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Byron Shire
August 6, 2021

Uncovering the mangrove fiddlers

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An example of the female fiddler crab Tubuca coarctata that has two small feeding claws. Fiddler crabs scrape up the surface sediment that they filter to extract organic matter to feed on. Photo Denis Riek.

Story & photo Denis Riek

The Brunswick River still has some extensive areas of mangroves that, thankfully, have not been sacrificed for development, and are a great place for photography if you know what to look for, and where to find it.

The only downsides are that on a hot summer’s day in the mangroves it can get as humid as a fettlerʼs armpit; the mud is thick, and the sandflies and mosquitoes annoying. An occasional wallaby or snake make it more interesting, and with climate change – keep one eye open for crocodiles!

Crustaceans haunt the mangroves, with Fiddler Crabs being the most colourful and definitely the most interesting. They are closely related to the Ghost Crabs that can be seen racing around the dunes. Female fiddlers have two small feeding claws while the males have one large and one small, and feed by scraping up the surface sediment, which is sifted in their complex mouth parts to obtain organic matter.

An example of the colourful male fiddler crab of the Tubuca dussumieri speicies with its large and small feeding claws.
Photo Denis Riek.

Gone before you get there

As the tide runs out, uncovering their holes, they come out to feed, attract a mate, or argue with the neighbours.

If you walk through the areas they favour, you will most likely never see one, they have already heard or seen you approaching and are away in a blink down their holes. You have to wait, almost motionless, until they slowly begin to re-emerge, and for some species this can take a considerable amount of time.

The Tubuca coarctata fiddler crab. Photo Denis Riek.

Not having a telephoto lens I have to spot a likely subject, and note the hole it disappears down as I approach, to get as close as I can. I move closer, then it’s back to waiting again, with camera up to face, and finger on the shutter. Some legs first feel over the edge of the hole, then ‘up periscope’ as one of the stalked eyes appears – and heʼs looking right at me, the large object that wasnʼt there the last time he looked. Donʼt move. Wait a little longer, and he moves further out, until eventually heʼs one of a number of Fiddlers out and about, waving their large claws to attract females, or warn other males.

Colourful species

I get some shots before I make a mistake and move, because he hasnʼt forgotten about me. This works fine with the species that favour firmer sand or sand/gravel but there are two very colourful species (Tubuca coarctata and Tubuca dussumieri) that prefer very muddy sand on the banks of some small creeks that drain through the mangroves.

To get good images of these crabs, that show the full colour pattern, requires catching them, washing off the mud, putting them back near their hole and getting the shots before they collect their wits and bolt back down to safety.

This species is called the Gelasimus vomeris. Photo Denis Riek.

Agility and speed the key

Catching a Fiddler crab requires far more patience than it does to photograph one, plus a fair amount of speed and agility that I can hardly muster these days.

There are six species of Fiddlers that I have seen in the Brunswick River and its tributaries, and luckily I have images of all.

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  1. Nice story and pics there Denis.i have worked with fiddlers for many years. Love them. Keep up the good work. It’s saddening to hear how the habitat is disappearing. “Gone before you get there” could be that special place.

  2. Respected Dr. Denis Riek
    May I have the permission to share your image “Frillagalma vityazi”
    ( appeared in http://www.roboastra.com/Cnidaria2/brac354.htm)
    for my new title “Bioluminescent Marine Plankton” to be published by Bentham Science Publishers, Singapore
    Due acknowledgment will be given
    Thanking you and with best wishes


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