Aquatic weeds -- Control -- Florida, Carp, Water hyacinth -- Florida


The biomass of the submersed macrophytic vegetation in four hydrilla (Hydrilla verticillata Royle) infested lakes in central Florida was monitored for one year. Lake Orienta and Little Lake Fairview received 2,320 and 960 grass carp, respectively, while Clear Lake and Lake Mann did not receive grass carp. Hydrilla was eliminated in Lake Orienta within six months of stocking; the lake was stocked at 19 grass carp/mt hydrilla (45 fish/ha). Hydrilla was not eliminated from Little Lake Fairview which contained 9 grass carp/mt hydrilla (30 fish/ha). The growth of hydrilla was restricted in Little Lake Fairview which produced 0.380 mt hydrilla, dry organic wt., in contrast to Clear Lake and Lake Mann in which annual net primary production was 0.728 and 0.880 mt organic matter/ha, respectively. The rate of hydrilla growth was greater in the two unstocked lakes. Clear Lake produced 0.31 g/m2/day, dry organic wt., while the net primary productivity of hydrilla in Lake Mann averaged 0.38 g/m2/day. The net primary productivity of hydrilla in Little Lake Fairview was 0.14 g organic matter/m2/day. Three species (in addition to hydrilla) were common to Little Lake Fairview and Lake Mann and provided the only data upon non-target species. Pondweed (Potamogeton illinoensis Morong.) and stonewort (Nitella sp.) were more abundant and more widely distributed in Little Lake Fairview than in Lake Mann. The poor representation of pondweed and stonewort in Lake Mann was attributed to competitive pressure exerted by hydrilla which comprised 83%, by weight, of the annual mean biomass of submersed macrophytic vegetation. In comparison, hydrilla comprised 74% of the annual mean biomass in Little Lake Fairview. The effect of the grass carp in Little Lake Fairview may have been to ease the competitive pressure exerted by hydrilla, allowing pondweed and stonewort to remain well established. The percentage frequency of occurrence was concluded to be a poor criterion for measuring changes in the hydrilla population. Changes in biomass as great as 900% resulted in no change in the percentage frequency of occurrence of hydrilla in Lake Mann.


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Graduation Date

Spring 1981


Osborne, John A.


Master of Science (M.S.)


College of Arts and Sciences

Degree Program

Biological Sciences




53 p.




Public Domain

Length of Campus-only Access


Access Status

Masters Thesis (Open Access)



Contributor (Linked data)

John A. Osborne (Q59504803)

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Biology Commons