Tridacnid Clams Research Articles

Mass culture of giant clams (F. Tridacnidae) in Palau

This article describes methods developed over a 4-year period at the Micronesian Mariculture Demonstration Center in Palau for mass culture of tridacnid clams from egg to maturity. Production of 5,000–10,000 5-mm giant clam seed per tank per 4-month rearing cycle has been achieved on six occasions. The process relies on natural spawning of clam broodstock, low larval stocking densities, feeding with mixed local phytoplankton, and postlarval culture in sunlit raceways. Byssate juveniles are reared on a basalt chip substrate in Nestier trays and are eventually released unprotected on shallow fringing reefs for grow-out to commercial size. Potential rates of autotrophic meat production for 1- to 3-year-old Tridacna derasa are estimated and found to compare favorably with values reported for intensively managed, highly heterotrophic mussel farms in Europe. Preliminary data on size-specific mortality rates are presented for seed clams released in nature. Logistics of air shipping seed clams and reintroduction to new habitats are discussed based on our experience shipping Tridacna juveniles to Guam, Hawaii, and the U.S. mainland. We reexamine earlier views that tridacnids exhibit seasonal breeding “peaks.” Data are presented showing that T. gigas spawns with lunar and diel periodicity in Palau. We conclude that no serious biotechnical constraints would prevent commercial or subsistence farming of these autotrophic animals in the Indo-West Pacific.

Larval biology of tridacnid clams

Previous attempts at the mariculture of tridacnid bivalves have emphasized parameters such as growth rates of metamorphosed spat and adults. Many of these studies agree that larval mortality in these clams is high, but there have been few attempts made to define culture conditions that would enhance larval survival. We have attempted to address aspects of the larval biology of Hippopus hippopus and Tridacna gigas with an aim toward improving larval survival. We emphasize the effects of larval density and exogenous food (dissolved and particulate) supply on survival and growth of tridacnid larvae. The brief trochophore stage showed high mortality, but optimal survival was found at densities between 0.2 and 5 larvae/ml. Survival and growth rate of veligers were found to be optimal at densities of 0.2–10 larvae/ml. Control (unfed) veligers demonstrated high growth rates during the first half of the veliger stage, after which growth rates declined to zero, and mortality increased markedly. In contrast, veligers provided with particulate food ( Isochrysis galbana, Tahitian strain) had significantly higher growth rates (p < .05) and lower mortality than the controls. Phaeodactylum tricornatum is not an effective food for tridacnid larvae. Optimal growth and survival of veligers fed I. galbana occurred with algal densities of 10 4–10 5 cells/ml. Dissolved organic nutrients in the form of vitamins and yeast extract significantly enhanced veliger growth and survival. Although all adult tridacnids possess symbiotic algae which contribute significantly to their nutrition, these algae are not passed from one clam generation to another. Under experimental conditions, veligers take all strains of Symbiodinium microadriaticum provided into their stomachs, but symbiosis is not established until after metamorphosis. A larval history of adequate nutrition may well enhance veliger growth, shorten the developmental time to metamorphosis, and improve growth after the establishment of symbiosis.

Investigations on the substance which causes sperm release in tridacnid clams

1. KCl had no effect on sperm-release in T. squamosa. 2. Prostaglandins E 1. E 2 and F 2α were found to be without effect on sperm release in T. squamosa, T. maxima and T. gigas. 3. H 2O 2 potentiated the response to gonad homogenate in T. squamosa. 4. The active principle in the gonad homogenate did not go into solution in water, nor in the range of non-aqueous solvents tried. 5. Attempts to solubilize it using a detergent and changing the pH of a suspension of gonad homogenate failed. 6. The active principle did not pass through a 4.8 μm filter. 7. Some evidence that it is a protein, possibly a membrane-protein associated with the eggs, is provided. 8. Acetylcholinc and 5-hydroxytryptamine (serotonin) did not induce sperm-release in T. squamosaand T. maxima and the active principle in the gonad homogenate did not cause smooth muscle of guinea-pig ileum to contract.

SPAWNING, DEVELOPMENT, AND ACQUISITION OF ZOOXANTHELLAE BYTRIDACNA SQUAMOSA(MOLLUSCA, BIVALVIA)

Spawning and development of the clam T. squamosa was investigated in Belau, Western Caroline Islands in February and March 1980. Five of the six species of tridacnid clams spawned in response to various stimuli, but only T. squamosa released mature eggs. Factors influencing gonad development and spawning are discussed.Development of T. squamosa was followed from post-fertilization to post-metamorphosis, with emphasis on the acquisition of the zooxanthella Symbiodinium (=Gymnodinium) microadriaticum Freudenthal. The symbiotic algae were not seen in either the fertilized eggs or trochophore stages. We found that all strains of S. microadriaticum introduced to veliger clams were taken into the stomach via the mouth. Veligers ingested motile zooxanthellae more readily than non-motile ones. Within 2-9 days after metamorphosis, zooxanthellae moved by an unknown mechanism into the developing siphonal tissues. Most of these zooxanthellae appeared to be in spaces, probably the developing haemal sinuses. However, i...

Spawning induction and rearing of larvae of tridacnid clams (Bivalvia: Tridacnidae)

A new, reliable method of inducing spawning in Tridacna maxima, using freeze-dried gonad is described. A direct induction technique useful for underwater work is also presented. The effect of food supply on larval growth and metamorphosis was investigated and larval growth in the absence of particulate food is discussed. It is suggested that inclusions visible in the larval velum are symbiotic algae, which must have been acquired at the egg stage either before or during extrusion of eggs from the adult. The role of dissolved organic matter in larval nutrition is discussed. Settlement of pediveligers onto plastic panels was tested, and the substrate found to be acceptable to larvae as weel as convenient for the culturist. Methods to improve juvenile survival are suggested.

Comparative investigations on the protein components of the haemolymph fluid of the tridacnid clam family using two-dimensional gel electrophoresis

1. 1. Haemolymph components from all six Tridacnid clams were separated and characterized by O'Farrell's (1975) two-dimensional electrophoretic technique. 2. 2. A qualitative analysis of the haemolymph patterns obtained after the two-dimensional electrophoresis is presented and the species relations are established by comparing the developed “haemolymph fingerprints”. 3. 3. Haemolymph components of Tridacna squamosa with anti-galactosyl specificity are identified after affinity chromatography on a galactose substituted column.

Isolation and first characterization of a cell-wall-degrading agent of Chlorella

serum type of lectins and two other '~ serum lectins" with anti-galactan specificity. One of these occurs in eel serum [2] and is probably identical with the so-called anti-H "antibody" [3], and the other is found in the haemolymph of bivalve clams of the genus Tridacna [4, 5]. The results of the comparative precipitin experiments are illustrated. In Fig. 1 a tridacnin lectins from three different tridacnid clams are compared with eel serum. One can see that Tridacna squamosa lectin reacts nearly identically with the snail galactan in comparison with eel serum, with which it gives also a precipitin reaction, on account of the glycoproteins in eel se

Isolation and cultivation of diatom symbionts from larger Foraminifera (Protozoa)

THERE has been increasing interest in larger Foraminifera that have symbiotic algae which apparently adapt them to thrive in certain shallow, nutrient-poor tropical seas where they are responsible for a significant or even dominant fraction of the carbon fixed in the benthos1,2. Studies of fine structure of several species of these giant protozoa have suggested that their algal symbionts are diatoms6–12 without frustules (shells). This suggestion is itself remarkable because almost all marine invertebrate–brown algal associations (for example, those of corals and tridacnid clams) involve dinoflagellates. Unfortunately, knowledge of the architecture of the frustule is needed for the identification of a diatom. However, because the formation of the outer envelopes of the dinoflagellate and chlorophyte endosymbionts of other large species of Foraminifera is repressed within the hosts6,713 but not in culture5,14, we hoped that if the diatom endosymbionts could be isolated and cultivated they would form characteristic frustules. We report here the successful isolation and cultivation of diatom symbionts from foraminifera.

Different tridacnins in different tridacnid clams: A comparative study

1. 1. Haemolymph samples from different Tridacnid clams were tested for haemagglutinin activity, using normal and enzyme-treated red cells from different sources. 2. 2. Precipitin reactions with these haemolymph fluids were performed in agar gel, using several defined glycosubstances of different origin. 3. 3. In several experiments it could be demonstrated that in all Tridacnid haemolymph samples antigalactosyl (“anti-galactan”) specific lectins do occur, however, they definitely differ from each other.

INTRACELLULAR DIGESTION OF SYMBIONTIC ZOOXANTHELLAE BY HOST AMOEBOCYTES IN GIANT CLAMS (BIVALVIA: TRIDACNIDAE), WITH A NOTE ON THE NUTRITIONAL ROLE OF THE HYPERTROPHIED SIPHONAL EPIDERMIS

The question of utilization of zooxanthellae as a holozoic food source by their tridacnid clam hosts was explored utilizing techniques of electron microscopy and electron microscopical histochemistry. It is apparent from the results that older or senescent zooxanthellae are selectively culled from the algal population of the mantle edge by amoebocytes and are intracellularly digested via amoebocyte lysosomes both in the circulatory system and the interdiverticular spaces of the digestive gland. This process cannot be considered "farming," as figured by earlier work, but rather the slow systematic removal and utilization of degenerate zooxanthellae from the algal population of the clam's mantle edge.Electron photomicrographs of the microvillous surface of the hypertrophied siphons of the Tridacna revealed extensive pinocytosis of fluid and particulate material from seawater bathing the clam. It is suggested a priori that this endocytosed material contributes to the nutrition of the clam.

Self Righting by Tridacnid Clams

TRIDACNID clams can be divided into two distinct groups on the basis of whether they are physically fastened to the substrate. Of the six species comprising the family Tridacnidae1, Tridacna crocea, T. maxima and T. squamosa live byssally attached to dead coral, coral rubble or limestone during the whole of their adult lives. The other species, T. gigas, T. derasa and Hippopus hippopus, live byssally anchored as juveniles, but when approaching maturity their byssus glands atrophy, and the adult clams take up unattached existence on coral rubble or hard packed sand. This habitat difference is also expressed in the weight and morphology of their shells. The byssally attached species possess shell valves which are in most respects larger editions of those found in other bivalves (Fig. 1 A). The unattached clams, on the other hand, possess bizzare shells which are unusually massive resulting from a unique deposition of solid shell material within the cavities of the umbones (Fig. 1 B).

PHOTOSYNTHETIC PIGMENTS OF SYMBIOTIC DINOFLAGELLATES (ZOOXANTHELLAE) FROM CORALS AND CLAMS

1. The photosynthetic pigments of the brown symbiotic algae (zooxanthellae) isolated from five tridacnid clams and nine corals were found to be identical with the pigments of the dinoflagellate Amphidinium. Identifications were carried out by two-dimensional paper chromatography and by absorption spectrophotometry. Both zooxanthellae and dinoflagellates contained cholorphylls a and c, β-carotene, peridinin, neo-peridinin, dinoxanthin, neo-dinoxanthin, diadinoxanthin, and three minor xanthophyll fractions not previously described.2. Peridinin, crystallized from Tridacna gigas, or isolated by paper chromatography from Tridacna crocea, Pocillopora or the dinoflagellate Amphidinium, showed similar absorption characteristics in different solvents. The extinction coefficient of crystalline peridinin in acetone was E1 cm1% 1340.3. Clam zooxanthellae (and the dinoflagellates Amphidinium and Gymnodinium) contained a much higher proportion of chlorophyll c than coral zooxanthellae.4. No chlorophyll decomposition products were found in any freshly prepared zooxanthellae preparations.