Here are PDF reports in Spanish by Alejandro Arrivillaga,
to CONAP and the Scientific Commission
The native home of hydrilla is not known with certainty.
Cook reports that he believes hydrilla is native to the Indian subcontinent which is particularly rich in Hydrocharitaceae species, but is not strongly opposed to the theory that hydrilla may be native to east Africa. Hydrilla also was reported in Europe early in the 1900s, and most recently in Poland and Lithuania, but only isolated and small populations currently exist. Though classified as a single taxonomic species worldwide, recent enzymatic and DNA analyses suggest the existence of several "types" of hydrilla including monoecious and dioecious plants (Madeira et al. 1997). Hydrilla produces excessive growth, causing problems in the western hemisphere, Asia and Australia, but it is not a problem in Europe and Africa.Dr. Margaret Dix, University del Valle, indicated that she had collected hydrilla outside the Polochic watershed in Guatemala in approximately 1990. Fishermen noted that hydrilla was first observed in Lake Izabal in approximately 2000. This date seems correct based upon the current characteristics of the distribution in Lake Izabal. Hydrilla now occurs in many locations, with some areas of growth approaching 400-500 acres in size, and other areas of less than1 acre, suggesting that hydrilla is in an early colonization mode. Likely, hydrilla was present in the watershed, in a pond or isolated area, in 1998 when flood water from Hurricane Mitch moved it into the lake.
In Florida, the "type" of hydrilla is the dioecious female plant which only produces female flowers twice a year near the fall and spring equinox. Hydrilla in Lake Izabal was flowering during early September 2002 and no rhizomes suggestive of tuber production were located. Consequently I believe that the hydrilla in Lake Izabal is the same type as that in Florida, Texas, Mexico and Panama. This could be confirmed by planting hydrilla in shallow pans in October to determine if tuber production occurs during October through April, indicative of dioecious female plants in the southern USA where hydrilla produces tubers during short day conditions (<12-13 hours of day length).
Hydrilla in Lake Izabal
Recent surveys conducted by Alejandro Arrivillaga for the Scientific Commission and CONAP (Consejo Nacional de Areas Protegidas) show over 2,000 ha (5,000 acres) currently growing in the 170,000 acre lake. The lake is sustained by several rivers, primarily the Polochic entering Lake Izabal from the west. The lake outlet to the east is a heavily populated area, the Rio Dulce, which after approximately 3-4 miles widens into the Golfete. The Golfete is a large (approximately 15,000 acre) shallow, tidally influenced area which contains a manatee preserve and is largely surrounded by public lands. Further east, the Golfete narrows once again and passes through the "Gorges" area for approximately 4-6 miles, emptying into the Gulf of Honduras at the City of Livingston.My visit coincided with the end of the wet season and water flows in the Rio Dulce were high with whirlpools and strong currents very noticeable wherever the river was narrow. During and for a period after the wet season, the system from the shallow Golfete through the Upper Rio Dulce is essentially fresh water, with salinities sufficiently low for hydrilla growth. (Additional data are needed on the salinity levels in the Golfete during the dry season (Nov-May)). Hydrilla was present to the water surface in the upper Rio Dulce and western Golfete during September 2002, near the end of the wet season. It is possible that salinity will control this growth during the dry season, but it appears hydrilla will become a problem in the Golfete for 2-3 months at the end of the wet season and persist until killed by saltwater intrusion in the dry season. The water depth of the Golfete appears to be suitable for hydrilla growth; the limiting factor in this area will be the effects of salinity as hydrilla cannot tolerate extended periods in excess of 6 parts per thousand or 20% of the salt concentration of seawater. The Rio Dulce east of the Golfete is too deep and too saline (I believe) for hydrilla to cause problems, though it may grow into creek deltas of inflowing fresh water in the lower Rio Dulce and interfere with local boat traffic. Research on the salinity and water depths of the Rio Dulce and Golfete will permit more accurate prediction of the future extent of hydrilla growth downstream of the Central Golfete.
Extent of Problem
At the current level of infestation, primarily in beds in Lake Izabal, hydrilla is causing relatively minor problems to fishing and transportation. Hydrilla is currently growing to water depths of approximately 15 feet. If hydrilla continues to expand to cover the 15-18 foot contour of the lake bed, it is estimated that it will cover 10-15% of the lake surface (20-30,000 acres of the 170,000 acre lake). While this level of infestation may appear small, it will cause access and navigation problems for villagers and create problems for fisherman.The major concern I envision is if hydrilla were to establish in the upper Rio Dulce, near the river bridge, where marinas, transportation, and tourism would be severely impacted. Many people in this area rely upon river transport for commerce, and tourism and recreation is a significant industry. Though water flow in this area is high during the wet season, flows are negligible during the dry season which will permit hydrilla to become established in these shallow waters. In fact, hydrilla beds have already been found in the upper Rio Dulce and western Golfete. The Golfete provides access to the transportation and commerce center of the upper Rio Dulce and is likely to be severely impacted as well. It is in these areas, the western Golfete and the upper Rio Dulce that I fear hydrilla will cause severe economic hardship.
Hydrilla is currently too widespread to be eradicated from this system and Guatemala needs to be prepared for expansion of hydrilla into areas which will be economically affected. While we can hope hydrilla does not spread further, historically it has and likely will continue expansion.
The Scientific Committee and concerned Guatemalan officials and agencies have already initiated much needed research, monitoring, and evaluation of management options. The following information is critically needed to be able to accurately predict the ultimate effects of hydrilla: vegetation surveys; a new bathymetric map (Hurricane Mitch in 1998 may have changed the depth contours of the lake); fisheries surveys; salinity monitoring; insect surveys; herbicide acute toxicity studies; and baseline limnological studies. While the current hydrilla infestation is causing problems in the lake, it has not invaded what I consider high priority economic sites, and it is critical to be prepared for this event. This a very large and dynamic system in which it is impossible to predict with certainty the ultimate infestation.
Aquaphyte Contents | Aquaphyte page | Home