We will not be diving this weekend, but if you are able to get into the water then do so. False Bay looks promising. We will be back to full dive mode on Monday morning.
Thank you to Jerrel for this week’s gorgeous photo of strawberry anemones, which he took on a dive off our boat to Roman Rock on Freedom Day.
Things to do
The winning photographs from the prestigious international Underwater Photographer of the Year Competition are on display at the Chavonnes Battery Museum until 30 September. The exhibition is in partnership with the NSRI. If you have a Wild Card, take it along for discounted entry.
Last year the carcass of a smallish – about 8 metre long – humpback whale (Megaptera novaeangliae) washed up on one of the less-frequented beaches around the Cape Peninsula. I am very belatedly sharing some pictures of it, not least because one doesn’t often get an opportunity to examine an animal like this up close. I view these things with a mixture of sadness and awe; I think it’s easier to process objectively when the animal has already died. Strandings of live cetaceans can be extremely distressing.
Some pieces of the whale’s baleen, which these animals use to filter their food from the water, were lying nearby on the beach. A large group of whales had been passing by the Atlantic seaboard in the days preceding the carcass washing up, and it may have been one of them.
The whale had been dead for a few days by the time it washed up on shore, but not so long that a lot of its skin had sloughed off (sometimes dead whales look white all over – as this whale’s belly does – for this reason). There was no obvious cause of death visible on the underside of the whale’s body. It was lying upside down so the top of its body wasn’t accessible.
It is possible that an anthropogenic cause (ingesting plastic, or a ship strike for example) could be responsible for this whale’s death. It’s also possible that the whale was sick or otherwise compromised and died of natural causes. Sometimes, when things in the ocean die, they wash ashore, and we find them.
I’m not sure what ultimately happened to the whale’s remains – it was in the surf line when I saw it, being pushed back and forth by the waves. It might have been taken back out to sea with the tide. I would like to think that it was.
Winter arrived rather quickly in my opinion, and it went rather quickly from shorts and T shirts weather to requiring much more clothing. There has also been a fair amount of swell rolling around, but the wind direction is becoming more northerly and westerly and that is what we need on our (western) side of False Bay.
Our boat will be in Table Bay on Saturday for the Robben Island swim so we will provisionally plan to launch on Sunday for diving. There is some south easter on Sunday but hopefully it does not blow as hard as predicted and we can get out. If you have a chance to dive on Saturday you should take it as I think it will be the best day of the weekend, but let me know if you want to be notified of Sunday dives and I will keep in touch.
Last Friday while diving out of Hout Bay we were visited by what felt like an overwhelming number – but was approximately fifty – whales. Most of them seemed intent on staying close to the boat and in fact a few rubbed themselves on the boat’s keel strip, which was slightly alarming. I stood dead still, wearing my life jacket, with the engines off and the boat stopped right next to the divers, hoping that they wouldn’t get too rowdy (the whales, not the divers). The divers had the amazing experience of whales at the safety stop.
We have been experimenting with early (6.00 am) and late (3.00 pm) launches for quick double tank dives to slot in as part of a well-planned work day. We’ve had lovely conditions and we’ve enjoyed seeing familiar places in a different light!
We are starting to have fewer days of howling south easterly winds and it is a sign of good things to come, especially for those who prefer diving in False Bay. There is nothing spectacular in the weekend forecast: no howling wind, no huge swell and maybe a spot of rain. I think False Bay will be the place as the temperature of the Atlantic hit 19 degrees celsius today.
I have a backlog of students currently so we will try to shore dive and boat dive on both days. Once I have confirmed numbers I will text those on the “ready to dive” list. You know what to do!
DAN Divers Day
If you aren’t diving this coming Saturday afternoon (13 February), consider the DAN Divers Day at False Bay Underwater Club in Wynberg. It’ll be an afternoon of talks about dive safety and research, with local and international speakers. Register here – if you want to see the full program drop me an email and I’ll forward it to you.
After foraging on the sea shore for edible seaweeds and mussels under the guidance of Roushanna and Gael from Good Hope Gardens, we returned to Gael’s house in Scarborough to prepare a meal with our finds. The group divided into four, and we worked together to prepare the food using recipes provided by Roushanna.
Sushi rice mixed with finely chopped sea lettuce (Ulva spp) formed the base of vegetarian sushi rolls, which were decorated with kelp, tongue weed, radishes, avocado, mayonnaise, and a secret sauce (recipe for the rolls here). Sea lettuce was also the seaweed of choice for a couscous and rocket salad, decorated with hibiscus flowers and miniature tomatoes (recipe for the salad here).
I worked on the coleslaw, made from finely sliced red cabbage, carrots, and hanging wrack (Brassicophycus brassicaeformis) – a seaweed I found so tasty and crunchy I could have sat right there in a rock pool and eaten it directly off the rocks. The mussels were picked over, scrubbed, and prepared with white wine, cream, onion, and garlic. Crusty ciabatta soaked up the sauce. Once we were done, it looked as though we had enough mussel shells for our own personal shell midden!
Roushanna prepared nori (purple laver, Porphyra capensis) crips for us (like kale chips, but with a crispier texture and more flavour), and chocolate nori ice cream for dessert. We supplied our own drinks. During breaks in the lunch preparation some of the group enjoyed a face (and hand) mask made from seaweed ingredients. Others of Roushanna’s recipes you can explore for yourself are for sea biscuits (scones made with sea lettuce), fruity vegan jelly, and kelp and avo salad.
Lunch was a collaboration, and a tasty culinary adventure. I found it marvelous to discover what is available on the sea shore, and to get a small hint of how our strandloper ancestors foraged on the Cape Peninsula.
(Puzzled what this is all about? Read my first post about coastal foraging here.)
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!
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.
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.
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!
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…
Cats are useful when it comes to boats. Despite using them to sleep, play and look at the world from, they can also perform useful inspection duties, making sure everything is in order. Here, showing unusual devotion to duty given that both the boat cover AND the console cover are on, Junior inspects the interior of the console to make sure that I didn’t forget to tell him there are sardines there, or something.
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.
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.
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!
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.
Perhaps you have wondered what causes the patterns of strange coloured water in False Bay during the summer months. Perhaps you have dived in it, and wondered why sometimes you can’t see your hand in front of your face! Wonder no more – I am here to help.
Frequent visitors to and residents of the shores of False Bay will observe that at certain times of the year, the ocean is marked by bands and arcs of sharply contrasting coloured water. This phenomenon is known as a colour front. In oceanography, a front is the interface or boundary between two separate masses of water. In this case, the water masses are easy to discern, because they are of different colours. There are usually other characteristics of the water on each side of the front that differ, too. Fronts are either convergent (the water masses are moving towards each other) or divergent. The presence of marine debris (like pieces of kelp) at the front boundary suggests that it is convergent.
Causes of colour fronts in False Bay
Prior to 2005, there was much conjecture about the causes of these fronts (including the usual pollution bugbear), but little evidence to support any of the theories. By sampling, the fronts were found not to be caused by pollution, or by plankton blooms in the surf zone. It was known that a colour front was most likely to occur in False Bay after a period of southerly or south easterly wind lasting a few days. October and November seem to be prime months for the phenomenon.
When a large, obvious colour front arose near Simon’s Town in November 2005 with milky green water on one side, and darker blue-green water on the other, researchers from UCT and IMT sprang into action, sampling the water on each side of the boundary so that they could measure its characteristics. Speed is of the essence in these situations; colour fronts can disappear quickly. The one in the picture below is busy decaying – notice the smudged boundary.
Measurements revealed that the milky green water overlaid the clearer, bluer water, down to a depth of 11-12 metres (this will vary from front to front). The milky water did not extend to the ocean floor. Scuba divers around the Cape Peninsula will be familiar with the experience of diving through two or more layers of water, with varying turbidity (clarity) and temperature! (Here is picture of Tony and Christo diving near Oudekraal in the Atlantic that shows what the boundary between two layers of water can look like.)
The researchers found that the milky coloured greenish water was full of fine, almost neutrally buoyant particles of calcium-rich sediment. The green-blue water contained much less calcium, but relatively more silicon, which would suggest the presence of diatoms (a kind of phytoplankton – you can think of them as teeny tiny plant-like organisms) or sand in the water. The origins of the calcium-enriched sediment in the milky water are interesting: one source is from the shallows (less than 30 metres deep) of north western corner of False Bay, where the ocean floor is made up of rocks that are rich in calcium carbonate (such calcrete and limestone), some areas covered by a thin layer of sand.
The second probable origin for the particles of calcium-rich material is the interface between the sea and the land at the northern end of False Bay. The cliffs at Wolfgat/Swartklip at the head of the bay are made of calcrete, and at Swartklip the beach narrows to the extent that the cliffs erode directly into the water when the sea is high. Strong southerly winds create a wide (of the order of one kilometre) surf zone at Muizenberg and Strandfontein; a spring tide also adds to ideal conditions for the generation of a colour front.
The temperature of the milky water was found to be slightly (0.4 degrees Celcius) higher than the green-blue water. This measurement will also vary from front to front. The researchers speculate that the temperature difference could be because the milky water originated in the surf zone, which is shallower and therefore warmer, or because the high concentration of suspended particles in the milky water caused greater absorption of heat from the sun.
Here’s the tl;dr: strong southerly and/or south easterly winds, perhaps coupled with spring tide conditions, set up a very wide surf zone along the northern end of False Bay, which disturbs the sediment on the ocean bottom and drives the waves further up the beach than usual. Particles of buoyant calcium carbonate from the sea floor and eroded from the cliffs at Swartklip are lifted up into the water column, changing its colour to a milky-green shade. Wind-driven circulation patterns in the bay push the front from its original location in a southerly direction, towards Simon’s Town.
What to do?
Contrary to what your friends on social media may claim, not all colour changes in the ocean around Cape Town can be attributed to a giant sewerage plume. Hardly any of them can, in fact. In summer, the reason for the ocean looking green, red or even brown is likely to do with a plankton bloom of some description, or related to suspended sediments (as in this case) or other naturally arising material in the water. Instead of using this as an opportunity to become hysterical on the internet, how about celebrating the incredibly dynamic system that we can observe, living near the ocean? Drive up a mountain next to the ocean and take in the spectacle from on high. Dip your face in the water and see what it does to the viz. Take some pictures for posterity. And – if you don’t know what’s causing it – try to find and question someone who does know, like a scientist, or consult a good non-fiction book, to find out some facts.