. Bulletin. Histoire naturelle ; Natuurlijke historie. Des études d'HISTOIRE DE LA VIE 99 d'autre part, un règlement d'anlysis sur du marbre blanc au lieu de gris foncé phyllite ne réussit pas à démontrer une tendance pour l'un d'être favorisés par rapport à l'autre. Comparaison de s'installer sur les deux de ces substrats, ainsi que sur les coquilles de Crassostrea virgiyiica (fig. 29) révèle que le règlement sur les plusieurs types de milieux est es- sentially aléatoire. Dans la figure, la moitié du nombre total de colonies qui se sont installés sur d'huîtres est ombragée de façon à permettre la comparaison avec les mêmes zones de surface sur du marbre et phyllite. C'est de

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. Bulletin. Natural history; Natuurlijke historie. LIFE HISTORY STUDIES 99 On the other hand, an anlysis of settling on white marble as opposed to dark gray phyllite fails to show any tendency for one to be favored over the other. Comparison of settling on both of these substrata, as well as on shells of Crassostrea virgiyiica (fig. 29) reveals that settling on the several types of backgrounds was es- sentially random. In the figure, half the total number of colonies which settled on oyster shells is shaded so as to permit comparison with similar surface areas on marble and phyllite. It is of interest to note that McDougall (1943) found that Adocia tubifera was the only organism which settled in his light box at random. McDougall pointed «rt 20. 5 19 2 Oct. Nov. Figure 29. Larval settling of Haliclona loosanoffi in relation to color of substra- tum. See text. out that the glass top on his box eliminated ultra-violet radiation which may be the injurious element of sunlight for some organisms. However, the amount of ultra-violet light which penetrates turbid coastal waters is probably insignifi- cantly low, at least at a depth of I1/2 meters at which these organisms settled. Consequently, it is likely that a basic difference in phototactic responses exists in these two species. The distribution of Haliclona loosanoffi colonies with depth is shown in Table 35. Their exclusion from the shells on the bottom is doubtless a result of the heavy silting in the Harbor so that only those colonies could survive which settled on substrata suspended off the bottom where water currents were more likely to be effective in preventing silt accumulation. The upper limit of settling found here agrees with field observations elsewhere in the Sound where, in gen- eral, mean low water represents the shoreward extreme of distribution. Haliclona loosanoffi colonies were observed to die back in mid-November each year from 1947 through 1949. The regularity with which the colonies perished ea

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