THE RELATIONSHIPS BETWEEN MORPHOLOGY AND PHOTOSYNTHETIC PARAMETERS WITHIN THE POLYMORPHIC GENUS CAULERPA

The functional form theory predicts that surface area vs. volume ratio (SA:V) and maximum productivity (P-max) decrease as morphological com plexity of an algal thallus increases. The genus Caulerpa demonstrates a tremendous range of morphological forms as well as interspecific pl asticity which make it ideal to study intrageneric relationships betwe en photosynthesis and morphology. We used two approaches to assess fun ctional-morphology relationships: 1) an extensive survey of P-max for 15 Caulerpa taxa in relation to SA:V from species and forms of the Car ibbean and 2) an intensive study of photosynthetic attributes [P-max, photosynthetic efficiency (alpha), compensation irradiance (I-c), satu ration irradiance (I-k)] and respiration (R) for 4 Caulerpa taxa from the Indian River Lagoon, Florida, focusing on SA:V and surface area vs . biomass (SA:B) ratios. These two sites represent areas of relatively low and high nutrient water respectively. SA:V ratios for Caribbean C aulerpa ranged from 0.5+/-0.10 to 11.7+/-3.53 cm(2) . cm(-3) and were highly correlated (r(2)=0.74, p=0.01) to net photosynthetic rates (val ues from 0.4 to 4.6 mg C . g ODW-1. h(-1)). However, for clumped forms , e.g., C. sertularioides var. brevipes (J. Ag.) Svedelius, from the I ndian River Lagoon, P-max Values were lower than predicted possibly du e to an auto-shading effect of thin-overlapping branches. In these for ms, SA:B ratio was more highly correlated to photosynthetic attributes than SA:V ratio. Our data from the Caribbean, with a mean P-max of 2. 23 mg C . g ODW-1. h(-1), suggest that the genus Caulerpa, in low nutr ient systems, approaches the lower mid-range of net primary production of other algal forms. Conversely, Indian River Lagoon values are much higher, reaching a maximum of 17.2 mg C . g ODW-1. h(-1), possibly du e to nutrient enriched waters of this system that enhance P-max. Photo synthetic efficiency ranged between 0.007 to 0.042 mg C g ODW-1. h(-1) per mu M m(-2). s(-2). s(-1) PAR. P-max was mantained at 2500 mu M m( -2). s(-1) and only one species, C. prolifera f.zosterifolia Borgesen, showed a photoinhibitory effect at 3000 mu M m(-2). s(-1). Our data in dicate that photosynthetic attributes of Caulerpa from shallow water i n the Indian River Lagoon are characteristic of sun-adapted plants, i. e., high saturation and compensation irradiances, low efficiencies for capturing low photon flux densities and high exposure resistance to e levated light irradiances.