Diel pattern of segment production in Halimeda simulans was 

 quantified by collecting 65 plants every 3-4 hrs from a 20-25 m 

 deep sand plain near Coki Point, St. Thomas, U.S. Virgin Islands. 

 The proportion of branches having initial buds or expanding but 

 unpigmented tips was determined as described previously for H. 

 incrassata . 



To follow the time course of production and expansion of 

 individual segments, we marked 23 individual Halimeda incrassata 

 plants by placing numbered surveyor's flags next to their bases. 

 As new buds were just becoming apparent (1200-1600 hrs), we 

 marked 5-13 branches per plant by loosely attaching very small 

 cable ties around the base of a mature segment that was beginning 

 to produce a bud. This is a slight modification of Drew's (1983) 

 previously proven method for following growth in Halimeda . The 

 growth of expanding segments on each plant was monitored every 4 

 hrs for the next 51 hrs by placing a small centimeter rule behind 

 each branch tip and recording its width to the nearest mm. The 

 fatigue associated with continuously monitoring the plants for 

 more than 2 days caused us to miss some plants at some sampling 

 intervals; our sample size thus varied from 16-23 plants. 



Nitrogen content of Halimeda incrassata segments of 

 different ages was determined by CHN analysis. The organic 

 content of segments of different ages was determined by drying 

 them to a constant mass at 60°C and then determining their ash 

 free dry mass after maintaining them at 450°C for 24 hrs. 



Concentrations of the 3 abundant secondary metabolites 

 produced by Halimeda , halimedatrial , epihalimedatrial , and 

 halimedatetraacetate (see Paul, 1985), were determined by high 

 performance liquid chromatography (HPLC). The retention time and 

 peak size for known amounts of each metabolite had been 

 determined previously under identical solvent and flow rate 

 conditions (45% ethyl acetate in isooctane). Each extract from 

 each compound was measured by cutting out and weighing the peak; 

 this provided concentration data by reference to the peak sizes 

 for known amounts of each compound. The identity of the peaks 

 was confirmed by proton nuclear magnetic resonance spectrometry 

 (NMR) . 



Although we made every effort to minimize the time between 

 collection of the plants and determination of compound 

 concentration, concentrations were usually not determined until 

 several hours following collection. This delay was necessitated 

 by the time required for blotting and clipping the plant tips, 

 transporting these from the Hydrolab to the shore-based chemists, 

 and the extraction and purification procedures performed prior to 

 HPLC analysis. Since secondary metabolites produced by Halimeda 

 are somewhat unstable (V. Paul, personal observation), we suspect 

 our concentration data are low despite our attempts to stabilize 

 these compounds by rapid extraction, chromatographing over 



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