Coastal Habitats

Common Sandpiper on mangrove creek

So, in what's probably going to be the last coastal blog until I get back to the beach again, I thought I'd give a first introduction to some of the interesting coastal habitats. (Note the logical progression - off stuff in the sea, interesting things on the shore, and now interesting things on the land but near the sea. Anyone would think I had it planned!) So, let's start by thinking about what's down by most beaches. And in East Africa you don't have to spend long before realising it's basically a mixture of coconut plantations and sisal estates, with a bit of cashew thrown in for good measure. So you won't be surprised to learn that the northern coastal regions have some of the highest population densities in Tanzania (here), though to be fair most of the plantations were originally started by colonial Germans and Brits some time ago. So the remaining native habitat fragments are in a rather bad way, and can be hard to find. They are worth seeking out, though, as ther are some special things living in them.

For the purpose of this post, I think I'm going to focus on the two of the most interesting coastal habitats: coastal forest and mangroves. Coastal forest has obvious functional similarities to forests elsewhere in Africa, though the species composition can be pretty different. Mangroves, on the other hand, have no inland analogues, so let's start there.

Mangroves still do grow on open coasts here north of Pangani

If you've not seen them, mangroves are starkly different to any other habitat. They're mainly tropical in distribution (there are some in the Australian temperate zone, and a few on the East Coast of the US, but these are the exception that prove the rule), and once upon a time would have occured on any tidal zone (ie, on land covered by the high tide, but exposed at low tide) with a minimal degree of shelter from the full force of the sea - they used to cover over 3/4 of tropical tidal areas. At one time, that included even rather isolated islands like Maziwe, but now you'll rarely find them on the beach front themselves, but mostly limited to tidal creeks. And you'll know when you find one, because you'll be walking through the coconut plantation and suddenly hit a dense, dark and glossy thicket growing like a wall out of the bar mud or sand (sometimes even rock) substrate.

Mangrove edge in cocnut plantation, Ushongo Beach July 2011

If you can make your way through the mangroves, you'll see some interesting sights. Down on the ground the most obvious things are the arial roots - sometimes poking up like fingers, other species rely on multiple branches from the stem. These have a wonderful scientific name - pneumatophores - and their purpose is simply to allow the plants absorb air. But they also form a unique and busy microhabitat of their own - a mini-forest that traps passing mud and can harbour much richer muds than surrounding areas as well as providing lots of nice little places to hide from predators. Consequently, the root systems of mangroves are home to lots of life - there's always crabs to see, and in areas nearer to low tide limit there are often air breathing fish called mudskippers, which are kind of neat and perhaps remind us of our distant ancestry... What's more, these root systems are often extremely important nurseries for the young of reef fish important in many local fisheries.

Aren't those roots odd! Mangrove pneumatophores, Ushongo Beach

These pneumatophores aren't the only interesting adaptations of mangroves though - not only do the have to survive in water-logged soil, but it's very salty too (and in areas where shallow seawater sits around in the hot sun the concentrations of salt can be extremely high) and most plants can't tolerate salt. Mangroves have a number of adaptations to help, of which the most obvious is the glossy, thick leaf itself which reduces water-loss. But more fundamental are adaptations to the root that we can't see that simply filter the salt out of the water - by the time water arrives in the root, 82 - 97% of the salt has been filtered out. Given how difficult we find it to extract frest from salt water mechanically in desalinisation plants, that is a remarkable adaptation! And then what salt does get into the plant can be collected and excreted through the leaves, giving them a silvery appearance at times.

These roots also  absorb air in another mangrove species, Ushongo Beach

In such harsh environments, it's going to be particularly tricky for seedlings to thrive, so mangrove species have another neat adaptation up their leaves - they're (mostly) viviparous. What? Live-bearing plants?! Yes indeed, most mangrove species don't immediately drop their fruits, but retain them on the plant whilst the seedlings develop to a stage where they can photsynthetise themselves - some seedlings growing entirely inside thr fruit, others growing through and out. Then, when they're ready, the plant drops them either like a dart into the mud below them, or into water to float the seas until washed up in some suitable substrate, when the young plant is ready to go. Which explains why many mangrove species have extremely large distributions, dispersing on cross-oceanic currents.

Mangrove fruits germinating on the plant and ready to fall.

So, that's the structure of the mangrove, and it's obvious that this sort of harsh environment is going to be home to species of plants that are survivors - all their obvious competitors are eliminated by the environment itself. And just as the roots are home to lots of little beasties, the trees themselves are home to a pretty good selection fo birds and animals too. The really special bird to look out for in this area is Mangrove Kingfisher, but the mangroves can often be full of mixed species flocks of starlings (mainly Black-breasted), barbets and greenbuls, etc. Some great birding to be had if you can see into the thickets!


So, all in all, mangroves are wierd but great coastal habitats. And it's a shame there aren't more of them, because they are fantastically useful to us too, not least through their very impressive abilities to mitigate against the impacts of tsunamis.


Hmmm. Well, seems like this is probably a long enough post for now anyway, so coastal forests can wait for another time. Ecologically, they're rather similar to other forest types anyway, even if the species they hold are sometimes very different!

On the shore

As I mentioned in the last post from the beach, there's both a huge density and diversity of invertebrates (mostly Annelid worms and molluscs) in the sand and mud. So much so, in fact, that the intertial mud and sand is a huge feeding resource for wading birds. I was once told that if you extract all the worms and molluscs that birds like to feed on from a sample of estuarine mud 1m square and 10cm deep, you'd have a food sample with a total energetic content of around about 1.5 Mars bars. Now, I've had a quick search online for the primary literature that back this statement up, and I wasn't too surprised to discover that althere the cubic metre equivalent is easily found on a google search (you get many answers from 13 mars bars per cubic metre, to 20, with most around about 14 or 15) none of them pointed me to the primary literature at all. And I can't do so either. But I did find papers like this and this that, once you do the sums, suggest it's not a bad approximation. And it's a nice thing to help people understand just how rich an environment this is - everyone knows what will happen to them if they eat to many Mars bars, and there's lots more than 1 square metre in most estuaries! What's more, the rate of productivity is prolific too, so even as it gets eaten, the resource is being continuously replenished. And, of course, the mud isn't the only place with massive densities of invertebrates either - if there's seaweed left to decompose on the beach it harbous massive densities of arthropods, another favoured food resource.

Spot the white-fronted sandplover on it's nest...

White-fronted sandplover nest - two eggs here.

Unsurprising, therefore, that many birds choose to forage in these rich habitats. Some of them, like the White-fronted Sandplover I found nesting at Ushongo (can you spot it on the nest?! This seems to be the first breeding record for the northern coast of Tanzania) are resident. But most of them are migrants fron the north and now, in mid July, most of them are busy finishing off their breeding season. Not all, though - a few first year birds will hang around in Africa all year, waiting to breed for another year, and already those adults who failed in their breeding attempt have come back. In the next few weeks more and more will pour south - and they don't just look for coastal estuaries either, the soft mud around many shallow lakes are similarly rich feeding areas so even if you're only passing the odd soda lake in the traditional safari areas you'll be able to see many of these birds as they start to return in ever bigger numbers. In fact, places like Lake Manyara will soon be home to truly spectacular gatherings of wading birds from the north - well over 1 million little stint are there in most years, and even more at times (up to 3 million have been estimated by Neil Baker of the Tanzanian bird atlas project).

Turnstones, curlew sandpipers and sanderling

Curlew sandpipers and turnstone

So, let's have a little look at some of these migrants that I saw last week - if only to illustrate some of the amazing migrations these birds are capable of. In the pictures above there's a mixed group feeding on invertebrates in rotting seaweed. Most of them - the ones with the orange legs and beaks - are (ruddy) turnstones. These birds, if they migrated this year, will have attemtped to breed right on the tundra beside the Arctic ocean - check here for a map. That's an extraordinary movement - and amazingly, these birds can easily live for 30 or so years, doing these phenomenenal migrations each year. (They also have a remarkably wide diet, with a memorable series of papers reporting ever increasingly bizarre food items from soap and other rubbish, to dead whales, until the editor finally stopped the correspondence when the title reached "Turnstones feeding on human corpse". Nice.). Anyway... You'll alsoalso see (at the right of the top picture, and several in the lower picture) lots of grey waders with rather longer beaks. These are Curlew Sandpipers, and have a similar breeding distribution in the Arctic (but only the Russian Arctic, not North America). These are clearly birds that didn't migrate this year, as the breeding adults at this time are a beautiful rusty red colour and we'll start seeing them soon. Long, decurved beak, long black legs and a white stripe above the eye help identify this species. And if you look carefully on the top picture you can spot one other grey bird running up the sand bank, a bit stockier looking, with a shorter beak - this is a sanderling, and when not breeding in the Arctic is a typical bird of sandy beaches around the world.

Greater sandplover and turnstones

Standing still among the rushing turnstones in this picture is a non-breeding Greater Sandplover, a species with a rather different migration route - this time breeding in the areas around the Caspian Sea in central Asia - not anywhere near as far as the other two, and obviously closely related to the other plovers we see around here, which a much shorter beak and big looking head. We also saw a few lesser sandplovers, which are extremely similar, but tend to have smaller beaks, small heads and shorter, blacker legs (you can see this is a bit greenish on this bird).

There were plenty of others around too, but I didn't get any good pictures I'm afraid. It's always worth checking through the wading bird flocks, though, as anything might turn up - many species show amazingly long migrations and occassionally extreme vagrants turn up among the flocks of commoner species. All very nice.

Marine life

I've been at the beach for the last week (hence silence on the blog!) having fun with family and friends. Despite the fact I grey up about as far away from the sea as is possible in the UK (which, I admit, isn't really that far...), I love beaches and sealife. It's a lot further to the sea from most of the safari circuit than where I used to live, but many visitors to East Africa will combine a safari with a beach trip, so you might find youself down there from time to time. And if you don't, I thoroughly recommend it for a fun trip some time. Tourists don't usually think of the beach as a place where wildlife happens, but actually marine and coastal habitats are completely fascinating and I thougth I'd make use of the pictures I took down there to give a few hints about what you might talk about if you do find yourself on the long drive to the beach. So today I'm going to start with what I think is most amazing about sea life - it's extraordinary diversity and plain weirdness.

This mollusc has an unusual foot - and you can see its eyes too!

Now, you have probably been told that after kingdom, the main division of all life is the phylum (in fact, if you were told this, it wasn't quite right - botanists refer to plant divisions, leaving phyla to zoologists - that's the  plural, btw, it's from the Greek phylon meaning race or stock). And the Animal kingdom is divided into around 40 phyla (12 divisions for plants). Being such a basic division of animal life, animals in different phyla can be expected to be remarkably different - insects belong to the phylum Arthropoda, and it's fairly clear they different to us humans, being representatives of the phylum Cordata. Similarly, snails belong to Mollusca and are pretty different to earth worms, belonging to Annelida. You get the idea - these divisions are pretty fundamental. Now, of the 40 phyla out there, I wonder how many you could name? (I don't think I'd do too well either, to be honest...) But what I do know is that whilst there are no extant Onychophora (velvet worms) living in the oceans, all the other phyla are found there but only 10 are found on land (if we exclude internal parasites of other species). So three-quarters of the most fundamental of divisions of the animal kingdom are entirely aquatic, most of them restricted to marine environments. Which, of course, means life is pretty different in the sea. Why this should be is obvious, of course - the original animals that formed the ancestors of modern phyla lived a very, very long time ago (during a period known as the Cambrian explosion, about 500-580 Million year ago) when there was only life in the sea (there's a nice time line of life here).

Tide-line discoveries from Ushongo beach, July 2011

Cuttlefish shell, also a mollusc

Why does this interest me? Well, when you go to the beach you have a chance of finding some of those rather more bizarre life-forms that never made it onto land. The above picture shows a few of the more obvious things we found on the beach. As everyone knows, there are lots of mollusc shells (phylum Mollusca) - but look at the major divisions within this phylum too - only gastropods, the snail type, have made it onto land, but the sea is full of bivalves and other classes we never see too. In fact, nearly a quarter of all classified marine species are molluscs and there's every reason to believe that some of them (octopus - the're also molluscs and belong to the same group as cuttlefish in the picture beside) have evolved remarkable intelligence, capable of solving problems and allowing them to practice deception.

Note crab carapace, top right, sponge top left and corals.

Hermit crabs have almost made the terrestrial transition but still return to sea to breed

Then you'll see a crab exoskeleton. Crabs are members of the Arthropoda, just like insects and spiders, and some of them have taken to the land - though they must return to water to lay eggs. The subphylum they belong to Crustacea does have truly terrestrial representatives - the woodlice are an example - but most are still aquatic creatures and there's another example here too in the goose barnacles near the back in the middle. Look further and you'll start seeing som true aquatic specials. There's a couple of sorts of coral there, belonging to phylum Cnidaria which also includes the sea anemones and jelly fish. These, in the form of hydra, make it to fresh water, but no cnidarian with their usually soft bodies have made it onto land. And there's also a cnidarian look-alike in the sponge belonging to Porifera. Actually, this phylum probably includes animals from more than one group and excludes some of the descendents of the original sponge (all the rest of the animal kingdom, in fact!), so we'd call if polyphyletic and expect taxonomists to break it into other groups when they understand the relationships better. Poriferans are an extraordinary group of animals that, when I was doing my first degree, everyone was excited to think might be a whole different kingdom (or even several kingdoms). Now this seems less likely, but it seems very likely that all the rest of animal life did evolve from a sponge, rather a long time ago.

Note sea-urchin top centre and goose barnacles bottom right

What else is there? Ah, a sea urchin, belonging to phylum Echinodermata. Here, at last, we find a purely marine phylum - starfish, sea urchins, sea cucumbers and crinoids are all here, and none of them has even moved up the rivers. They all have five-sided symmetry as adults (or there abouts), but as larvae they start life, as us, with bilateral symmetry. Very odd, but very important in some places, as grazing by these species can completely alter the ecology of a coral reef or sea-weed forest.

Casts from some annelid worm (I expect) in roots of a mangrove

Annelid tentacle trails radiate from the animals home in the centre

A few other things didn't make it into the group photo, but are interesting too - the vast numbers of 'worms' of one sort or another (mostly Annelida, but maybe one or two other phyla are around too, I've certainly found others before on these beaches). They're responsible for these casts and the strange patterns around this hole - at high tide the inhabitant stick lots of tentacles out of the hole to filter food back to the mouth at the top of the hole. And these worms and other invertebrates can occur at fantasic densities, providing masses and masses of food in the intertidal zone, for lots of nice birds and beasts. Those will have to wait for another time now, though, whilst we remain amazed by the extraordinarily diverse numbers of ways marine organisims seem to have evolved to survive. Remarkably, I'll leave you with the surprising thought that despite this huge diversity of live-forms, there are far more species of animals on land. In fact, far, far more. And most of them are beetles, phylum Arthropoda. Why should it be that such extraordinary diversity has evolved on the land and not in the sea, where evolution has been going on for an awful lot longer? Odd...