The objective of this trip was to meet oyster growers. We had a spectacular drive from Windhoek to Henties Bay on Jan 30, newly ensconced in the Combi (VW van). We passed through a blizzard of butterflies – they seem to be bursting forth in droves just on the edge of where it’s rained. And we passed underneath a maelstrom of hawks, literally hundreds of them circling and zooming across the road, reason unknown. It was particularly surprising to find them all together since we’d commented so often on the striking absence of raptors – we’d seen less than a dozen in our travels of the previous month. We took the sand road “short cut” to bypass Swakopmund and go straight to Henties Bay, past the Spitzkoppe, a dramatic promontory that rises from the flat sandy plain in a series of sheer drops from rounded peaks. All along the road, tables were set out with rocks for sale, crystals of a variety of colors. (We have yet to visit the Crystal Museum in Swakopmund, which boasts the biggest crystal in the world, almost twice the height of a person. And of course we won’t visit the vast stretches of coast that are closed to entrance because of diamonds being collected from the sand.) On this road, we were also treated to our first experience of springbok “pronking”. They bounce, apparently straight-legged, a few meters straight up – a sign of vague unease that the Combi had stopped so the people inside could appreciate the two-dozen animals in the small herd. Springbok are excellent desert-dwellers because they never need to drink, getting sufficient water in the vegetation they eat.
One weekend morning this trip, we traveled north from Henties Bay for less than an hour to Cape Cross, which is famous for tens of thousands of Cape Fur Seals. Certainly, we’d had a fine look at them at Walvis Bay, but the Cape Cross colony was pretty amazing. The rocks were polished from generations of seals sliding across them, and the depressions in between boulders were filled with scat and carcasses, tiny skulls showing white through reddish-brown background. The smell was incredible – I actually took a shower that evening because I was convinced I could still smell seal in my hair! Also on the beach was an enormous dead sea turtle – Alan says its head was the size of a basketball and total length around 15 feet. I thought less but still impressive… and sad that such a giant is no longer roaming the oceans. The seals seemed a little more expendable, with pups rolling on and off the beach in the surfable waves – only the ones at the upper edge of the ribbon of seals along the shoreline seemed to stay put, mostly sleeping and covered in sand. The pups are darker than the adults (also, of course, smaller), so it seemed to us that most of the mothers must be off hunting for fish, or perhaps just sleeping offshore, flippers held out of the water, away from all the fuss. When mothers returned, they would bellow and haul themselves through the pack of seal bodies (adults snapping at them as they jostled and bumped), presumably looking for their own pup among the thousands there on the beach. We saw one mother very deliberately keep all pups away except one, which she let nurse.
The meetings with growers were great. We heard some familiar stories, hemispheric restatements of the problems experienced in Washington: difficult markets, mass mortalities of unknown cause, clients stolen away by other growers who undercut prices, nearby practices that exacerbate a pest problem…. The primary cultivated species is the Pacific oyster, Crassostrea gigas, which has been introduced to the US west coast, Namibia, and more than 60 other countries. As far as we have seen here, it has not established. We are puzzled by this, because the growers are complaining that the oysters are soft with gonad (spawn-y, or even spawned out), reflecting high summer water temperatures. The temperatures may be particularly high this year because, essentially since our arrival in Namibia, this high-upwelling coast has not been upwelling! The winds have blown from the northwest, pushing surface water onshore, keeping the deep cold water down deep, and allowing the warm Angola Current to push southwards to Namibia. Water temperatures have been recorded in Swakopmund and Walvis Bay around 25C (quick translation: 77F), perfectly suitable for oyster larvae to survive and grow. Yet, no spat have appeared – in Walvis Bay, the larvae may simply not be retained in this small indentation in the coast.
The methods for growing oysters differ between Namibia and Washington. The oldest oyster company (young by US standards: second generation) is actually a tiny arm of a much larger company that produces salt (and seabird guano). Seawater is pumped up several meters and then flows by gravity through a series of ponds where water evaporates, impurities (gypsum) are precipitated out, and finally sandy salt is removed in foot-cube chunks for further refining. In its initial path, the seawater is divided into two ponds: a 30-ha pond, mostly <1 m deep, has racks for growing oysters, and a slightly larger pond contains the platform to attract cormorants to breed (and defecate). Mr Klein produces his own cultchless spat by raising larvae in tiny upwellers with ambient seawater, then allowing them to recruit onto smooth plastic sheets and brushing spat off daily – both C. gigas and Ostrea edulis (the only grower on the Namibian coast to produce edulis). Larger oysters are planted into the pond in open-top mesh bags/trays, just below the water surface. Oysters are packed into the trays, but the salt pan soup of phytoplankton must be incredibly rich, fueled both by the ocean inputs and by recycled nutrients from birds. Because of the importance of these shallow-water (albeit salty) habitats for birds, the whole salt company is also a game preserve! Even with our ornithologically naïve eyes, we’ve seen 2 flamingo species, 2 cormorant species, grebes, African ducks, turnstones, at least 4 tern species, and long-legged stilt-like birds with both upturned and downturned bills.
Mr Klein described the following food web in the salt pond “chemostat” where he grows oysters: Flamingos remove most of the organisms in the sediment. Fishing birds such as terns and cormorants feed on the fish (which include “freshwater” tilapia at 40 ppm!). Fish feed on the red alga Gracilaria (deliberately introduced as a prospective aquaculture product, because it can be refined to produce agar), and perhaps also on goggas (Afrikaans, so make sure the “g’s” are raspy in your throat) – Paridotea isopods. Mr Klein observed that, coincident with his introduction of Gracilaria, a pest of his oysters disappeared: polychaete worms that bore through the shell and cause mortality and disfigurement. He wonders if the Gracilaria provided a refuge for the isopods, which then removed the worms. Is this a cool food web, or what?!??? We are likely to work on testing these interactions while we are here. Of course, there are problems, such as: 1) we haven’t been able to find the polychaete worm at all, so it may be locally extinct from the salt pond (perhaps was even introduced with oysters from Chile or the US) – not because of isopods, but because of high salinity. If the worms are no longer present, it will be difficult to test whether isopods control the worms. 2) Worldwide, boring polychaetes in oysters are controlled by dipping oysters in high-salt baths (hmmm, like a salt pond) or moving the oysters onto wooden racks off-bottom (hmmm, did some husbandry practices change at the same time the Gracilaria was introduced?). So the isopods might not be responsible for a rapid decline in worms.
Most of the oyster growers other than Mr Klein are based in Walvis Bay, where oysters are grown exclusively by suspended culture in water that tends to be less than 15 m deep. There are less than 20 companies, some of which are just a few years old. Originally, in Walvis Bay, bags were suspended from wooden platforms, but now the dominant method is “Spanish longlines”. Blue plastic 55-gallon drums are used as floats, and single (cultchless) oysters are placed in stacks of trays suspended from the floats and lines in between them. Two major sources of mortality for the oysters appear to be: low oxygen conditions lasting more than a week during sulfide eruptions – the water can be deoxygenated right up to the surface; and stressful summer conditions, involving unknown combinations of high temperatures and pathogens. Right now, as downwelling conditions persist, and the warm Angola Current pushes south, many mass mortality events have been reported, with up to 60% crop loss. Given the millions of dollars spent worldwide to understand “summer mortality”, and the general conclusion that the only remedy is to raise genetically tough oyster families, we probably won’t get deeply involved in research on this problem – no one approaches it from an ecological perspective. Fortunately, from the growers’ perspective, one company has a beautiful hatchery facility and produces millions of spat from local broodstock.
Saturday, February 16, 2008
Health and safety
According to the US government, Namibia’s crime rate is Critical. Indeed, security firms appear to have a thriving business: uniformed guards are at every ATM, electronics (=cell phone) store, and high-end retail (e.g. safari outfitting, glasses), not to mention the main entrance and every building on the Polytechnic campus, 24 hours a day. When you park a car, you’re often asked if you’d like it kept under surveillance – at $N1 as an average tip, this is a bargain (<0.15 US$). Many stores have locked gates at their entrance, and a salesperson “buzzes” suitable customers inside. Houses have tall cement walls with concertina wire or electric fence on top. Our door has 3 locks (US embassy requirement, checked out personally by their security officer). The problem is property crime and theft, not (thankfully) risk of bodily harm. Actually, the problem is economic inequity. Based on average income, Namibia is a developing middle-income country, but with one of the highest variances in income worldwide (even worse than the US in GINI index). In a place where many people have little to lose, they’ll use an opportunity to take from the rich. Unemployment is high (we’ve heard various “statistics”, but likely over 40%), and, as evident by the compensation for car guards, many positions are poorly paid. Visitors are urged not to be easy targets – don’t carry iPods in outer pockets of backpacks or walk with a purse late at night across dark bridges. Well – undoubtedly the same advice would apply to most US metropolitan areas!
Namibia also has an extraordinarily high per capita rate of auto accidents. A deadly combination of break-neck speed, poor vehicle maintenance, intoxication (“We drink beer in Namibia because water’s too expensive”), and large animals that can leap 2-m fences and cross the road. The Namibian newspaper regularly shows mangled remnants of vehicles that have burned, flipped, split, or otherwise reached a bitter end. Driving sober, slow, and in daylight, we hope to avoid this fate. We are also now driving a Combi – the southern African version of a VW van – which we purchased for dirt-roads, camping/ sleeping in the rear, and hauling anticipated visitors from the States. In Namibia, one drives on the left hand side of the road, with the driver’s seat on the right hand side of the car: the biggest initial problem was turning on the windshield wipers instead of the turn indicator!
Namibia also has an extraordinarily high per capita rate of auto accidents. A deadly combination of break-neck speed, poor vehicle maintenance, intoxication (“We drink beer in Namibia because water’s too expensive”), and large animals that can leap 2-m fences and cross the road. The Namibian newspaper regularly shows mangled remnants of vehicles that have burned, flipped, split, or otherwise reached a bitter end. Driving sober, slow, and in daylight, we hope to avoid this fate. We are also now driving a Combi – the southern African version of a VW van – which we purchased for dirt-roads, camping/ sleeping in the rear, and hauling anticipated visitors from the States. In Namibia, one drives on the left hand side of the road, with the driver’s seat on the right hand side of the car: the biggest initial problem was turning on the windshield wipers instead of the turn indicator!
Monday, February 4, 2008
Katie news
Almost two and a half – often will answer the question of how old are you by putting up two fingers. Initially shy with new people, but also fascinated by people, especially kids.
Verbal changes: asks a lot of questions – Did you have fun on the boat? Can I sit up there? What does it smell like? Where is my house? Also prone to screaming and crying when thwarted.
Sings songs: Favorites are still ABC and Itsy bitsy spider. Also Where oh where is sweet little Katie? and Dem bones (The Katie bone’s connected to the daddy bone. The daddy bone’s connected to the mommy bone… Her knowledge of vertebrate anatomy still needs some refinement.) Sometimes she gets part of Magalena Hagalena Ookatoka Wokatoka Okamokapoka was her name. Usually more like Oka moka shmoka poka loka… was her name!
Can recognize most letters most of the time (sometimes too busy to bother). “Reads” boo, zoo, moo. Loves to hear stories – we only brought a few books with us, so we have repeatedly gone through the anthology of 13 Dr Seuss stories (Thanks, Brian and Carol!), and, just recently, she’s begun to appreciate Frog and Toad. We purchased a book of stories compiled for primary school students in Namibia, which apparently deal with universal themes, as Katie certainly appreciates them. One day, Katie asked for a sad story, and I realized that the stories were all a little sad initially, but then a problem is overcome – a universal questing theme. For instance: A red ball gets stuck in a tree. A bird pushes it back to the children. Or, another example: Two kids are sent to get water, but the full buckets are heavy. They solve their problem by putting a stick through the handle and carrying each bucket together. In all fairness, we should get her some more local books: after all, her parents just bought 10 field guides! Katie also often asks for “Kaffy’s book,” which means she wants you to hold your hands like a book and make up a story about a little girl named Kathy who has adventures much like Katie. (What does Kathy do before she goes to bed? “Pees! Brushes her teeth!” Often followed by an emphatic, “Don’t have to go pee-pee.”)
Loves the beach. Katie will literally spend hours digging holes, looking for interesting objects cast ashore in the wrack, sticking gull feathers in patterns, or picking up eye-catching orange and white smooth stones (like grandma, like granddaughter). She has discovered that, if she squeezes the dried floats of bluebottles (easier to wrap your tongue around than Portuguese man-of-war) in her fingers, they give a satisfying pop when they burst, sort of like bubble wrap. This trip, she was initially a little frightened of the waves – I asked if she would come jump in them, and she just clung for a little while, watching the water pass underneath. But then she became more excited, standing up to take waves up to her chest, and squealing when I lifted her up to avoid the larger ones. “Go in farther, Mom!”
Most adorable when: chasing butterflies (the plants at the marine station are festooned with at least a half-dozen species); correctly distinguishes between oysters, clams, and mussels; just wakes up – very snuggly.
Favorite foods: apple juice, pasta, pizza, eggs, pancakes, ice cream (especially pink). Today, Katie and Alan went out for second breakfast together, and I heard the report later: “They didn’t have pancakes.” (Oh? What did you eat?) “I had toast. And eggies.”
Favorite games: Matching cards (a memory game of spatial locations where the child can already beat the adult); “You are the ant. I am the anteater.” (chase), calling Abby and Teddy or Grandma and Grandpa on the “telephone” (anything with buttons – usually hopefully not our actual cell phone).
Very minor emergencies: Katie usually has scabs on her knees. She’s reached down to lower steps twice now, falling and cutting her lip. She got terribly bitten by mosquitos on the first night of our most recent stay in Henties Bay. This is outside the malaria zone, but still distressing, so she had to wear long sleeves, long pants, and socks thereafter. Any ill can pretty much be remedied with a bandaid.
Verbal changes: asks a lot of questions – Did you have fun on the boat? Can I sit up there? What does it smell like? Where is my house? Also prone to screaming and crying when thwarted.
Sings songs: Favorites are still ABC and Itsy bitsy spider. Also Where oh where is sweet little Katie? and Dem bones (The Katie bone’s connected to the daddy bone. The daddy bone’s connected to the mommy bone… Her knowledge of vertebrate anatomy still needs some refinement.) Sometimes she gets part of Magalena Hagalena Ookatoka Wokatoka Okamokapoka was her name. Usually more like Oka moka shmoka poka loka… was her name!
Can recognize most letters most of the time (sometimes too busy to bother). “Reads” boo, zoo, moo. Loves to hear stories – we only brought a few books with us, so we have repeatedly gone through the anthology of 13 Dr Seuss stories (Thanks, Brian and Carol!), and, just recently, she’s begun to appreciate Frog and Toad. We purchased a book of stories compiled for primary school students in Namibia, which apparently deal with universal themes, as Katie certainly appreciates them. One day, Katie asked for a sad story, and I realized that the stories were all a little sad initially, but then a problem is overcome – a universal questing theme. For instance: A red ball gets stuck in a tree. A bird pushes it back to the children. Or, another example: Two kids are sent to get water, but the full buckets are heavy. They solve their problem by putting a stick through the handle and carrying each bucket together. In all fairness, we should get her some more local books: after all, her parents just bought 10 field guides! Katie also often asks for “Kaffy’s book,” which means she wants you to hold your hands like a book and make up a story about a little girl named Kathy who has adventures much like Katie. (What does Kathy do before she goes to bed? “Pees! Brushes her teeth!” Often followed by an emphatic, “Don’t have to go pee-pee.”)
Loves the beach. Katie will literally spend hours digging holes, looking for interesting objects cast ashore in the wrack, sticking gull feathers in patterns, or picking up eye-catching orange and white smooth stones (like grandma, like granddaughter). She has discovered that, if she squeezes the dried floats of bluebottles (easier to wrap your tongue around than Portuguese man-of-war) in her fingers, they give a satisfying pop when they burst, sort of like bubble wrap. This trip, she was initially a little frightened of the waves – I asked if she would come jump in them, and she just clung for a little while, watching the water pass underneath. But then she became more excited, standing up to take waves up to her chest, and squealing when I lifted her up to avoid the larger ones. “Go in farther, Mom!”
Most adorable when: chasing butterflies (the plants at the marine station are festooned with at least a half-dozen species); correctly distinguishes between oysters, clams, and mussels; just wakes up – very snuggly.
Favorite foods: apple juice, pasta, pizza, eggs, pancakes, ice cream (especially pink). Today, Katie and Alan went out for second breakfast together, and I heard the report later: “They didn’t have pancakes.” (Oh? What did you eat?) “I had toast. And eggies.”
Favorite games: Matching cards (a memory game of spatial locations where the child can already beat the adult); “You are the ant. I am the anteater.” (chase), calling Abby and Teddy or Grandma and Grandpa on the “telephone” (anything with buttons – usually hopefully not our actual cell phone).
Very minor emergencies: Katie usually has scabs on her knees. She’s reached down to lower steps twice now, falling and cutting her lip. She got terribly bitten by mosquitos on the first night of our most recent stay in Henties Bay. This is outside the malaria zone, but still distressing, so she had to wear long sleeves, long pants, and socks thereafter. Any ill can pretty much be remedied with a bandaid.
Week 4 trip to the coast
1/23-27/08: We stayed Wednesday and Thursday nights at the Seagull B&B in Swakopmund, Friday and Saturday nights at Kleines Nest in Walvis Bay. Trip objective – learn as much as we could about the coastal organisms by exploring multiple sites at low tide. To that end, we also purchased 8 field guides (actually, only one for marine organisms, called Two Oceans reflecting its focus on the eastern and western sides of South Africa). Altogether, we looked at about 3 places around Swakopmund, all rocky intertidal, 2 places in the Walvis Bay lagoon, and two sandy beaches on either side of the “mouth” (it’s a wide one) of Walvis Bay. On our final day, we joined a lot of tourists on a 4-hour speedboat tour of Walvis Bay by water, including the Cape Fur Seal colony, derelict/confiscated Russian fishing boat, lighthouse, close pass by two cargo ships waiting to go into port, hanging oyster culture, and “largest table in the world” built almost 100 years ago to collect guano. Along the way, we saw Benguela endemic dolphins, bottlenose dolphins, and a mola mola. Three rather tame (but still very large with sharp teeth!) seals leaped onto the boat to get a treat and a scratch, pelicans flew alongside to catch fish that were tossed to them, and gulls and cormorants took more fish out of hand. A lot of close encounters with charismatic megafauna, but not much environmental education or interpretation. The skipper served sparkling wine, juice, quiche, brotchen, and oysters on the half shell. By the way, Walvis is pronounced Valfish.
As temporary residents in Namibia, we are thankful for the low biodiversity of the coast. Two Oceans is a thick book of vertebrates, invertebrates, and algae, but most of the species are restricted to the eastern side of the Cape, reflecting oceanic connections to biodiverse regions of the south Pacific. Fewer species occupy the western side, and fewer still extend their range past the Orange River into Namibia. Why would this be? Possibly, the alternation of warm Angola and cold Benguela currents make conditions too variable, or sulfur “blooms” kill off many species, but likely there is a huge effect of substrate: the Namibian coastline is 60-80% sand (we’ve seen variable reports), with small pockets of sand-scoured rock interspersed. Sandy beaches are notoriously species-poor, so perhaps there is just not enough rock around to support many species. But, again, this low diversity is a happy occurrence for newly-arrived marine ecologists. It’s also interesting to hear that essentially no Tatoosh-type experimental research has been carried out on the rocky shores – the scientists here are too busy working on economic problems of fisheries and aquaculture. The only rocky intertidal “fisheries” (artisenal or otherwise) are for rock lobsters, which we saw being collected by guys wading out in wetsuits into the surf and reaching into crevices in the rock.
Standard rocky intertidal zonation in Namibia:
Highest = 1. Afrolittorina – definitely hides during hot days and low tides, but similar in size and shape to Washington’s littorine snails. Small grazers of epilithic scum.
2. Chthamalus – just one barnacle species that’s obvious. All the individuals we observed were similarly-sized, <5 mm, which suggests pulsed recruitment.
2. Siphonaria – a limpet-like grazer that can reach rather large size (3 cm). Small ones seemed to be spatially separate from the larger ones. Possibly they have cleared out some bare space among the barnacles by bull-dozing, and we wondered what would happen to the “bare” rock if Siphonaria were removed. This species apparently does well even in sand-scoured areas: we saw rock-tips poking up out of the sand that were covered with Siphonaria.
3. Semimytilus – mussel that does not often exceed 2 cm in length. In sandy areas, it grew into hummocks, catching sand between the byssal threads and the rock. This seems not to be a very stable existence, as large areas of the bed were sometimes obviously washed away, leaving only the border where mussels were actually connected directly to the rock.
3. Limpets – intermixed with Semimytilus. Some of the classic species of ecological fame in South Africa are missing here (arganvillea, cochlear), and as yet we have a hard time distinguishing the two large species of the Namibian coast (Scutellastra granularis, Cymbula granatina). Both have scalloped edges to the shell and occur at high density. A third species (Cymbula miniata) we have found as shells in beach drift but have not noticed live – probably a bit too low to be safely accessible given the week’s tides and waves.
4. Perna perna – a much larger mussel, probably the competitive dominant. Hey! There’s a competitively dominant mussel here, too! (But what is it outcompeting? There’s not much else.) (And is there a keystone predator that keeps mussels in check? Seastars are decidedly absent; the two common crabs (Pilumnoides rubus, Plagusia chabrus) are herbivorous; perhaps spiny lobsters could set the lower limit.)
In the mussel zone, we saw anemones with their columns pimpled with shell hash (Aulactinia reynaudi), a fuzzy red alga reminiscent of Endocladia on Washington’s shores, with the same ability to grow on rock or epiphytically on mussel shells, and occasional clumps of Gunnarea capensis, a tubeworm.
Interspersed among Semimytilus and Perna, which tend to be brown, are two species of black-shelled mussel, particularly interesting because one is native and one not. From Two Oceans, we understand that it might be possible to tell them apart based on whether there are pits (Mytilus galloprovincialis) or not (Choromytilus meridionalis) in the ligament near the hinge on the inside of the shell. Obviously, this characteristic does not make it possible to identify live individuals. We are still looking for reliable shape/ color trends. We have now picked up probably 3 dozen shells from beach drift, and they all seem to have pits. So, either M. galloprovincialis is more common than we’ve been led to believe, or we don’t really have a “pits” clue.
In our quest to find predators on this shore, we kept a close look out for predatory snails such as whelks. We found a few individuals at just one of the rocky sites we visited, and these appear to be Burnupena – they look a lot like Nucella on Washington’s coast but their diet does not involve barnacles or mussels; they’re scavengers. Washed up in the drift, we’ve seen shells of Nucella dubia, which is indeed a predator and supposedly broadly distributed in the intertidal zone. We’ll have to continue to keep an eye out for these in real life! The beach drift has been full of clumps of egg capsules that clearly derive from a neogastropod such as these snails. The capsules must pop off the rock after the young snails emerge, as they generally have 1-mm holes at the top that have served as an escape hatch. Given the number of egg capsules in the drift, whoever laid them must be very abundant. It’s odd and fun and challenging to be in a place where a question as simple as “who laid those?” is entirely unknown to us.
5. Below the mussels, red algae go crazy! A quick look at 2 Oceans shows why: whereas in most other taxa, there are just a handful of species that occur on the west coast, among reds, 43 species are likely to occur in Namibia, and just 23 are not. (I based my count on distribution maps included with each species in the book, and I assumed that anything shown to reach the Orange River, which serves as the South Africa-Nambia border, could also extend north. We’ve already found many such species on intertidal rocks in Namibia, and we’re not sure if the distribution maps are curtailed because sampling has been lower in Namibia, or because habitat is relatively rare.) We haven’t really even attempted to begin identifying them yet. Most sites were a rather jumbled mess of rocks and boulders, so zonation was a bit obscure. But one site had a shallow bench that showed a dramatic line between higher fleshy reds and lower erect pink coralline algae.
6. And, of course, Namibia’s only kelp species – Laminaria pallida – is anchored in the low intertidal with blades that float to the water surface so are obvious from a distance. It is legal to collect beach-drift Laminaria to use as a feed for abalone, but harvest of living kelp is unlikely ever to be allowed.
One more comment about the rocky intertidal zone: there is not very much bare space. Species interactions, therefore, look like they could be very strong. We were surprised at how much life covered the rocks, since a coastal hydrodynamics hypothesis might suggest that larvae are entrained in upwelled water that moves away from the coast, thus leading to recruitment limitation and very few new arrivals on the shore. What might account for the discrepancy? It is possible that many of the species do not have planktonic larvae but instead produce local offspring (but we know this is not true for barnacles and mussels). It appears that, over 100s of km, this stretch of coastline is a retention zone even under strong, persistent upwelling, perhaps because the upwelling occurs slightly farther offshore (is the continental shelf wider here?) This retention zone explains the high productivity that drops to the bottom, accumulating and decomposing until unknown forces lead to catastrophic release of hydrogen sulfide. It may also explain the high cover we observed on rocks.
Wave-exposed sandy beaches in Namibia:
On the outside of the sandy peninsula that constitutes the western side of Walvis Bay, we encountered surf clams (Donax serra) at incredible abundance. Anywhere we dug over a wide range from about lower high water to the waves, we found several clams in each 10x10 cm area. An incredibly detailed study of these clams was done as a PhD thesis, including mark-recapture for density, growth and recruitment at multiple sites, chemical composition, and condition index, so we can take this species off the To Do list! It has been fun to compare the western peninsula of Walvis Bay with the western peninsula of Willapa Bay – Willapa’s is longer (but not by much), taller and wider. Walvis’ has no trees (but of course not, it’s the desert) and only extends several meters above the water. The lighthouse appears to be sort of in the middle of the peninsula, which is extending north at a rate of about 20 m per year. (Willapa’s is not growing quite so fast.)
Walvis Bay lagoon:
Imagine a north-facing bay, red sand dunes on the east side, low-lying sand peninsula on the west, divided into three parts. The northern third holds the port, with a channel dredged for 7 km through a shallow bay (20-30 m depth). The middle third is a functional lagoon that dries almost entirely at low tide. Water has to move in and out on the western edge, near the port, because a sand spit extends from the peninsula on the west. The southern third is cut off by an extensive network of salt ponds. The Kuiseb River historically entered here, in the one-in-10 years that enough water fell in Namibia to reach the ocean. This delta is now cut off from the lagoon by the salt ponds and road. We spent most of our time walking out in the middle section, and the boat ride occurred in the northern section. The southern section looked and smelled terrible – foam and feathers and salt and sulfurous stench and black goo under the feathery crust wherever a disturbance went through. The most amazing part of the middle section is… FLAMINGOS. Thousands of them, both the pale Greater Flamingos, which show bright pink and black on their wings when they fly, and the more dramatically pink all over Lesser Flamingos. The Walvis Bay population is supposed to represent 60-80% (respectively?) of the whole number in southern Africa. I think we were lucky that the rains were late, because they should all fly inland to breed as soon as sufficient freshwater is available in pans. The greater flamingos do an amazing dance to feed: they alternately pick up their feet, stomping in a circle with their head submerged upside down. The sediments that they suspend are filtered for small invertebrates and algae. They leave donut-shaped depressions about a half-meter wide, and the tideflats are packed with these donuts. Of course, we don’t know how long an individual donut lasts once it’s been stomped out, but the overall sense is one of extraordinary disturbance by birds. Indeed, 2 Oceans says that the presence of flamingos dramatically reduces the abundance of infaunal organisms. (But it would still be fun to do a flamingo exclosure: the swimming beach, perhaps an unreplicated flamingo “exclosure” where we saw no donuts, had a high abundance of tube-building worms and heart clams.) The lesser flamingos filter feed cyanobacteria (giving them their pink color), so are not responsible for sediment disturbance. Flamingos seem to feed in water that is about mid-calf deep. Consequently, as the tide ebbs and flows, the flamingos also seem to flow like water back and forth across the lagoon. At low tide, we were able to see many birds quite close on the eastern side of the lagoon, but at high tide, most had congregated in a vast pink horizon on the other side of the water.
At one point, after I’d just seen a pigeon, I exclaimed, “Wow, we haven’t seen very many birds in Walvis Bay!” And then I laughed. Land-birds are indeed uncommon, particularly compared to the busy, melodic tufts of fluff we’ve seen inland. (Many of the birds in Windhoek look strangely familiar – because they include the masked weaverbirds and longtailed grey capped mousebirds housed in the African Savannah aviary at the Woodland Park Zoo in Seattle. I guess they do just fine in close proximity to humans! English sparrows are also in Namibia.) But Walvis Bay is also full of birds: cormorants, pelicans, grey herons, small waders such as stilts, avocets, curlews, large and small gulls, large and small terns, even some ducks. But the flamingos are definitely the highlight. They would still be pink and beautiful in a zoo, but not nearly so ecologically interesting!
As temporary residents in Namibia, we are thankful for the low biodiversity of the coast. Two Oceans is a thick book of vertebrates, invertebrates, and algae, but most of the species are restricted to the eastern side of the Cape, reflecting oceanic connections to biodiverse regions of the south Pacific. Fewer species occupy the western side, and fewer still extend their range past the Orange River into Namibia. Why would this be? Possibly, the alternation of warm Angola and cold Benguela currents make conditions too variable, or sulfur “blooms” kill off many species, but likely there is a huge effect of substrate: the Namibian coastline is 60-80% sand (we’ve seen variable reports), with small pockets of sand-scoured rock interspersed. Sandy beaches are notoriously species-poor, so perhaps there is just not enough rock around to support many species. But, again, this low diversity is a happy occurrence for newly-arrived marine ecologists. It’s also interesting to hear that essentially no Tatoosh-type experimental research has been carried out on the rocky shores – the scientists here are too busy working on economic problems of fisheries and aquaculture. The only rocky intertidal “fisheries” (artisenal or otherwise) are for rock lobsters, which we saw being collected by guys wading out in wetsuits into the surf and reaching into crevices in the rock.
Standard rocky intertidal zonation in Namibia:
Highest = 1. Afrolittorina – definitely hides during hot days and low tides, but similar in size and shape to Washington’s littorine snails. Small grazers of epilithic scum.
2. Chthamalus – just one barnacle species that’s obvious. All the individuals we observed were similarly-sized, <5 mm, which suggests pulsed recruitment.
2. Siphonaria – a limpet-like grazer that can reach rather large size (3 cm). Small ones seemed to be spatially separate from the larger ones. Possibly they have cleared out some bare space among the barnacles by bull-dozing, and we wondered what would happen to the “bare” rock if Siphonaria were removed. This species apparently does well even in sand-scoured areas: we saw rock-tips poking up out of the sand that were covered with Siphonaria.
3. Semimytilus – mussel that does not often exceed 2 cm in length. In sandy areas, it grew into hummocks, catching sand between the byssal threads and the rock. This seems not to be a very stable existence, as large areas of the bed were sometimes obviously washed away, leaving only the border where mussels were actually connected directly to the rock.
3. Limpets – intermixed with Semimytilus. Some of the classic species of ecological fame in South Africa are missing here (arganvillea, cochlear), and as yet we have a hard time distinguishing the two large species of the Namibian coast (Scutellastra granularis, Cymbula granatina). Both have scalloped edges to the shell and occur at high density. A third species (Cymbula miniata) we have found as shells in beach drift but have not noticed live – probably a bit too low to be safely accessible given the week’s tides and waves.
4. Perna perna – a much larger mussel, probably the competitive dominant. Hey! There’s a competitively dominant mussel here, too! (But what is it outcompeting? There’s not much else.) (And is there a keystone predator that keeps mussels in check? Seastars are decidedly absent; the two common crabs (Pilumnoides rubus, Plagusia chabrus) are herbivorous; perhaps spiny lobsters could set the lower limit.)
In the mussel zone, we saw anemones with their columns pimpled with shell hash (Aulactinia reynaudi), a fuzzy red alga reminiscent of Endocladia on Washington’s shores, with the same ability to grow on rock or epiphytically on mussel shells, and occasional clumps of Gunnarea capensis, a tubeworm.
Interspersed among Semimytilus and Perna, which tend to be brown, are two species of black-shelled mussel, particularly interesting because one is native and one not. From Two Oceans, we understand that it might be possible to tell them apart based on whether there are pits (Mytilus galloprovincialis) or not (Choromytilus meridionalis) in the ligament near the hinge on the inside of the shell. Obviously, this characteristic does not make it possible to identify live individuals. We are still looking for reliable shape/ color trends. We have now picked up probably 3 dozen shells from beach drift, and they all seem to have pits. So, either M. galloprovincialis is more common than we’ve been led to believe, or we don’t really have a “pits” clue.
In our quest to find predators on this shore, we kept a close look out for predatory snails such as whelks. We found a few individuals at just one of the rocky sites we visited, and these appear to be Burnupena – they look a lot like Nucella on Washington’s coast but their diet does not involve barnacles or mussels; they’re scavengers. Washed up in the drift, we’ve seen shells of Nucella dubia, which is indeed a predator and supposedly broadly distributed in the intertidal zone. We’ll have to continue to keep an eye out for these in real life! The beach drift has been full of clumps of egg capsules that clearly derive from a neogastropod such as these snails. The capsules must pop off the rock after the young snails emerge, as they generally have 1-mm holes at the top that have served as an escape hatch. Given the number of egg capsules in the drift, whoever laid them must be very abundant. It’s odd and fun and challenging to be in a place where a question as simple as “who laid those?” is entirely unknown to us.
5. Below the mussels, red algae go crazy! A quick look at 2 Oceans shows why: whereas in most other taxa, there are just a handful of species that occur on the west coast, among reds, 43 species are likely to occur in Namibia, and just 23 are not. (I based my count on distribution maps included with each species in the book, and I assumed that anything shown to reach the Orange River, which serves as the South Africa-Nambia border, could also extend north. We’ve already found many such species on intertidal rocks in Namibia, and we’re not sure if the distribution maps are curtailed because sampling has been lower in Namibia, or because habitat is relatively rare.) We haven’t really even attempted to begin identifying them yet. Most sites were a rather jumbled mess of rocks and boulders, so zonation was a bit obscure. But one site had a shallow bench that showed a dramatic line between higher fleshy reds and lower erect pink coralline algae.
6. And, of course, Namibia’s only kelp species – Laminaria pallida – is anchored in the low intertidal with blades that float to the water surface so are obvious from a distance. It is legal to collect beach-drift Laminaria to use as a feed for abalone, but harvest of living kelp is unlikely ever to be allowed.
One more comment about the rocky intertidal zone: there is not very much bare space. Species interactions, therefore, look like they could be very strong. We were surprised at how much life covered the rocks, since a coastal hydrodynamics hypothesis might suggest that larvae are entrained in upwelled water that moves away from the coast, thus leading to recruitment limitation and very few new arrivals on the shore. What might account for the discrepancy? It is possible that many of the species do not have planktonic larvae but instead produce local offspring (but we know this is not true for barnacles and mussels). It appears that, over 100s of km, this stretch of coastline is a retention zone even under strong, persistent upwelling, perhaps because the upwelling occurs slightly farther offshore (is the continental shelf wider here?) This retention zone explains the high productivity that drops to the bottom, accumulating and decomposing until unknown forces lead to catastrophic release of hydrogen sulfide. It may also explain the high cover we observed on rocks.
Wave-exposed sandy beaches in Namibia:
On the outside of the sandy peninsula that constitutes the western side of Walvis Bay, we encountered surf clams (Donax serra) at incredible abundance. Anywhere we dug over a wide range from about lower high water to the waves, we found several clams in each 10x10 cm area. An incredibly detailed study of these clams was done as a PhD thesis, including mark-recapture for density, growth and recruitment at multiple sites, chemical composition, and condition index, so we can take this species off the To Do list! It has been fun to compare the western peninsula of Walvis Bay with the western peninsula of Willapa Bay – Willapa’s is longer (but not by much), taller and wider. Walvis’ has no trees (but of course not, it’s the desert) and only extends several meters above the water. The lighthouse appears to be sort of in the middle of the peninsula, which is extending north at a rate of about 20 m per year. (Willapa’s is not growing quite so fast.)
Walvis Bay lagoon:
Imagine a north-facing bay, red sand dunes on the east side, low-lying sand peninsula on the west, divided into three parts. The northern third holds the port, with a channel dredged for 7 km through a shallow bay (20-30 m depth). The middle third is a functional lagoon that dries almost entirely at low tide. Water has to move in and out on the western edge, near the port, because a sand spit extends from the peninsula on the west. The southern third is cut off by an extensive network of salt ponds. The Kuiseb River historically entered here, in the one-in-10 years that enough water fell in Namibia to reach the ocean. This delta is now cut off from the lagoon by the salt ponds and road. We spent most of our time walking out in the middle section, and the boat ride occurred in the northern section. The southern section looked and smelled terrible – foam and feathers and salt and sulfurous stench and black goo under the feathery crust wherever a disturbance went through. The most amazing part of the middle section is… FLAMINGOS. Thousands of them, both the pale Greater Flamingos, which show bright pink and black on their wings when they fly, and the more dramatically pink all over Lesser Flamingos. The Walvis Bay population is supposed to represent 60-80% (respectively?) of the whole number in southern Africa. I think we were lucky that the rains were late, because they should all fly inland to breed as soon as sufficient freshwater is available in pans. The greater flamingos do an amazing dance to feed: they alternately pick up their feet, stomping in a circle with their head submerged upside down. The sediments that they suspend are filtered for small invertebrates and algae. They leave donut-shaped depressions about a half-meter wide, and the tideflats are packed with these donuts. Of course, we don’t know how long an individual donut lasts once it’s been stomped out, but the overall sense is one of extraordinary disturbance by birds. Indeed, 2 Oceans says that the presence of flamingos dramatically reduces the abundance of infaunal organisms. (But it would still be fun to do a flamingo exclosure: the swimming beach, perhaps an unreplicated flamingo “exclosure” where we saw no donuts, had a high abundance of tube-building worms and heart clams.) The lesser flamingos filter feed cyanobacteria (giving them their pink color), so are not responsible for sediment disturbance. Flamingos seem to feed in water that is about mid-calf deep. Consequently, as the tide ebbs and flows, the flamingos also seem to flow like water back and forth across the lagoon. At low tide, we were able to see many birds quite close on the eastern side of the lagoon, but at high tide, most had congregated in a vast pink horizon on the other side of the water.
At one point, after I’d just seen a pigeon, I exclaimed, “Wow, we haven’t seen very many birds in Walvis Bay!” And then I laughed. Land-birds are indeed uncommon, particularly compared to the busy, melodic tufts of fluff we’ve seen inland. (Many of the birds in Windhoek look strangely familiar – because they include the masked weaverbirds and longtailed grey capped mousebirds housed in the African Savannah aviary at the Woodland Park Zoo in Seattle. I guess they do just fine in close proximity to humans! English sparrows are also in Namibia.) But Walvis Bay is also full of birds: cormorants, pelicans, grey herons, small waders such as stilts, avocets, curlews, large and small gulls, large and small terns, even some ducks. But the flamingos are definitely the highlight. They would still be pink and beautiful in a zoo, but not nearly so ecologically interesting!
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