California mussel

TheCalifornia mussel(Mytilus californianus) is a large ediblemussel, amarinebivalvemolluskin the familyMytilidae.
This species is native to the west coast ofNorth America, occurring from northernMexicoto theAleutian IslandsofAlaska.  California mussels are found clustered together, often in very large aggregations, on rocks in the upperintertidal zoneon the open coast, where they are exposed to the strong action of the surf.
The shell of this species is thick and is often 129 to 130 millimetres (5 to 5 in) in length, sometimes larger still. The shell is blue on the outside with a heavy brownperiostracumwhich is usually worn off except near the growing edge of the shell. The beaks of the shell are often eroded. The shell has coarse radial ribbing and irregular growth lines on the outer surface. The inner surface of the shell is blue and faintly pearly.
Like other mytilids, the animal is attached to the substrate with a very strong and elasticbyssus.
The shell is primarily made ofcarbonates.In the 1950s that was mostlyaragonitewith somecalcite,but by 2017/2018 the proportions had reversed.This was surprising given that previouslysomeincrease in aragonite was observed inwarmerwaters, and theocean temperaturehas risen since then, making researchers expect an increase in aragonite.However it was the opposite - showing that the deciding factor inM. californianusshell carbonate composition isocean acidification- because calcite withstands acidity better.
The California mussel prefers the highsalinity, lowsedimentconditions found on open rocky coasts.  However, they do notcolonizebare rock easily, instead preferring the shelter of pre-existing mussels and their biological filaments.  Mussels attach themselves to the hard surfaces using their thread-likebyssus.
Given the right circumstances, California mussels can grow up to 200 mm (8 inches) in length and may live for more than 20 years.However, mortality in intertidal open coastal environments is often high, resulting from battering fromdriftwoodand other debris,wavepounding,predation,desiccation, anddisease.Predators of California mussels include thePisasterstarfish. They feed on plankton.
California mussels were an important food source for theNative Americanswho lived on the Pacific Coast prior to European contact. On California's Northern Channel Islands, archaeological evidence shows that they were harvested continuously for almost 12,000 years.Erlandsonet al. (2008) documented a decline in the average size of harvested California mussels onSan Miguel Islandduring the past 10,000 years, a pattern they attributed to growing human populations and increased predation pressure from human fishing. Hogan (2008) notes more specific archaeological recovery from theChumashin the period 800 to 1300AD.
California mussels continue to be harvested as sources of both food and bait up and down the Pacific Coast of North America. The flesh of the California mussel tends to be orange in color.  They can be baked, boiled, or fried like othermussels,clams, andoysters.
While these mussels are usually edible, care needs to be taken, because during times ofred tidein any given locality, California mussels may contain harmful levels of the toxins which can causeparalytic shellfish poisoning.
Thekeystone speciesconcept was coined, in 1969,by thezoologistRobert T. Paine,professor emeritusof theUniversity of Washington, to explain the relationship betweenPisaster ochraceus, a species ofstarfish, andMytilus californianus.