Reproduction & Life History of Katharina tunicata
Black Katies are dioecious animals in which fertilization occurs externally. The females release very small, (about 230 mm in diameter) brown-colored eggs. These yolky eggs are enveloped in a spiny covering and are released into the sea. Fertilization occurs when the male releases his sperm, through two gonoducts that are found near the posterior end of the animal, and they come in contact with the female egg. Once fertilized, the zygote develops into a free-swimming trochophore larvae. This larval stage of the lifecycle is terminated once the trochophore settles. Settling occurs when the ciliated bands of the prototroch, a preoral band of cilia on the larvae, decrease in activity. These swimming larvae demonstrate selective tendencies in terms of the substrate they choose to settle on. Black Katie’s prefer to settle on a specific genus of algae, Lithothamnium sp. Once K. tunicata has selected this coralline algae as it’s site the degeneration of the prototrochal ciliary band and the early stages of metamorphosis, which involves modification of the girdle tissues, occurs very quickly. The metamorphosis into a juvenile begins only 2.5 hours after settling on the algae surface. This time is considerably longer when the chiton settles on a substrate lacking Lithothamnium sp. There are no veliger larvae in these animals.
K. tunicata typically reaches sexual maturity after two years when it grows to about 35 mm in length. Spawning season for these animals varies depending on their geographic range. Springtime spawning is typical in the southern ranges (southern California and northern Mexico) while reproduction in the northern ranges (British Columbia and Alaska) typically occurs in the summer months (June and July). These preferential spawning seasons are also important in relation to gonadal growth. It is evident that, in some regions, gonad development is elicited by the reduction of water temperatures. Warm water is necessary in the spring to ensure gamete maturation.
Once these animals have matured into adults they are expected to live for about three years in their southern ranges and possibly have longer lives in their northern zones.