Clams reproduce sexually. They are male, female or hermaphroditic, but this is almost impossible to discern by appearance. One reason clams are not often found by themselves, but grouped in beds, is their reproduction. Commercial or cultured clam operations put the straightforward means of clam propagation to good use. The Romans made use of marine aquaculture, as Pliny notes, as early as one hundred years before the birth of Christ.
Let us use the hard-shell clam or quahog as our example. A mature quahog will produce up to two million monocellular clam seeds annually, spermatozoa and oocytes. It releases seed as part of its normal adult life cycle when food (monocellular sea creatures suspended in seawater) is sufficient, tidal conditions do not interfere and the sea bed is welcoming. Clam seed floats free in the seawater in a manner analogous to pollen in the air. The sperm and eggs of clams meet in suspension to form zygotes. These develop briefly into swimming organisms, then settle to the bottom to grow, adapting to such conditions as the sea bottom affords. Clams at this stage of their development resemble adult clams but in miniature. These “mini-clams” are what marine biologists, harbormasters and research groups install drop into shallow offshore waters, to create new clam beds.
As quahogs grow, they take up minerals from their surroundings. These are used to form the clam’s two hinged shells, composed of calcium carbonate. Darkened rings in the shell attest to a clam’s origin and age. Cultured clams, generally hard-shell, can be distinguished from the non-industrial variety by darker rings about two-thirds of the way in from the edge of the shell.
Clams reach maturity as soon as they have reached harvestable size. If left unmolested, quahogs in the wild may live for several decades. They are best consumed as soon as they are legal to harvest.|