REPRODUCTIVE ECOLOGY OF THE ASCIDIANS MOLGULA-CITRINA ALDER AND HANCOCK, 1848 AND APLIDIUM-GLABRUM (VERRILL, 1871) FROM THE GULF OF MAINE, USA

We examined long-term patterns of sexual reproduction in the solitary ascidian Molgula citrina, and both sexual reproduction and colony grow th in the colonial ascidian Aplidium glabrum from the shallow subtidal zone in the Gulf of Maine, U.S.A.. Ascidians of each species were col lected regularly from two sites over a three-year period, then examine d in the laboratory to determine size and fecundity, and, for the colo nial species, density of individuals (zooids) in colonics. Reproductiv e characteristics were compared between ascidian species and between s ites. In both species, sexual reproduction was highly seasonal, exhibi ting marked peaks from late spring throughout summer. Periods of peak asexual reproduction in A. glabrum generally occurred when ascidians w ere not reproducing sexually. Fecundity of M. citrina (# larvae per gr am of parent ascidian) during peak periods of sexual reproduction diff ered between sites. Colonies of A. glabrum also differed between sites in several characteristics: #zooids per gram, #larvae per zooid, #lar vae per colony, and # larvae per gram. To determine whether size const rained brood capacity, we examined the allo-metric relationship betwee n fecundity (also zooid number for the colonial species) and weight, a nd compared this relationship between sites within species. Fecundity of M. citrina exhibited an iso-metric relationship with body weight, a nd this relationship did not differ between two populations. Colony-wi de fecundity in A. glabrum increased isometrically with colony weight, but fecundity of individual zooids was independent of colony weight. Both types of fecundity relationships in A. glabrum differed between s ites. Zooid number increased allometrically with colony weight, with l arger colonies containing disproportionately fewer zooids than smaller colonies.