Effects of temperature on the vegetative cell liberation of seven species of red-tide algae from the bottom mud in Osaka Bay

Mud samples were collected from the eastern coast of Osaka Bay from April 1984 to August 1985 and were incubated atin situ mud temperatures to examine the effects of temperature on the liberation of seven species of red-tide algae. Skeletonema costatum appeared extensively over a wide temperature range of 9–25°C. The percentage of liberation of benthicHeterosigma akashiwo cells tended to decrease with decreasing temperature, but this species also showed high percentages of liberation (40–100 %) in April whenin situ mud temperatures were still low (9.5–10°C). Germination of benthicHeterocapsa triquetra cells was active at temperatures lower than 10°C but was inhibited to below 20% at temperatures higher than 21°C. This indicates that the supply of vegetativeHeterocapsa cells from bottom muds to seawaters becomes inactive from summer to early autumn. The optimum temperature range for the liberation of benthicChattonella sp. cells was 16–21°C. ForProrocentrum micans, Prorocentrum minimum, andProrocentrum triestinum, no vegetative cells were released from bottom mud at any of the temperatures examined (9–25°C).Field observations on the population dynamics of vegetative cells conducted from April to September 1984 revealed that a close link exists between liberation ofS. costatum andH. triquetra and their blooms in the waters of Osaka Bay. On the basis of these findings, the ecological role of benthic cells in initiating red tides in Osaka Bay is discussed.