Temperature promoting the asexual life cycle program in Bangia fuscopurpurea (Bangiales, Rhodophyta) from Esashi in the Hokkaido Island, Japan

Abstract

In the asexual life cycle of the marine red seaweed Bangia fuscopurpurea gametophytic thalli produce multiple monospores that develop into thalli as clones. We investigated the effects of heat stress on the production and release of monospores in B. fuscopurpurea from Esashi, in northern Hokkaido Island of Japan. Non-lethal high temperatures of 25℃ and 28℃ strongly promoted monospore discharge, whereas no spore release was observed at 30℃, the limiting growth temperature of Esashi B. fuscopurpurea. These findings differed from previous reports using B. fuscopurpurea collected at Fukaura, the northern Japan, and at the Fujan province of southern China, for which growth and monospore release were observed at 30℃. Thus, the temperature range promoting asexual propagation with monospore discharge in B. fuscopurpurea varies and appears to be unrelated to the thermal conditions of harvesting areas. Since each B. fuscopurpurea strain had a unique upper-limit temperature for survival and release of monospores was accelerated under non-lethal high temperature conditions, the temperature range enabling the asexual life cycle program seems to be restricted by the degree of heat stress tolerance of the B. fuscopurpurea strains themselves.