''Mulinia coloradoensis'' is the junior synonym of ''Mulinia modesta'', a species of
clam
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 she ...
endemic
Endemism is the state of a species being found 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 found elsew ...
to the northern and central Gulf of California. 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 ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid drainage basin, watershed that encompasses parts of ...
, this species might have been the most common
mollusc
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...
in the Colorado River delta, 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 m
2 to three per m
2.
It has been hypothesized that the increase in
salinity
Salinity () is the saltiness or amount of 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 dimensionless and equal ...
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, but may also be caught from stocked bodies of water such as ponds, canals, park wetlands and reservoirs. Fishing techniques inclu ...
.
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 web ...
of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
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
* Trop ...
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, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
and predatory
gastropods
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from 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.
Carlos E. Cintra-Buenrostro, Karl W. Flessa, Guillermoavila-Serrano, "Who Cares About a Vanishing Clam? Trophic Importance of Mulinia coloradoensis Inferred from Predatory Damage", ''PALAIOS''; June 2005; v. 20; no. 3; p. 296-302
References
{{Taxonbar, from=Q6934017
Mactridae