Abstract
M.Sc. (Botany)
In South Africa, controlling and eradicating Azolla filiculoides and Eichhornia
crassipes cost annually approximately US$ 60 million to the national budget.
However, the success of these operations is mixed because invasive aquatic plants
often spread very rapidly either before they are spotted or before decisions are taken
to implement control actions. This limitation is further exacerbated by difficulties in
determining the invasion potential of newly introduced or unknown aquatic plants, as
well as difficulties inherent to species identification. Resolving these drawbacks
requires pre-emptive actions such as identifying areas that are most vulnerable to
invasion by alien plants. In this study, I first explore whether molecular technique
such as DNA barcoding can be useful to: i) overcome potential limitation of
morphology-based identification of invasive aquatic plants; and ii) establish
successful control of these invasives. For this purpose, I tested the utility of official
DNA barcodes (rbcLa + matK or core barcodes), trnH-psbA, and the core barcode +
trnH-psbA to identify invasive aquatic plants of South Africa’s freshwaters. Second, I
use the technique of ecological niche modeling to identify most vulnerable freshwater
systems to species invasion under current and climatic conditions.
My analysis indicates that the core barcodes and matK regions perform
poorer compared to trnH-psbA, which provides 100% successful identification alone
or in combination with the core barcodes. This study therefore validates trnH-psbA
as single best DNA barcode for invasive alien aquatic plants of freshwater systems
in South Africa. Using this DNA region in BLAST analysis to screen plants species
sold in aquarium market in Johannesburg, I found surprisingly that some prohibited
species are already in circulation in the market. These include Hydrilla verticillata, egeria densa, Myriophyllum spicatum, and Echinodorus cordifolius. Furthermore,
based on climatic parameters, I explored the distribution of the "bad five" aquatic
species in South Africa, i.e. the most damaging invaders of freshwater systems. I
found distinct distribution potentials for these species under current climatic
conditions. Overall, 38% of all South Africa’s dams occur in areas climatically
vulnerable to the invasion by the bad five with the Western Cape Province being the
most vulnerable. However, under predicted climate change scenario, I found
evidence for contrasting shifts in species range: species such as Azolla filiculoides,
Eichhornia crassipes, Salvinia molesta might increase their range by at most 2%
whilst the ranges of Myriophyllum aquaticum and Pistia stratiotes might contract by
at most 5%. This range contraction and expansion will result in some dams currently
vulnerable to invasion becoming resilient whilst others that are currently resilient
might become vulnerable owing to climate change. This result demonstrates not only
the utility of DNA barcoding in implementing control measures, but also provides
ways of prioritising control/management efforts.