Are the Mediterranean ascoglossan molluscs Oxynoe olivacea and Lobiger serradifalci suitable agents for a biological control against the invading tropical alga Caulerpa taxifolia?

The Mediterranean ascoglossan Oxynoe olivacea and Lobiger serradifalci, whi ch are scarce in meadows of their usual food the alga Caulerpa prolifera, h ave become adapted to;feeding on the invading tropical alga Caulerpa taxifo lia. Grazing rates are low (O. olivacea destroys only a 5-cm C. taxifolia f rond in 3-7 d). The grazing rates are a function of temperature. Despite a high spawning frequency (0.25 egg-mass.day(-1)) and a large number of eggs released per spawning event (O. olivacea: from 2 545 to 29 128 eggs.spawnin g(-1); L. serradifalci: from 12 112 to 48 448 eggs.spawning(-1)), the recru itment on Caulerpa meadows is usually low due to the hazardous pelagic deve lopment of the larvae. The possible use of these molluscs as agents of biol ogical control against C. taxifolia appears to be possible only through an artificial enhancement of their populations after cultivation of the velige rs and release of juveniles during the winter season. This means of control is discussed and compared with the possible use of tropical ascoglossan sp ecies. (C) 2000 Academie des sciences/Editions scientifiques et medicales E lsevier SAS.