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Relative Growth Rate and
Doubling Time of the Submerged Aquatic Macrophyte Egeria densa
Planch
PISTORI, R.E.T1,
CAMARGO A.F.M.2 & HENRY-SILVA, G.G.1
1
Programa de Pós-Graduação em Aqüicultura/CAUNESP;
2
Departamento de Ecologia/CAUNESP, Instituto de Biociências, Universidade
Estadual Paulista – UNESP - Av. 24 A, 1515, 13506-900 Rio Claro, SP.
e-mail:
mafmc@rc.unesp.br
ABSTRACT:
Egeria
densa
is a
species native of the South America that has been introduced in other
continents. It invasive capacity causes the reduction or elimination of
native species of certain water bodies. In Brazil, E. densa has
been growing abundantly in reservoirs, and having adverse effects on the
hydroelectric power generation. The objective of this work was to
determine the relative growth rate (RGR)
and the doubling time (DT) of
E. densa in laboratory experiment. Every 4 days, during 44 days, the
length of shoots was measured. Along the experiment, physical and
chemical variables of water and nitrogen and phosphorus concentrations
from sediment were measured. The length of shoots was transformed in dry
mass using a linear regression model between these two variables. In the
firstly 20 days there are a rapid increase in dry mass
(gain of 0.065 g)
and between 20 and 44 days a slightly increase
(gain of 0.025 g). Significant differences of RGR of
E. densa were recorded between 4 days periods
(F=31.46, p<0.001). The values of RGR were significantly
higher in the period of 8-12 days (RGR=0.063 day-1 and DT=12
days) when compared with the values of the other periods. During the
last period of experiment (20- 44 days)
we observed the minor values of RGR (0.009 to 0.016 day-1)
and highest DT values (90 to 194 days).
This species growth in water with low availability of inorganic forms of
nitrogen and phosphorus, and probably, the gradual reduction of the RGR
of E. densa during the time is due to the increase of biomass and
density. Our data showed that E. densa have higher growth
capacity, similar to free-floating species considered some of most
aquatic weed species of the world.
Key-Words:
Egeria densa, relative growth rate, doubling time, submerged
aquatic macrophyte. |
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