more likely to take additional bites from a control blade than 

 from a treatment blade. Fish that initially bit control blades 

 usually took several bites; fish that initially bit treatment 

 blades usually swam away without feeding more (Table 2). 

 Surgeonf ishes showed a significant ability to avoid treated 

 blades without biting them (.025>p>.01, Contingency Table 

 Analysis) and also took fewer bites from treated blades 

 (.01>p>.005, Paired-Sample t-Test ) . 



DISCUSSION 



Nocturnal growth 



Studies assessing diel variation in the growth of seaweeds 

 are rare. The limited data presently available show that photo- 

 synthesis and growth are synchronous in most species and that 

 elongation of the thallus is a light-dependent process. 

 Stromgren (1977a, b) investigated growth in length of five brown 

 seaweeds common to the west coast of Norway by using a laser 

 diffraction method (Stromgren, 1975) to measure very small 

 changes in length with great accuracy. He found growth rates, 

 measured over a few hours, to be stimulated by both increasing 

 light intensities and increasing day length up to some saturation 

 intensity or period of illumination. When placed in the dark, 

 some species could use stored material to continue to grow in 

 length but growth rates were always greatly reduced. One 

 species, Fucus serratus , showed significant shrinkage during 

 periods of darkness (Stromgren, 1977a). More recent studies of 

 both red ( Rhodophyta ) and brown ( Phaeophyta ) seaweeds from the 

 southern California intertidal show similar patterns (Stromgren, 

 1984). 



The nocturnal initiation of new growth in Halimeda (Fig. 3) 

 is clearly different from these previously documented patterns 

 even though expansion of new segments continues throughout the 

 next day (Fig. 4). Our casual observations of numerous siphonous 

 green seaweeds from tropical habitats suggest that similar growth 

 patterns may occur in Udotea , Penicillus , Caulerpa , 

 Rhipocephalus , and Avrainvillea . 



Nocturnal increases in growth-related processes are not 

 unique to seaweeds. Many terrestrial plants in habitats subject 

 to severe water stress possess crassulacean acid metabolism (CAM) 

 which allows them to acquire carbon at night and fix it during 

 the day. This temporal separation of carbon acquisition and 

 fixation results in large savings of water for terrestrial plants 

 but obviously will not be of value for subtidal seaweeds. 

 Additionally, several terrestrial plants that do not use CAM 

 appear to increase in length at night. They produce new cells 

 during the day but do not expand them until after dark when 

 turgor pressure increases due to decreased evapotranspiration (F. 

 Putz, personal communication). Again, this daily pattern of 



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