Visitors to Cape Town's beaches over the past few weeks may have noticed a huge number of jellyfish washed up, especially on the West Coast, Lagoon Beach, Milnerton Beach, Bloubergstrand and Melkbosstrand, but also in False Bay and other areas.

UPDATE (24 April 2019): Over the Easter long weekend, thousands of purple-pink jellyfish washed up in False Bay near Gordon's Bay and Strand, and with the strong Southeasterly winds we have had reports of smaller numbers of these jellies washing up on the opposite side of False Bay at Dalebrook at Muizenberg. These jellies are called night-light jellyfish (Pelagia noctiluca) and are a common jellyfish that naturally occurs in large blooms in deeper waters off the Western Cape coast. Their presence on the False Bay beaches is because of strong winds and swells carrying them in from deeper waters and should not be a cause of alarm.


Please be aware that night-light jellies can sting humans, and although it is not likely to be serious, they are best avoided. If you are in an area where these are washing up, keep an eye on the waterline at night - some populations of night-light jellies are able to flash their own glowing lights when struck by waves, so you may be lucky enough to see this phenomenon.

UPDATE (24 December 2018): Several people have asked us about dead crabs that they've been spotting on the West Coast. When water oxygen levels drop (eg. as a result of an algal bloom), large numbers of crustaceans take part in "walkouts" where they climb up out of the water. The walkouts seen this month have been on a very small scale, and should not be a cause for alarm - we're just letting everyone know that this can take place as a result of natural processes.

Small crustaceans that may have been washed up in a small walkout near Cape Town. Credit: Angus Kelly

For those of you who would like to track South Africa's algal blooms yourself, check out the National Ocean and Coastal Information Management System.

UPDATE (10 December 2018): Increasing misinformation has been spreading about the ongoing algal bloom around the Cape, which we can assure you is a natural occurrence and poses no risk to humans. The algal bloom has no connection to the City's wastewater. For your information, we've added the City of Cape Town's media release to the bottom of this post.

Credit: Helena Sousa

These beautifully patterned marooned maroon (yes pun intended) jellyfish are called compass jellies, a family of three closely-related South African species -  the Benguela compass jelly (Chrysaora fulgida), the purple compass jelly (Chrysaora africana) and the Cape compass jelly (Chrysaora agulhensis).

In this case, the majority of the washed-up jellies appear to be Cape compass jellies - a particularly localised species that is still subject to some pretty amazing research!

Are the jellies dangerous to humans?

Not really, most species of compass jellies are only able to give a sting as severe as a bee sting. Other than being very painful, there is little danger to humans, unless you are allergic or get stung over a large portion of your body.

Did you know: Recent studies have shown that urinating on a jelly sting is actually not the best medicine. Get the sting off, pour vinegar over the affected area, and then submerge the affected area in hot water.

Jellies that wash up and are exposed to dry air lose their ability to sting once they are dried out, but can still give you a nasty sting as long as they remain moist. Luckily, the tentacles of compass jellies are fragile and most of the washed-up specimens we've seen seem to have lost their tentacles, so those that are found on the beaches are unlikely to pose much risk to children, bathers and pets that may accidentally touch one.

Credit: Helena Sousa

Why are they washing up? Is something wrong with the environment?

Jellyfish are planktonic, which means that they drift with the ocean. In this case, the combination of wind and current means that we are seeing a large number of these jellies, with their vivid mature colouration, washing up. This poses no problem to their species as a whole - they are very abundant offshore.

Credit: Helena Sousa

Large blooms occurring so near to Cape Town indicates that our local waters are very nutrient-rich, and thus rich in phytoplankton - the microscopic plants which form the base of the foodchain, and feed the tiny animals that jellyfish, in turn, rely on. Sometimes this can be an indication of pollution adding nutrients to the water, but it can also be due to natural variation, eg. windborne sediments. At this point, it is not clear what the cause is.

When these nutrient influxes are particularly high, ocean plants can grow so rapidly that they cause a phenomenon called "red tide" - getting its name from the colour and toxicity of some of the microorganisms that flourish in these conditions. Algal blooms like this can also result in the depletion of oxygen in the water column, usually from all the bacteria involved in the decomposition of the plants after the bloom. Both of these conditions can be harmful to sea life, and humans consuming it, but at the time of writing, no red tide warning has been issued by the Department of Agriculture, Forestry and Fisheries (DAFF), so no need to be concerned!

Please find the City of Cape Town's media release about this algal bloom at the bottom of this article.

How can I tell the different types of compass jellies apart?

In general, compass jellies develop from translucent juveniles with longer oral arms (the thick frilly mass that hangs out from the middle of the jelly) with tentacles hanging around their bell margin.  As they mature their banded "compass" pattern becomes more prominent, and this is the pattern that most people will recognise. Be aware that the tentacles and oral arms of jellies are their most fragile parts, so will usually be missing from washed-up jellies that have been damaged by the waves.

Cape compass jellies

Cape compass jellies are the most widespread species of compass jellies around South Africa, ranging from Durban to Namibia. They have a characteristic compass pattern, consisting of purple-maroon elongated V-shapes that point towards the centre of the bell. These V-shapes have thick outlines, with transparent maroon centres. The jellies also appear to be covered in freckles. The rest of the bell is transparent, sometimes with a purple-pink tint which varies regionally.

Credit: Krish Lewis

Benguela compass jellies (also called sea nettles)

These compass jellies have the same typical compass pattern seen in the other species but tend to develop this pattern much later during their lifespan. While they are in their juvenile state, their tissues have a white to light pink colouration. When mature they develop dark pink to maroon markings. Their compass patterns tend to be a dark pink-maroon colour. Benguela compass jellies usually have about 42 tentacles.

Several Benguela compass jellies are on display at the Two Oceans Aquarium - a great chance to learn more about these amazing creatures.

Purple compass jellies

Purple compass jellies are found from the West Coast of South Africa to Gabon. They have a white bell and oral arms, with purple V-shaped compass spokes covering the bell, a thin purple line sits between each spoke. They are very uncommon off Cape Town but become more common as you move north toward Namibia. 

Any other cool compass jelly facts?

In 2005, huge numbers of compass jellies on the West Coast actually blocked the water intakes of Koeberg Nuclear Power Station, causing Eskom to have to reduce the power production of the reactor!

City of Cape Town media release (10 December 2018):

Please note that the release below is taken verbatim from the City of Cape Town.

Naturally occurring algal blooms along False Bay coastline not toxic

The City of Cape Town advises residents that, contrary to what is being reported by some news outlets, the naturally occurring algal blooms along the False Bay coastline are not toxic and have nothing to do with inland or wastewater quality. Read more below:

Algal blooms

The particular species of algal bloom occurring along the coastline was identified by the National Department of Agriculture Forestry and Fisheries (DAFF) as Lepidodimium chloroforum and has no known toxins. DAFF holds the mandate to monitor the occurrence of algal blooms as well as for issuing any consumer warnings in the event of a toxic bloom (red tide).

Algal blooms are a normal and common occurrence off the coastline of Cape Town, and South Africa more broadly. The phenomenon is mostly caused by ocean upwelling events that brings colder, nutrient-rich water, and the accompanying dinoflagellate cells, into warmer surface waters. The combination of nutrients, warmth and sunlight causes the cells to bloom.

Alarmist stories have been carried by some news outlets after an article was released by a UCT scientist about water quality matters. The City has not seen the findings of the research first-hand but understands that the scientist has requested certain news outlets to print corrections to their stories to more accurately reflect the true state of affairs. The City welcomes this call as inaccurate reporting does a disservice to readers and the broader community.

As a matter of record, the City also has the highest number of Blue Flag beaches in the country, 10 of which five are in False Bay between Fish Hoek in the west and Bikini Beach in the east. As part of the Blue Flag criteria, water quality at these sites is independently analysed by the South African Bureau of Standards.   

Impact of the algal blooms on the Strandfontein and Monwabisi desalination plants

It must also be noted that there are organisations who are creating the impression that the City’s desalination plants have not been working at all due to some functional failure or cover-up by the City. This is simply not true.

The operations of the desalination plants in Strandfontein and Monwabisi have at times been affected by algal blooms and the high turbidity of the sea water. The algal blooms occur naturally and the high turbidity in the ocean is normally caused by bad weather and sea conditions (strong winds and big swells). Algal blooms cause damage to the sensitive membrane filtration systems of the desalination plants, while the high turbidity affects the pre-treatment processes of the desalination plants, which can result in reduced production by the plant. Halting operations temporarily is thus a precautionary approach while ongoing monitor and technical assessments continue to ensure the optimal functioning of the plants.

The Strandfontein plant was producing little to no water over the period 1 to 7 November 2018 due to the high turbidity of the sea water. The Monwabisi plant could not operate for four days during the same period. After resuming the production, both plants again stopped producing drinking water on 16 November 2018 due to the occurrence of the algal bloom but are fully functional otherwise.

The algal bloom has dissipated in the False Bay area and the Strandfontein plant is in production again while the Monwabisi plant will be in production again soon. It must be noted that the City only pays for water that is actually injected into the reticulation system, hence the temporary suspension is not for the City’s account, as claimed.

The contractors who have been appointed to run the desalination plants as part of the City’s Water Emergency Water Augmentation Scheme are contractually required to deliver water that meets South African National Standards (SANS 241:2015) requirements. These are the standards set nationally for drinking water quality. The City has a proud record of always meeting these standards. The desalination plants have online monitoring equipment to check the quality of the desalination process and adherence to the SANS standard.

Desalination, at this stage, is a relatively small component of our augmentation programme and as such temporary drops in production are not expected to have a very significant impact on the overall water supply.

Zandvliet Waste Water Treatment Plant (WWTP) upgrade to benefit Sandvlei community and surrounds

The inland wastewater treatment upgrades for the Zandvliet plant have also been conflated with the algal bloom situation. It thus bears no correlation with the water quality issue discussed above.

The City has started to undertake measures to mitigate environmental impact. Currently, 8 million litres of flow per day that is currently going to the Zandvliet WWTP is being diverted to the Bellville WWTP (completion of diversion expected in early 2019). Furthermore a R1,5 billion upgrade to the Zandvliet WWTP is planned to cater for rapid ongoing development in the Khayelitsha, Delft, Blackheath and Eerste River areas.

The City has for several years been attempting to upgrade the plant but this has been delayed by five tender appeals, including a High Court appeal, and a land claim.

Encouragingly, most of the upgrade work has been approved by Council in the past few months, and it is expected that work will begin in the first half of 2019. We still, however, require residents to obey the laws which state that nothing should be flushed down the toilet or thrown into manholes which could interfere with the free flow of sewage, such as rags, litter, rubble, cooking oil and fat, and anything other than greywater and toilet paper.

The commissioning of the new plant is anticipated by December 2023. Soon thereafter, a further expansion will be implemented to cater for continuing urban growth in the area. Work will see construction of a membrane bioreactor (MBR), sludge dewatering facilities, new inlet works, pump stations, primary settling tanks and maturation ponds where effluent is purified before discharge.

Importantly, it must be noted that the City does not discharge untreated sewage into the river. The plant currently operates within the design capacity in term of flow rates. However, it is over its capacity in terms of nutrient load due to the population growth in the area which is serviced by the plant. The City is implementing a number of initiatives such as the addition of polymers for treatment to settle the nutrients while the expansion is under way.

The City’s sampling and testing frequency has been increased to a weekly schedule, and will include input from the community on agreed sampling locations. These results are being shared with the National Department of Water and Sanitation, and with the CSIR.

Humans produce waste

There are over 84 000 synthetic chemicals in common use and no wastewater treatment plant in the world is able to remove all of these components from effluent. They will continue to be present in the environment so long as we continue to use them as a society. Our understanding is that further research into the long-term effects of these various chemicals on public health and the environment is necessary, as the effects of these chemicals in aquatic ecosystems are largely unknown. 

In general, the treated effluent discharged from the City’s WWTPs achieve a compliance rate of more than 80% with the standards required by the Regulator; and the plants operate in accordance with ISO standards. The City is committed to ensuring that it continues to evolve its processes to manage waste and to ensure that it does absolutely everything in its power to put in place enhanced processes for sustainable urban management.


Issued by: Media Office, City of Cape Town

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