A (lovely, rain-bringing) onshore wind left great rafts of kelp all over Noordhoek beach one weekend in mid May. Finding anything of substance on this beach is unusual; it’s on an exposed piece of coastline and all but the most robust objects are dashed to pieces before they arrive on the sand. Seeing all the washed up kelp also reminded me that frequenting the beaches inside False Bay, that are daily cleaned of washed up kelp by the City of Cape Town, is liable to give one a skewed idea of just how much kelp naturally washes up on the sand.
Kelp stipe covered in goose barnacles
This time, there was kelp, and lots of it. Several of the pieces of kelp had been colonised by goose barnacles. There are several species of goose barnacle that occur off South Africa’s coast, but these ones are Lepas testudinata. They are incredibly strange looking animals, and some of them were still alive and writhing slowly in the drying sun.
In parts of the world (I’m looking at you, Iberian peninsula), goose barnacles are an expensive delicacy. I have nothing to say about that.
Goose barnacles, with my paw for scale
Lepas testudinata larvae most often attach to free-floating pieces of kelp (Ecklonia maxima) and plastic debris, which is why you have probably never seen these mesmerisingly gross-looking creatures while on a dive. In the picture below, you can see that they’re attached to the bottom of a kelp holdfast, where it would ordinarily attach to the rock. This shows that they attached after the kelp broke off.
A kelp holdfast encrusted with goose barnacles
Each barnacle is possessed of a long fleshy peduncle, or stalk, which attaches to the kelp holdfast, stipe or fronds. On the end of the peduncle is a carapace (shell) made up of five separate pieces. The large part of the barnacle on the end of the peduncle (what you’d think of as its body), covered by the carapace, is called the capitulum. The apparatus that the barnacle uses for feeding – essentially six pairs of hairy legs – reside inside the carapace, along with the mouth. There’s some more detail and a nice diagram at this link. If you are familiar with other kinds of barnacles – the volcano-shaped ones that live on rocks, ships, whales and piers for example, then most of this (except the peduncle) should sound familiar to you.
Lepas testudinata goose barnacles
Research done around South Africa’s coast (published here) by Otto Whitehead, Aiden Biccard and Charles Griffiths, identified the marked preference of Lepas testudinata for attaching to kelp. The researchers surveyed a selection of beaches around South Africa’s coast, from the west coast of the Cape Peninsula up to northern KwaZulu Natal, between June and October 2009. When they found goose barnacles washed up, they recorded the species of barnacle, the type of material they were attached to, the dimensions of the object, and its location. They also estimated the number of barnacles in each colony they found.
Lepas testudinata was the species they found most commonly, of the six species in total that they identified along the area of coast that was surveyed. (There’s a nice picture of the six species in their paper, which I used to identify the ones I found.) This species of goose barnacle was found to prefer kelp, as mentioned, and also tended to colonise large objects compared to the other species (this could, of course, be because pieces of kelp are usually larger than items such as bits of plastic, glass, feathers, and shells that some other species prefer).
Kelp fronds with goose barnacles
Lepas testudinata was the only species of goose barnacle that the researchers regularly found to form colonies comprising more than 1,000 individuals. It is also the only species of goose barnacle recorded by the survey that is only found in temperate (cooler) waters, which happens to be where kelp is found, too.
The researchers note that the goose barnacles of the Lepas testudinata species that they found on kelp seemed to have exceptionally long peduncles, some more than 25 centimetres long, and that this seems to differ from what has been previously known about them (which is that they have “short, spiny” peduncles). They suggest that perhaps the variety of Lepas testudinata that colonises kelp may even be a separate species from the one previously described (more research obviously required to ascertain this). You can see from my photographs that the peduncles of the washed up Noordhoek beach goose barnacle colonies are also quite long, some easily 20 centimetres in length.
Clusters of goose barnacles on a kelp stipe
They also found that the increasing prevalence of long-lasting and buoyant plastic marine debris and other anthropogenic objects around our coastline, which some species of goose barnacles preferentially attach to, gives these weird little creatures increased opportunities to form colonies, and to spread to new places. This is one of those interesting phenomena to keep in mind, as humans inexorably alter the environment. Some creatures will benefit in strange ways from warming oceans, and others will find new homes in the garbage we leave lying around.
Capetonians are familiar with the tea-coloured water that runs in our mountain streams. Most people know that the brown colour comes from tannins, leached naturally from the indigenous fynbos vegetation. Perhaps less well known is the reason for the brown water that is sometimes seen in the surf zone along Muizenberg beach, stretching all the way to Strandfontein, Monwabisi and beyond.
Tea-coloured water at Muizenberg
The most frequent explanations that are offered on social media are, of course, pollution, “raw sewage”, and the like. This is not the reason for the brown water, and it does not necessarily impact the water’s safety or healthfulness for humans to swim in.
Like False Bay’s famous colour fronts, the reason for the brown waves at Muizenberg beach turns out to have much to do with the topography of False Bay, particularly of the kilometres-long beach at its head (Muizenberg-Strandfontein-Macassar-Monwabisi), and something called a diatom.
View of Muizenberg showing patches of brown water
Diatoms
Diatoms are a type of phytoplankton (plant plankton or microalgae). They are single celled, usually symmetrically shaped organisms that multiply by dividing in half at a constant rate. Their cell walls are made of silica, SiO2. Chicken keepers and gardeners may be familiar with diatomaceous earth – this is made up of the fossilised shells of ancient diatoms.
Diatoms are what are called primary producers or autotrophs, meaning that they generate organic material from carbon dioxide and other inorganic nutrients (for example nitrates and phosphates), through the process of photosynthesis, which uses light as an energy source. Primary producers sit at the base of the food chain and all life relies on them, directly or indirectly. Everything else produces organic material from other organic material (such as diatoms).
I am telling you all about diatoms because the brown water at Muizenberg contains an accumulation of a diatom that you can call Anaulus australis Drebes et Schultz the first time you mention it, but usually just Anaulus australis, or Anaulus for short. There are several members of the genus Anaulus, but usually just one tends to be dominant at each beach where these accumulations occur, and Anaulus australis is the main species found along the South African coast.
Analaus are pillow-shaped diatoms. If you wanted to see what an individual Anaulus diatom looked like, you’d use a microscope, but when enough of them are in one place, they can be seen to change the colour of the water. There’s a picture of them under a microscope at the bottom of this webpage (they also occur in Brazil). They occur at beaches with particular topograhical characteristics, which explains why you haven’t seen them at Camps Bay, Kogel Bay, or Scarborough.
At hospitable beaches, the diatoms are always there, spending much of the time lying dormant in the sand behind the surf zone. A proportion of the diatom population is able to survive for relatively long periods (estimated to be more than two months) like this, in the dark on the seabed, not photosynthesising or dividing, until the correct meteorological conditions arise for an accumulation. But first – what sorts of beaches are hospitable to Anaulus?
a nutrient source close to the surf zone (often an unconfined aquifer overlaid by a dune field)
Muizenberg and Strandfontein beach tick all these boxes. The beach stretches from Surfers Corner all the way across the top of False Bay to Monwabisi, a distance of over 20 kilometres. It is a high energy beach, meaning that it is exposed to large waves and strong winds, and is not protected by any offshore features such as sandbars or headlands that might reduce the force of the waves. Rip currents do occur at the beach, and both these and the exceptionally wide surf zone – wider during south easterly winds in summer – can be observed from the mountainside on Boyes Drive. (A rip current is like a hidden river flowing out to sea from the beach. The Sydney Morning Herald has an excellent visual explainer of rip currents here.)
The head of False Bay where Muizenberg is situated is incredibly nutrient-rich, much of it thanks to urbanisation. The canalised Zandvlei estuary – the only vaguely functional one on False Bay’s coast – is situated a short distance down the beach, and supplies nitrates, phosphates and other nutrients to the surf zone. Many of these nutrients are technically pollutants, added to the river further upstream. The Cape Flats Waste Water Treatment plant at Strandfontein also discharges 200 million litres of treated water per day (under normal, non-drought circumstances) via a canal onto Strandfontein beach. This is essentially an artificial estuary for Zeekoevlei. This waste water has spent some time working its way through the settlement ponds at Strandfontein, but is nevertheless rich in ammonia and other nutrients, and Anaulus accumulations are a very common sight in the surf around this discharge point. The dunes that run along Baden Powell drive overlay a high water table, and groundwater seepage – specially during times of heavy rainfall – may also leach nutrients out of the ground and into the surf zone.
Meteorological conditions
The meteorological conditions required for an Anaulus accumulation involve strong wind and a large swell. These act together to create rough sea conditions, which stir up the dormant diatoms from the ocean floor. The diatoms adhere to air bubbles in the surf zone, staying suspended in the water column, which is when you would notice the water turning brown. Exposed to light, they awaken from their dormant state and start to photosynthesise, take up nutrients, divide and multiply. The presence of rip currents creates an onshore-offshore flow all along the beach. This forms a semi-closed ecosystem, and the diatoms are essentially trapped in gyres in the waves. Longshore currents that run parallel to the beach transport Anaulus cells out of the surf zone at one end, and bring fresh (sea)water in at the other end of the beach.
It may seem surprising that anything manages to accumulate in the waves of a beach, but the surf zone is actually quite retentive, meaning that things that end up there often tend to stay there. (Incidentally, this is why it’s a terrible idea to discharge the byproduct of reverse osmosis seawater desalination – a super-salty brine – into the surf zone. It must be discharged offshore so that it can disperse and mix with the surrounding water.)
Diatoms in the surf zone at Muizenberg
You’ll notice that, contrary to what you may have seen when large amounts of plankton are under discussion, I’ve been using the word “accumulation” instead of “bloom” to talk about Anaulus. This is deliberate, because of the constant presence and constant rate of division of the diatoms. When the water goes brown, it doesn’t mean that Anaulus is suddenly multiplying faster than usual. It means that it’s all been gathered together in patches, is exposed to light and therefore photosynthesising (at its usual steady rate), and is thus more visible than it was when it was lying on the ocean floor.
Anaulus at Muizenberg in November 2017
The human factor
You may also be thinking that everything I’ve said about the nutrients that Anaulus requires to survive and thrive points to the fact that humans – and pollution – are ultimately responsible for these brown-water plankton accumulations at Muizenberg. Well yes, in a way. But accumulations of Anaulus australis and related species have been observed and documented for well over 100 years at suitable beaches around the world, and are a natural phenomenon.
Yes, we are providing more nutrients to the False Bay diatom population than they would otherwise have received without human settlement in the greater Cape Town area, but these accumulations would likely occur regardless. They are certainly more intense now than they would have been in the past, but estuaries are nutrient-rich locations even when not surrounded by a large city. Furthermore, the water table is high on the Cape Flats, which would supply nutrients to the surf zone regardless of whether humans lived nearby.
Anaulus is in fact performing a vital and useful function by mopping up the excess nutrients that the city discharges in the ocean. The mass of diatoms – primary producers – also provides a food source to bivalves such as mussels, and other invertebrates. We can be grateful that the excess nutrients that urbanisation directs towards the ocean at the head of False Bay leads only to accumulations of harmless diatoms, rather than to frequent occurrences of harmful algal blooms that can kill marine life and exacerbate respiratory problems in humans.
Muizenberg during a diatom aggregation
Sources
Most of the original scientific study on surf zone diatoms in South Africa was done by a group of researchers (primarily M Talbot, Eileen Campbell and Guy Bate) from the University of Port Elizabeth, working at the Sundays River Beach in the Eastern Cape. I did quite a bit of reading to research this post, but you can start with this paper for a description of the topographical characteristics of beaches where surf zone diatoms accumulate. The first few chapters of this Masters thesis also provide a good overall survey of what is known about surf zone diatoms.
Putting knowledge into practice
Not every instance of brown, foamy water at the beach will be an Anaulus accumulation. On the west coast of South Africa, for example, there are no beaches where Anaulus occurs, but you may see brownish foam that is the result of heavy wave action frothing up organic matter in the surf (nothing sinister – there is a lot of organic material in the ocean). A clue to help you distinguish diatom accumulations from other brown-water phenomena – apart from running through the checklist of required beach characteristics above – is that an Anaulus accumulation doesn’t stretch much beyond the back of the surf zone. If the brown water stretches beyond the furthest row of waves, it’s probably something else. (And this seems like an apposite time to remind you that sewage looks whitish-grey, not brown, when it’s pumped out into the ocean.)
The number of beaches worldwide where surf zone diatom accumulations occur is so small – less than 100 – that Odebrecht et al could enumerate them in a 2013 paper. I hope this helps to convince you that the brown water at Muizenberg beach (and beyond) is something special and interesting, not to be feared. Go surfing!
Into a Raging Sea: Great South African Rescues – Tony Weaver & Andrew Ingram
I insensitively packed this book for Tony to read while we were aboard MSC Sinfonia for the BirdLife cruise we took in April. It’s a rip-roaring read about various rescues that the NSRI has been involved with over the years, but – perhaps unsurprisingly – Tony wasn’t keen to read about maritime disasters (even ones that ended well) while we were at sea.
One of the things I loved about this book was that it reveals the men and women behind the daring, often dangerous rescues. The rescuers are allowed to recount the events they experienced, using their own words, and this is revealing. These rescuers are not usually lionised by the general public or, as a rule, afforded prolonged media attention, and neither does this book glamorise them or romanticise their achievements. The challenge of the rescues – and occasional raw fear felt by the rescuers – are vividly portrayed. The writing is beautifully matter of fact, without downplaying the seamanship, strength of character and perseverance required to do this (unpaid) work.
It reminded me fondly of the “drama in real life” stories that I used to devour from the pages of the Readers Digest magazines my grandmother used to bring whenever she came to visit. There are many, short chapters, each one offering its own little catharsis. The rescues span South Africa’s coastline, as well as a few other locations, and not all of them are maritime disasters.
Proceeds of this book support the NSRI. Get a copy for yourself, and all your friends. It will entertain anyone who loves a good story of heroism and adventure, and it will encourage anyone who’s feeling jaded about humanity’s capacity for good. It’s an excellent read.
You can find a copy on Loot if you’re in South Africa, otherwise here or here.
We were surprised by the intensity of the birding that took place on Flock At Sea AGAIN! 2017. In retrospect we shouldn’t have been, but being around 2,000 serious twitchers was, at turns, overwhelming and hilarious. Tony and I spent quite a lot of time on deck 4 of MSC Sinfonia, bothering our friend Ian. An enduring memory of this time was turning around from the rail to see a wall of K-Way clad birders charging towards us like buffalo, heading for the stern of the ship, where something special had just been spotted.
Annoying Ian
There was serious camera hardware on board. Tony’s modest 200-500mm Sigma lens sometimes gets admiring glances from the uninitiated, but on this cruise it left something to be desired (as you can see in comparison to Ian’s rig in the photo above).
The gun show
It is known by anyone who’s been on a boat that taking photos on the ocean is difficult, especially of a fast moving, distant subject such as a bird. Tony had a go at some bird photos, with reasonable success. Trying to identify what we’d seen afterwards was fun. We were definitely not the people who were calling the name of the bird before photographing it! Once we came across a large aggregation of birds feeding on something on the surface, and once some dolphins, but there were fewer marine mammal sightings than we’d hoped.
An older wandering albatross
Juvenile wandering albatross
Young wandering albatross showing the underside of its wings
Juvenile southern giant petrel
I loved seeing the albatross, and because of their great size and confidence in approaching the ship, I found them easiest to identify. Both Peter Harrison’s talk and Carl Safina’s brilliant Eye of the Albatross emphasised the extraordinary longevity and fidelity of these birds, and the loneliness of their lives in between visits to the breeding islands. In addition to the ones pictured above, we also saw Indian yellow-nosed albatross, which I’d previously seen sitting on the surface of the ocean above the wreck of the Fontao in Durban, waiting for snacks from the fishermen there.
There were plenty of places to watch the sea all around the ship. Deck four ran along both sides of the vessel close to the ocean, and the triangular viewing platforms that protrude at the stern were a popular sunset location. Around the central area on the top deck that contains the swimming areas, a raised wrap-around deck also provided good viewing opportunities, but it was too high up for proper bird watching.
Sunset birding on departure
Birders on board
Birding in the sunshine
The light varied a lot depending on the time of day (duh!) and the degree of cloud cover. It was windy almost all the time. I was surprised by the speed of the ship; when we were moving between birding locations we cruised at up to 25 knots. Only on one of the days was the sea rough enough to splash onto the lower decks.
Wind protection
We saw some things we’d never seen before, like an extravagant double rainbow just before sunset. It was wonderful to be completely surrounded by ocean, and to watch how the colour of the sea changed through the day. We were travelling over deep water, and the profound blue of the ocean when the bottom is hundreds of metres below is something special. Look at the wake in the rainbow picture for an example.
Double rainbow
We saw a few other ships, but not as many as I’d expected. There was some tooth-gnashing among the twitchers when, on the last full day of the cruise as we headed back towards Cape Town, some fishing trawlers were seen in the distance. It was fascinating to watch the trawlers turn on a dime and mow back and forth, but the clouds of seabirds behind the ship remained just out of proper sight.
Fishing trawler at work
There’s an album of photos (including some of the ones I’ve included here) on facebook, if you’re interested! And if you’re interested in seabirds, I can’t think of a better place to start than Carl Safina’s Eye of the Albatross.
After a few days of rain and southerly swell False Bay does not look that great. This swell direction is set to stay for a few more days and in fact changes only on Monday. There is some south easterly wind on Friday and Saturday but not really strong enough to clean up the Atlantic enough for decent visibility.
Storm clouds at Zeekoevlei
I think it may well be a dry weekend as far as diving is concerned, however if things start to look more promising than they currently do, I will be in touch. Let me know if you’d like me to message you if we go diving.
The Bay has been on and off this week with some swell interfering with good diving. A 7 metre swell is expected tomorrow and this means that Dungeons may be worth a look early on Saturday. Odds are the swell doesn’t quite reach the forecast size, and Sunday diving in False Bay may pan out.
Text, whatsapp or email me if you want to be on either list and I will keep you posted… Saturday big wave watching or Sunday False Bay diving.
A day early in April was the date for the annual Freedom Swim, a 7.5 kilometre open ocean cold water swim from Murray’s Bay harbour on Robben Island to Big Bay near Blouberg. As we have in several previous years, we provided boat support for a swimmer.
This entails providing a straight course for the swimmer so as to minimise the distance swum, and keeping an eye on them to ensure that they don’t get too cold or show any other symptoms of hypothermia or distress. It requires communication with race control by radio, and a bit of boat and swimmer dodging in the early stages of the race when the water is thick with activity.
Cloudy skies over Robben Island
Tony waiting for the start
Team de Mooij at the start
Rougher seas closer to Big Bay
Green water close to shore
Table Mountain
There was a 3.5 metre swell on the day, which made the ride out to the island a bit bumpy. As soon as we were in the shelter of the island, however, the sea was flattened as the swell diverted around the island. The water remained calm until we got quite close to shore, at which point the swell picked up. The final stretch from the rocks at Big Bay to the beach must have been very hairy for the swimmers!
Our swimmer, Maryna, swam in a wetsuit. She was part of the Lighthouse Swim relay team we supported last year. The water was relatively warm (13-16 degrees) clear at the island, and we could see kelp and quite far down into the sea. Great red streaks of water, probably an algae bloom, were filled with sea jellies (which stung Maryna, but she continued strongly). These were replaced by murky green water close to the shore, where the swell had lifted the sand particles into the water column.
It was a good day out, and always a pleasure to see Table Mountain in its majesty from the water.
Sunday: Boat dives in False Bay (conditions permitting)
We are set for the first real winter swell and the forecast is saying that we should expect 10 metres with a 20 second period by tomorrow evening. It tapers off thereafter and Sunday will be a lot more mellow.
I am really not sure what False Bay will look like by Sunday so will make an early call on launching. We will however launch out of Hout Bayon Saturday and watch some of Cape Town’s top surfers ride the monster high speed slopes that Dungeons will produce.
Dungeons in action
Let me know if you want to come on the boat on Saturday, and whether you’d like to be notified of any dives that may take place on Sunday if the conditions pan out.
A chance conversation with a friend who also volunteers at the Two Oceans Aquarium led to me enrolling in a coastal foraging course with Roushanna and Gael Gray from Good Hope Gardens, the nursery between Scarborough and Cape Point. Their coastal foraging courses are run during the summer months (I went in December), on dates close to spring tide, so that the maximum possible area of shoreline is available to forage on. The course takes the form of a rock pool expedition on Scarborough beach, followed by lunch – prepared by the participants – at Gael’s beach cottage.
Foraging for edible seaweed
Clouds at Scarborough
Scarborough beach
Seaweed covered rocks at Scarborough
As I get older I am finding it increasingly difficult to suppress a wildly eccentric streak that frequently finds me – consciously or unconsciously – making small preparations for some kind of apocalypse (zombie or otherwise). This might be related to living on the South African roller coaster for too long, but whatever the origin of this latent anxiety, it has served to make our home life more sustainable and – little bit by little bit – more independent of the electricity grid, the municipal water system, and grocery stores. The idea of coastal foraging dovetails nicely with my desire to learn how to live a little bit more off the land than off the shelves at Woolworths!
Mollusk permit inspection by fisheries officials
It is important to respect some simple rules to ensure that your foraging is sustainable, safe, kind to the environment, and legal. Each of us had purchased a mollusk permit allowing us to harvest mussels, obtainable from the post office (available for R94 using the same form as the scuba diving in marine protected areas permit), and these were inspected by fisheries officials quite early on in our forage. You don’t need a permit to harvest seaweed (however if you wanted to do it on an industrial scale you might need to go through official channels).
There are three types of mussels found on South Africa shores: the ribbed mussel and black mussel are indigenous, and the Mediterranean mussel is introduced. Unfortunately Mediterranean mussels out-compete the indigenous varieties, and we only saw one or two black mussels while we were out. The mussels we harvested were the Mediterranean variety, distinguishable from black mussels by the thick, flat edge to their shells. Black mussels have pointy edges all around their shells, making them more streamlined.
Mediterranean mussel (left) and black mussel (right)
There is only one type of seaweed growing along our coast that is harmful to eat (acid weed – Desmarestia firma, which has sulphuric acid in its fronds). This brown algae species does not grow on the rocky shore but only further out in the surf zone. This gives rise to the simple rule of only harvesting seaweed that is growing on the rocks, and never collecting seaweed that is floating free.
Purple laver (Porphyra capensis) on the rocks in the foreground
Sea lettuce (genus Ulva)
Hanging wrack: (Brassicophycus brassicaeformis)
When harvesting seaweed, we used a pair of scissors to avoid pulling the entire plant off the rocks, and cut no more than a third of the leaves. Seaweed is full of vitamins and minerals, particularly iodine and potassium. It isn’t something you’d make a whole meal of, but it is a healthful addition to many dishes and – once you know how to prepare it – tastes pretty good!
Clouds at Scarborough
You can read more about the Good Hope Gardens coastal foraging experience here and here. Watch this space for more about what we prepared with our seaweed spoils…
Today we took a load of surfers out to Dungeons. Amongst them were a few first timers at Dungeons and the happy cheers and bear hugs when they caught their first serious Dungeons roller was a sight worth seeing. Dungeons is a spectacular sight so if you haven’t been there do so at least once in your life.
A surfer at Dungeons
Back to diving… We dived the Atlantic last weekend. Maori Bay was cold and clean-ish. Visibility was around 10 metres but then the temperature was also in the single digits. Die Josie was a lot cleaner and just as cold.
Returning to the jetty in Simons Town
On Sunday we dived in False Bay – doing Search and Recovery for an Advanced course in 2 m visibility makes it a little more realistic!
This weekend
Well… There is swell and wind in the forecast. The swell was not all that noticeable in False Bay today but was very surf-worthy at Dungeons and Muizenberg today. The wind is forecast at around 30 km/h for both days and for students doing their first boat dives I think it’s not that good an idea. So I have no launches planned for this weekend.
