Acanthocardia tuberculata (Linnaeus, 1758) is a marine bivalve mollusk that lives from the intertidal zone to 100 meters depth, in sand, mud or gravel bottoms. For what concern its size, the mean value and maximum shell length differ significantly by locations and populations.

I made a study in Lido di Camaiore (Tirrenic Sea, Italy); the sampling operations were carried out between February and June 2012 at two sampling stations, located at the mouth of 2 small rivers (Fiume Camaiore and Fiume Baccatoio); I found a mean value of 41,18 mm (±9,14mm) out of a sample of 180 specimens; size ranged from 20,1 to 52,9 mm. This population shows beautiful colors, a thick and glossy shell with strong and bold ribs that can have several smooth and thick tubercles at the anterior and some at the posterior dorsal margin; these tubercles usually tend to fade toward the ventral margin; in the area (Versilia) seldom A. tuberculata reach a size bigger than 57 mm.
In the Tirrenic Sea can be found bigger specimens, in Torvaianica, has ben reported a 70+ mm  specimen (1982 - F. De Santis Collection) this specimen was collected by hydraulic dredge in a infralittoral bottom of very thin sand at 15/20 meters of depth.

In Grado, Northern Adriatic Sea have been documented several big specimens over 65 mm and some over 70 mm with a maximum shell length of 74 mm (1975), which are comparable to the size of the biggest  Alborean and Atlantic specimens.
In the Eastern Adriatic Sea, a study (sampled from 2008 to 2010) made by Melita Peharda, Daria Ezgeta-Balic, Margita Radman, Nela Sinjkevic, Nedo Vrgoc and Igor Isajlovic of the Institute of Oceanography and Fisheries of Split -Croatia, showed a size ranged from 19,7 to 62,9 mm, with a mean value of 41,21 (±8,96 mm). They were analyzed a sample of 381 shells collected by hydraulic dredge and scuba diving in the area of Rab Island, Pag Bay and Cetina River estuary.

In Aegean Sea, Lesvos Island, Gulf Kalloni, seldom big specimens reach more than 56/57 mm; local divers report a main value around 40/41 mm; I have several specimens coming from this area that are in line with that value; these specimens have beautiful colors, with a glossy and thick shell; they show similar features either in size, shine of the colors and shell structure, than the specimens that can be found in Versilia.
In Salamina Island, there’s an increment in the mean size; around 7/15meters of depth it’s possible to find a large number of 54+ mm specimens; Panayotis Ovalis, one of the best divers in the area, has taken some 67/69 mm huge individuals; their shells are beautiful, multicolored, the shell is thinner and usually less glossy than the ones of Gulf Kalloni’s samples.

Alborean Sea provides the biggest specimens in the Mediterranean Basin, with  several  documented individuals 70+ mm, the shells are usually beautifully colored, very thick, with big and bold ligament.
Josè Ahuir, an expert of that area reports a big sized albino population located 20 km east of Malaga, where the fisherman boats, with trawl, take these shells in muddy sand at about 6 to 20 meters deep. Their mean size is big, with thick and glossy shells; this population counts several specimens over 65 mm with two documented albino giants of 75,16 mm (2011 - KM Collection) and 79,63 mm (the largest albino known, J.Ahuir Collection).
It's important to point out that only an exam of the mollusk's tissues can reveal if a specimen is a true albino. So here, when you read the word "albino" is referred to samples with a full "white shell" or a "white shell" that have few colored spots. There is another population with very big individuals at 15 km west of Malaga, but generally all the populations of Malaga and Almeria are well known for their  size and beauty. It’s possible to find very big specimens in Getares, near Gibiltair where are documented two single halve of 73,5 mm (2011 - P.Trillò Collection).

In the Atlantic Coast, a study (Gaspar et al. 2002) indicates for A. tuberculata collected along the Algarve Coast (Portugal) at depths <25 m, a mean value of 40,66 mm (±17,21mm); so, the mean value is in line with many Mediterranean populations, but in Algarve several individuals reach huge sizes; in that study the maximum shell length was 77,10 mm; Atlantic populations count several documented giant specimens 75+ mm; big sized individuals can be found in Amacao de Pera, but generally in all the Algarve Coast are reported very big specimens of A. tuberculata, A. aculeata  and  A. spinosa, including several cases of hybridism between A. aculeata  and A. spinosa, as documented by Voskuil and Onvervagt in their study about the great catch of the third of November 1989 at Sagrès harbor.
Other huge samples come from Setùbal and Sesimbra.

Poppe & Goto’s European Seashells 2 reports that A. tuberculata can attain a maximum shell length (maximum size) of 90 mm; however the biggest documented specimen comes from Morbihan Gulf, in the Atlantic coast of France: a giant specimen of 82,10 mm; from the same gulf comes a giant albino specimen of 78,36 mm; both were taken at 3 meters of depth in 2004 (KM Collection). These two specimens have been registered in the WRS (World Record Size - Shell) by me and Walter Renda, a malacologist counselor of S.I.M. (Società Italiana di Malacologia); Guido T. Poppe, author of the book I mentioned earlier, writes he never saw specimens of A. tuburculata as big as these two. In the near Quiberon Bay are reported giants of A.echinata, the biggest documented is 70,41 mm (1971 - KM Collection), one of the largest known.
We still don't know much about how the impact of the benthic environment can affect growth and size of
A. tuberculata; it’s not unusual that groups of individuals located in the same area, but just at different depth, differs in the mean size; In a study (by  A. Rharrass, M. Talbaoui, N. Rharbi, H. El Mortaji, M. Idhalla, M. Kabine of the National Institute for Fisheries Research, aquaculture center of Morocco), regarding the population of  A. tuberculata located in the north west of Morocco, it has been noticed a decrease in the number of smaller individuals and an increase in the number of larger individuals with depth.
This can be due also by different water temperature, variation of salinity, density and water composition, different chlorophyll and nutrients concentration, different types of sand, mud or gravel, environmental changes, abiotic and biotic factors.
Big specimens are often found in population living next to the mouth of rivers or bays, where the water has lower salinity than the open sea, and is present an abundant concentration of chlorophiyll and nutrients.
In the Melita Peharda, Daria Ezgeta-Balic, Margita Radman, Nela Sinjkevic, Nedo Vrgoc and Igor Isajlovic reaserch, was reported how shell growth of A. tuberculata was most intensive  during the winter period, where (in the Cetina River estu¬ary), higher concentrations of chlorophyll a (0.263±0.102 mg m-3) were recorded. There’s a proved relation between higher chlorophyll concentrations and phytoplankton - zooplankton growth (Russell R Hopcroft, Jennifer Questel, Cheryl Clarke-Hopcroft -Institute of Marine Science, University of Alaska Fairbanks); consequently the growth of A. tuberculata can be strongly affected by this value.

Marc’antonio Modaro – September 30, 2012


References


Forum of S.I.M.  Società Italiana di Malacologia (Italian Society of Malacology)

Poppe & Goto’s European Seashells 2  -  Conchology, Inc

Age, growth and population structure of Acanthocardia tuberculata (Bivalvia: Cardiidae) in the eastern Adriatic Sea - Melita Peharda, Daria Ezgeta-Balic, Margita Radman, Nela Sinjkevic, Nedo Vrgoc and Igor Isajlovic, of the Institute of Oceanography and Fisheries of  Split –Croatia

Oceanographic assessment of the planktonic communities in
the Klondike and Burger prospect regions of the Chukchi
Sea - Report for Survey year 2008
Russell R Hopcroft, Jennifer Questel, Cheryl Clarke-Hopcroft - Institute of Marine Science, University of Alaska Fairbanks

Studies on Cardiidae. 2.1 – An Acanthocardia hybrid from southern Portugal –
R.P.A. Voskuil  & W.J.H. Onverv

Depth segregation phenomenon and the macrofaunal diversity associated to Acanthocardia tuberculata (Linné, 1758) and Callista chione (Linnaeus, 1758), populations of the Northwest of Morocco. A. Rharrass, M. Talbaoui, N. Rharbi, H. El Mortaji, M. Idhalla, M. Kabine
of the National Institute for Fisheries Research, aquaculture center of Morocco

Special thanks to: Guido and Philippe Poppe - Walter Renda - Panayotis Ovalis - Josè Ahuir -  Flavio De Santis – Piergiorgio Trillò.