The dark periostracum is flaking off this dried valve of Arctica islandica from Wales
The ocean quahog (Arctica islandica) is a species of edible clam, a marinebivalvemollusk in the family Arcticidae. This species is native to the North Atlantic Ocean, and it is harvested commercially as a food source. This species is also known by a number of different common names, including Icelandic cyprine,[1] mahogany clam, mahogany quahog, black quahog, and black clam.[2]
The typical Arctica islandica resembles the quahog, but the shell of the ocean quahog is rounder, the periostracum is usually black, and on the interior of the shell, the pallial line has no indentation, or sinus. Unlike the quahog, which lives intertidally and can be collected by clam digging, this species lives subtidally, and can only be collected by dredging. They grow to sizes exceeding 50mm or two inches shell height.[3]An individual specimen was reported to have lived 507 years, making it the longest-lived non-colonial metazoan whose age was accurately known.[4]
Life cycle and longevity
Arctica Islandica shows slower growth rate than other species of clams, it takes an average rate of 4 days for birth (embryo to larvae stage). Furthermore, it takes an average of 5.8 years for A. Islandica to reach maturity; at this point the somatic costs start going down. Dynamic Energy Models (DEM) predict that Arctica islandica's extreme longevity arises from lowered somatic maintenance costs and a low aging acceleration.[5] For individuals in populations in cold areas the growth rate is probably further slowed because growth only occurs in summer.[6] This slow life style results in exceptional longevity with a highest reported age, for Ming the clam, of 507 years. This makes it the longest living non-colonial metazoan species with an authenticated lifespan.[4][7][8] It is unknown how long it could have lived if it had not been collected alive by an expedition in 2006.
This characteristic has proven useful in the science of sclerochronology, the study of periodic physical and chemical features in the hard tissues of animals that grow by accretion, and is especially valuable for modeling of paleoclimates. In 1868 one specimen, collected alive near Iceland, was 374 years old. The study of its growth rate and the oxygen isotope data showed that it had a highly variable growth at the peak of the Little Ice Age around 1550–1620 and mild climate near its end around 1765–1780 and had recorded the volcanic eruption of Mount Tambora in 1815.[9]
One study found that in animals aged 4–192 years, antioxidant enzymes declined rapidly in the first 25 years, which includes the growth and sexual maturity stages, but afterwards remained stable for over 150 years. Though more detailed studies are warranted, it appears this species is a case of negligible senescence.[10] In contrast to the exceptionally long-lived populations in relatively deep, cold parts of its range, more southern populations that experience greater seasonal variations in salinity and temperature are typically far shorter-lived. For example, A. islandica from the German Bay of Kiel typically only reach an age of about 30 years and those from the German Bight about 150.[11]
Feeding ecology
Like other clam species, Arctica islandica is a filter feeder. Feeding activity appears regulated by light levels, which can be used as a proxy for food availability. This means that at the northern extreme of the distribution, feeding is concentrated during eight months of the year, while during the rest of the year the clams only feed for a few days a month.[6]
↑ Hackney, Cameron R.; Thomas E. Rippen (2000). "The Molluscan Shellfish Industry". In Roy E. Martin; Emily Paine Carter Jr.; George J. Flick; Lynn M. Davis (eds.). Marine and Freshwater Products Handbook. CRC Press. pp.323–324. ISBN1-56676-889-6.
1 2 Butler, P.; Wanamaker, A. Jr.; Scourse, J.; Richardson, C.; Reynolds, D. (2013). "Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica". Palaeogeography, Palaeoclimatology, Palaeoecology. 373: 141–51. Bibcode:2013PPP...373..141B. doi:10.1016/j.palaeo.2012.01.016.
↑ Strahl, Julia (2011). Life strategies in the long-lived bivalve Arctica islandica on a latitudinal climate gradient – Environmental constraints and evolutionary adaptations. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, University of Bremen.
Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shells of equal size connected by two adductor muscles and have a powerful burrowing foot. They live in both freshwater and marine environments; in salt water they prefer to burrow down into the mud and the turbidity of the water required varies with species and location; the greatest diversity of these is in North America.
Benthos, also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone. This community lives in or near marine or freshwater sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.
Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bivalves have no head and they lack some usual molluscan organs, like the radula and the odontophore. The class includes the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances.
The Pacific geoduck is a species of very large saltwater clam in the family Hiatellidae. The common name is derived from the Lushootseed (Nisqually) word gʷídəq.
Maximum life span is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the maximum amount of time that a member of a given species could survive between birth and death, provided circumstances that are optimal to that member's longevity.
A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold does not mean that the temperature of the seepage is lower than that of the surrounding sea water. On the contrary, its temperature is often slightly higher. The "cold" is relative to the very warm conditions of a hydrothermal vent. Cold seeps constitute a biome supporting several endemic species.
The giant clams are the members of the clam genus Tridacna that are the largest living bivalve mollusks. There are actually several species of "giant clams" in the genus Tridacna, which are often misidentified for Tridacna gigas, the most commonly intended species referred to as "the giant clam".
Soft-shell clams or sand gaper, scientific name Mya arenaria, popularly called "steamers", "softshells", "piss clams", "Ipswich clams", or "Essex clams", are a species of edible saltwater clam, a marine bivalve mollusk in the family Myidae.
The hard clam, also known as the round clam, hard-shellclam, or the quahog, is an edible marine bivalve mollusk that is native to the eastern shores of North America and Central America from Prince Edward Island to the Yucatán Peninsula. It is one of many unrelated edible bivalves that in the United States are frequently referred to simply as clams. Older literature sources may use the systematic name Venus mercenaria; this species is in the family Veneridae, the venus clams.
Mercenaria is a genus of edible saltwater clams, marine bivalve molluscs in the family Veneridae, the Venus clams.
Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves.
Ming, also known as Hafrún, was an ocean quahog clam that was dredged off the coast of Iceland in 2006 and whose age was calculated by counting annual growth lines in the shell. Ming was the oldest individual (non-colonial) animal ever discovered whose age could be precisely determined.
The Arcticidae are a family of marine clams in the order Venerida. The only living species in the family is Arctica islandica. There are also many fossil species classified in a number of genera.
Negligible senescence is a term coined by biogerontologist Caleb Finch to denote organisms that do not exhibit evidence of biological aging (senescence), such as measurable reductions in their reproductive capability, measurable functional decline, or rising death rates with age. There are many species where scientists have seen no increase in mortality after maturity. This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age.
Solemya velum, the Atlantic awning clam, is a species of marine bivalve mollusc in the family Solemyidae, the awning clams. This species is found along the eastern coast of North America, from Nova Scotia to Florida and inhabits subtidal sediments with high organic matter (OM) content and low Oxygen, such as salt ponds, salt marshes, and sewage outfalls.
Lutraria lutraria is a species of large marine bivalve mollusc in the family Mactridae. Its common names include the otter shell and the common otter shell. It occurs in coastal regions of the north east Atlantic Ocean where it lives buried in the sand.
Teredo is a genus of highly modified saltwater clams which bore in wood and live within the tunnels they create. They are commonly known as "shipworms;" however, they are not worms, but marine bivalve molluscs in the taxonomic family Teredinidae. The type species is Teredo navalis.
Iceland is geologically quite young, and mostly formed from volcanic processes, so fossils there are rare. The oldest fossils found in Iceland are from the Miocene, about 15 mya, and are plant remains. In addition to plant remains, fossilized remains of insects from the Miocene and Pliocene have been found. Miocene and Pliocene fossil sites are found mainly in the West of Iceland and the Westfjords. Remains of invertebrates have been found In Ice age strata, especially in fresh water and marine sediments. It is rare to find fossil remains of land animals in Iceland, although remains of deer bones have been found.
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