''Mulinia modesta'' is a species of

clam Clam is a common name for several kinds of bivalve mollusc. The word is often applied only to those that are deemed edible and live as infauna, spending most of their lives halfway buried in the sand of the sea floor or riverbeds. Clams h ...

belonging to the family

Mactridae Mactridae, common name the trough shells or duck clams, is a family (biology), family of saltwater clams, marine (ocean), marine bivalve mollusks in the order (biology), order Venerida. Description These clams have two short siphons, each with a ...

. MolluscaBase eds. (2023). MolluscaBase. Mulinia modesta (P. P. Carpenter, 1864). Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=505739 on 2023-10-07

Description

The longitude of a medium sized specimen is 49 mm, the altitude 36.5 mm and the diameter 82 mm. The shell is solid, rude and equilateral. It resembles ''Mulinia modesta'', but is larger and has the posterior dorsal margin more arched. The base behind the posterior dorsal angle is somewhat concavely flexuous, and the surface anteriorly and on the dorsal area is marked with obsolete, little elevated radii.

Distribution

It is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the northern and central

Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...

. The clam is known to live in both brackish and fully marine habitats. It is a shallow-water filter feeder that prefers mud-sand bottoms.

Conservation history

Prior to the diversion of water upstream in the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

, this species might have been the most common

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

in the

Colorado River Delta The Colorado River Delta is the region where the Colorado River once flowed into the Gulf of California (also known as the Sea of Cortez) in eastern Mexicali Municipality in the north of the state of Baja California, in northwestern Mexico. The ...

, in the extreme northwestern region of the northern Gulf of California. It has been estimated to have constituted 80-90% of the clams throughout the delta and was so abundant that heaps of the shells formed ridges that stretched for miles. The density of ''Mulinia modesta'' has estimated to have been reduced from 25 to 50 per m² to three per m². It has been hypothesized that the increase in

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

of the water and decrease of nutrient input from the river as a result of diversion and use of water led to the decline of the clam in the extreme northeastern region of the upper Gulf of California. The clams are not harvested and are not affected by pressure from

fishing Fishing is the activity of trying to catch fish. Fish are often caught as wildlife from the natural environment (Freshwater ecosystem, freshwater or Marine ecosystem, marine), but may also be caught from Fish stocking, stocked Body of water, ...

. Studies of the clam have been used to infer the original extent the estuary in the absence of earlier survey data. Shells of the clam became sharply less prevalent about south of the river's mouth, constituting only 25% of shells in this area, and becoming rare to absent at a distance of . These observations have been used to infer that the mixing zone of river and sea water probably extended as far as south of the river's mouth.

Isotope analysis Isotope analysis is the identification of isotopic signature, abundance of certain stable isotopes of chemical elements within organic and inorganic compounds. Isotopic analysis can be used to understand the flow of energy through a food we ...

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

in the shells of the clam have also been used to independently estimate rates of salinity, and the results from this approach were found to correspond with observations of the prevalence of the clam shells, and also to agree with numerical models proposed in the past.

Ecology

Damage to shells was used to assess the

trophic Trophic, from Ancient Greek τροφικός (''trophikos'') "pertaining to food or nourishment", may refer to: * Trophic cascade * Trophic coherence * Trophic egg * Trophic function * Trophic hormone * Trophic level index * Trophic level * ...

importance of this species, and it was found to be a major source of food for

crabs Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek), which typically have a very short projecting tail-like abdomen, usually hidden entirely under the thorax. Their exoskeleton is often thickened and ha ...

and predatory

gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...

. On the basis of these studies, it was predicted that restoration of water flow in the Colorado River would result in an increase in this species, which would result in an increase of species that depend on it for food, including commercially valuable crabs.

References

* Huber, M. (2010). Compendium of bivalves. A full-color guide to 3,300 of the world's marine bivalves. A status on Bivalvia after 250 years of research. Hackenheim: ConchBooks. 901 pp., 1 CD-ROM * Coan, E. V.; Valentich-Scott, P. (2012). Bivalve seashells of tropical West America. Marine bivalve mollusks from Baja California to northern Peru. 2 vols, 1258 pp {{Taxonbar, from=Q6934017 Mactridae