Invasive Aquatic Plants

Introduction to Limnology

• The instructor is Andrews Agyekumhene, reachable via [email protected] or 0208829002.

Objectives

• Students will understand what invasive aquatic plants are.
• Students will learn the traits of invasive aquatic plants.
• Students will learn methods for eradicating invasive aquatic plants.

Invasive Aquatic Plants

• Invasive aquatic plants are either freshwater or marine flora.
• They spread or have been introduced beyond native ranges.
• They may cause harm or have the potential to do so.
• These plants are not native to a region.
• They out-compete native species for available resources.
• Invasive aquatic plants often form dense populations.
• They dominate aquatic ecosystems.
• Invasive species are also called "alien", "exotic", or "introduced" species.
• These species are not necessarily invasive.
• They have to show inclination to spread and overtake native species to be considered invasive.

Mode of Invasion: Natural Invasion

• Natural invasions occur in the absence of anthropogenic influences.
• They occur through the removal of an intervening barrier.
• Biotic and abiotic transporting mechanisms are able to overcome the barrier.
• Hydrological characteristics are the main medium by which invasive aquatic plants move.
• Wind can act as a transport mechanism for some aquatic plants.
• Phragmites and Typha produce numerous light seeds which rely on wind for dispersal

Mode of Invasion: Anthropogenic Invasion

• Human activities can introduce spores or seeds of aquatic plants.
• Ships and cargo vessels can transport species into new areas becoming invasive.

Stages of Invasion

• There are five main stages of invasion.
• These are transport, introduction, establishment, spread, and negative impacts.

Stages of Invasion: Transport

• Transportation is the first stage.
• The species is transported beyond its native range.
• Transportation is mainly done through shipping of goods and commodities across oceans.
• Ships transport more than 80% of world trade by volume as of 2021.

Stages of Invasion: Introduction

• Introduction of the species into a suitable habitat in the wild happens once the species is transported.
• Introductions can be accidental or intentional.
• Introductions can include release in nature, release from confinement, and escape from confinement.
• Introductions can also include contaminants or stowaways.

Stages of Invasion: Establishment

• Introduced species reproduce continuously.
• They attain viable population in the wild.
• High survival of individuals result in a population capable of maintaining itself in the wild.
• Reproduction and survival depend on existing abiotic and biotic factors.

Stages of Invasion: Spread / Dispersal

• Spread/Dispersal is an expansion phase.
• There will be an increase in range/area occupied by a species.
• Spread is dependent on reproductive success, localized offspring dispersal or propagules, and long-distance dispersal aided by humans.
• Species with high reproductive rates or plants producing easily dispersed seeds have a high probability to spread.

Stages of Invasion: Impacts

• This is the final stage of invasion.
• Nonnative species cause negative impacts.
• Impacts can affect the environment (ecological), economy (economic), or human health.
• Ecological impacts: changes in watershed hydrology, nutrient cycling, and reductions in biodiversity.
• Economic impacts: costs to control invasive species and lost revenue in recreational activities.
• Human health impacts: mild allergies and rashes, spreading life-threatening diseases, and potentially deadly attacks.

Aquatic Weeds Common in the Tropics

• Typical species include Nymphaea lotus, Vossiacus pidate, Aeschynomene nilotica, A. indica, Oryza barthii, O. longistaminata, Cyperus digitatus, and Acacia nilotica.
• Species often present at the edges of lakes include: Pistia stratiotes, Potamogeton schweinfurthii, and Utricularia spp.

Negative Impacts of Aquatic Weeds

• Invasive weeds have major negative effects on ecosystems.
• These include alteration of habitats, and the structure of the foreshore.
• This causes a decline of species that rely on native plants
• Species are displaced by invasives for resources or habitats.
• Invasive weeds cause an incidence of water-borne diseases, and makes water transport difficult.
• Recreation, tourism, and fishing activities also suffer, along with destruction of water quality.
• Economic burden from managing invasive plants is also created.

Management of Aquatic Weeds

• Methods for getting rid of invasive aquatic plants include: manual removal, mechanical removal, chemical control, biological control, and environmental manipulations.
• Direct use of aquatic plants for economic benefits is also a solution.

Management of Aquatic Weeds: Manual Removal

• This method is labor intensive,.
• It is a low-efficiency technique.
• It can be hampered by water depth and physical quantities of materials that can be handled in a given time.

Management of Aquatic Weeds: Mechanical Removal

• Use machinery to cut, shear, shred, crush, press, lift, and convey aquatic plants and associated organic material from water bodies.
• Mechanical controls range from small cutting boats to 90-foot-long harvesters,.
• Shredders slurry plants to track hoes.
• Draglines stationed on shorelines or barges are utilized to lift plants and debris out of the water.

Management of Aquatic Weeds: Chemical Control

• This involves the use of inorganic or organic herbicides usually as a last resort.
• Herbicide is applied directly to the plant for floating and emergent aquatic plants.
• Alternatively it is applied into the water for submergent plants.
• The high cost of mos