Creatures that Live in Logs in Mangrove Swamps

There is a small fish that lives inside worm holes in mangrove trees.  I first saw this fish 25 years ago on a university field trip and I remember the fish being called a cobra fish but googling that term finds nothing and I cannot find its name.  Finding names for mangrove log creatures seems to be harder than normal as not much is published.  The first step is to get a good photo of the creature, not easy when you have to open up muddy logs to find them and then try to get clean enough to use a camera.  What I discovered is that the fish are certainly not alone.  The biodiversity in rotting mangrove logs is as high as the biodiversity of a rock pool.

The mangrove forest where most of the photos were taken - Redden Island

Shipworm holes can be large enough to put your finger in and many are calcified

A small shipworm showing the shells that bore into the wood

The key species in the rotting log ecosystem is the ship worm. These worms, which are actually bivalve molluscs grind away wood using their shells.  Logs soon end up riddled with hole that provide habitat for a wide range of creatures.  Logs also have other habitats. Common mangrove crabs make tunnels under logs, not that they need logs, just that they prefer to tunnel under logs than burrow out in the open.  Another range of creatures live in the space that opens up under the bark when the bark becomes lose.  As logs can be different sizes, in different states of decay and in a different position relative to tide heights, each logs is different and no log supports all species.  In all at least 20 species of macro-invertebrate depend on mangrove logs in north Queensland. 

The photos that follow show some of the creatures that I found under or within logs.  Every tenth log has something interesting.

These dartfish were under the bark of a tree that was completely exposed and had been so for possibly hours or days.  I assume the fish were in this position before I lifted the bark

The fish which are about 20 mm long can also be found inside the trees in shipworm holes.  This fish came out of a hole when I chipped into a shipworm infested log.

Non-descript crabs are the most common inhabitant

Giant flatworms up to 60 mm long glide through cracks

A giant flatworm coming out of a shipworm hole.  See the eye spots.

My new species for yesterday - looks like a species of stone crab

This snapping shrimp was as long as my hand and was found under a log

A colony of shrimps was present in the tunneled log shown above

I have very little idea what these 80 mm long creatures are

Constructing Machans Beach Seawall

Machans Beach which is a sandy island in the mangrove-infested Barron River delta is getting major seawall upgrade.  Category 5 cyclones have become regular events during the previous decade with at least 5 nearly landing at Machans (Ingrid, Larry, Monica, Yasi and Ita).  When you live here you can remember them well as you have pack up your bags each time and flee.  Machans Beach was lucky and was not directly hit but a place that is very similar in almost all respects was hit-Tully Heads.

The old seawall is very steep and many of the rocks are not supported from below

Graphic of seawall design from public notice sign -showing the lower angle and extended toe.

Like Machans Beach, Tully Heads did not have a properly engineered seawall.  The seawalls were constructed over time in response to local erosion events or storm damage.  Clearly these sorts of seawalls do not stand up to category 5 cyclones and at Tully Heads, nearly all the homes in the first 2 rows were lost. Seawalls can also be dangerous and kids playing on seawalls are sometimes killed by shifting stones and there have been local incidents.  Upgrading the Machans Beach seawall became a priority project.

Gap bashed though seawall by Cyclone Yasi - Tully Heads

Rocks thrown up from seawall onto lawns

To begin at the beginning, Machans Beach needs a seawall because the beach eroded.  The beach eroded because someone cleared the vegetation between the headwaters of two creeks and during a flood, one of the creeks, Thomatis Creek flowed backwards from the Barron River, over land and into the headwaters of the Richters Creek.   As a result of that flood in 1922 was that a channel was scoured between the two creeks and the Barron River developed a new path to the sea that was 7 km shorter than the old channel.  Much of the sand carried by the river followed the new path to the sea and Machans Beach lost much of its sand supply.  Adding to the issue, the old mouth of the Barron also shifted and the sand that was coming out was channeled out into deeper water.  Sand miners were also dredging very large amounts of sand out of the river channel.  It is an open question whether the mulit-million dollar seawall now under construction would have been needed if some controls had been placed on inappropriate land clearing 100 years ago and sand extraction from the bed of the Barron River was banned earlier.  A full description of the root causes of the beach erosion issue was written up in a Mulgrave Shire Council report, dated 1986.

Machans Beach Esplanade is very narrow, so another way had to be found to access the seawall

Construction of the seawall began at the northern end near Barr Creek at the beginning of May 2014.  A causeway was constructed about 15 m out from the existing seawall.  This method of construction avoided having to use the narrow esplanade and having to remove all the trees that were perched at the top of the old seawall. Seventy tonne trucks would reverse down the causeway and dump stone to the side of the wall so that a large excavator (30 tonne?) could individually pick them up and place them at the end of the causeway to extend the causeway. The size of the largest rock approaches the size of some of the smallest cars and it surprising that the excavator could handle them so easily.

Tipping out rocks

A larger rock barely fits in the bucket

Reversing along the wall to the excavator

Mirrors are handy for this job

By November 2014 the seawall stretched more than half way along the Esplanade and the causeway was in excess of 1 km long.  Trucks would drive forwards along the causeway and turn on little ramps that ran from the causeway to the Esplanade.  These ramps are also where the excavator is parked when the tide is high.  The trucks then reverse the final hundred metres or so the the waiting excavator.

The causeway is now so long, that the excavator has to wait for loads of stone to arrive

Before placing rock, mud is dredged from the tip of the causeway and placed on the side

A bucket full of mud - the mud was plastic so not much turbidity resulted

Dumping large rock with the excavator poised to catch the truck should it start to roll over

View along the top of the partially finished new seawall, showing soil being laid where the footpath will be

The seawall is made up in layers, which small stone (~150 mm) being formed into bank, which is then covered with a layer of geotextile.  Geotextile will add strength to the seawall as it has a very high tensile strength but its main purpose may be to stop fine material being eroded out of earth behind the wall by the movement of tides and waves.  Loss of fine material can create deep holes in the ground.  On top of the white geotextile is a layer of smaller rock, each of the smaller stones would be the size of the bucket on a builders wheelbarrow, which is roughly the size of the stone in parts of the original seawall.  On top of the smaller stone, truly large stones are being places with may having a long dimension of close to 3 metres.

Layered construction of seawall

The project will continue well into 2015 and I will keep you posted.

Fig Parrot Chicks

Of highest priority to saving the endangered southern race of fig parrot is finding a next with chicks so that a captive breeding program can be established.  If you live south of Rockhampton and you see parrots like the ones in this post, take photos if you can and contact the Department of Environment and Heritage Protection (email address is in recovery plan). Look for cheerful little faces looking at you from the trees.

My favourite fig parrot - this little chick watches what I get up to (1/11/2014)

I stand about 5 m away and take photos with a superzoom camera.

According the species recovery plan published in 2005, “Coxen's fig-parrot [the endangered subspecies] is thought to nest in the same manner as the red-browed fig-parrot [the subspecies shown in this post]. Training in north Queensland will be undertaken to hone the skills necessary for locating the nest holes of Coxen’s fig-parrot. This exercise will enhance observers’ abilities in nest recognition, particularly with respect to the height, aspect, positioning and appearance of nest holes, the tree species favoured for nesting and the preferred breeding habitats. In addition, familiarity will be increased with the appearance, flight style, behaviour and calls of the similar red-browed fig-parrot. The training exercise in north Queensland should be conducted by members of the recovery team in October or November so that the experience gained can be passed on to others and applied”.  Most of that information can be found in this post and previous posts on this subject.

A chick in a large dead paperbark in the mangroves about 15 m above the ground (5/11/2014)

When I first saw the hole in September, a parrot was in it but taking photos with a smart phone through binoculars was not successful. When I went to take a photo a few days later, green ants were trying to claim the hole.  However the chick above survived the green ants  

In late September, I started to hear the noise of chicks begging for food.  Sometimes, I would even glimpse a bit of baldy head but the parent would enter the nesting hole and push the chick back if I observed too closely.  Now the chick or chicks are older, they are getting interested in the outside world and spend a lot of time with their heads out of the burrow looking around.  This may be the best time to look for active nests as you can make some funny sounds and the chicks come up for a look.  They are much less timid than the adults.  Fig parrots never become tame and do not make good pets.  With their really small tails they do not make good aviary birds as they can’t turn quickly and tend hit the end of the aviary as full speed, hurting themselves.  I would be careful about handling a bird that is not tame and that can chew through wood, not to mention that handling an endangered species would get you in serious trouble.

Dad to my favourite fig parrot chick

Most of the time, the fig parrots that visit my yard target green figs.  They eat some figs including Ficus racemosa and ignore other figs such as Ficus superba.  Ficus variegata is also a favourite.  They eat the seeds of the fruit and spit out the flesh and normally feed on green fruit, which would are dreadful tucker from a human perspective as they are full of sap-flavoured, glue-like resin.  Ficus racemosa fruit are very good to eat when fully ripe and have a flavour like strawberries.  I a pretty sure that Ficus variegata never really ripens and is never good to eat.  When the figs are the best for me, the fig parrots have long lost interest and think the idea that they normally feed on ripe fruit needs to be discarded.  Fig parrots tend to pick a cluster of figs and quietly chew for hours.  Cluster figs may be far more important that species of fig which have fruit dispersed through the canopy.  Normally, I detect the parrots by hearing the plugs of fruit the spit out landing on the leaf litter beneath the tree. When a few birds are present, the tree literally drips bits of fig.  The birds also make small squeaks as contact calls and the parent generally calls to be chick before approaching the nest hole.

Green Ficus racemosa is the best.  There are two birds in the photo.

This is the first and only time I have seen a fig parrot on ripe figs.

Previous posts:

• Saving the fig parrot; and
• Where fig parrots nest.