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Last updated: 08 May 2006

Seashore Foraging & Fishing Study

Mangroves - Fit For Human Habitation? 

Union - Enclosed Lagoon - Saline

Katangnan Estuary - Brackish

Dominated by Red Mangrove 

Other 'mangrove' tree species on higher banks of mud, Nipa palms at the margins, and coconut trees above the tide line.

Oysters on roots

No oysters

No Telescopium snails

Family gathering Telescopium

Libo-o clams

No clams

Sandy base

Deep black mud

Mangrove swamps are not welcoming places 

Union Lagoon Mangroves:

Katangnan Estuary Mangroves

Left to right above (both photo sets) -  Red mangrove (Rhizophora mangle)  - Grey mangrove (Avicennia marina)  - & species unknown

While mangroves are undoubtedly productive (nearly on a par with temperate farmland in terms of grams of carbon fixed per unit area) they are well below tropical rainforests (up to 3 times as much) and coral reefs (3 to 6 times as much).

It was estimated  that 60-75% of all tropical coasts were until recently fringed with mangroves, but they are disappearing at a very rapid rate.

See: Indo-Pacific Shoreline Ecotone

There are about 80 species, mostly unrelated, commonly called mangroves, but just two dominate the SE Asian mangrove forests, the red and the grey mangroves. Red mangroves grow sturdy prop roots, peppered with breathing pores. Their fruit grows a root while still on the tree - it simply drops and spears the mud. (If it doesn't, it floats). Grey mangroves have flat roots with vertical aerial extensions up from the mud to help them breathe.

Mangroves are also chockful of defensive chemicals, such as tannins, many useful as medicines. Perhaps it's no coincidence that Linnaeus named one mangrove family Avicennia after Avicenna, a Persian-born Muslim, perhaps the best-known doctor of his time. His Canon of Medicine, which combined his own knowledge with Roman and Arabic medicine, was a standard medical text in the medieval world.

See also: Aboriginal use of mangroves

In the Philippines bakhawon mangrove bark is used for tanning leather, and to give a red colour and tannin flavour to tuba coconut wine. Some might say that the French learned from this ancient technique when they began making red clarets and burgundy wines.

Sure - There's food.....of sorts

Fiddler crabs - but tiny, and with a poisonous 'bite' say the locals

Fiddler crabs use their highly decorated claws to signal territorial and sexual rights:

I scanned the above picture from a textbook (Marine Biology - Peter Castro, Michael Huber - Wm C Brown). By chance, I also took advantage of the program to scan and optically read the accompanying article.

It read  the above picture, too, and happily interpreted and transcribed the alphabetical characters the signals represent:

9^sCS ^jss^j ^•^¹^ ^H^^iAJ ^S^^SL it^t v^y e~% €^ c^»c^ c^

I will have to be very convinced before I concede that I have not stumbled across the ancient origins of some unfathomable Slavic language.

Libo-o (Venus clam - very like N American quahogs) - but you have to dig them up, open them, then squeeze their insides to get rid of the ruminating mangrove mud - even then they're no taste treat.

Alimango Mud Crabs (Scylla serrata) these are safely tied up in the market - they are very vicious indeed. They can weigh more than a kilo each.

Oysters - but these wouldn't make it into a Western seafood restaurant - the flesh is a mere smear. They grow 'vertically' into the tidal current, like the dorsal fin of a fish, at about high tide mark. 

They cement themselves to the mangrove roots (or anything else they can find at the right tidal level). The cement they use is so complex (it sets under water, it glues mineral  to wood, it resists salt water, fresh water, sunlight, heat, etc) that no glue manufacturer has come remotely near emulating it. 

(But see: Biomimicry - Janine M. Benyus (William Morrow & Co - New York - 1997) - a young American lady, infused with all the idealism and optimism that used to exist pre-George W. Bush, tackles just this problem - particularly on byssus - the glue/thread that holds mussels to rocks in even the strongest currents and waves)

The oyster shells have very sharp, tough edges, quite unlike the 'soft' chitinous margins of Atlantic or Pacific oysters. A less tidal mangrove swamp has more relaxed creatures, like hammer oysters and coxcomb oysters, but even these are not very rewarding finds.

These mangrove oysters are also a very major obstacle to getting around the mangroves at anything other than very low tide. A razor cut to the mid-thigh can be somewhat painful, if not fatal

Liswe - Telescopium shells are frequent in the mangroves, but they are also prized as a 'cash crop' so we didn't find any. (This picture comes from Surigao City Market). 

You knock off the pointed end, then parboil them and suck out the flesh through the blunt end. 

Unless you 'release' the holding muscles by boiling and softening them, you cannot suck out the flesh.

In the Katangnan mangroves, we came across this family gathering telescopium shells. 

I only walked round the very margins of the Union mangroves, at low tide. I could see enough to step from sandy sea-worm mound to sandy sea-worm mound, and miss the muddy squelchy knee-deep bits in between. I didn't even attempt to penetrate the mangrove forest, except at one point, when I saw a genuine

 wild coconut tree, 5 metres away, but found the tangled

 undergrowth too difficult to penetrate, to even that small distance. 

And, Thank God, there are no crocodiles left nowadays in these particular mangroves.

And we left before I thought the mosquitoes would wake up. I didn’t know then that mangroves are remarkably mosquito-free.

In the Katangnan estuary, higher, drier and fresher parts of the brackish water swamps are kinder, and lined by 'semi-domesticated' nipa palm trees, in much demand as waterproof roofing material.

Nipa fruit are used to make 'nipa wine' distilled as pa-oroi or 'Gigaquit Rum' - local moonshine.

Nipa palms have the kind of flowers and fruit that make you think of 'The Thing from the Swamp'. The flower stems are cut, bent over and tapped for their sugary sap, just like coconut flowers for tuba. In the heat, the juice begins to ferment even before it is collected in the morning. Then it is distilled in a crude still, and by early afternoon it is Pa-oroi, the local spirit drink.

At a mainland Mindanao town, Lanuza, I asked to see the local nipa 'wine' distillery, imagining copper stills, ancient craftsmen plying their ancient craft, spring water, barrels of ageing spirits etc, and just a few wee drams of the good stuff, just as one would find at a '12-year-old Glenlivet' Scotch whisky distillery.

No such luck. I got up too late, and missed the whole process, which went from fruit to distributor in half a day.

But if you filter it through coconut charcoal, add some butterscotch, and keep it for a month, you can still pretend you have Glenlivet 12-year-old at $1.20 per gallon.

But the rest of the mangrove swamps are very unforgiving, as Joay's son is finding.

I first wrote this page a year ago, in early 2005, after my first real, searching visit into the mangroves, when I was, frankly, intimidated by the very idea of visiting a noisome swamp. 

Since then, I've found that the local people actually choose to build their homes right in the middle of them, and that mangroves are far more productive than I imagined.

Pilar, a small town just north of General Luna, has extensive mangrove swamps around it, and most of the 'garden suburbs' are built right in the swamp. 

It doesn't make sense to build a house like the one above, twenty yards from the dry land of the raised roadway/dike, if it doesn't have positive advantages.

But it does make sense - the salt water tide inhibits mosquitoes, and carries away wastes, and the mangrove trees calm the weather - no fear of tsunamis here. And you can fish in your back yard.

They don't have cars, but having a boat port just by the house is useful.

Aborigines in Northern Australia still forage among the mangroves, for almost identical species as those shown above in the Philippines. 

See: Aboriginal use of mangroves which also details some of the uses (mostly as timber or for medicines) for

mangrove  plants.

It  makes much mention of 'mangrove worms' - Teredo clam species that bore through dead wood. Known as shipworms throughout the tropics, they can cause great damage to wooden ships. 

In Europe, we have a similar,  but stone-boring clam, Pholas. It doesn't harm ships much, but it sure buggers up their harbours.

This is a piece of kamagong - Pacific ebony - that I once found on a beach, riddled with shipworm holes. I had the idea of slicing it, and filling the holes with polyester resin and Paua (abalone) shell fragments, to make attractive black shell inlaid pendants, etc., keeping the 'sawdust' for black filling powder for the resin. But some oil or other chemical in the wood inhibited the resin from 'taking' and it remained liquid. Maybe the shipworms liked it, even if the resin didn't.

But Teredo 'worms' cannot tolerate fresh or brackish water. I leave my boat at anchor by a small creek estuary, while fishermen just along the shore religiously carry their boats onto dry shore every single day.

In the Katangnan estuary, many old dugout tree-trunk canoes are still in use. That doesn't suggest they need worry too much about shipworms. But half a mile around the corner into the open sea at Cloud 9, a friend of mine lost his boat completely to shipworms.

Worldwide Mangrove Distribution 

Source: (Marine Biology - Peter Castro, Michael Huber - Wm C Brown)

The largest concentrations of mangroves are in SE Asia, from Burma to New Guinea, including the Northern Coast of Australia. They grow best on shallow gently sloping coasts - much of South East Asia used to be Sundaland or Sahul, shallow areas drowned when the glaciers in N America and Europe melted.

Areas that are now deserts, like most of Somalia, Arabia, the Northern coast of the Gulf and Baluchistan, and much of India may have been fringed with mangroves during their Pluvial Periods (Ice Ages further north). 

But it also may have been ever so - due to steep coasts, anomalous colder currents - we will have to find out. As for Baluchistan, I haven't the remotest idea what its coastline is like - it's not the kind of place I imagine for a beach holiday.

But Truly Modern Humans, about 70,000 years ago, and Homo erectus, nearly 2 million years before that, must have travelled through there, going from Africa to Asia somehow, without knowing what was beyond each day's travel or wander, so perhaps it was once inviting.

See: The Indo-Pacific Shoreline Ecotone

Mangroves are very good for other reasons, and therefore good for us:

• A vital protective screen for the shoreline, 'smoothing' the effects of tsunamis and storm surges, and filtering the run-off of soil and chemicals from the land - allowing coral reefs to survive.

• A 'nursery' for fish, shrimps, crabs, and other fry, letting a few more of them live until they go out into the open sea.

• An interface between open sea, brackish waters, and freshwater rivers - a rapidly changing and stressful environment - just the sort of ecotone between different environments that 'pushes' evolution along, by offering constantly changing environmental conditions.

• A protective screen for our ancestral women and children foraging in the open coral lagoons and seagrass beds. Around most of South and South-East Asia, both tigers and lions were plentiful, until just a very few years ago, together with rhinoceroses. In the Pleistocene, there were certainly some equal or even more horrible beasts 

Asian lions and tigers still haunt the semi-aquatic Sundarbans on the Bengal coast.

Panthera tigris lived 750kya in the Philippines - and the Philippine carabao, perhaps the dumbest, most docile beast of burden in the world, had ancestors who were generally your good old-fashioned, bad tempered, rip-snorting water buffaloes.

But, there are also saltwater crocodiles, (Crocodilus porosus), once frequent in the mangroves, and an occasional danger in the lagoons fronting them.

A captured one was kept in Numancia until it died of neglect a year ago, and two years ago, I saw one splash off the bank and swim under my boat in Sohoton Lagoon.

See: Shoreline Reptiles

Many of the mangroves along the coasts of SE Asia were cleared long ago, and, recently, more have been sacrificed to allow fish farming - a classical case of the powerful taking over the 'general good' and appropriating it for their own short-term (lifetime) purposes. In more 'developed' areas of the Philippines, intensive fish farming has led to huge fish kills, when disease has struck a large, overcrowded captive fish populations of semi-clones.

Many fish ponds are now reverting back to nature - it was a craze for a time, but the infrastructure was never built to take the products to market, and natural water systems cannot cope with massive overdoses of 'fish food' and fish shit.

You cannot maintain a monoculture in conflict with long-evolved natural systems - as Americans may find out soon when their wheatlands in the Great Plains suffer the depletion of the once-rich prairie soil and the Oglala fossilized aquifer dries up. (And when the men, if there are any still left there, find their sperm counts dwindling due to persistent agri-chemicals in their drinking water - and their beer, of course).

They've only been farming the Midwest for about 150 years, and San Joaquin Valley, California for about 80.

See what happened to the Aral Sea in Central Asia in only a few decades. 

It took more time for the Harappans of the Indus Valley, and the ancient Iraqis (Sumerians, etc) to deplete their soils and salinize their agriculture to death. But not much.

See: African Lakes & Rivers for what's happening there.

New Pages as at April 2006

Contents

Siargao Mangroves

Not welcoming places 

There's food...of sorts

Ever A Good Habitat ?

Good for other reasons,

& good for us