. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 268 S. M. BAKER AND R. MANN in 144 h, nearly doubling in length. Juveniles in hypoxic treatments grew only 77 jum of new shell in 144 h, ap- proximately one third as much as those in normoxic treatments. Juveniles in anoxic treatments did not increase in shell height. Juvenile survival Juvenile oyster survival was similar in all three treat- ments for the first 72 h (Fig. 4). At 96 h and 120 h, the anoxic treatment mean was significantly different (P < ) from both hypoxic and normoxic treatment means. All three treatm
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 268 S. M. BAKER AND R. MANN in 144 h, nearly doubling in length. Juveniles in hypoxic treatments grew only 77 jum of new shell in 144 h, ap- proximately one third as much as those in normoxic treatments. Juveniles in anoxic treatments did not increase in shell height. Juvenile survival Juvenile oyster survival was similar in all three treat- ments for the first 72 h (Fig. 4). At 96 h and 120 h, the anoxic treatment mean was significantly different (P < ) from both hypoxic and normoxic treatment means. All three treatment means were significantly dif- ferent (P < ) from each other at 144 h. Juveniles in the anoxic treatments had a median mortality time (time to 50% mortality) of 84 h. Mortality of juveniles in anoxic treatments was 100% by 144 h. Juveniles in the hypoxic treatments had a median mortality time of 131 h. Nor- moxic treatments, in contrast, had a mean of only 13% mortality at 144 h. Discussion Under hypoxic and anoxic conditions, oyster pediveli- ger larvae significantly reduce energetically costly activi- ties, thereby reducing total metabolism and oxygen re- quirements (Widdows el a!., 1989). The results of this study indicate that settlement is another costly activity that oyster pediveliger larvae avoid when in oxygen-lim- iting environments. In a recent paper on the effects of hypoxia and anoxia on Mytilus edulis larvae, Wang and Widdows (1991) re- port that moderate hypoxia has little effect on larval set- tlement. Settlement of mussel pediveliger larvae onto adult byssus filaments is approximately 12% after two days in conditions of mg O2 P' ( kPa pO2, 98% of air saturation at 15°C and 31%»), mg O2 I"1 ( kPa pO2, 29% of air saturation), or mg O2 1~' ( kPa pO2, 15% of air saturation). An oxygen concentration of mgO: P1 ( kPa^O2. 7% of air saturation) shows 1% settlement. Settlement of C. virginica appears to be more sensitive
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