These are other natural hazards that have been identified, and which are being mitigated by City officials. Click on each to find out more:
- Stranding of Marine Animals and Shark Activity
- Pest Infestation
- Plant Disease
- Harmful Algal Blooms
- Cosmic Impact
Stranding of large Marine Animals and Shark Activity
Although a relatively rare occurrence, Cape Town with over 300km of coastline, does experience strandings of large marine animals such as whales, dolphins and seals. These events, when they do occur, require a collective, co-ordinated and organised response by various authorities and agencies to be effective. A Policy and Response Plan has been developed to cover aspects such as:
- Rescue attempts for live animals
- Public control and management
- Volunteer control and management
- Environmental protection
- Carcass removal and disposal
Awareness of sharks along Cape Town’s beaches
An increase in shark activity can be associated with certain sea conditions and or the presence of food sources such as schools of fish, the presence of other marine mammals feeding, high marine bird activity or any fishing or chumming operations from boats in the vicinity.
All beach users are urged to exercise the necessary caution by swimming in the demarcated areas and adhering to Life Guard and Shark Spotter advice and Special Notifications and Warnings.
Shark Spotting services are available at Muizenberg, St James-Kalk Bay, Clovelly (until April), Fish Hoek, Glencairn (until April) and Noordhoek. Beach users are reminded that there are no shark spotting services at the Simonstown beaches or beaches along the north shore of False Bay between Sunrise Beach and Gordon’s Bay, nor on beaches on the north-western seaboard. Click here for more information.
Pest Infestation is the state of being invaded or overrun by parasites or other pests. Cape Town still has large agricultural and fynbos (rural) areas within its boundaries which may be susceptible to this type of hazard. However, even in the built-up areas, pests like insects (ants, termites, fleas, cockroaches, ticks, spiders, etc.), rodents (mice, rats, etc.), and exotic plants, birds and animals, may occur.
The agriculture, nature conservation, environmental health and specialised pest control agencies continuously monitor for all types of pest infestation and have plans and methodology to deal with any infestation.
Pest infestations may also occur in areas which have been affected by a major disaster and may even affect the health of the survivors. These aspects will be monitored after any incident and the appropriate control and rehabilitation measures undertaken.
By drafting your own Family Emergency Plan (Link to Family Disaster Preparedness Guidelines pdf in Resources) and identifying all your risks, including those hazards affecting your own environment, you can make a positive contribution to preparedness.
Fungal diseases can be controlled through the use of fungicides in agriculture, however new types of fungi often evolve that are resistant to various fungicides.
The oomycetes are not true fungi but are fungal-like organisms. They include some of the most destructive plant pathogens including the genus Phytophthora which includes the causal agents of potato late blight and sudden oak death. Despite not being closely related to the fungi, the oomycetes have developed very similar infection strategies and so many plant pathologists group them with fungal pathogens.
Most bacteria that are associated with plants are actually saprotrophic, and do no harm to the plant itself. However, a small number, around 100 species, are able to cause disease. Bacterial diseases are much more prevalent in sub-tropical and tropical regions of the world. Phytoplasma and Spiroplasma are a genre of bacteria that lack cell walls, and are related to the mycoplasmas which are human pathogens. Together they are referred to as the mollicutes. They also tend to have smaller genomes than true bacteria. They are normally transmitted by sap-sucking insects, being transferred into the plants phloem where it reproduces.
There are many types of plant virus, and some are even asymptomatic. Normally plant viruses only cause a loss of crop yield. Therefore it is not economically viable to try to control them, the exception being when they infect perennial species, such as fruit trees. Plant viruses must be transmitted from plant to plant by a vector. This is often by an insect (for example, aphids), but some fungi, nematodes and protozoa have been shown to be viral vectors.
Nematodes are small, multicellular wormlike creatures. Many live freely in the soil, but there are some species which parasitize plant roots. They are a problem in tropical and subtropical regions of the world, where they may infect crops.
There are a few examples of plant diseases caused by protozoa. They are transmitted as zoospores which are very durable, and may be able to survive in a resting state in the soil for many years. They have also been shown to transmit plant viruses. When the motile zoospores come into contact with a root hair they produce a plasmodium and invade the roots.
Parasitic plants such as mistletoe and dodder are included in the study of phytopathology. Dodder, for example, is used as a conduit for the transmission of viruses or virus-like agents from a host plant to either a plant that is not typically a host or for an agent that is not graft-transmissible.
Harmful Algal Blooms
Eutrophication in lakes and rivers
Eutrophication can be human-caused or natural. Untreated sewage effluent and agricultural run-off carrying fertilizers are examples of human-caused eutrophication. However, it also occurs naturally in situations where nutrients accumulate (e.g. depositional environments), or where they flow into systems on a short-term basis.
Eutrophication generally promotes excessive plant growth and decay, favouring simple algae and plankton over other more complicated plants, and causes a severe reduction in water quality. Enhanced growth of aquatic vegetation or phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen needed for fish and shellfish to survive. The water becomes cloudy, typically coloured a shade of green, yellow, brown, or red. Eutrophication also decreases the value of rivers, lakes, and estuaries for recreation, fishing, hunting, and aesthetic enjoyment. Health problems can occur where eutrophic conditions interfere with drinking water treatment.
Some algal blooms, otherwise called "nuisance algae" or "harmful algal blooms", are toxic to plants and animals. Toxic compounds they produce can make their way up the food chain, resulting in animal mortality. Freshwater algal blooms can pose a threat to livestock. When the algae die or are eaten, neuro- and hepatotoxins are released which can kill animals and may pose a threat to humans. An example of algal toxins working their way into humans is the case of shellfish poisoning. Biotoxins created during algal blooms are taken up by shellfish (mussels, oysters), leading to these human foods acquiring the toxicity and poisoning humans. Examples include paralytic, neurotoxic, and diarrhoeic shellfish poisoning. Other marine animals can be vectors for such toxins, as in the case of ciguatera, where it is typically a predator fish that accumulates the toxin and then poisons humans.
Limiting the discharge of agricultural fertiliser, sewerage and household pollutants can limit algal bloom occurrences, and the community needs to assist in this regard.
“Red Tide” or harmful algal blooms (HAB) in the sea
A harmful algal bloom is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings.
"Red tide" is a term often used to describe HABs in marine coastal areas, as the dinoflagellate species involved in HABs are often red or brown, and tint the sea water to a reddish colour. The more correct and preferred term in use is harmful algal bloom, because:
- these blooms are not associated with tides
- not all algal blooms cause reddish discoloration of water
- not all algal blooms are harmful, even those involving red discolouration
Off the west coast of South Africa, HABs caused by Alexandrium catanella occur every spring. These blooms of organisms cause severe disruptions in fisheries of these waters as the toxins in the phytoplankton cause filter-feeding shellfish in affected waters to become poisonous for human consumption, including mass crayfish “walk-outs” onto the beach.
Other effects of HABs could be the massive die-off of certain fishes or the mass stranding of certain larger marine animals due to stress or ill-health.
Solar storms A solar storm can refer to:
- Solar flare - a large explosion in the Sun's atmosphere (also known as sunspots).
- Coronal mass ejection (CME) - a massive burst of solar wind associated with solar flares.
- Geomagnetic storm - the interaction of the Sun's outburst with Earth's magnetic field.
Some effects of solar storms are:
- The collapse of the power grids, as equipment protection relays may trip in a cascading sequence of events. The result may be no power for a few hours, with significant economic loss.
- Telephone wires may experience induced electro-magnetic field (emf), in some cases even shocking telegraph operators and causing fires.
- Auroras may be seen much further south or north - phenomena that are usually only seen near the poles.
- Microchips in computers and other electronic equipment may be affected.
- Radio communications, especially short and medium wave frequencies, may also be affected.
Space debris and bolide (meteorite) impact
Space debris (‘old’ satellites falling out of orbit) and meteorites, are almost always burned up by the Earth’s atmosphere and will very rarely cause any significant damage as there will be no, or very minor impact, onto the Earth. This type of hazard therefore has an extremely low probability of occurrence and its risk can be regarded as very low.