The Ecological Physiology Of The Siphonaceous Marine Alga Caulerpa Paspaloides (chlorophyta) In The Waters Off South Florida

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Degree Name

Doctor of Philosophy (Ph.D.)




The seasonal variations of growth, photosynthesis, respiration starch reserves and rhizome meristem mortality in Caulerpa paspaloides (Bory) Greville were concurrently monitored in situ at Key Largo, Florida. In addition, the seasonal rates of photosynthesis and respiration of C. paspaloides were compared with the rates of a congeneric species. C. prolifera (Forsskal) Lamouroux. The effects of light intensity, temperature, nitrogen, phosphorus and salinity on the metabolism of C. paspaloides were studied under controlled laboratory conditions.Caulerpa paspaloides possessed a bimodal pattern of annual growth with maximum growth rates occurring in the spring (8.71 mm x day('-1)) and fall (6.60 mm x day('-1)) and minimum rates occurring in the summer (4.52 mm x day('-1)) and winter (3.76 mm x day('-1)). The summer decline in growth was found to be related to an increase in mortality of the rhizome meristems, which may have been caused by hypotonic stress during the summer rainy season. Meristems of C. paspaloides were found to be susceptible to damage by salinity reductions of 3 ('o)/oo (time to 20% mortality = 19 min). The winter reduction in growth was found to be related to a decline in photosynthetic production, which was caused by an inhibition of photosynthesis at temperatures less than 20(DEGREES)C. The photosynthetic metabolism of C. paspaloides seasonally adapted to temperature and light intensity; however, the alga was apparently unable to completely compensate for the low winter temperatures at the study site. The adaptations involved (1) the tracking of the seasonal environmental temperature by the photosynthetic-temperature optimum and (2) the lowering of the light compensation point of winter plants. A 56% decline in the starch reserves indicated that C. paspaloides utilized these reserves in order to maintain metabolic activities during the winter. Assays for nitrogen and phosphorus limitation did not detect limiting conditions in plants from the study site.Photosynthetic comparisons of C. paspaloides with C. prolifera suggested that the latter species was more tolerant of winter conditions. Based upon this differential, photosynthetic response, it is hypothesized that the northern geographic limits for these two species are determined by different tolerances to low temperatures.


Biology, Botany

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