Tridacna Maxima Research Articles

The Role of Zooxanthellae in the Growth of the Giant Clam Tridacna maxima in Outdoor Aquaculture System, Red Sea, Egypt

The Role of Zooxanthellae in the Growth of the Giant Clam Tridacna maxima in Outdoor Aquaculture System, Red Sea, Egypt

Of Clams and Clades: Genetic Diversity and Connectivity of Small Giant Clams (Tridacna maxima) in the Southern Pacific Ocean.

Giant clams (Tridacna and Hippopus) are large marine bivalves occupying tropical and subtropical reefs in the Indo-Pacific. Giant clam populations have declined in many areas of the Indo-Pacific and continue to be threatened by harvesting and environmental change. The small giant clam (Tridacna maxima) occurs throughout the Indo-Pacific and has been subject to several phylogeographic studies across its range. However, given its broad range, there are several areas where the genetic diversity and connectivity of T. maxima populations has not been characterised. Here, we analyse the mitochondrial marker cytochrome oxidase 1 (CO1) to examine the genetic diversity and connectivity of T. maxima in two regions: Australia's Coral Sea Marine Park and the Cook Islands. Samples were collected from 13 reefs within the Coral Sea Marine Park and ten islands within the Cook Islands archipelago. Tridacna maxima across the sampled region of the Coral Sea did not display any population structure, whereas significant population structure was detected for T. maxima within the Cook Islands. For the Cook Islands, most pairwise comparisons involving an island in the northern group (Manihiki) were significant, as were comparisons for Palmerston (a more centrally located island) and the southern islands, Rarotonga and Mangaia. Both regions displayed high haplotype diversities (> 0.90), indicating that they are important repositories of genetic diversity. Additional CO1 data from throughout T. maxima's distribution showed that the Coral Sea clams belonged to the clade occurring in the South-Western Pacific Ocean, whilst those from the Cook Islands belonged to a unique clade found in the Central Pacific Ocean. This clade extended from Fiji in the west to French Polynesia in the east and the atolls of Palmyra and Tarawa (Kiribati) in the north. Our assessment of genetic diversity and population structure in these regions will assist with management decisions for the species.

Vanishing giants: An assessment on the population status of giant clams across Malaysia

The iconic giant clams are known for its multifaceted importance throughout the Indo-Pacific –for functional, ecological, or cultural purposes. In Malaysia, habitat destruction and illegal poaching were main reasons behind the declining populations of giant clams. As previous surveys date back to 1990 s, an update on the status of giant clam populations in Malaysia is overdue. Using the extensive monitoring data from Reef Check Malaysia, we analysed and provided an assessment of population trends of giant clams between 2007 and 2021 in Malaysia. This study showed a decline in giant clam population in the east coast Peninsula and Sabah, while their abundances have always been low in the west coast Peninsula and Sarawak. In the east coast Peninsula, Tridacna maxima and T. crocea were most common (2.7 ± 7.3 and 1.4 ± 7.6 clams per 100 m2, respectively), followed by T. squamosa (0.7 ± 1.4 clams per 100 m2), and Hippopus hippopus (0.3 ± 2.5 clams per 100 m2). The boring species, T. maxima and T. crocea, typically displayed highly aggregated populations, reaching densities of 41.5 and 70 clams per 100 m2, where a reciprocal abundance shift between both species was observed between northern and southern sites of east coast Peninsula. The demography of T. maxima and T. crocea is either positively skewed or normally distributed, indicating abundant recruits that correspond to their higher densities. In contrast, T. squamosa showed a negative skew, suggesting poor recruitment rates. Findings here underscore the need to tailor conservation strategies for respective giant clam species in Malaysia. Proposed initiatives include establishing conservation zones in key areas like Perhentian, Lang Tengah, Redang, and Tioman Islands, which have significant T. maxima and T. crocea recruit populations. Also, targeted restocking efforts are necessary for T. squamosa and H. hippopus to ensure long-term viability of populations.

Effect of coral‐giant clam artificial reef on coral recruitment: insights for restoration and conservation efforts

Coral recruitment is a vital process for the maintenance and recovery of coral reefs, particularly due to their decline from global change. While it is well established that larval settlement cues significantly influence coral recruitment, the investigation of recruitment success associated with the surrounding community mainly focuses on algae. To investigate other factors controlling this process, we examined the impact of benthic invertebrate assemblages on coral recruitment using artificial reefs. Three types of artificial reefs (mono‐, bi‐, and tri‐species) with different assemblages of three common species, Pocillopora acuta, Acropora cytherea, and Tridacna maxima, were studied over 8 months. This study revealed that benthic assemblages play a significant role in coral recruitment and survival. High biodiversity was found to enhance coral recruitment and inhibit potential negative cues from A. cytherea. Our findings underscore the importance of preserving high biodiversity using not only hard coral but a wide range of phyla, including bivalves, in coral restoration efforts. Maintaining sustainable populations is an important goal to reach in the face of the multiple threats that impact coral reefs.

Microstructure and growth rate variability in a giant clam (Tridacna maxima) from the Lakshadweep Archipelago, India: implications for their use as biological monitors to trace extreme weather events

Microstructure and growth rate variability in a giant clam (Tridacna maxima) from the Lakshadweep Archipelago, India: implications for their use as biological monitors to trace extreme weather events

Genetic confirmation of Tridacna noae (Röding 1798) in the Cook Islands

Giant clams are common across a broad geographic range and contribute important ecological functions within coral reef environments. However, giant clams are subject to considerable harvest pressure and require careful management that is underpinned by accurate data collection. The taxonomy of giant clams has undergone many changes, and recently, Tridacna noae (Röding 1798) has been resurrected as a valid species, distinct from the morphologically similar Tridacna maxima (Röding 1798). Using genetic analysis, this research confirms the presence of T. noae for the first time in the Cook Islands, extending the currently known distribution of the species by 1340 km south-east. This confirmation highlights that T. noae was possibly previously misidentified, causing overestimations of the abundance of other giant clam species. This new record improves the accuracy of identification and stock assessments, and ongoing management in the Cook Islands.

Metallic trace element contamination of the giant clam Tridacna maxima in French Polynesia

This study is a first assessment of Metallic Trace Elements (MTE) contamination of four lagoons in French Polynesia, chosen because their main anthropic uses are potential sources of MTE (military, agriculture, maritime). We used the giant clam Tridacna maxima as a biointegrator of fifteen MTE to assess the environmental footprint of human activities. The study of organotropism showed that not only the kidney but also the gonad and digestive system (GDS) are accumulator organs of interest for ETM biomonitoring. This result confirms that heterotrophic feeding is the pathway of ETM accumulation. Here, T. maxima appeared to be a super-accumulator of Ni (2700 ppm.dw), but also revealed at Tubuai (As, Fe, Mn) and Arutua (Cd, Zn) the environmental footprint of agricultural and maritime activities. The concentration of Cd recorded in Arutua (5 ppm.dw) both in KID and GDS, also underline the need for better control of effluents resulting from human activities.

Insights into the genetic makeup of French Polynesian peripheral populations of the small giant clam Tridacna maxima

Abstract The small giant clam, Tridacna maxima, is distributed from the Red Sea and East African coast to French Polynesia. Across this widespread Indo‐Pacific range, T. maxima shows strong population structure, in agreement with its limited dispersal abilities. Peripheral populations may have smaller effective population sizes, increasing their vulnerability under any environmental changes. Understanding evolutionary processes at play in such regions located at the edges of T. maxima distribution is a prerequisite in the context of transfers and restocking programmes. In this study, giant clams were sampled from 14 atolls and islands within four archipelagos in the peripheral region of French Polynesia, in 2001–2002 and/or in 2012–2013, then genotyped at the COI gene and at nine microsatellite loci. Mitochondrial lineages of T. maxima from French Polynesia diverged from those sampled in Micronesia, Melanesia, the Coral Triangle and the Red Sea by 6.6–7.3%. Within French Polynesia, significant genetic structure was found, indicating restricted gene flow, and it was stable through time. Most of the genetic variation at microsatellite loci was between archipelagos. The most differentiated archipelago was the most geographically isolated (the Austral Islands). The current patterns of genetic structuring of T. maxima in French Polynesia probably result from long‐term genetic isolation with limited dispersal ability. In addition, these results underlined that sufficiently large populations of T. maxima have persisted in the Central Pacific during the last sea‐level regression. Strategies to optimize transfers and restocking programmes should be designed to preserve the genetic diversity and structure observed here, to avoid the risks of altering the genetic structure, allele loss and/or introduction of maladapted alleles in the receiving populations.

STUDY OF GIANT CLAMS RESOURCES AND CORAL REEF ECOSYTEM FOR MARINE ECOTURISM MANAGEMENT

ABSTRACTGiant clams that protected by CITES Appendix II is important marine organism as a stock in and also has potential as a marine tourism. This study aims to analyze the potential of clams which are part of the coral reef ecosystem as an alternative ecotourism management of diving and snorkeling in Morella and analyzing appropriate management strategies for the development of tourism areas in Morella. The method used for the analysis of clams is 1) the density of clams Di = ni / A; 2) diversity index H '= - (∑ni (ln (ni / N)); 3) dominance index D = ∑ [Ni / N] 2, and Analysis Hierarchy Process (AHP) method. There are five types of clams such as Tridacna maxima, T. squamosa, T. gigas, T. crocea and Hippopus hippopus. The widest distribuiton was T. maxima, which was found at each research areas and the lowest was H. Hippopus. The population of clams was found at Lettang Beach with the most species being T. squamosa. The highest percentage of coral reef cover was found at Lubang Buaya Beach at 81.10% and the lowest at station I at 55.53%. The highest number of species of reef fish is found at Lettang Beach, which is 197 types. The management strategy that needs to be prioritized is integrated management, which takes into account all aspects of ecological, economic, social and institutional aspects.

Ultradian rhythms in shell composition of photosymbiotic and non-photosymbiotic mollusks

Abstract. The chemical composition of mollusk shells is a useful tool in (paleo)climatology since it captures inter- and intra-annual variability in environmental conditions. Trace element and stable isotope analysis with improved sampling resolution now allows in situ determination of the composition of mollusk shell volumes precipitated at daily to sub-daily time intervals. Here, we discuss hourly resolved Mg / Ca, Mn / Ca, Sr / Ca, and Ba / Ca profiles measured by laser ablation inductively coupled plasma – mass spectrometry (ICP-MS) through shells of the photosymbiotic giant clams (Tridacna maxima, T. squamosa, and T. squamosina) and the non-photosymbiotic scallop Pecten maximus. Precise sclerochronological age models and spectral analysis allowed us to extract daily and tidal rhythms in the trace element composition of these shells. We find weak but statistically significant expressions of these periods and conclude that this cyclicity explains less than 10 % of the sub-annual variance in trace element profiles. Tidal and diurnal rhythms explain variability of, at most, 0.2 mmol mol−1 (∼ 10 % of mean value) in Mg / Ca and Sr / Ca, while ultradian Mn / Ca and Ba / Ca cyclicity has a median amplitude of less than 2 µmol mol−1 mol mol−1 (∼ 40 % and 80 % of the mean of Mn / Ca and Ba / Ca, respectively). Daily periodicity in Sr / Ca and Ba / Ca is stronger in Tridacna than in Pecten, with Pecten showing stronger tidal periodicity. One T. squamosa specimen which grew under a sunshade exhibits among the strongest diurnal cyclicity. Daily cycles in the trace element composition of giant clams are therefore unlikely to be driven by variations in direct insolation but rather reflect an inherent biological rhythmic process affecting element incorporation. Finally, the large amount of short-term trace element variability unexplained by tidal and daily rhythms highlights the dominance of aperiodic processes in mollusk physiology and/or environmental conditions over shell composition at the sub-daily scale. Future studies should aim to investigate whether this remaining variability in shell chemistry reliably records weather patterns or circulation changes in the animals' environment.

The giant clam commensal shrimp Anchistus miersi (de Man, 1888) (Decapoda: Palaemonoidae) new to Lakshadweep Sea, India

The genus Anchistus Borradaile, 1898 is a colourful shrimp from the commensal group. In this study, we are reporting a new occurrence of Giant Clam commensal shrimp Anchistus miersi (de Man, 1888 [in de Man, 1887–1888]) caught from Agatti Island, Lakshadweep Sea during February 2020. The present specimens (one each matured male and female) were collected from the mantle cavity of the Giant Clam, Tridacna maxima (Roding, 1798) in the coral lagoon at a depth of 4 m. Anchistus miersi is morphologically very similar to Anchistus demani, which is easily distinguished by the presence of a strong antennal spine and conspicuous accessory spinules in the third─fifth pereopods and presence of small blue spots all over the body. The molecular analysis confirms that, the morphological identification of the present Indian specimens displays an intraspecific genetic divergence of 0.3─1.2%. Besides, the remarkable taxonomic features and colour patterns, distributional ranges are also attested with the report of the species from the present area.

Anomalous δ18O signal in a giant clam shell (Tridacna maxima) from the Lakshadweep Archipelago, India: signature of thermal stress during a coral bleaching event

Anomalous δ18O signal in a giant clam shell (Tridacna maxima) from the Lakshadweep Archipelago, India: signature of thermal stress during a coral bleaching event

Population structure of giant clams (subfamily: Tridacninae) across Palau: Implications for conservation

Abstract Giant clams (subfamily: Tridacninae) are an important food and economic resource for the Republic of Palau and the greater Indo‐Pacific region. However, giant clam diversity and distribution data for Palau are out of date. This study reports the species diversity and distribution of giant clams across the Palauan archipelago (total survey area of 3,3002 m) from data collected between 2015–2017. This is the first documented finding of Tridacna noae in Palau, however, it was rare. Only four individuals were found at only two locations. Results show that Palau is home to a diverse and abundant population of giant clams. Tridacna crocea (an important food and economic resource) exhibited the highest abundance, with an average of 20.0 ± 2.9 individuals per 50 m2. Tridacna maxima and Tridacna squamosa were ranked next in abundance. In contrast, T. noae, Tridacna derasa, Tridacna gigas, and Hippopus hippopus were found in low numbers or only found in few locations. The density of all recruits, juveniles, and adult T. crocea and T. maxima did not differ significantly between conservation areas and open fishing sites, which suggests the possibility that ecological factors such as habitat loss, acute weather events, or changes in sea surface temperatures could be impacting replenishment or recruitment. However, one protected area was found to have a higher abundance of T. crocea recruits and adults, which suggests that protection from fishing may have increased recruitment rates and lowered mortality rates at this site. Taken as a whole, clam populations in Palau remain reasonably abundant and healthy. As demand for giant clams continues to rise in Palau and the region, local regulations should focus on sustainable fishing practices by establishing size limits, species bans, and long‐term monitoring plans to maintain the diverse populations of giant clams found there.

Diversity of Three Small Type’s Giant Clams and Their Associated Endosymbiotic Symbiodiniaceae at Hainan and Xisha Islands, South China Sea

Giant clams are found in a mutualistic association with Symbiodiniaceae dinoflagellates, however, the diversity of the giant clams, as well as the diversity and distribution of Symbiodiniaceae in different Tridacnine species remain relatively poorly studied in the South China Sea. In this study, a total of 100 giant clams belonging to small type’s giant clams, Tridacna maxima, T. crocea, and T. noae, were collected from Hainan and Xisha Islands. Based on mtDNA cytochrome c oxidase subunit 1 gene (COI) and 16S rRNA fragments, T. maxima and T. crocea showed a closer phylogenetic relationship than T. noae. All the three species of giant clams hosted Symbiodiniaceae including genera Symbiodinium (formerly Clade A) and Cladocopium (formerly Clade C). Geographically, symbionts in Cladocopium are restricted to Xisha Islands, probably because Cladocopium prefers to inhabit in waters with higher mean temperatures. The endosymbiont specificity among the three giant clam species was also detected. T. noae and T. crocea are found to harbor Symbiodinium preferentially, compared with Cladocopium. These results could provide important information to understand various endosymbionts occurring in giant clams in the South China Sea.

Giant clam growth in the Gulf of Aqaba is accelerated compared to fossil populations.

The health of reef-building corals has declined due to climate change and pollution. However, less is known about whether giant clams, reef-dwelling bivalves with a photosymbiotic partnership similar to that found in reef-building corals, are also threatened by environmental degradation. To compare giant clam health against a prehistoric baseline, we collected fossil and modern Tridacna shells from the Gulf of Aqaba, Northern Red Sea. After calibrating daily/twice-daily growth lines from the outer shell layer, we determined that modern individuals of all three species (Tridacna maxima, T. squamosa and T. squamosina) grew faster than Holocene and Pleistocene specimens. Modern specimens also show median shell organic δ15N values 4.2‰ lower than fossil specimens, which we propose is most likely due to increased deposition of isotopically light nitrate aerosols in the modern era. Nitrate fertilization accelerates growth in cultured Tridacna, so nitrate aerosol deposition may contribute to faster growth in modern wild populations. Furthermore, colder winter temperatures and past summer monsoons may have depressed fossil giant clam growth. Giant clams can serve as sentinels of reef environmental change, both to determine their individual health and the health of the reefs they inhabit.

Giant clam inspired high-speed photo-conversion for ultraviolet optical wireless communication

Organisms have evolved the ability to manipulate light for vision, as a means to capture its energy, to protect themselves from damage, especially against ultraviolet (UV) and other high flux radiation, and for display purposes. The makeup of the structural elements used for this manipulation often discloses novel pathways for man-made photonic devices. Iridocytes in the mantle of giant clams in the Tridacninae subfamily manipulate light in many ways, e.g., as reflectors, scattering centers, and diffusers. There is, however, a void in understanding the absorption and photoluminescence (PL) emission dynamics of these cells. In turn, a profound understanding of iridocytes’ photophysics can offer the prospect for a new generation of advanced optoelectronic materials and devices. Here, the structural and optical properties of the iridocytes embedded in the mantle tissue of the Tridacna maxima are investigated and their use as a high-speed color convertor for UV photodetection, well-suited to application in UV optical wireless communication, is demonstrated.

Flexibility in Red Sea Tridacna maxima-Symbiodiniaceae associations supports environmental niche adaptation.

Giant clams (Tridacninae) are important members of Indo‐Pacific coral reefs and among the few bivalve groups that live in symbiosis with unicellular algae (Symbiodiniaceae). Despite the importance of these endosymbiotic dinoflagellates for clam ecology, the diversity and specificity of these associations remain relatively poorly studied, especially in the Red Sea. Here, we used the internal transcribed spacer 2 (ITS2) rDNA gene region to investigate Symbiodiniaceae communities associated with Red Sea Tridacna maxima clams. We sampled five sites spanning 1,300 km (10° of latitude, from the Gulf of Aqaba, 29°N, to the Farasan Banks, 18°N) along the Red Sea's North‐South environmental gradient. We detected a diverse and structured assembly of host‐associated algae with communities demonstrating region and site‐specificity. Specimens from the Gulf of Aqaba harbored three genera of Symbiodiniaceae, Cladocopium, Durusdinium, and Symbiodinium, while at all other sites clams associated exclusively with algae from the Symbiodinium genus. Of these exclusively Symbiodinium‐associating sites, the more northern (27° and 22°) and more southern sites (20° and 18°) formed two separate groupings despite site‐specific algal genotypes being resolved at each site. These groupings were congruent with the genetic break seen across multiple marine taxa in the Red Sea at approximately 19°, and along with our documented site‐specificity of algal communities, contrasted the panmictic distribution of the T. maxima host. As such, our findings indicate flexibility in T. maxima‐Symbiodiniaceae associations that may explain its relatively high environmental plasticity and offers a mechanism for environmental niche adaptation.

Analysis of Pelecypoda Ecology Index in Rancabuaya Beach Garut District

This study aims to determine the Pelecypoda species and Pelecypoda Ecological Index values include diversity, abundance, evenness, dominance and density in Rancabuaya Beach Garut District. The method used is descriptive method with purposive sampling technique, Line transect and Quadrat transect. Sampling was carried out by dividing the study area into three observation stations totaling 90 samples. Observations were obtained, Pelecypoda species as many as 12 species including: Barbatia foliata, Antigona puerpera, Antigona materna, Anadara turonica, Cardita aviculina, Anodontia vesícula, Gafrarium pectinatum, Antigona puerpera, Antigona materna, Anadara turonica, Cardita aviculina, Anodontia vesicula, Gafrarium pectinatum, Anigontia edentpera, Antigona materna, Anadara turonica, Cardita aviculina, Anodontia vesicula, Gafrarium pectinatum, Anigontia edentperula, Anigontia edentula Septifer bilocularis, Tellina scobinata, Tridacna maxima, and Anadara antiquata. The results of the analysis of diversity index 0.0069-0.1596 are in the low category, an abundance index of 0.3-35.3% are in the average category enough, evenness index 0-0.0753 evenness is in a depressed condition, 0-0,12456 which is in the low category and the density index ranges from 0.1 to 13.2 is in the low category. This indicates the threat to the survival of Pelecypoda and the low quality of waters on the coast of Rancabuaya.

Drivers of the Abundance of Tridacna spp. Giant Clams in the Red Sea

Giant clams (Subfamily Tridacninae), are important members of Indo-Pacific coral reefs, playing multiple roles in the framework of these communities. Although they are prominent species in Red Sea reefs, data on their distribution and densities in the region are scarce. The present study provides the first large-scale survey of Red Sea Tridacna spp. densities, where we examined a large proportion of the Saudi Arabian Red Sea coast (1,300 km; from 18° to 29°N). Overall, Tridacninae were found at densities of 0.19 ± 0.43 individuals m–2 (±SD). Out of the total 4,002 observed clams, the majority (89%) were Tridacna maxima, with 0.17 ± 0.37 individuals m–2, while only 11% were Tridacna squamosa clams with 0.02 ± 0.07 individuals m–2. We also report on a few (total 6) Tridacna squamosina specimens, found at a single reef. We identified different geographical parameters (i.e., latitude and distance to shore) and local environmental factors (i.e., depth and reef zone) as the main drivers for local Tridacna spp. densities. Our results show that the drivers influencing the densities of Red Sea giant clams are complex due to their co-occurrence and that this complexity might explain the high variation in Tridacninae abundances across the Indo-Pacific, but also within a given reef. We also estimate that giant clam calcification likely contributes to an average of 0.7%, but potentially up to 9%, of the overall mean calcium carbonate budget of Red Sea coral reef communities.

Reproduction and Early Juvenile Growth of the Giant Clams Tridacna noae and Tridacna maxima in Taiwan.

The reproductive cycle, larval development, and juvenile growth of Tridacna noae and Tridacna maxima were investigated to improve their hatchery production for conservation and commercial use in Taiwan. To study the giant clam reproductive cycle, hypodermic extraction of oocytes from T. noae and T. maxima was conducted in Dongsha and Kenting, Taiwan, from March 2013 to May 2014; ripe eggs were observed in both species from March to August. There was no apparent correlation between reproduction and water temperature. Artificial fertilization was successfully conducted in T. maxima, T. noae, and a hybrid of T. maxima♀/T. noae♂. The diameter of fertilized eggs was 99.0 ± 8.1, 113.8 ± 18.5, and 116.3 ± 6.2 μm, respectively. On day 6, the hybrid died. Tridacna maxima grew more than T. noae in both 1-and 10-month-old juveniles. The juvenile growth of T. noae was compared between the artificial breeding sites of Penghu and Linbian, which represent the main ornamental aquatic animal culture areas of Taiwan. Starting with individuals with a shell length of 15.9 ± 2.5 mm (265 days old), the juveniles observed in Linbian were significantly larger than those in Penghu, i.e., 26.6 ± 3.6 mm on day 307 vs. 18.6 ± 2.9 mm on day 321 (p < 0.001). This might be linked to the differences in local water temperatures between the two locations, i.e., 20.3-27.0°C vs. 16.9-23.9°C, respectively. These results can be used to further research ways to maximize spat production and minimize giant clam operational costs.