The Ecology of the Tropical Compound Ascidian Trididemnum solidum. II. Abundance, Growth and Survival

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Abstract
The distribution of T. solidum (Van Name) was investigated in 42 transects over the coral reef on the leeward coast of Curacao [Netherlands Antilles]. Ascidian colonies were abundant at depths from 1.5-34 m along the central part of this coast, but absent toward the tips of the island. This reflects characteristics of the life history of T. solidum, such as short pelagic life and the local current regime. Another factor influencing the distribution is the ambient light level. For 9 mo. (July 1978 to April 1979), the monthly in situ growth of a population varying between 38-50 colonies was measured. Each fortnight these colonies were checked for presence or absence. The constancy in population size makes a highly dynamic system. During the study period 85 novel colonies appeared through division, 43 colonies disappeared through fusion with other colonies and 33 colonies ceased to exist (dead) or were lost. Growth rates were extremely rapid, up to 13 cm mo.-1 in linear direction, compared with the most common spatial competitors (Scleractinia). Although T. solidum overgrows corals, growth rates are reduced over living coral tissue. Homogenates of the ascidian had variant but adverse effects on different coral species and, apart from simple overgrowth, allelochemicals could be involved in spatial competition. There is little evidence of predation on T. solidum and artificial lesions were rapidly regenerated. T. solidum had a life span largely exceeding the study period. Clones may survive indefinitely.