In Everglades National Park

PHOTOSYNTHESIS BY ALGAL EPIPHYTES OF UTRICULARIA IN EVERGLADES NATIONAL PARK

THOMAS D. BROCK Department of Microbiology, Indiana University, Bloomington, Indiana 47401

ABSTRACT This paper reports some studies on photosynthesis, as measured by the HC method, in Utricularia and its associated algal epiphytes in the Ever- glades National Park. The results provide evidence that the rate of photosynthesis is much greater in epiphyte-laden Utricularia than in epiphyte- free plants. This evidence leads to the suggestion that the epiphytes, rather than the macrophyte, are responsible for most of the primary production in this aquatic ecosystem.

INTRODUCTION In many aquatic habitats, macrophytes are colonized by variable amounts of epiphytic algae, and it would be desirable to measure the relative rate of photosynthesis in the macrophyte and in its associated epiphytes. During some observations in the Shark River system of Everglades National Park, it was observed that new shoots of the macrophytes Utricularia purpurea and U. lutea were bright green, whereas older shoots were a dull brown color. The color of the latter shoots was due primarily to a heavy population of epiphytic diatoms, desmids, and blue-green algae. Photosynthesis was measured by a He method (Brock & Brock, 1967) of epiphyte-free and epiphyte-containing fronds and the chlorophyll content and epiphyte content were estimated simultaneously. The data show that there is no correlation between chlorophyll content and photosynthesis but that there is a strong correlation of photosynthesis with epiphyte content. These results lead to the tentative conclusion that the epiphytes rather than the macrophyte are responsible for the bulk of the primary production in this aquatic ecosystem.

METHODS Habitat.- The studies were done in early March 1967 in the Shark River Valley of Everglades National Park at a location designated Station VI by Dr. E. J. F. Wood and associates of the Rosenstiel School of Marine and Atmospheric Sciences of the University of Miami. This area, reached easily by air boat, is a slough of semi-open water between dense stands of saw grass. The submerged macrophytes, U. purpurea and U. lutea, varied in color from bright green to dull brown, and Dr. Wood and associates had shown that the green fronds were free of epiphytes, whereas the brownish 1970] Brock: Photosynthesis by Algal Epiphytes 953 ones contained heavy populations of diatoms, desmids, and blue-green algae. Samples of fronds with varying intensities of color were selected visually. Studies of Photosynthesis.-Small pieces of fronds were cut and placed in 5-m1screw-capped vials filled with water from the habitat. Into each vial was injected 0.1 ml of a 1OlLc/ml solution of NaHl4C03 to give a final concentration of 0.2 ILc/ml, equivalent to 2ILg of added NaHC03. The vials were incubated in a large plastic bag at the site from 10: 45 AM to 11: 45 AM in full sunlight. The temperature of the water was 28°C. At the end of the incubation period, 0.5 ml of formalin was added to each vial and the vials placed in the dark. The samples were processed in the laboratory about a week later. Processing involved homogenization, filtration of aliquots for HC counting, and extraction of aliquots for chlorophyll, as described by Brock & Brock (1967). Epiphyte content was estimated visually and micro- scopically on samples of the homogenate. Because there is no simple way to quantitate the concentrations of epiphytes, numerical values of 0 to 5+ were assigned to samples with increasing amounts of epiphytes. A value of 5+ represents an epiphyte concentration so high that there were more than 100 2 cells or filaments per microscope field of about 3 X 10-4 cm , whereas at a value of 1+ there was only an occasional cell or filament per field. To check for chlorophyll degradation products, absorption spectra of acetone extracts were made using a Beckman DB-G recording spectrophotometer. Observa- tions of the height of the absorption peak at 665 nm before and after acidification of the extract, and of the shift of the absorption peak at 430 nm to 405 nm upon acidification, revealed that less than half of the chlorophyll was in the form of the pheophytin degradation product. No attempt was made to correct the chlorophyll assays for pheophytin content, since this correction would not affect the basic conclusion of this study.

RESUL TS AND DISCUSSION The results of this study are presented numerically in Table 1 and graph- ically in Figure 1. As can be seen, there is no correlation between chlorophyll content and HC02 fixation, whereas there is a strong correlation between HC02 fixation and epiphyte concentration. Although it would be desirable to quantitate the epiphyte concentration more precisely, the results -even using the approximate measurements-are sufficiently clear-cut so that it seems safe to conclude that l4C02 fixation in this ecosystem is pre- dominantly by the epiphytes rather than the macrophyte. It may at first seem surprising that clean, bright green macrophytes photosynthesize more slowly than dull brownish plants containing a heavy coating of epiphytes. However, when the growth rates of the two kinds of organisms are considered, the results seem reasonable. In the present system it is likely that the turnover rates of the microbial epiphytes are high, so that energy flows 954 Bulletin of Marine Science (20( 4)

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TABLE 1 14COZ FIXATION, CHLOROPHYLL CONTENT, AND EPIPHYTE CONTENT OF FRONDS OF Utricularia, SHARK RIVER, EVERGLADES NATIONAL PARK*

Counts per min. "CO. per sample Sample Epiphyte Chlorophyll (counts per min. No. concentration (p,gjsample) per sample) p,gchlor.

I o 23.1 458 19.8 I-Dark o 27.6 94 3.4 2 o 18.5 520 28 3 1+ 4.7 489 103 4 1+ 9.5 645 68 5 4+ 12.6 2028 161 6 4+ 9.5 1446 152 7 5+ 7.1 2444 344

• Incubation time, 10:45 AM to 11:45 AM. Water temperature, 28°C. Full sunlight. through the epiphytic component rapidly, whereas the turnover rates of the macrophytes are low. We can thus view the role of the macrophytes in the Shark River ecosystem as providing a stable site for attachment and growth of the epiphytes. In most studies of photosynthesis by macrophytes, the role of adhering epiphytes is usually not considered (Westlake, 1965; Wetzel, 1965). For instance, the latter author has stated: "The biomass of epiphytic periphyton ... is generally small in comparison to the biomass of the larger plants." Although this was also true for the present case, it was not true that the productivity by these epiphytes was small. It is likely that epiphytes playa considerable role in productivity in most aquatic ecosystems where macrophytes predominate, and this may be especially so in warmer waters such as those of the Everglades. ACKNOWLEDGMENTS I am grateful to Dr. E. J. F. Wood and his associates, especially Miss Nancy Maynard, for guidance through the Everglades National Park, and to the U.S. National Park Service for airboat facilities and permission to do research in the Park. The technical assistance of M. L. Brock and S. Murphy is also acknowledged. This work was supported in part by a grant from the National Science Foundation (GB-5258) and a Research Career Develop- ment Award of the U.S. Public Health Service.

SUMARIO FOTOSINTESIS POR ALGAS EPIFITAS DE Utricularia EN EL PARQUE NACIONAL DE LOS EVERGLADES Este trabajo reporta algunos estudios hechos usando el metodo del HC sabre fotosintesis de Utricularia y las algas epifitas can ella asociadas en el 956 Bulletin of Marine Science [20( 4)

Parque Nacional de los Everglades. Los resultados poveen evidencia de que la proporci6n de fotosintesis es mucho mayor en Utricularia con epifitas que en plantas libres de ellas. Esta evidencia lleva a la sugerencia de que las epifitas y no las macrofitas son responsables de la mayoria de la producci6n primaria en este ecosistema acmitico.

REFERENCES BROCK, T. D. AND M. L. BROCK 1967. Methodology for measurement of chlorophyll, primary productivity, photophosphorylation, and macromolecules in benthic algae. Limnol. Oceanogr., 12: 600-605. WESTLAKE, D. F. 1965. Some basic data for investigations of the productivity of aquatic macrophytes. Pp. 229-248 in Goldman, C. R. (Ed.), Primary productivity in aquatic environments. University of California Press, Berkeley, 464 pp. WETZEL, R. G. 1965. Techniques and problems of primary productivity measurements in higher aquatic plants and periphyton. Pp. 249-270 in Goldman, C. R. (Ed.), Primary productivity in aquatic environments. University of California Press, Berkeley, 464 pp.