. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 234 R. R. OLSON TABLE V Juvenile survivorship experiment* Total Mean % number survivorship Standard Level of Treatment of larvae after 4 days deviation significance Shade 34 Control 54 Clear plexiglas 35 P < Full sunlight 28 P < * See text for explanation of treatments. Data tested for significant difference from shade treatment using single factor analysis of variance (Fs = , P < ) with Student-Newman-Keuls multiple comparisons test. Data were arcsine t
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 234 R. R. OLSON TABLE V Juvenile survivorship experiment* Total Mean % number survivorship Standard Level of Treatment of larvae after 4 days deviation significance Shade 34 Control 54 Clear plexiglas 35 P < Full sunlight 28 P < * See text for explanation of treatments. Data tested for significant difference from shade treatment using single factor analysis of variance (Fs = , P < ) with Student-Newman-Keuls multiple comparisons test. Data were arcsine transformed (Zar, 1974). Each treatment was replicated 3 times. The ability of larvae to delay their settlement is important in an habitat like the Lizard Island lagoon. Patch reefs provide plenty of suitable habitats for the larvae, but between them lie bright white sand flats with little or no shaded substrata. By postponing settlement, larvae can drift over the sand flats until they encounter another patch reef, thus achieving inter-reef recruitment. DISCUSSION The larval stage ofDidemnum molle is not substantially different from the typical colonial ascidian larval phase as described by Millar (1971). Upon release, larvae are positively phototactic, swimming towards bright light. They gradually change to negative phototaxis and negative geotaxis, swimming upwards and settling on the undersides of dark surfaces. What appears to be distinguishing about D. molle (and perhaps all ascidian-algal associations, see Table II) is that the larvae are released only in the middle of the day with a peak shortly after meridian passage of the sun. This phenomenon held true for D. molle during the three seasons (spring, summer, winter) in which it was studied. Duyl el al. (1981) reported a similar midday timing of larval release for Trididemnum solidum, a Caribbean ascidian-algal symbiosis. Larval release by colonial ascidians has previously been reported to occur pri- marily at dawn or fir
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
