Consequences of crowding on life-histories of cheilostome bryozoans in Bombay waters

Abstract

In Bombay harbour waters cheilostome bryozoans Electra bengalensis, Acanthodesia sp., Hippoporina indica, Membranipora annae and M. tenuis occurred in that order of abundance. Field observations with the help of exposure coupons were carried out to examine the life-history of the species competing with one another for a limited space. Each species as an isolated colony achieved sexual maturity at specific size but in M. annae and M. tenuis, sexual reproduction was triggered by conspecific crowding. The incidence of breeding in all 5 species was more amongst interacting colonies as compared to isolated colonies of identical ages. Under the stress of crowding, the species showed between 25 to 50% suppression of zooid growth in interacting vector as compared to non-interacting vector of the colony. Different life-history characters may help different species in competing with one another. However, ability to breed continuously as noted in E. bengalensis seems to be a major factor that determines the success.