Growth of the Colony and Maturation of Zooids of a Bryozoan Bugula neritina in the Sea

Abstract

The larvae attached on slide glasses were immersed two meters below the surface at two stations in Omura Bay and Nomo Inlet located near Nagasaki City. Colonial growth shown by the increase of zooid number, sexual maturation and the time span of the colony from attachment on to falling off from the slide glass (life span of the colony) were investigated in four seasons from 1982 to 1983.There was a linear relation between the number of zooids (N) and the height (Hmm) of the colony, which was represented as follows: ln N=2.46 ln H-0.22 (r=0.96).The lowest temperature for survival of the colony and the lower limit of temperature for the exponential growth were estimated as about 9°C and 13°C, respectively. The life span of the colony varied from 1.5-2 months in spring and summer to more than 3 months in fall and winter, depending on water temperature.We could observe the first brood chamber in zooids when the colony had grown up at zooid number of 200-1, 000. Our observation suggested that the colony could release the larvae after growing up at the zooid number of 1, 000 to 5, 000 (height, 2-4cm). The minimal size of the colony in sexual maturation showed little fluctuation seasonally in zooid number.The maximal size of a colony was estimated as 20, 000-50, 000 in zooid number (height of the colony, 6-10cm).