids 10 Ranellid Predators of Other Cultured Bivalves 12 Aims and Scope of the Present Work 13 2 . Feeding Behavior of Cymatium spp . Introduction 14 Materials and Methods 16 Feeding Methods 16 Preference Experiments 17 Time Required byC . muricinum to KillT . gigas 17 Results 18 Feeding Methods 18 Preference Experiments 21 Time Required by C . muricinum to KillT . gigas 23 Discussion 24 Feeding Methods 24 Prey Preference 25 Time Required byC . muricinum to KillT. gigas 27 Implications for the Ocean-Nursery Culture of Tridacnid Clams 27 EvolutionaryAdaptations of Bivalves to Ranellid Predation 28 3 . Growth Rates and Consumption of Prey by Cymatium spp . 3.

Nitrogen flux in giant clams: size-dependency and relationship to zooxanthellae density and clam biomass in the uptake of dissolved inorganic nitrogen

Tridacnid clams live on coral reefs in the Indo-Pacific, in waters containing low concentrations of inorganic nitrogen. This study examined nitrogen flux in the giant clam Tridacna gigas. Adults and juveniles of this species typically occur with symbiotic dinoflagellates of the genus Symbiodinium sp., often referred to as zooxanthellae, which live in their tissues. Intact clams took up or released dissolved inorganic nitrogen (DIN), with the direction and magnitude of the fluxes dependent on clam size. Non-symbiotic larvae and newly-settled juveniles with few zooxanthellae released ammonium. Larger juveniles and adults depleted ammonium or nitrate from seawater, when offered separately. Rates of uptake of DIN, standardized to either clam wet weight or number of zooxanthellae, were highest in small clams (1 to 5 cm in length), and decreased with increasing clam size (>5 cm). Clams maintained in seawater containing high concentrations of ammonium (ca. 20 μM) for ≥ 1 wk generally released ammonium in the dark and exhibited net uptake in the light. Freshly isolated zooxanthellae (FIZ) from small clams had higher uptake rates than FIZ from larger clams, implying that the latter may be more nitrogen-sufficient than the former. The gradient of nitrogen sufficiency in giant clams is related to zooxanthellae density, with peaks of both algal density and rates of uptake of DIN occurring in small sizes of clams, whose growth also appears to be limited by nitrogen availability.

Utilization of dissolved inorganic nutrients in growth and mariculture of the tridacnid clam Tridacna derasa

The zooxanthellate clam Tridacna derasa takes up dissolved inorganic nitrogen (DIN) in the form of ammonia/ammonium (NH 3) or nitrate (NO 3), as shown by depletion from the medium. Rates of uptake were 5 to 18 times higher in the light than in the dark, and when measured separately the rate of NH 3 uptake was typically higher than the rate of NO 3 uptake. However, uptake of NO 3 was repressed in the presence of NH 3. A similar pattern was seen when ammonium nitrate (50 μM final concentration) was added to a 5000-l raceway containing 14 000 clams. Nitrate was depleted from the raceway only after the NH 3 concentration dropped below 2.5 μM. About half of the ammonia added to the raceway was calculated as taken up by clams in both light and dark, the other half was presumably removed by algae and other organisms in the raceway. Growth rates of small juvenile clams (2–3 mm) increased by about 75% upon addition of 50 μM NH 3 or NO 3, compared to control clams with no additions. Addition of 2 μM phosphate appeared to inhibit growth when added alone, but had little effect on clams maintained in 50 μM NH 3 or NO 3. Zooxanthellae in clams ‘fertilized’ with NH 3 or NO 3 had division rates (mitotic index, MI) a third to two times higher than those of zooxanthellae from control clams. The density of zooxanthellae in clams incubated with DIN for 10 days was approximately double that of controls, correlating positively with both increased MI and clam growth rate. The relative increase in linear shell growth of Tridacna derasa with addition of DIN increases with increasing clam size to at least 3.5 cm. The average time required for T. derasa to reach 1-year size in raceways in Palau (ca. 5 cm) has been reduced an average of 2 months with additions of DIN.

Occurrence of a turbellarian from Australian tridacnid clams

The symbiotes, commensals and parasites of the giant clam Tridacna gigas (Linn.) (Mollusca:Bivalvia) are not well known. This clam is now the focus of a budding mariculture industry in Australia, so work has been initiated to determine the usual fauna associated with this host. The turbellarian, Urastoma cyprinae (Graff, 1882), was found on the surface of the gill of cultured Tridacna gigas from both Fitzroy and Orpheus Island (Great Barrier Reef). It was also found in a wild Tridacna maxima from Heron Island. This turbellarian has not previously been recorded from Australian waters or from tridacnids. It has previously been found associated with various lamellibranch molluscs, particularly the American commercial oyster, Crassostrea virginica, and free-living.

A comparison of two benthic survey methods

The belt transect and the flowmeter methods, used to survey sedentary benthic organisms, were compared based on abundance estimates of tridacnid clams in the Cagayan Islands, Philippines, in April 1985. Two-way ANOVA and chi-square tests (P<0.05) show that both methods recorded similar estimates for the number of clams (regardless of species), both methods gave similar estimates for the number of individuals per species, and one or both methods may be biased for certain sizes of clams. Individuals smaller than 6 cm shell length seemed to be underestimated by the flowmeter method. Future studies must investigate the size selectivity of the method used, for instance by conducting permanent belt, transect surveys of varied belt widths (e.g. 1, 1.5,2,2.5 m) and then comparing the recorded lengths of the most abundant clams. This will aid investigators to evaluate their data properly, and enable comparison of clam-stock estimates between surveys.

Contribution of the symbiotic dinoflagellate Symbiodinium microadriaticum to the nutrition, growth and survival of larval and juvenile tridacnid clams

The role of the symbiotic alga Symbiodinium microadriaticum (= zooxanthellae) in growth, development, and survival of larval and juvenile tridacnid clams was investigated. The zooxanthellae were not present in eggs released from adult Tridacna gigas and Hippopus hippopus, but were ingested by veliger larvae after development from the trochophore stage. Growth of veligers of the clam H. hippopus fed freshly-isolated S. microadriaticum was significantly higher than the growth of starved veligers. In contrast, veligers fed cultured strains of S. microadriaticum and 1–5-day-old isolates of S. microadriaticum from H. hippopus had growth and survival rates not significantly different from starved veligers. These results suggest that translocated photosynthetically-fixed carbon from the ingested freshly-isolated algae was responsible for increased veliger growth and survival. The presence of zooxanthellae in the stomachs of veligers before metamorphosis facilitated establishment of a symbiosis with S. microadriaticum and a concurrent increase in growth after metamorphosis. The establishment of the symbiosis with S. microadriaticum entailed passage of the algae from the stomach, through the digestive gland, and into the developing haemal sinuses. The contribution of photosynthetically-fixed carbon from the symbiotic zooxanthellae could theoretically account for the respiratory demand of 6-week-old juveniles of H. hippopus, corroborating positive growth of unfed symbiotic juvenile clams maintained in filtered seawater. When offered a variety of free-living and symbiotic species of algae, juvenile H. hippopus established a symbiosis only with strains of S. microadriaticum. Other species of algae were apparently digested if small enough to be ingested. Less than 7% of the free-living phytoplankton species Isochrysis galbana and Platymonas subcordiformis that were ingested by symbiotic juvenile Tridacna gigas (3–12 months old) were passed intact through the digestive system after 3 days. In contrast, when freshly-isolated zooxanthellae from T. gigas were offered to symbiotic juvenile T. gigas, up to 76% of the zooxanthellae ingested passed through the clam's digestive system and were released in faecal pellets intact. The symbiotic dinoflagellate Amphidinium klebsii and the diatom Phaeodactylum tricornutum were not ingested by veliger or juvenile clams.

The effect of ammonium on photosynthesis and the pathway of ammonium assimilation in Gymnodinium microadriaticum in vitro and in symbiosis with tridacnid clams and corals

The effects of added ammonium ion (10-1000 μM) on photosynthetic 14 CO 2 fixation by tissues slices from the mantle of tridacnid clams, by coral tips, and by isolated zooxanthellae from clam mantle were examined. Ammonium ions stimulated photosynthesis in tissue slices but not in freshly isolated zooxanthellae. When ammonium stimulated 14 CO 2 fixation by coral tips an increase in water-soluble labelled compounds, especially amino acids, was observed. Even though ammonium ions did not stimulate photosynthesis in isolated zooxanthellae from clam mantle, light stimulated ammonium uptake in these cells. Studies with 15 NH + 4 confirmed earlier observations (in zooxanthellae isolated from Hippopus ) of light-stimulated transfer of ammonium from the amido-N of glutamine to the amino-N of glutamate, glutamine and other amino acids. This observation, in isolated zooxanthellae and tissue slices, suggests that the glutamine synthase-glutamate synthetase pathway of ammonium incorporation is light-driven in these systems. The possible significance of these processes during ammonium recycling by symbiotic algae in marine animals is discussed.

Serotonin-induced spawning in giant clams (Bivalvia: Tridacnidae)

Six species of tridacnid clams were induced to spawn by intragonadal injection of 2 m M serotonin solution. Dosages ranging from 0.5 ml to 7.0 ml were tested in situ and in laboratory-held clams. Mean time to first-spawning of sperm in all species ranged from 1.7 to 3.8 min. Egg spawning followed sperm in four species but only reliably in Hippopus hippopus.