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Tridacna (Chametrachea) costata ROA-QUIAOIT, KOCHZIUS, JANTZEN, AL-ZIBDAH & RICHTER from the Red Sea, a Junior synonym of Tridacna squamosina STURANY, 1899 (Bivalvia, Tridacnidae)



Analysis of the material of Tridacnidae collected during the Pola Red Sea Expeditions 1895/96 and 1897/98 revealed that the recently described Tridacna (Chametrachea) costata, ROA-QUIAOIT, KOCHZIUS, JANTZEN, AL-ZIBDAH & RICHTER in RICHTER, ROA-QUIAOIT, JANTZEN, ALZIBDAH & KOCHZIUS, 2008 is identical with T. elongata var. squamosina STURANY, 1899. For more than one hundred years the material has been kept in the Mollusca collection of the Natural History Museum in Vienna without proper identification. During the analysis of the material it was possible to identify the relevant specimens with the consequence that T. costata has to be considered a junior synonym of T. squamosina. With this newly designated lectotype the southernmost occurrence of T. squamosina is recorded.
Tridacna (Chametrachea)costata ROA-QUIAOIT,KOCHZIUS,
a junior synonym of Tridacna squamosina STURANY, 1899
(Bivalvia, Tridacnidae)
M. Huber*& A. Eschner**
Analysis of the material of Tridacnidae collected during the Pola Red Sea Expeditions 1895/96
and 1897/98 revealed that the recently described Tridacna (Chametrachea)costata, ROA-
ZIBDAH & KOCHZIUS, 2008 is identical with T. elongata var. squamosina STURANY, 1899. For
more than one hundred years the material has been kept in the Mollusca collection of the Natural
History Museum in Vienna without proper identification. During the analysis of the material it
was possible to identify the relevant specimens with the consequence that T. costata has to be
considered a junior synonym of T. squamosina. With this newly designated lectotype the south-
ernmost occurrence of T. squamosina is recorded.
Key Words: Red Sea, Bivalvia, Cardioidea, Tridacna,squamosina,costata, Sturany, Pola type
Bei Untersuchung der Tridacnidae, die während der Pola Expeditionen ins Rote Meer 1895/96
und 1897/98 aufgesammelt wurden, zeigte sich, dass die jüngst beschriebene Tridacna (Chame-
QUIAOIT, JANTZEN, AL-ZIBDAH & KOCHZIUS, 2008 mit T. elongata var. squamosina STURANY,
1899 identisch ist. Über 100 Jahre war das Expeditionsmaterial in der Molluskensammlung des
Naturhistorischen Museum in Wien aufbewahrt worden, ohne eingehende Identifizierung.
Während der Bearbeitung des Materials konnten die entsprechenden Exemplare identifiziert
werden, mit der Konsequenz, dass T. costata als Juniorsynonym von T. squamosina anzusehen
ist. Mit dem neu designierten Lectotypus wird gleichzeitig auch die südlichste Verbreitung doku-
*Dr. Markus Huber, University Zürich, Zoological Museum, Winterthurerstrasse 190, 8057 Zürich,
Switzerland. –
** Mag. Anita Eschner, Naturhistorisches Museum Wien, 3. Zoologische Abteilung, Burgring 7, 1010
Wien, Austria, –
Ann. Naturhist. Mus. Wien, B 112 153–162 Wien, März 2011
Giant clams are among the most spectacular marine bivalves. Huge size, ease of recog-
nition, peculiar feeding mechanism and shallow reef habitats are well known features of
this group. Tridacna BRUGUIÈRE, 1797 encompasses the heaviest and after Kuphus
GUETTARD, 1770 the second largest recent bivalve. Numerous tridacnids have been
described. Most modern authors consider currently seven extant Tridacna as valid; in
one case, however, the validity is disputed. For Tridacna rosewateri SIRENKO & SCARLATO,
1991 it is unclear if this species is a habitat-variant – as indicated by BENZIE & WILLIAMS
(1998), or a distinct species endemic to the Mascarene Plateau, in the sense of NEWMAN
& GOMEZ (2000). LUCAS et al. (1990, 1991) described a new species from Tonga and Fiji
which turned out to be a junior synonym of T. mbalavuana LADD, 1934 from the Upper
Tertiary of Fiji. Paleontological studies, which tried to reconstruct the evolution and
radiation of Tridacnidae implied that modern lineages originated in the Paleogene and
early Neogene of the East African-Arabian Province (see HARZHAUSER et al. 2008).
Difficulties in the morphological classification of tridacnids have led to modern DNA-
based genetic studies. These molecular genetic analyses tried to clarify the situation of
giant clam populations in the northern part of the Red Sea and concluded that there live
at least three species of Tridacna (ROA-QUIAOIT 2005; MOHAMED et al. 2006). In fact
MOHAMED et al. (2006) even indicate the possibility of five extant Red Sea species. Fur-
thermore, there are doubts, whether the species commonly identified as T. squamosa
LAMARCK, 1819 from the Red Sea is indeed Lamarck’s true T. squamosa (J.J. ter
Poorten, pers. comm., Oct. 2010). Definitely, the number and identity of the living Red
Sea tridacnids is currently unresolved. Consequently, the respective Red Sea species is
here termed T. cf. squamosa.
Recently, an 8th Tridacna species has been described from the northern Red Sea. Tri-
clear morphological, habitat and genetic diagnostics compared to the other two well
known tridacnids occurring in the Red Sea, T. maxima (RÖDING, 1798) and T. cf.
squamosa LAMARCK, 1819.
In 1899, Sturany published the results of the "Pola"-Expedition to the Red Sea. He men-
tioned three Tridacna taxa found during this expedition of which one was new.
The material from the Pola expeditions forms a significant part of the scientific collec-
tions in the Naturhistorisches Museum Wien, Austria (NHMW). In the course of 7 expe-
ditions - all carried out by SM Ship Pola - clearly defined areas of the ocean were sys-
tematically explored. Between 1890 and 1894, the eastern Mediterranean, and from
1895 to 1898, the Red Sea were sampled. Compared to larger expeditions of other coun-
tries, these expeditions by the Austro-Hungarian monarchy turned out to be highly effi-
cient and minutely planned. Thanks to the use of modern oceanographic instruments, the
eastern Mediterranean and the Red Sea became the most thoroughly explored areas of
sea at that time. For more details concerning the expeditions, their scientific results and
the history of oceanography, see SCHEFBECK (1991).
Molluscs alone collected during the Pola expeditions in the Red Sea amount to 1300
series of gastropods and bivalves (STAGL et al. 1996). As the curator responsible at the
154 Annalen des Naturhistorischen Museums in Wien, B, 112
k.u.k. Hofmuseum, Rudolf Sturany worked on the mollusc material gathered during the
Pola expeditions. Sturany published a series of papers on gastropods (STURANY 1896;
1900a, b; 1904) and bivalves (STURANY 1896; 1899). Unfortunately, his works either
remained disregarded or were inaccessible to English speaking researchers.
Sturany’s publications are mandatory reading for every Red Sea bivalve specialist. His
report on the Red Sea "Lamellibranchiaten" dating from 1899 was first published sepa-
rately as a "Sonderdruck" and 1901 reprinted as part of the "Berichte der Commission
für oceanographische Forschungen" which were published in the "Denkschriften der
mathematisch-naturwissenschaftlichen Classe der kaiserlichen Akademie der Wis-
senschaften, Wien".
Sturany described many rare deepwater species dredged during the Pola Expedition.
Included were also many shallow water species collected near or on shore.
The complete dry and wet material of the Pola Expeditions - including the syntypes of
T. elongata var. squamosina – was originally inventoried at the Mollusca Collection
under the number NHMW Moll. 38076.
Sturany did not individually label each specimen. However, Sturany stated the respec-
tive Red Sea stations in his report and the station data are available for each of the spec-
imens. With very few exceptions the whole wet and dry material of Sturany was avail-
able and conformed to the stations indicated.
Six T. squamosina syntypes were collected in the Gulf of Aqaba, in Dahab (4 speci-
mens) and in Sharm el Sheikh (2 specimens). The seventh and largest specimen origi-
nated in the southern Red Sea at Kamaran Island, off Yemen. Altogether Sturany studied
7squamosina specimens ranging in size from 102 to 190 mm.
Almost 30 Pola specimens conform to T. maxima. More than 30 Pola specimens con-
form to T. cf. squamosa. Contrary to the situation nowadays, T. cf. squamosa was around
1900 the most commonly collected Tridacna in the Red Sea.
Unfortunately, many authors including ROSEWATER (1965) and ZUSCHIN & OLIVER
(2003) as well as ROA-QUIAOIT et al. (2008) and very recent works of RUSMORE-VIL-
LAUME (2008) and KNOP (2009) have overlooked Sturany’s publication. Only OLIVER
(1992) mentioned his paper and he assigned Sturany’s T. rudis Rve. to T. squamosa
LAMARCK, 1819.
Sturany sorted the well over 60 tridacnids collected by the Pola expedition and recog-
nized 3 taxa. Two Red Sea species – T. maxima and T. cf. squamosa – were found com-
monly in various lots with approximately 30 specimens each, one species in just 3 lots
with 7 specimens. This is in accordance with modern findings.
STURANY (1899) briefly described the nov. var. T. elongata squamosina: "... hingegen
HUBER & ESCHNER:Tridacna costata a junior synonym of Tridacna squamosina (Bivalvia) 155
eine Varietät besonders hervorzuheben, die systematisch zur Tr. squamosa Lm. hinüber-
führt. Diese mit squamosina nov. var. zu bezeichnende Form liegt von den Localitäten
12, 14 und 43 in mehreren Exemplaren vor ...". He pointed out the characteristic "...
gegen den Unterrand blättrig aufgestellte Querschuppen der Rippen ...".
ROA-QUIAOIT (2005: table 9) elaborated precisely the characteristics of T. costata – shell
asymmetrical, hinge length < half shell length, scutes crowded and well spaced, wide
byssal orifice, and 5–6 deeply triangular radial folds (Table 1).
A close morphological comparison of Sturany’s T. squamosina with the newly described
T. costata left no doubt that these two species are identical. This assessement was con-
firmed by J. J. ter Poorten, a well known cardioid specialist. In addition, two of Stu-
rany’s three collecting stations conform to the type locality of T. costata in the Gulf of
Although Tridacna squamosina STURANY, 1899 was not found cited in other publica-
tions, Sturany’s species was validly proposed and is recognizably characterized. Seven
syntypes are unambiguously available. Sturany’s name is not preoccupied.
Consequently, a lectotype of T. squamosina is herein designated and T. costata formally
With respect to the description of the habitat, spawning, genetics of T. squamosina and
comparisons with other species of Tridacna, the works of ROA-QUIAOIT et al. (2008) and
especially the thesis of ROA-QUIAOIT (2005) provide an excellent overview. These
aspects are not discussed in this article.
However, two facts merit being added. More than 100 years ago T. squamosina was also
the species least commonly collected. The locality of station 43 further indicates that T.
squamosina may be found throughout the Red Sea and not just in its northern part.
Tridacna squamosina STURANY, 1899
(Figs. 1–6)
Tridacna elongata var. squamosina STURANY, 1899: 283
Tridacna nov. sp. ROA-QUIAOIT, 2005: 67, 72, 75–77 (with an extended characterization of nov. sp. and a
comparison of the other Red Sea species)
JANTZEN, AL-ZIBDAH & KOCHZIUS, 2008: 1349–1354 (syn. nov.)
Type material. Lectotype (Figs. 1–6) selected herein: largest specimen selected from the material Sturany
described as Tridacna elongata var. squamosina. – Red Sea, Yemen, Kamaran Island, ca. 15°17’ N; 42° 37’
E, shallow water, Pola expedition leg. F. Steindachner & F. Siebenrock 1.-3. Nov. 1897 [Loc. 43], (NHMW
Moll. 107075); paralectotypes: Egypt, Dahab, shallow water, Pola expedition leg. F. Steindachner & F.
Siebenrock 6. Apr. 1896 [Loc. 12] (4 specimens, NHMW Moll. 107076; Figs. 7, 10); Egypt, Sharm el
Sheikh [Sherm Sheik], shallow water, Pola expedition leg. F. Steindachner & F. Siebenrock 1. Apr. 1896
[Loc. 14] (2 specimens, NHMW Moll. 107077).
156 Annalen des Naturhistorischen Museums in Wien, B, 112
Comparative material. Tridacna cf. squamosa (Figs. 8, 11) – Red Sea, Egypt, Gulf of Aqaba, Nawibi,
Pola expedition leg. F. Steindachner & F. Siebenrock 9.-10. Apr. 1896 [Loc. 10] (NHMW Moll. 38076);
Tridacna maxima (Figs. 9, 12) – Red Sea, Egypt, Shadwan Island, Pola expedition leg. F. Steindachner & F.
Siebenrock 18.-20. Feb. 1896 [Loc. 16] (NHMW Moll. 38077).
Earlier workers treated tridacnids as their own superfamily (e.g. KEEN 1969;
STAROBOGATOV 1992). However, most modern analyses, including SCHNEIDER (1998),
BRALEY & HEALY (1998), SCHNEIDER & FOIGHIL (1999), GIRIBET et al. (2002) and MAT-
SUMOTO (2003) demonstrate a close relationship between tridacnids and cardiids, either
to Fragum RÖDING, 1798 or even to Nemocardium (Keenaea) HABE, 1951 (MATSUMOTO
2003). Consequently, many modern researchers attribute tridacnids subfamilial status
within Cardiidae. From an exclusive phylogenetic point of view, this placement may be
A superfamily Tridacnoidea LAMARCK, 1819 is certainly no longer valid. Tridacnids
must be understood as firm portion of Cardioidea LAMARCK, 1809, see BIELER et al.
(2010). However, the restricted biogeography of tridacnids, their peculiar habitats and
mode of life, their unique anatomy, together with their size and weight nonetheless jus-
tifies a special treatment within Cardioidea. As such, a familial treatment as Tridacnidae
LAMARCK, 1819 is here preferred and T. squamosina is understood as member of this
small bivalve family.
IREDALE (1937) started to divide Tridacna and proposed five additional genera for Aus-
tralian and Pacific species. He even created for the most variable tridacnid, T. maxima,
two distinct genera (i.e. Vulgodacna for T. fossor and Sepidacna for T. throughtoni,
which today are both considered synonymous to T. maxima). But it is doubtful if Per-
sikima is genetically distinct from Tridacna s.s. (ROA-QUIAOIT 2005; SCHNEIDER & Ó
FOIGHIL 1999). In addition, the subgenus Chametrachea MÖRCH, 1853 was earlier used
by HERRMANNSEN (1846), which is based on Chama aspera RUMPHIUS, 1705. Taking
further into account the characteristic features of each species and the small number of
HUBER & ESCHNER:Tridacna costata a junior synonym of Tridacna squamosina (Bivalvia) 157
Table 1: Diagnostic criteria in tridacnids after ROA-QUIAOIT (2005) and HUBER (2010)
T. squamosina T. squamosa T. maxima
Shell symmetry asymmetrical symmetrical asymmetrical
Hinge length < half shell length = half shell length < half shell length
Scutes crowded, well spaced large, well spaced low, crowded
Radial folds 5–6 deeply triangular 4–6 pointed to usually 5 sharply
bluntly rounded triangular
Byssal orifice wide narrow moderate to wide
Mantle patterns subdued subdued mottled colored
Incurrent tentacles distinct distinct indistinct
Maximum size 320 mm (Red Sea) 476 mm (Tonga) 500 mm (India)
Distribution Red Sea only Indo-Pacific Indo-Pacific
Habitat to 2 m, byssally to 25.5 m, to 32 m,
weakly attached byssally attached usually embedded
8 valid tridacnids, a forced differentiation of various subgenera within Tridacna adds lit-
tle benefit. More important are the real differences between species regarding habitats,
modes of life, genetics and detailed morphology. This was excellently worked out by
ROA-QUIAOIT (2005). Consequently, the subgeneric level is here abandoned and T.
squamosina is placed as Tridacna.
158 Annalen des Naturhistorischen Museums in Wien, B, 112
Figs. 1–6. Tridacna squamosina – lectotype, NHMW Moll. 107075 from Kamaran. 1, right valve
inside; 2, left valve inside; 3, right valve outside; 4, left valve outside; 5, byssal orifice; 6, radial
folds. Scalebar: 2 cm. Photographs: A. Schumacher.
STURANY (1899) recognized three Red Sea taxa. He clearly used the monograph of
REEVE (1862) on Tridacna as an identification guide. He identified elongata correctly.
Sturany’s elongata conforms to T. elongata LAMARCK, 1819. But in the 1950s and 1960s
it was recognized that Lamarck’s elongata is a junior synonym of Tridachnes maxima
RÖDING, 1798. Tridacna maxima (RÖDING, 1798) is today recognized as valid, earliest
name for this widely distributed species.
HUBER & ESCHNER:Tridacna costata a junior synonym of Tridacna squamosina (Bivalvia) 159
Figs. 7–12. Comparison of the three Tridacna species from the Red Sea in the collection of the
NHMW; top: radial folds; bottom: byssal orifice. 7, 10, Tridacna squamosina – paralectotype,
NHMW Moll. 107076a from Dahab; 8, 11, Tridacna cf. squamosa – NHMW Moll. 38076 from
Nawibi; 9, 12, Tridacna maxima – NHMW Moll. 38077 from Shadwan. Scalebar: 2 cm. Pho-
tographs: A. Schumacher.
The second common Red Sea species identified by Sturany was T. rudis. REEVE (1862)
described T. rudis from the Philippines. Indeed, Reeve’s pl. 5 fig. 4 a, b, c superficially
resembles the material identified by Sturany. Based on Rosewater’s treatment of this
family, modern authors today accept Reeve‘s rudis as a peculiar form of maxima. Con-
sequently, this second species was erroneously identified by Sturany as rudis. This was
recognized by OLIVER (1992), who identified it as Lamarck’s T. squamosa, here termed
T. cf. squamosa. It is not excluded that Tridachnes imbricata RÖDING, 1798 was the ear-
lier name for Lamarck’s famous species. Large portions of the Bolten collection, on
which Röding based his imbricata, are still to be found in Museum der Natur at Gotha,
Germany. However, a critical review of the respective material at Gotha in September
2010 led to the following conclusion: "Overall, due to missing descriptions and specific
marks in Röding, due to lack of original numbers and labels, due to the peculiar sup-
pressing and renaming method of Schmidt and finally due to the curational condition of
the collection we could not unambiguously identify any Bolten/Röding Bivalve type."
(HUBER &TER POORTEN in prep.). Thus, Tridachnes imbricata RÖDING, 1798 is best
treated as nomen dubium
The third, the least common species was described by Sturany as squamosina. ROA-
QUIAOIT (2005) stated the closest morphological affinities for T. costata are to T. max-
ima. STURANY (1899) came to the same result in considering squamosina closer to elon-
gata (=maxima) than to squamosa. From a molecular phylogeny based on mitochondrial
16 rDNA, ROA-QUIAOIT (2005) concluded that T. costata‘s closest relative is T. maxima,
whereas lower affinities were found between T. squamosa and T. crocea. For further
detailed information on T. squamosina we refer to ROA-QUIAOIT et al. (2008 as T.
costata) and especially to ROA-QUIAOIT (2005 as T. nov. sp.).
As such, Tridacna squamosina STURANY, 1899 is the 8th member of the genus Tridacna
within the family Tridacnidae. Currently, it is only known from the Red Sea, likely liv-
ing throughout. It is the least common of the described three Red Sea tridacnids. The
known habitat is very shallow within approximately 5 meters and the maximal size
reported is 320 mm.
Thanks are due to: Prof. Tony Wilson for editorial support, Dr. Peter C. Dworschak for fruitful
discussions and valuable help with the plates, Dr. Mathias Harzhauser for help with paleontological
literature and to Alice Schumacher for the photographs of the material.For their precise remarks
and additions, the authors are deeply indebted to one anonymous reviewer and J.J. ter Poorten,
The Netherlands.
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Bivalvia.– Wien: Naturhistorisches Museum Wien, 304 pp.
162 Annalen des Naturhistorischen Museums in Wien, B, 112
... To date, at least 31 reported sightings of T. squamosina have been documented from the Red Sea since their first description during the Pola Red Sea Expeditions 1895/96 and 1897/98 (Huber and Eschner, 2011). The observations from the literature include 16 individuals from Roa-Quiaoit (2005) and Richter et al. (2008), seven individuals from Huber and Eschner (2011), two individuals from Fauvelot et al. (2020) and six individuals from Rossbach et al. (2020). ...
... To date, at least 31 reported sightings of T. squamosina have been documented from the Red Sea since their first description during the Pola Red Sea Expeditions 1895/96 and 1897/98 (Huber and Eschner, 2011). The observations from the literature include 16 individuals from Roa-Quiaoit (2005) and Richter et al. (2008), seven individuals from Huber and Eschner (2011), two individuals from Fauvelot et al. (2020) and six individuals from Rossbach et al. (2020). The past and present known distribution of T. squamosina are Egypt, Jordan, Yemen, Saudi Arabia, and possible sightings in Israel based on photographic anecdotes (Richter et al., 2008;Huber and Eschner, 2011;Neo et al., 2017;Fauvelot et al., 2020;Rossbach et al., 2020). ...
... The observations from the literature include 16 individuals from Roa-Quiaoit (2005) and Richter et al. (2008), seven individuals from Huber and Eschner (2011), two individuals from Fauvelot et al. (2020) and six individuals from Rossbach et al. (2020). The past and present known distribution of T. squamosina are Egypt, Jordan, Yemen, Saudi Arabia, and possible sightings in Israel based on photographic anecdotes (Richter et al., 2008;Huber and Eschner, 2011;Neo et al., 2017;Fauvelot et al., 2020;Rossbach et al., 2020). Although a recently published analysis using genome skimming has provided highly credible phylogenetic relationship between T. squamosina and the other Tridacninae (Tan et al., 2021), information about their population genetic structure across the Red Sea is still lacking. ...
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Giant clams are an important ecological component of coral reefs in the Red Sea, as they enhance the reef’s productivity and provide habitat that can increase diversity. Three species of giant clams, namely Tridacna maxima , T. squamosa , and T. squamosina have been described within the Red Sea. However, due to its scarcity, information about the distribution and ecology of T. squamosina in the Saudi Arabian Red Sea is still lacking. This study used DNA barcoding to confirm the identity of the rare T. squamosina in the Farasan Banks. Six mtCOI fragments (500 bp) of T. squamosina were successfully amplified using the SQUA-primers for the first time. We used our data along with 18 reference sequences (16S) from the online database to assess the genetic diversity and population structure of T. squamosina . Low genetic diversity among the T. squamosina populations inferred from the 16S sequences implies a recent bottleneck for this species, which is supported by their historically higher diversity based on the coalescent-based estimator. Given the small population abundance and limited genetic variation of T. squamosina , it may warrant immediate local protections such as biobanking and fertility preservation programs as well as effective integrated coastal zone management plans.
... It is worth noting that such reef gathering can cause considerable physical damage to the reef . Mzeina gleaning, particularly for Tridacna has historically been intense, and it has been suggested that overexploitation was responsible for the possible local extinction of T. squamosina Huber and Eschner 2010). ...
... Juvenile recruitment is patchy, so uncontrolled harvest of adults quickly leads to local extinctions (Yamaguchi 1977). Tridacnidae are restricted to limited areas of the tropical Indo-Pacific (Copland and Lucas 1988;bin Othman et al. 2010) and significant population declines and localized extinctions have been reported (Wells et al. 1983;Lucas 1994 Huber and Eschner 2010). More broadly, the Mollusca are the phylum most affected by extinction worldwide yet are largely neglected by conservationists (Régnier et al. 2009). ...
... Tridacna species found in the Gulf of Aqaba (Figure 2.1) include: T. squamosa, T. maxima, (Roa-Quiaoit 2005) and T. squamosina Huber and Eschner 2010). Although it is the northwestern limit of their range, Tridacna densities in South Sinai are the highest in the Red Sea (Roa-Quiaoit 2005). ...
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Coral reef ecosystems around the world are declining as a result of human impacts including overfishing, pollution and climate change. The coral reefs of South Sinai are significant because of their unique biodiversity, the income that they generate for Egypt through diving tourism and their importance as traditional fishing grounds for the Mzeina Bedu. This PhD takes a multidisciplinary approach to evaluate the status of coral reefs in South Sinai, with particular emphasis on Bedouin fishers and their fisheries. In Chapter 1, I examine the importance of culture and traditional knowledge in the successful management of coral reefs and natural resources in general. In Chapter 2, I focus on the Bedouin tribes of South Sinai to understand their history and socioeconomic status; investigating their fishing techniques and sites as well as their traditional understanding of coral reef biodiversity and ecology. Chapter 3 focusses on the ecological status of finfish populations at sites along the South Sinai coastline, evaluating the status of stocks and potential Bedouin fishery impacts. Chapter 4 examines the invertebrate fishery, which is mainly practised by Bedouin women and targets Tridacna clams. Chapter 5 takes a fishery-dependent approach to assess the catch of Bedouin fishers, to understand important biological and socioeconomic parameters that influence the fishery. In Chapter 6, I use statistical modelling techniques on long-term coral reef ecosystem data sets from the study area to analyse longer-term trends in the ecological status of reefs in South Sinai and likely causes for these trends. Coral reefs provide income, tourism, food and coastal protection to local communities and indigenous people throughout the tropics. The socio-cultural facets of the Mzeina Bedu have been inextricably connected to the reefs and associated fisheries of South Sinai for generations. However, exploited finfish and invertebrate communities have declined in both size and abundance with increased fishing pressure, resulting in ecosystem-wide impacts. The Mzeina themselves should be integral to any proposed fisheries monitoring or management initiatives, and technological approaches may provide useful cost-effective tools. Fisheries ecosystem-level declines have been apparent over at least the last decade and sustained monitoring is essential to ensure that the impact of management initiatives may be measured. If urgent collaborative management and enforcement actions are implemented alongside a programme to develop livelihood opportunities for the Mzeina, the reefs of South Sinai could return to a state that supports both the socioeconomic needs of the Bedu and continues to generate substantial tourism income.
... Hence, they are now considered as a subfamily, Tridacninae Lamarck, 1819, within the family Cardiidae Lamarck, 1809 (Yonge 1936;Schneider 1992Schneider , 1998Maruyama et al. 1998), although some have argued to maintain Tridacnidae at the family level, based mainly on its highly unique morphology (e.g. Huber and Eschner 2011;Penny and Willan 2014). Tridacninae species are classified in two genera, Hippopus Lamarck, 1819 and Tridacna Bruguière, 1797 (Rosewater 1965;Schneider 1998;Schneider and Ó Foighil 1999), with the latter being further subdivided into three subgenera: Tridacna (Tridacna) Bruguière, 1797, Tridacna (Persikima) Iredale, 1937 and Tridacna (Chametrachea) Herrmannsen, 1846 (Benzie and Williams 1998;Maruyama et al. 1998;Newman and Gomez 2000). ...
... In 1991, 'Tridacna tevoroa' was discovered in Fiji and described as a new species (Lucas et al. 1991), but later considered synonymous with Tridacna mbalavuana Ladd, 1934 through morphology (Newman and Gomez 2000). Similarly, 'Tridacna costata' discovered from the Red Sea in 2006 (Richter et al. 2008) was later synonymised with Tridacna squamosina Sturany, 1899 based on morphology (Huber and Eschner 2011). First observed by Kubo and Iwai (2007) at Ishigaki-jima Island, Tridacna noae (Röding, 1798) is a cryptic species resurrected from its synonymy under the widespread T. maxima by the use of molecular tools (Su et al. 2014). ...
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Giant clams are conspicuous bivalves inhabiting Indo-Pacific reefs. Since Rosewater’s seminal paper in 1965, the number of giant clam species described or resurrected has exactly doubled. The increased number of species reported and accessibility to genetic material of rare or uncommon species therefore call for a reappraisal of the phylogenetic relationships within the Tridacninae subfamily. Here, we aim to reconstruct the evolutionary relationships among all 12 extant species by performing a comprehensive phylogenetic analysis of mitochondrial genome and nuclear 18S rRNA data from a combination of genome skimming, Sanger sequencing and previously published sequences. Comparing the mitogenomes among Tridacninae species, we report two new findings: (1) the T. crocea mitogenome length obtained here (18,266 bp) is shorter than previously known, and (2) the mitochondrial gene order in T. crocea and T. squamosa differs from the other species. Our phylogeny based on a concatenated 16-gene dataset (15 mitochondrial markers and nuclear 18S rRNA) reveals highly supported relationships within and between the three subgenera, Tridacna (Tridacna), Tridacna (Persikima) and Tridacna (Chametrachea). Overall, the inclusion of new molecular markers greatly improves the confidence and support for the subfamily’s phylogeny. The availability of this comprehensive phylogenetic dataset serves as the foremost baseline of Tridacninae relationships to support future studies examining giant clam systematics, ecology and conservation.
... Rudolf Sturany, curator of the molluscan collection at the Natural History Museum in Vienna (NHMW) between the late 19 th and early 20 th century, described 56 species of Red Sea molluscs based on the pioneering expeditions of the vessel "Pola" between 1895 and 1898, the first to explore the deep-sea regions of the basin (Schefbeck 1996;Stagl 2012;Janssen and Taviani 2015). However, his work went unnoticed for long, possibly also due to the use of the German language (Huber and Eschner 2011). ...
... This species had been poorly known for a long time but was recognised as a distinct entity on the basis of a molecular phylogeny with the mitochondrial gene 16s rRNA (Richter et al. 2008). However, Richter et al. (2008) described this entity with the new name Tridacna costata which was recognised as a junior synonym of T. squamosina by Huber and Eschner (2011). ...
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Rudolf Sturany, the curator of molluscs of the Natural History Museum of Vienna between the late 19 th and early 20 th century described 21 species of bivalves from the Red Sea collected by the pioneering expeditions of the vessel “Pola” which took place between 1895 and 1898. We here list and illustrate the type material of these species, provide the original descriptions, a translation into English, and curatorial and taxonomic comments. All species are illustrated in colour and with SEM imaging. To stabilize the nomenclature, we designate lectotypes for Gastrochaena weinkauffi , Cuspidaria brachyrhynchus , and C. dissociata , whose type series contained specimens belonging to other species. This paper concludes the series on the type specimens of marine molluscs described by Sturany from the “Pola” expeditions.
... Most of them are considered to be at a lower risk/conservation-dependent status; however, according to , the IUCN status of Tridacninae is in urgent need of updating. For the Red Sea, three species of giant clams have been previously reported (e.g., by Roa-Quiaoit, 2005;Richter et al., 2008;Huber and Eschner, 2010;Ullmann, 2013), namely Tridacna squamosa Lamarck, 1819, Tridacna squamosina Sturany, 1899 (previously described as T. costata by Richter et al., 2008) and Tridacna maxima Röding, 1789. The latter, also called the "small giant clam, " is assumed to be the most abundant giant clam species in the Red Sea Pappas et al., 2017;Lim et al., 2020). ...
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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.
... Mitochondrial markers have been found to be suitable to resolve population genetics structures of marine bivalves (Schneider and Ó Foighil, 1999;Mohamed et al., 2006;Richter et al., 2008;Huber and Eschner, 2011;Pappas et al., 2017;Fauvelot et al., 2020), although with limited geographical scope. Previous surveys of Tridacna maxima by Pappas et al. (2017) and Othmen et al. (2020) were restricted to coral reefs in the northern and central Saudi Arabian Red Sea. ...
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The Red Sea serves as a natural laboratory to investigate mechanisms of genetic differentiation and population dynamics of reef organisms due to its high species endemism. Giant clams, important yet understudied coral reef engineering species, are ideal candidates for such study in this region. This paper presents the first population genetics study of giant clams covering the entire East coast of the Red Sea. Our study aimed to investigate the population structure of the small giant clam, Tridacna maxima, based on 501-bp fragment of the cytochrome c oxidase I gene from 194 individuals (126 new sequences from this study plus 68 sequences from GenBank), collected from 14 locations in the Red Sea and Gulf of Aden (RSGA). For the genetic analysis, each sampling site was treated as a population. T. maxima showed high genetic diversity, with high gene flow in almost all sampling sites. The insignificant global ϕST-value of 0.02 (p > 0.05) suggests the presence of one large, panmictic population across a wide range of temperature and salinity gradients in the RSGA. Despite this, the population in Djibouti was genetically differentiated from the other 11 populations in the Red Sea, suggesting a connectivity break between the Red Sea and the Gulf of Aden. These results could be explained by the oceanographic features facilitating wide larval transport inside the Red Sea, and creating a dispersal barrier to the Gulf of Aden. Besides larval dispersal by currents, apparent successful establishment following dispersal is probably facilitated by the mode and time of reproduction as well as the ability of T. maxima to achieve high fitness in the highly variable environmental conditions of the Red Sea.
... Therefore, the use of morphological characteristics as identification tools has led to errors in giant clam identification and classification occasionally. For example, until recently, T. costata was misclassified as Tridacna squamosina Sturany, 1899 (Huber and Eschner 2011), and T. noae was only separated from T. maxima by their genetic and morphological description (Su et al. 2014). In addition, this method is ineffective for identifying larvae and in forensic cases where exhibits are often of degraded and/or processed quality. ...
In an effort to develop molecular tools for giant clam species identification, this study reveals the usefulness of a multiplex species-specific PCR for the reliable, rapid and low-cost identification of five giant clam species found in the South China Sea: Hippopus hippopus, Tridacna maxima, Tridacna derasa, Tridacna squamosa and Tridacna noae. We used the mitochondrial COI gene for marker development. Five reverse primers and a common forward primer were designed to generate five different size species-specific PCR fragments. These six primers were combined in a multiplex PCR to enable identification of five giant clam species in a single reaction. This molecular approach provides a simple and rapid identification of the giant clam species from the South China Sea, thus increasing the efficiency and quality of giant clam stock management, protecton and forensic identification by reducing the risk of wrong species identification.
... are globally distributed (Neo et al., 2017) while T. squamosina (=T. costata Roa-Quioait et al.) 66 was only recently recognized as a distinct species and is believed to be endemic to the Northern 67 Red Sea (Huber & Eschner, 2010;Richter et al., 2008). The species is extremely rare and 68 potentially endangered today but was the most common Tridacna species in Pleistocene fossil 69 reefs . ...
... Although reputedly a Red Sea endemic (Huber & Eschner, 2011), recent anecdotal sightings suggest that the species may also occur in Mozambique (Neo et al., 2017). The two other endemic species from this region were described based on morphology: T. rosewateri, known only from Saya de Malha Bank (Sirenko & Scarlato, 1991), and T. lorenzi, known only from the Cargados Carajos archipelago, Mascarene Plateau (Monsecour, 2016). ...
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The unique biodiversity in the Red Sea is the result of complex ecological and evolutionary processes driven by Pleistocene climatic change. Here we investigate the species diversity, phylogenetic relationships and phylogeographical patterns of giant clams in the Western Indian Ocean (WIO) and the Red Sea to explore scenarios of marine speciation in this under‐studied region. Mozambique Channel, Madagascar, and the Mascarene Islands (WIO); the Farasan Islands (Red Sea). Giant clams of the genus Tridacna (Cardiidae: Tridacninae). Giant clams were sampled as complete organisms or through underwater biopsies. Nuclear (28S) and mitochondrial (16S and COI) DNA sequences were subjected to Bayesian and maximum likelihood analyses to generate a phylogenetic hypothesis for all known species within the genus Tridacna. Bayesian inference with molecular and fossil calibration was used to infer their colonization history. From the 10 genetically distinct clades recovered from the analyses of 253 sequenced specimens, five distinct Tridacna lineages were sampled, three of which were endemics of the WIO and the Red Sea. Each lineage corresponded to a distinct species, except one grouping the two formerly known WIO endemics, T. lorenzi and T. rosewateri. This lineage clustered with two other well‐supported lineages: the Red Sea endemic T. squamosina, and a previously unrecognized lineage, restricted to the WIO, for which we resurrect the long‐forgotten name T. elongatissima Bianconi, 1856. For the two other species sampled (T. maxima and T. squamosa), contrasting phylogeographical patterns were observed. Our data confirm the validity of the species T. rosewateri, a WIO endemic genetically indistinguishable from T. lorenzi, which should be considered a junior synonym. The phylogenetic placement of the newly resurrected T. elongatissima provides insights into the probable origin of T. squamosina, which split from its sister species no later than 2 Ma, likely during Middle Pleistocene glacial periods. Two scenarios are discussed. Our results also suggest that T. maxima invaded the Red Sea more recently and that contemporary gene flow between Red Sea and WIO T. maxima is highly restricted. The deep Red Sea partition observed in T. squamosa suggests a much older divergence and raises the question of a possible cryptic lineage.
... This paper aims to illustrate the diversity of giant clams in the genus Tridacna and the diversity of their algal symbionts from reefs along the central Red Sea coast near Thuwal, Saudi Arabia. We expect to find the following species of Tridacna giant clams: T. maxima, T. squamosa, and T. squamosina, as these have been previously reported from the Red Sea (Bodoy 1984;Richter et al. 2008;bin Othman et al. 2010;Huber and Eschner 2010). Samples were collected from nine reefs on a cross-shelf gradient, including sampling from both the exposed and sheltered sides of the reefs. ...
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The biodiversity of the Red Sea remains relatively understudied, particularly for invertebrate taxa. Documenting present patterns of biodiversity is essential for better understanding Red Sea reef ecosystems and how these ecosystems may be impacted by stressors (such as fishing and climate change). Several species of giant clams (genus Tridacna) are reported from the Red Sea, although the majority of research effort has occurred in the Gulf of Aqaba. We investigated the genetic diversity (16S rDNA) of the Tridacna species found in the central Saudi Arabian Red Sea. We also investigated the genetic diversity (ITS rDNA) of symbiotic dinoflagellates Symbiodinium associated with these clams. Samples were collected from nine reefs on a cross-shelf gradient near Thuwal, Saudi Arabia. Two species, T. squamosa and T. maxima, were recorded, with the latter being the most abundant. Tridacna squamosina, a species recently reported in the northern Red Sea, was not found, suggesting that this species is not present or is very rare in our study region. All tridacnids sampled were found to harbor Symbiodinium grouped in Clade A, considered an opportunistic, heat-tolerant symbiont group in anemones and corals. The consistent association with Clade A Symbiodinium in central Red Sea tridacnids may reflect the consequence of adaptation to the relatively extreme conditions of the Red Sea. This study contributes to an ever-growing catalog of Red Sea biodiversity and serves as important baseline information for a region experiencing dynamic pressures. © 2017 Senckenberg Gesellschaft für Naturforschung and Springer-Verlag Berlin Heidelberg
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Some 1,048 names at the rank of subtribe, tribe, subfamily, family and superfamily have been proposed for Recent and fossil bivalves. All names are listed in a nomenclator giving full bibliographical reference, date of publication, type genus, and their nomenclatural availability and validity under the International Code of Zoological Nomenclature. Another 274 names, established for categories above the family-group are listed separately. A working classification attempts to group all bivalve family-group names into a single system based on current hypotheses of relations and synonymies. At several rank levels, the groups are given in alphabetical rather than some assumed phylogenetic arrangement, reflecting current uncertainties and conflicting results from anatomical, molecular, and fossil data. Altogether, the classification recognizes as valid a total of 324 families, of which 214 are known exclusively as fossils and 110 occur in the Recent with or without a fossil record. Key words: Bivalvia, nomenclature, taxonomy, taxon listing.
The cardiid bivalve taxa Plagiocardium, Maoricardium, Clinocardiinae, Fraginae, Goethemia, Lymnocardiinae, and Tridacninae form a monophyletic group. The most parsimonious cladograms of this group have a topology of (Plagiocardium (Maoricardium (Clinocardiinae (Fraginae (Goethemia (Lymnocardiinae, Tridacninae)))))). The giant clams form a subfamily (Tridacninae) of Cardiidae. In the ontogeny and phylogeny of giant clams, the morphology and position of the muscle scars and hinge changes from that resembling the dimyarian Cerastoderma to the monomyarian morphology displayed by Hippopus and Tridacna, which have lost the anterior half of the shell. This peramorphic trend is the result of differential growth: tremendous growth rate of the posterior portion of the shell and a zero or even negative growth rate of the anterior half of the shell. All tridacnines and several species of fragines are known to harbor photosymbiotic zooxanthellae. These algae transfer excess carbon to its cardiid host. It is known that the chemosymbiotic lucinid and solemyid bivalves reduce or lose many features of their digestive systems. The sulfur-reducing bacteria in lucinids and solemyids provide most of the nutrients that the host clam needs, thus making a full digestive system unnecessary. Most fragine cardiids reduce numerous structures of their digestive systems. Only a few fragines have been examined for the presence of photosymbionts. Based upon their anatomy, it is predicted that most or all of the derived fragines harbor photosymbionts. Tridacnines harbor photosymbionts but do not appreciably reduce their digestive systems. The possession of both photosymbionts and a fully functional digestive system allows tridacnines to be the fastest growing and largest of the extant bivalves.
Giant clams are among the most spectacular but also the most endangered marine invertebrates. Their large size and easy accessibility has caused overfishing and collapse of the natural stocks in many places and local extinction in some of the species [1, 2]. The diversity of giant clams is extremely low because of reliction in this Tethyan group [3, 4]. The latest additions of living species date back almost two decades [5–7], fixing the number of extant Tridacna at seven species [3]. Here, we report the discovery of a new species of giant clam: Tridacna costata sp. nov. features characteristic shells with pronounced vertical folds, is ge- netically distinct, and shows an earlier and abbreviated re- production than its Red Sea congeners. This species repre- sents less than 1% of the present stocks but up to >80% of the fossil shells. The decline in proportion and shell size (203) indicates overharvesting [8] dating back to the early human occupation of the Red Sea >125,000 years ago [9]. This earliest depletion reported so far of a shallow-water megafaunal invertebrate has important ramifications for hu- man dispersal out of Africa [10]. Its oversight in one of the best-investigated reef provinces [11–13] illustrates the dearth of knowledge on marine biodiversity.