been hypothesized (P. Coley, personal communication) that 

 pigmentation is delayed in these species to avoid loss of 

 chlorophyll to herbivores before the leaves are capable of rapid 

 production. 



A unique curiosity or a general pattern? 



Since so few other studies have assessed diel patterns in 

 plant growth and since none have evaluated its ecological 

 consequences, we are unable to say whether Halimeda represents an 

 interesting but unique curiosity of nature or simply the first of 

 many species that will eventually be found to exhibit this growth 

 pattern. However, a few other studies on seaweeds, and many 

 other studies on phytoplankton, suggest that the growth pattern 

 is not unique to Halimeda and that diel patterns of growth may 

 function to reduce herbivory in other species as well. 



In contrast to the daytime growth of seaweeds documented for 

 the temperate algae studied by Stromgren (1977a, b, 1984), Dawes 

 and Barilotti (1969) conducted laboratory experiments showing 

 that growth of the noncalcif ied, siphonous green, Caulerpa 

 prolif era , occurred primarily at night and peaked 2-4 hr after 

 initiation of the dark period. The presence of nocturnal growth 

 in this siphonous, chemically defended (McConnell et al . , 1982) 

 species, which does not calcify, suggests that physiological 

 constraints associated with calcification in Halimeda need not be 

 responsible for its nocturnal growth pattern. 



Although little information is available on diel patterns of 

 growth in seaweeds, diel patterns of growth in dinof lagellates 

 and diatoms have been documented on numerous occasions. Phased 

 cell division, synchronized on light/dark cycles, is well known 

 and common in most major taxa of phytoplankton (Sournia, 1974). 

 Division in marine diatoms occurs at various species-specific 

 times throughout a 24 hr cycle (Sournia, 1974) while division of 

 photosynthetic marine dinof lagellates is generally in the late 

 night or early morning under both laboratory and field conditions 

 (Weiler and Chisholm, 1976; Weiler and Eppley, 1979). 

 Individuals of several of these phytoplankton species may be more 

 susceptible to herbivores during, or just after, cell division. 

 For the marine diatom, Ditylum brightwellii , the probability of 

 being consumed by the copepod, Calanus helgolandicus , increases 

 three fold during division ( Richman and Rogers, 1969). 

 Additionally, the dinof lagellate genus Ceratium has imperfectly 

 developed horns (proposed defensive structures) for several hours 

 following division (Sournia, 1974). Weiler and Eppley (1979) 

 noted that division in more than 40 species of the dinof lagellate 

 genus Ceratium occurs at about 10 hr after darkness begins and 

 suggested that this might reduce losses to vertically migrating 

 herbivores. The considerable evidence that different life stages 

 of Calanus graze with variable intensity at different times of 



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