Lake Ossa in Cameroon — A lake in Cameroon choked with invasive weeds is a scientific project for biologists, but for Charles Ellingua it means starvation.
“I’ve been fishing on this lake for over 30 years,” said Eringa, 56, a fisherman leader at Lake Osa.
“Salvinia natan weeds have confused fishing quite a bit. I was once able to save up to FCFA 10,000 (US $ 17.99) from daily fishing. But today, FCFA 1,000 (US $ 17.99) from this activity. Even getting 1.80) is very difficult and we can hardly afford to provide three meals to our family, “eight fathers lamented.
Since appearing on the lake in 2016 Lake OssaOne of the largest natural lakes in Cameroon, Rapidly spreading aquatic plants It is called Salvinia Morsta.
Today, about 70% of the lake’s 4,000-hectare surface is swallowed by this floating aquatic fern, which is slow-moving, nutrient-rich, and breeds in warm freshwater.
However, the country has launched a nature-based solution to control unpleasant weeds.
Over 6,000 individual black aquatic insects, 2 to 3.5 mm (.07 to .13 inches) in length, Salvinia weevil It is bred in large numbers for final release to the lake.
July 27, 2021, a small amount of weevil Released in part of the lake, Mark the experimental stage.
“They were brought in from Louisiana State University in the United States with the permission of the Cameroonian government,” he said. Dr. Aristide Takou Kammura, Founder of African Marine Mammal Conservation Organization (AMMCO) In Cameroon.
“Weevils are effective because when the shoots are damaged, the rest of the plant is likely to die and sink.” Matthew Purcell, Director of the Australian Institute for Biological Control, a facility operated by the United States Department of Agriculture Federal Scientific and Industrial Research Organization..
The plant salvinia moresta grows naturally in southeastern Brazil and northern Argentina, although Has become widespread all over the world in the last 50 years.. Water streams, floods, animals, and humans make up the main vector that spreads it.
The human factor is partly due to its spread in Cameroon.
“The economic center of the coastal zone, especially Douala, is Cameroon’s most industrialized municipality, and about 60% of the country’s industrial emissions are often released in open spaces,” said Kenfack Voukeng Sonia Nadège. I told the time report. Kenfack is a Cameroonian weed scientist working with Green Connection, a local environmental protection non-governmental organization.
“Housing built without a proper flushing system contributes to the increase in nutrients in the environment,” said Kenfak.
With Lake Ossa Sanaga RiverKamla says that the largest river in Cameroon, the river, is connected by waterways that are less than two miles long, which also facilitates its spread.
“The two main nutrients that invading weeds need to grow are nitrogen and phosphorus coming from upstream. When this river is polluted, so is the lake,” he said.
According to environmental groups, more than 80% of locals depended on fishing to earn a living. Global Water Partnership.. But today it is no longer possible.
NS African Marine Mammal Organization (AMMCO) and Partners We have been at the forefront of mass breeding of weevil released into Lake Ossa.
According to scientists, water-dwelling salvinia natans eat only salvinia plants and die without a host.
This method — known as biological Control— Very successful in controlling invading plant populations and restoring waters to ecological balance.
It was first collected from a native species of Salvinia morsta by Australian researchers Southern Brazil in 1980..
Since the first release of Mount Isa on Lake Moondarra Australia in 1980, Salvinia weevil has been successfully controlled in many countries in Asia, Pacific and Africa.
“”Lake moondarra There is almost no salvinia today, “says Purcell.
“The larvae can eat the roots first, then move to the shoots, and finally dig a tunnel in the rhizome to kill the plant. Adults eat all parts of the plant from the outside.”
Dr. Arnold PietersWe also agree with senior staff members of the Royal Tropical Institute, who have coordinated tropical ecology and weed control projects in different parts of the world.
“insect cyrtobagous salviniae [scientific name of the weed-eating insects] It was very effective at that time against Salvinia Morsta on the Senegal River. It is host-specific for salvinia natans and does not form an environmental risk, “said Pieterse.
According to Australian biologist Parcel, “Salvinia natan reproduces asexually, allowing one small plant to” eventually grow and restore the entire water system. “
In summer and high temperatures, plants often grow faster than mechanical harvesters remove them.
“The weevil population closely follows the growth of weeds. In spring and summer, salvinia natans increase, then weevil breeding begins, increasing and decreasing populations. [kills] “Salvinia natan,” said Purcell.
Herbicides, another option to eliminate invasive alien species, have not yet been tested on Lake Osa, as they can have a negative impact on living organisms and the environment.
Herbicides and mechanical controls “must be reapplied indefinitely as the plants re-grow seasonally,” says Purcell.
Although considered the most effective method compared to manual removal or chemical control (use of herbicides), scientists have found that even if defects are registered in some countries, they are biological. Control claims that it is likely to work in Cameroon.
“Effects vary from site to site, depending on environmental parameters, temperature, nutrient availability, water flow, shade, etc.,” says Purcell.
“The 50,000 tons of salvinia natan on Lake Moondarra Killed by a weevil in an invasion of over 400 hectares.. Within 14 months, 200 hectares of salvinia natan were replaced by open waters on Lake Moondarra, achieving excellent management. This is the best scenario. Control in other areas may not be as effective as with shading, “he added.
One of the drawbacks of biological control is that invading plants do not disappear. “Some salvinia natans must be tolerated, as they maintain weevil populations and never undergo complete eradication,” Parcel explained.
Biologists, meanwhile, are seeing a bright day on the troubled Lake Ossa. Julie Kotze, Deputy Director and Manager of the Aquatic Weed Biological Control Program at Rhodes University, South Africa.
“Cameroon is tropical, so biological control is likely to be successful,” she said.
“I predict that coverage will be significantly reduced within 18 months. This process is not perceived to be faster than herbicides, but it is sustainable in the long run. Patience is the key. “
Purcell also has hope, but one of the enemies of controlling salvinia natans and other aquatic weeds is “eutrophication, the influx of fertilizers from agriculture and sewers into the water system, which stimulates the growth of aquatic weeds. It’s possible, and sometimes weeds are faster than they can be controlled. ” plant. “
These inflows into the water system should also be regulated to improve controllability, he said.
This report is GLF-Climate Tracker Drylands Fellowship