379j3 MORPHOLOGICAL VARIATION AND ECOLOGICAL STATUS OF HYDRILLA VERTICILLATA (L.f.) ROYLE IN GATUN LAKE, PANAMA DISSERTATION Presented to the Graduate Council of the University of North Texas in Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY By Jorge Bricefno M., B.S., M.S. Denton, Texas May, 1990 U- Bricefio M., Jorge, Morphological variation and ecological status of Hydrilla verticillata (L.f.) Royle in Gatun Lake, Panama. Doctor of Philosophy (Biology), May, 1990, 115 pp., 19 tables, 19 figures, bibliography, 114 titles. Research provides biological and ecological information Panama on Hydrilla verticillate (L.f.) Royle in Gatun Lake, for an ongoing management program of aquatic weeds in the Panama Canal. Morphological and genetic variation, standing crop and life cycle were determined. There were at least three 'morphotypes' of Hydrilla in Gatun Lake. Isoenzyme analysis of specimens from throughout the lake showed no genetic variation, indicating that the Gatun population is derived from a single clone. Standing crop was seasonally dependent showing significant correlation (P <0.05) with rain and temperature. Maximum biomass was 420 g dry mass/m2 during June and December (Bat Cove station) and 390 g dry mass/m2 in June, August and December (Salt and Pepper station). Chlorophyll concentration ranged between 0.7-1.3 mg/g fresh mass in the lake and root:shoot ratios averaged 0.57 in the Barro Colorado region. Density of the stands was depth dependent (220 shoots/m2 at 5 m). Extensive defoliation by the moth Parapoynx sp. occurred in Hydrilla stands during the 1988 and 1989 dry seasons, suggesting that this species of Pyralidae may be a potential biological control of Hydrilla in the lake. Life cycle of Hydrilla was affected by season of the year, turbulence and water transparency, and regulated partially by defoliation (Parapoynx sp.) and epiphytic algae. Patterns of stand decline were associated with micro-habitat variations in water flow, depth and substrate character. Flowering in Hydrilla occurred from November through March. Only male flowers were found in Gatun. Recommendations for integrated management of aquatic weeds in the Gatun Lake are: (1) modification in treatment timing in agreement with seasonality of Hydrilla biomass in particular habitats; (2) application of sublethal treatment concentration of herbicides to weaken Hydrilla plants; and (3) use of Parapoynx sp. as a biological control during periods of peak biomass in combination with mechanical or chemical controls. ACKNOWLEDGEMENTS Partial financial and logistical support were provided by the following institutions: Universidad de Panama, Smithsonian Tropical Research Institute, Panama Canal Commission and The Organization of American States. I greatly appreciate the collaboration and encouragement throughout the study of Yolanda Aguila, Jose A. Martinez, Luis D'croz, Haris Lesios, Ricardo Gutierrez, Gerardo Caceres, Alberto Taylor, Mireya Correa and Ligia and Axel Calderon. Special thanks to Denis Serrano, Liliana Arauz, Edgardo Munoz, Daniel Holness, Erick Viveros, Deisa Piedad Lamela, Rosana Dosman, Marisol Murillo, Amarilis Gutierrez and Martin Mitre, members of the 'Hydrilla team' for their enthusiastic field work and technical assistance. iii TABLE OF CONTENTS Page LIST OF TABLES ...................................... V LIST OF FIGURES.......................................VII CHAPTER I. INTRODUCTION ................... --.............. 1 II. STUDY AREA .................--.................. 6 III. MATERIAL AND METHODS............................15 Morphology ................--.......... 15 Isoenzyme analysis ...................... 18 Histology ..................-............ 19 Standing crop ........................... 20 Shoot length and mass relations ........ 21 Chlorophyll ............................ 22 Associated fauna ........................ 23 Life cycle .............................. 23 IV. RESULTS ...................-................... 24 Morphometric analysis .................. 24 Isoenzymes........................ .... 43 Fresh mass:Dry mass relations ........... 44 Chlorophyll ............................. 50 Length and mass relation ............... 53 Standing crop ........................... 61 Associated fauna ....................... 72 Life cycle .............................. 76 V. DISCUSSION.................................. 84 Morphology .............................. 84 Isoenzymes ............. .............. 91 Mass:length relationship ............... 93 Standing crop ........................... 96 Associated fauna ........................ 97 Life cycle .............................. 98 Summary............................... 103 REFERENCES........................................... 106 iv LIST OF TABLES TABLE Page 1. Stations sampled in Gatun Lake, Panama from September 1987 through February 1989 .............--............................ 8 2. Morphometric variables assessed in herbarium specimens of Hydrilla verticillata (L.f.) Royle from Gatun Lake, Panama ......... 16 3. Buffer description and characteristics of electrophoresis setting for isoenzymes tested .................... --................... 19 4. Descriptive statistics of leaf surface area index of Hydrilla verticillata in samples from Gatun Lake, Panama .............. 28 5. Descriptive statistics of number of teeth along the margin of leaves of Hydrilla verticillata in samples from Gatun Lake, Panama .....................-.................. 29 6. Descriptive statistics of stem diameter measurements (SDM) in Hydrilla verticillata from samples collected in different sites of Gatun Lake, Panama ......... 30 7. Descriptive statistics of leaf form index of Hydrilla verticillata in samples from Gatun Lake, Panama ....................... 31 8. Descriptive statistics of number of leaves in the main stem apex of Hydrilla verticillata in samples from Gatun Lake, Panama ........................................ 33 9. Eigenvalue, percent of discriminant power (%DP), and canonical correlation coefficient (CCORR) associated with each discriminant function..................................... 37 10. Correlation values for standardized discriminant coefficient and discriminant variables ..................................... 40 V 11. Isoenzyme phenotypes of SOD, MDH, PGI, TPI and PO in samples of Hydrilla verticillata from Gatun Lake, Panama ............----.----. 43 12. Fresh mass dry mass conversion factor estimated for Hydrilla verticillata in samples from Salt and Pepper station ..............----..-. 44 13. Root to shoot ratio estimated in individual plants of Hydrilla verticillata from Bat Cove station in April 19880.................. 49 14. Depth variation of shoot density, plant weight and biomass per unit of volume (B/V) of a stand in Arenosa station during April 1988..........................--..-..-..-50 15. Concentration of chlorophyll pigments estimated in Hydrilla verticillata from samples of different stations in Gatun Lake, Panama0.................-.-------------54 16. Comparison of mean standing crop values (g dry mass/m2) of Panamanian rainy and dry season in Barro Colorado Island ............. 66 17. Pearson correlation coefficient of selected environmental parameters with standing crop (g dry mass/m2) data of Hydrilla verticillata ......................... 71 18. Invertebrate fauna associate with Hydrilla verticillata in Gatun Lake .................. 75 19. Spearman correlation coefficients of water quality parameters and Hydrilla verticillata morphotypes in Gatun Lake, Panama ............ 88 vi LIST OF FIGURES FIGURE Page 1. Map of Gatun Lake, Panama showing the main stations collected during September 1987 through February 1989 ......... 12 2. Shoot section of Hydrilla verticillata (L.f.) Royle, showing characters assessed in the morphometric analysis of Gatun Lake population ...................... 26 :3. Dendrogram showing classification of 287 herbarium specimens of Hydrilla verticillata (L.f.) Royle, collected at 13 stations of Gatun Lake, Panama ........ 35 4. Plot of first and second canonical functions indicating group centroids (average group score) .............. 39 5. Transverse section of stems from (A) Dump 2 ,and (B) Chagres River stations showing central cylinder and lacunae .....................-............. 42 6. Electrophoretic phenotype of Triose Phosphate Isomerase in stem apex of Hydrilla verticillata (L.f.) Royle ........ 46 7. Electrophoretic patterns in Hydrilla verticillata (L.f.) Royle , for PO, TPI, SO, MDH, and PGI0....................... 48 8. Relationship between fresh mass (mg) and size (cm) of Hydrilla verticillata (L.f.) Royle.................................52 9. Biomass allocation in individual shoot (shoot weighed each 10 cm) of Hydrilla verticillata (L.f.) Royle. Total shoot length 1.24 m, total shoot mass 3.6 g..........56 10. Biomass allocation in individual shoot (shoot weighed each 10 cm) of Hydrilla verticillata (L.f.) Royle. Total shoot length 2.19 m; total shoot mass 5.5 g ........ 58 vii 11. Biomass allocation in individual shoot (shoot weighed each 10 cm) of Hydrilla verticillata (L.f.) Royle. Total shoot length 7.35 m; total shoot mass 14.9 g.......60 1:2. Schematic drawing of branching patterns observed at (A) Dump 2, and (B) Cuipo stations in Gatun Lake, Panama in May 1988...........................--------0......63 13. Schematic drawing of branching patterns observed at (A) Bat Cove and (B) Salt and Pepper stations in Gatun Lake, Panama in May 1988.............-------------65