Mulinia coloradoensis
Encyclopedia
Mulinia coloradoensis, also known as the Colorado Delta clam is a species of clam
endemic to the Colorado River Delta
. It is thin-shelled
, and in the Mactridae
family.
, this species was the most common mollusk in the estuary
. It 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 clams has been reduced from 25 to 50 per square meter to three per square meter. The clam has been largely replaced by several thicker-shelled species of Venus clam (Chione
spp.). These previously minority species now account for 95% of the clams in the area.
The increase in salinity
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, which is now endangered and only found in a few isolated locations, including Isla Montague, the largest island at the mouth of the Colorado river. The clams are not harvested and are not affected by pressure from fishing
.
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 65 km south of the river's mouth, constituting only 25% of shells in this area, and becoming rare to absent at a distance of 80 km. These observations have been used to infer that the mixing zone of river and sea water probably extended as far as 65 km south of the river's mouth. Isotope analysis
of oxygen
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.
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...
endemic to the Colorado River Delta
Colorado River Delta
The Colorado River Delta is the region where the Colorado River flows into the Gulf of California . The delta is part of a larger geologic region called the Salton Trough. Historically, the interaction of the river’s flow and the ocean’s tide created a dynamic environment, supporting freshwater,...
. It is thin-shelled
Seashell
A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers...
, and in the Mactridae
Mactridae
Mactridae, also known as trough shells or duck clams, is a family of marine bivalve clams of the order Veneroida.-Characteristics:...
family.
Conservation history
Prior to the diversion of water upstream in the Colorado riverColorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...
, this species was the most common mollusk in the estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
. It 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 clams has been reduced from 25 to 50 per square meter to three per square meter. The clam has been largely replaced by several thicker-shelled species of Venus clam (Chione
Chione (genus)
Chione is a genus of tropical American marine bivalve molluscs, in the family Veneridae.-Species:* Chione amathusia * Chione californiensis W. J. Broderip, 1835 - California venus, Banded venus...
spp.). These previously minority species now account for 95% of the clams in the area.
The increase in salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
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, which is now endangered and only found in a few isolated locations, including Isla Montague, the largest island at the mouth of the Colorado river. The clams are not harvested and are not affected by pressure from fishing
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
.
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 65 km south of the river's mouth, constituting only 25% of shells in this area, and becoming rare to absent at a distance of 80 km. These observations have been used to infer that the mixing zone of river and sea water probably extended as far as 65 km south of the river's mouth. Isotope analysis
Isotope analysis
Isotope analysis is the identification of isotopic signature, the distribution of certain stable isotopes and chemical elements within chemical compounds. This can be applied to a food web to make it possible to draw direct inferences regarding diet, trophic level, and subsistence...
of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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.