Technical highlights - Department of Primary Industries ...

24. Cabomba (Cabomba caroliniana) ecology
Project dates
October 2010 – July 2012
Project leader
Dr Tobias Bickel
Ecosciences Precinct
Tel: (07) 3255 4476
Email: tobias.bickel@deedi.qld.gov.au
Other staff in 2010–11
Cameron Clark
Objectives
• Research the ecological habitat
requirements and competitiveness of
cabomba.
• Investigate the regeneration ability
and establishment of cabomba
fragments to predict dispersal.
Rationale
Cabomba (Cabomba caroliniana) is a
submerged aquatic weed originating from
South America. It is a popular aquarium
species and was introduced to the wild
worldwide through intentional propagation
for the aquatic plant trade and disposal of
surplus aquarium material. Today, it is a
serious aquatic weed in many countries,
including Australia, the United States
and China. Cabomba was first recorded in
Australia in 1967 and is today naturalised
in several states. It is a WONS and a
Class 2 declared weed in Queensland.
Even though cultivation and sale of
cabomba is now prohibited, the plant is
increasing its range and could potentially
establish in large parts of Australia with
suitable habitat. Cabomba predominantly
reproduces through vegetative propagules
(stem fragments); viable seeds have so far
been observed only in Northern Territory
populations. Cabomba readily spreads
within catchments through the movement
of fragments via water currents,
particularly in floodwaters. However,
humans are the main vector for dispersal
between waterbodies, mainly through
boating and fishing activities (fouling of
fragments in equipment).
Once established, cabomba has serious
environmental and economic impacts
and is difficult to control due to limited
availability of effective control options.
While there is general knowledge in
aquarium literature about culturing
conditions for cabomba, there is little
scientific data available about the
ecology of cabomba, both from its native
and introduced range.
Such knowledge is necessary to predict
in which habitats cabomba is likely to
establish. This will allow concentrated
monitoring in areas deemed high risk,
and therefore will improve the likelihood
of detecting cabomba infestations in
early stages, when successful removal
is viable. A better understanding of
cabomba ecology is also crucial for
mitigating ecological and economic
impacts of this serious pest.
Methods
Cabomba regeneration—
nutrients in solution
Cabomba fragments (each consisting
of a stem piece with a single node and
one leaf pair) are incubated in shallow
plastic containers filled with culture
solution. There are five treatments
(five replicates each): no nutrients,
trace elements only, low nutrients
(0.5 mg nitrogen L –1 ), medium nutrients
(1 mg nitrogen L –1 ) and high nutrients
(5 mg nitrogen L –1 ).
These nutrient concentrations are
representative of trophic statuses of
freshwater systems: ultra-oligotrophic
(trace elements only), oligotrophic (low
nutrients), mesotrophic (medium nutrients)
and eutrophic (high nutrients). We inspect
fragments weekly and assess the number
of regenerating fragments (new shoot
development from nodes).
Regeneration (%)
70
60
50
40
30
20
10
no nutrients
trace elements only
low nutrients
medium nutrients
high nutrients
Cabomba establishment—
substrate types
We establish 16 outdoor mesocosms
(each 800 L) with a 10 cm substrate
layer comprising a lower 5 cm layer of
substrate mixed with topsoil and an upper
5 cm layer of clean substrate to prevent
nutrient leaching. There are four substrate
treatments (four replicates each): sand
(< 0.5 mm), fine gravel (< 5 mm), coarse
gravel (< 20 mm) and cobbles (> 100 mm).
The tanks are filled with rainwater and
seeded with 75 g wet mass of cabomba
material consisting of approximately 100
stem fragments (a mix of single-node
fragments and longer stem pieces). After
8 months we drain the mesocosms and
measure the total cabomba wet mass and
stem density. Water quality is monitored
throughout the experiment.
Cabomba regeneration—
substrate quality and pH
Four 100 L aquariums are filled with a
mixture of tap water and distilled water
in the laboratory and trace elements and
micronutrients are added. In three tanks,
we adjust the pH through CO 2 injection
to pH 6.5, 7.0 and 8.0; the fourth tank
does not receive added CO 2 and varies in
pH from 7.5 to 8.0. In each tank we plant
10 cm long apical cabomba shoots in little
pots filled with four different mixtures of
sand and topsoil: sand only, 25% topsoil,
50% topsoil and 100% topsoil. There are
three pots of each substrate quality per
tank. Shoot growth and establishment
of new shoots is then monitored over
6 weeks, after which we harvest all
cabomba and measure the dry mass of
shoots and roots.
0
0 1 2 3 4 5 6 7 8 9 10
Weeks after fragmentation
Figure 24.1 Regeneration of cabomba fragments (see Photo 24.2) as affected by nutrient availability
Part 2 Landscape protection and restoration 55