Wednesday, 14 February 2018

Wildlife of Clairview and St Lawrence

Clairview and St Lawrence are important habitats for larger creatures such as koalas, greater gliders, possums, goannas, emus and a wide variety of wallabies but these creatures are not easy to find. The area is on the threshold for many wildlife species and they occur only in the better pockets of land or at low densities. It is easier to find smaller creatures that can live in smaller patches habitat. Wetlands and watercourses are where the action is.

Roadside tree with koala and possum scratches (click to zoom in)

A brushtail possum in BarraCrab Caravan Park
At Clairview, at the southern end of the beach past the caravan park is a tidal creek with large colonies of fiddler crabs on the adjacent flats about 100 m out from the beach. There are two main species, a large species with hot pink nippers and green backs and a small species with a grey-white nipper. The smaller species makes up for lack of colour by waving so frantically that the crabs sometimes bounce across the ground. It is a great place for kids to discover a few wild creatures and perhaps even catch some. 

Fiddler crab colonies are on side opposite this large mangrove
Uca seismella - little white bouncing fiddler crabs are on the lower bank
Two-tone fiddler crabs (U. vomeris) and smaller pink fiddler crabs

Pink fiddler crab - Uca polita
Near the mangroves are red climber crabs (Metapograpsus latifrons)
Male fiddler crabs have one large nipper for demonstrating their power and a tiny nipper for feeding. Very rarely a crab will have two large nippers. Finding one of these is the Queensland equivalent of finding a four leaf clover and I found one at Clairview. In forty years, I have only seen four such crabs.

The fiddler crabs that dominates the banks of St Lawrence Creek are a different species, one which prefers salt pans to the intertidal mud flats. 

Uca signata (click to enlarge)
If you are lucky to be present when the tide is rising and filling the creek out from the beach, you may see popeye mullet. These strange fish swim with the eyes above water so that they can see predatory birds. The lower part of their eye has differently shaped optics so that they can see underwater. If the tide is out, the bottom of the creek is filled with fine soft silt that perfectly records the prints of a multitude of mostly unseen creatures including sea turtles, gropers, giant mud skippers, mud crabs and much more. Working out which creatures made which prints can be a challenge.

Pop-eye mullet in St Lawrence Creek
Unfortunately, the popeye mullet are not reliably present and chances of seeing these strange fish are better in St Lawrence Creek, which flows past the town of St Lawrence and is about 20 km from Clairview. Clairview is an old volcanic area and has low hills of volcanic origin, whereas St Lawrence is located in an ancient coal basin, filled with deep sediments. Despite their spatial proximity Clairview and St Lawrence are in different bioregions, which are the ecological equivalent of countries. The climate, landforms and geology differ enough that different groups of species dominate. At Clairview the eucalypts have green foliage and close to St Lawrence the foliage is usually grey. The boundary is diffuse being about 10 km wide and there is no sudden change. 

Colour of ironbark leaves near St Lawrence
Coal basins are full of fine mobile sediments. St Lawrence Creek is more like liquid mud that water and it is no wonder that popeye mullet with there ability to look above the water to see where they are are so abundant. Another fish that revels in liquid mud is the blue mud hopper, which is a relative of the mud skipper. This muddy world is alien and worthy of a visit. 

Small mudskipper (left) and a blue mudhopper (right)
In only 8 km, St Lawrence Creek which becomes tidal at the highway, increases from a few metres wide to approximately 500 m wide and with 8 m tides, has swirling waters and standing waves caused by racing tides. The Styx River, which is only 20 km away has tidal bore, a wave up to 1 m high caused by the rush of the incoming tide. Unfortunately this river is inaccessible and it is quite possible St Lawrence Creek also has dramatic incoming tides. Only some tides have strong bores but these are predictable. Perhaps the combination of soft ground and violent tides creates these strange creeks which are a metre wider for every ten metres downstream. 

St Lawrence Creek just beside Bruce Highway is about 10 m wide
St Lawrence Creek is 500 m wide, only 8 km downstream
St Lawrence is famous for wetlands and waterbirds. The small seasonal creeks also have their own fauna which is adapted to floods and droughts. However, it is the marine environment that interests me. I want to see and understand the biodiversity of the muddy waters, a largely ignored scientific frontier.

Where pipes run under the highway, there are often moulted crab shells

A freshwater crab caught in a drain beside the highway
See also: Postcard from Clairview

Friday, 15 December 2017

Coastal Coral Reef at Cape Tribulation

When the tide goes out near the famous tourist location of Cape Tribulation in tropical Queensland, reef flats and coral platforms are exposed. However these reefs at first sight appear to be mostly dead and some explanation is needed. The short answer is that these reefs flourished more than 5000 years ago when sea level was about one metre higher than it is today. After sea level feel to its present height, the top of the reef was about 80 cm above the level required for coral growth and coral cover was lost from the top of the reef. The mystery is why the reef platforms are still there at all after 5000 years of battering by rough seas from trade winds and cyclones.

Some areas have a wide flat platform
Fissures and porous reef absorb waves and no waves swashed over the top
Emmagen Creek is the best place to observe these old reefs, however almost all sections of coastline near Cape Tribulation have well developed reefs. Corals are still present in the fissures of the reef and on the reef slope. In fact these reefs hold the record for coral diversity on the Great Barrier Reef nd have even more coral species than the best of offshore reefs. In the order of 175 species of coral have been recorded. However most of what is visible is a yellow brown surface riddled with holes and coated with algae and sediment. It is opposite of an attractive coral reef.

In some areas there are shallow enclosed lagoons
The coral matrix is about 7 metres thick and is so porous that swells can flow into the reef. Twenty five metres back from the edge, I could hear the reef beneath my feet breathing, it sound like a sleeping baby. The reef platform is quite strong, although occasional thin sections can break underfoot causing me to lose some skin. Deep fissures surge with swells and even in the middle of the broad reef, I could not see the bottom through the clear waters. I am keen to investigate this underwater world, however it will likely have hazards including jellyfish which often concentrate in fissures and even moray eels and crocodiles which could be inconvenient. In one of the fissures, I observed large fish being attended by a cleaner fish.

A large fish at a clearer station in the middle of the reef platform
Live corals fill the deep fissures
When the corals could no longer grow on the reef platform, encrusting coralline algae took their place. The top 80 cm of the reef platform consists of a coralline algae matrix with embedded chunks of coral and terrestrial rock. I wonder if aborigines carried the rocks onto the reef as it is hard to imagine a natural process doing so. In any case, I consider the reef to be a living reef that is maintained by algae rather than coral.

Pink coralline algae is easily overgrown by brown algae
Some patches of reef edge have hand-sized stones in the reef matrix
Coralline algae are easily grown over by other types of algae and can only thrive when something is grazing the other algae. At Emmagen Reef, the grazing appears to be performed by air-breathing slugs. These slugs (Onchidium sp.) usually cruise the ground in mangrove swamps and to find them as the dominant herbivore on a coral platform is most unusual.

Onychidium slugs grazing on the algae
There are some specialised fish associated with this reef. Peppered moray eels hunt the crabs which scurry along the margins of fissures. Dart fish inhabit small pools. Larger pools have a subset of reef fish including angel fish and damsels. In wide fissures, there are concessional coral colonies and wave washed edges are covered with dense sargassum. Water clarity is limited.

Peppered moray eel under a coral ledge at the toe of the beach
The most interesting thing and the only thing I failed to record were two small fish that bounded over an exposed two metre wide sand bank on the tips of their tails. The fish were vertical and bouncing away like pogo sticks in a motion that was very different from a mudskipper. When they reached a pool, they swam away underwater. This leaves me wondering if they were rock skippers, which are an amphibious blennie known from islands in the Pacific Ocean.
Ships sail close to the coastline here

Sunday, 3 December 2017

The Life of Biting Sandflies

Given that sandflies are the curse of the coastline, it is surprising how little accessible information there is about them. Scientists have studied them on the behest of councils to understand where and when they breed, however these scientific studies do not present much of a window into the life of a sand fly. Being of inquiring mind, I would like to find out exactly where they breed and what their larvae look like so that I can study them for myself. In this post, I will attempt to provide a resource for those who want to study the humble saltwater sand fly.

A sand fly drilling into the back of my finger
There are lots of different types of sand fly and the species are identified by the vein patterns and colour patches in their wings. They belong to the genus Culicoides and C. molestus famously inhabits the canals and sandy shores of South-east Queensland. In the tropical north, C. subimmaculatus is known to breed in muddy mangrove environments. I am not sure which species I have investigated.
As sandflies are so small, a microscope is needed for identification of species. For this blog post, I have only used affordable equipment including a magnifying glass and a set of $20 close-up lenses that screw onto the front of my compact camera.

Sandflies were emerging along the receding water line where beach yields to estuary
Finding where sandflies might be breeding is as simple as squatting down and looking for sandflies walking across the muddy surface. I have observed them mainly at midday to early afternoon, usually walking across the surface toward the wind. In the late afternoon, strong trade winds blow across the ground and both insects and other creatures seem to seek shelter. Usually, I wear long clothes for sun protection and the sandflies do not seem to be biting at any rate in the middle of the day so I can study them unmolested. Most sand fly larvae inhabit a tidal band just below the high tide level of ordinary neap tides and above the level dominated by water breathing crabs and worms.  
Diagram of sandfly life cycle - WikiMedia
Studies have discovered that sand fly emergence occurs mainly during the spring tide part of the cycle. However nothing seems to have been written about the actual process of emergence, let alone any photos or videos taken.  Below is my best attempt so far to video emerging sandflies.  The cover image is a dead pupa that floated to top of one of my collected samples. It appears to be in a clear bag, which may be how the wings are protected.

Observing sandflies in the process of emerging is challenging, even when reviewing video footage things happen so quickly that it is difficult to work out what is happening. I believe a lab study will be needed to sort out what is really happening but this is what I think. As the girl sandflies emerge, they get jumped on by the boy sandflies and there is lots of violence. Alternatively the boys are jumping on the girls when they come in to lay eggs, but the first pattern is common other insect groups. I think that sandflies just pop up out of the mud and can fly a few seconds later. However males sandflies fly can in and land within the space of a single video frame at 30 frames per second. Sandflies suddenly appear and disappear in the footage and much higher frame rate is needed to track their movements. All this action occurs within a few minutes of the ground surface being exposed by the retreating tide. Small trumpeter fish (Therapon jabua) enthusiastically patrol the shallowest of waters and probably eat any sandflies that emerge before the tide has fully retreated.

To speculate about what I think that I have seen, sandflies may be cryptic about how they emerge, mainly to avoid the attention of their conspecifics. Even before they can fly, they appear to jump like fleas when spooked. The big question is where do they expand and harden their wings. A children’s program on sandflies claims that they do this in a bubble in the ground but I can’t find any published info that supports this. What I take to be freshly emerged sandflies seem to have smaller wings and the wings appear to expand over a short period. As the sandflies turn around frequently, they can be clearly visible when facing one direction and nearly invisible when they turn around. I am guessing that they emerge almost ready but need a few seconds to grow and harden their wings. They either jump around to avoid their mates or possibly hide their bodies in muddy pools in micro-depressions. Hiding their bodies in water hides their shadow, which is more visible that that the actual sand fly. In most of the cases when I see a sand fly emerge from the muddy water, running the video backward shows that it was already emerged and moved into the water from somewhere else. Most of these behaviours can be observed in the video, if you are prepared to go forwards and backwards enough times.  Furthermore, sandflies may emerge synchronously. There seem to be small patches of intense activity rather than dispersed trickle of newly emerged insects.

A dead sand fly larva beside the tip a dressmaking pin
Finding sand fly larvae and pupa is even more challenging. The one success I had was to put a few spoonfuls of mud into a small clear drinking water bottle and shake it so hard that the larvae would not have known which way was up or down. The larvae were probably killed by abrasion and when the muddy mixture settled, were in the fluffy sediments between the clear water and the heavier muds and sands. Pouring off the water and some of the fluffy sediment produced a dozen dead larvae.  Sand fly larvae have a head capsule, three small thoracic segments and nine larger abdominal segments.

Scientists have added sugar and golden syrup to sandy samples to make the seawater so heavy that the sand fly larvae could no longer swim down to the bottom of the container and floated to the top. I would prefer to find another method. I have poured the fluffy sediment from another sample of mud into a shallow tray to look for movement but none was seen save for springtails and tiny worms. However later, strange tracks covered the bottom of the tray suggesting that sand fly larva were present but cannot be seen.

Tracks that might be from sand fly larvae
My next attempt was to carefully excise a chunk of mud from prime habitat and use a dressmakers pin to flick crumbs of mud from the edges of my muddy sample until I had worked my way through. Small tunnels can be seen and even followed. I found that the mud was bound together by threads that were strong enough that I could feel their strength. The threads appear to be the rhizoids of a minute but advanced green algae and can be present even when there is no noticeable algal growth on the surface.  Threads within the mud are much finer than any green filaments that can be seen on the surface and are present and apparently alive even tens of millimetres below the surface. It is like discovering a miniature sea grass with tiny leaves and roots has been present in an area I have walked over hundreds of times but never noticed. Despite finding tiny worms below in miniature green meadows, I did not find any sand fly larvae. As a check, I added some water and shook up mud that had been processed and on the following day found a single sand fly pupa.

Culicoides pupa
Sand fly pupa and dressmakers pin
Mysterious threads holding the mud together (click to enlarge)
The threads are from a minute and unidentified green algae
Even in close-up (see baby mudskipper), the algal turf can go unnoticed.
My preliminary research is incomplete. I need to find a simple way of obtaining numbers of larvae. The frustrating search continues, however I did discover an unexpected ecosystem of algal turf and its associated fauna including springtails.

Additional sandfly information is as follows. Sand fly larvae are reported to be predators of small creatures, which I suppose means mainly springtails. The larvae breath via small hook gills at the end of their abdomen. Only female sandflies feed on blood. Mudskippers are their main victims although wading birds cop it too. Adult sandflies live only 2-3 weeks. Swarms are often visible in patches of sunlight in the lee of trees or other wind blocking objects. The swarms are reported to be where the boy and girls get together.

Control of sandflies is difficult as they live in estuaries which contain other biodiversity which we do not want to kill with chemicals. Fogging may be used when sandflies are severe but fogging has no persistent effect. Within their muddy habitat, sandflies may be predated by tiny robber flies and hover flies. Rove beetles also swarm over sand and mud surfaces and may be predators of sand fly sized prey.

Thursday, 23 November 2017

Miniature sand flat wildlife looks like a tiny African savanna

Imagine taking a photo of the most featureless and lifeless-looking patch of bare muddy sand in a tropical estuary and the photo revealing that even this place was seething with life.  In fact the place was full of creatures that were just too small to be seen when I was standing up.  The video below shows a swarm of springtails (Collembola).  It reminds me of the great migratory herds of Africa seen from an aircraft. A single sand fly near the centre of the frame provides an indication of scale.

I filmed the swarm at about four in the afternoon, in the cooler, cloud-shaded conditions when springtails had emerged after the heat of the day and were were swarming.  Scientific literature reports that springtails are one of the most common organisms on earth and that densities of 100 000 per square metre are common.  As these springtails are on the surface even during the middle of a summer day, I suspect that their yellow colouration is related to protection from UV rays  In some of the photos below, these animals are so small, even with high magnification, they are hard to see so please click on the photos to enlarge.

A muddy sand flat between a creek and the beach

Filming set-up, a compact camera with a screw-on close-up lens

Collembola grazing on sand flat, marine environmment
The original photo, each yellow or brown fleck is a springtail

Collembola tracks and holes in wet ground
Springtail tracks and holes can be seen in fine mud even when the creatures are hiding
Insect predators were also zipping around on the muddy surface. Large yellow and black striped hover flies fly at high speed just above the surface and probably catch sand flies. Rove beetles, which look like tiny earwigs seem to be the most abundant and roam over the surface and into and out of holes. Caterpillar-like beetle larvae that were considerably larger than the rove beetles were also occasionally seen. Tiny bugs, which are as small as some species of sand fly were also present. In truth it is difficult to know for certain which of these insects are predators as most groups have both predators and herbivores.

A tiny fly (robber fly?) that hunts by sight

Rove beetles often make chambers under stuck down mangrove leaves

A sand fly-sized bug, which runs across the surface at speed
In hot dry weather, a good place to find tiny animals is under a mangrove leave that has become stuck to the surface of the mud or under loose flakes of algae. Sometimes a full ecosystem of predators and prey can be found under a single leaf. On close inspection, there is a rove beetle and hundreds of blue-green springtails in the photo below, all of which were under a leaf.

Rove beetle and blue-green springtails
Some of these insects are not be restricted to the sheltered waters of a small tidal estuary. I have also found the rove beetles on open sandy beaches near the high tide line and on exposed sand flats where the blue soldier crabs march. 

Sand flats at Yule Point

Beetle tracks under the sand, near the work of a sand bubbler crab
A rove beetle beside a sand ball
It is beyond question that these creatures are present in vast numbers but are they ecologically important? Juvenile predatory fish such as whiting seek the shallow waters where these tiny insects live. Sand fly larvae are also predators and I wonder if springtails are their main dietary item. Certainly, the tiny fauna would consume algae and help to prevent purification of surfaces with excessive algal slime. More research needed.

Big hairy yellow stripe hermit crabs seem to graze algae and not hunt for springtails.

Sunday, 12 November 2017

Leaf-cutting Snapping Shrimps

Snapping shrimps, also known as pistol shrimps make more underwater noise than any other marine animals. Look up why snapping shrimps make loud popping noises and you will almost certainly find some dazzling claims such as “While hunting, pistol shrimps open the hammer part [of their nippers] and then release it, allowing it to snap into the other part. This release is extraordinarily fast and results in an enormously powerful low-pressure cavitation bubble. The bubble that is created serves the purpose of stunning a prey. How does that work? The bubble shoots out at a speed of 62 miles an hour, reaching a temperature of 4700 degrees Celsius for a very brief period of time. This temperature is actually close to the temperature of the Sun.” Indeed, it is the holy grail of videographers to capture this ultra high speed phenomenon as the clips listed below show.

However with my $400 dollar superzoom camera, I have filmed a completely different reason for snapping. I can find no trace of what the video below shows in the scientific literature and this may be the first time that this information has ever been reported.

If mangrove snapping shrimps use their large nippers to cut up mangrove leaves so that the leaves can be pulled down into their burrows and consumed, this makes the mangrove snapping shrimp the marine equivalent of leaf-cutter ants. A radical claim such as this must be supported by a lot of evidence.

I became suspicious of the standard explanation for snapping shrimp behaviour when it occurred to me that having a bright orange warning flag in the middle of an ambush predator’s lethal weapon does not make sense.
Giant snapping shrimp are large and powerful but not very aggressive
Ecological observations did not add up either. There were simply too many snapping shrimps in some swamps. On some nights, the noise from snapping shrimps is a dull roar, like giant raindrops falling on a tin roof. At low tide, these areas are completely cratered with snapping shrimp holes. As for preying on shrimps, crabs and fish, I have watched the tide flow into snapping shrimp areas and it carries with it very few potential prey. Other types of shrimps have eye-shine which is easily seen in torch light and even the tiniest fish can be seen when they move.

Stilt mangrove swamp near the seaward fringe

The entire floor of this area is pitted with snapping shrimp holes
The mangrove swamps that fringe the open mudflats of Trinity Bay are flooded by seawater that crosses at least one hundred metres bare sand and mud flats. Not that many small shrimps and juvenile fish want to cross such a space - so they hide in creeks. Many mangrove areas are more than 500 m from the seaward fringe of the mangroves and are flooded by seawater for less than 6% of the time, yet snapping shrimps are still abundant. The idea that snapping shrimps are mainly predators was starting to fall apart.

Snapping shrimp holes in stunted Ceriops backswamp near a salt pan
So far, I have discovered that snapping shrimps rarely leave their holes or even come to the entrances of their burrows. At low tide, there are occasional snaps. Snapping is most intense in the evening and when the outgoing tide has exposed the mangrove floor. Waters continue to drain from the forest floor for minutes to hours when the tide recedes and leaves are sometimes transported in the thin film of receding water. Snapping shrimps can be observed grabbing these drifting leaves and pulling them into their burrows. Very occasionally, it is possible observe a leaf being cut up on the surface. 

Snapping shrimp capturing a mangrove leaf
Observing the snapping shrimps is difficult as during the day, the sky reflects on the waters surface, making visibility through the surface quite low. At night, a powerful light is needed for photography and this usually suppresses snapping shrimp activity.  Once I turned my light out after scanning an area for several minutes and was greeted with roar of snapping shrimp pops. Snapping shrimp may also occasionally respond to snapping noises by making a pop themselves. Popping up my camera flash makes enough noise to trigger the occasional response.

The one time that snapping shrimps are quiet is at high tide. Bream and other snapping shrimp predators can be seen swimming through the milky waters and it is too dangerous for shrimps to be active. On the incoming tide, the shallow film of moving water that snapping shrimps need to catch floating leaves becomes too deep and too swift only sixty seconds after the incoming tide has arrived and they fall silent seconds later.

In the soft muds of the seaward edge of an accreting stilt mangrove swamp, snapping shrimp appear to outnumber crabs. Only in the infrequently flooded and very saline Ceriops swamps do numbers of snapping shrimp fall. The video in this post was filmed in a Ceriops swamp. Sometimes a few snapping shrimps even persist around the edges of salt pans. Middle areas which have a mix of mangrove species seem to have equal numbers of snapping shrimp and crab burrows. This unreported and extraordinary abundance would make snapping shrimps one of the most important components of the mangrove ecosystem.

Two tiny crabs can be seen but the glossy mud surface indicates that crab grazing is insignificant
My work in identifying the species of mangrove snapping shrimp is ongoing. They belong to the genus Alpheus. Alpheus strenuus and A. cf. lobidens are the leading contenders and are found from Australia to at least South East Asia. American mangroves have similar species.

Mangrove snapping shrimp live in burrows that resemble a the branches of a stag horn coral. Several sloping burrows that radiate out from a central chamber. The central chamber can be as much as 0.5 m below the surface and possibly even deeper. Tracing tunnel systems with ones fingers in semi-liquid mud has its limitations. The burrows also sometimes intersect the burrows of animals that I would not like to grab such as mantis shrimp. I have traced several burrows in newly colonised mangrove swamps where the snapping shrimp burrows are first generation and have not become part of an interconnected network of burrows. Most burrow systems have approximately a dozen entrances. Craters may form where part of the branched burrow system has a roof collapse. Originally, I thought the craters were by design and were to increase the surface area water within the burrow mouth to improve oxygenation.

Collapsing tunnels in sandy areas reveal the tunnel structure created by a single shrimp
Usually one or two small snapping shrimp is recovered together with a goby. It appears that even mangrove snapping shrimp have gobies as friends.

Goby and shrimp are rarely observed, the shrimp was touching the goby before the photo.

This goby was restricted to this hole for at least consecutive five days due to very low high tides.
When the tide goes out the goby become a prisoner within the snapping shrimps tunnel complex. In Cairns, which has two tides per day and tides are moderately large, six days can pass between tidal flushing of the seaward zone. That is a long time to be confined to a muddy hole the size of a tea cup. At night, a goby can be seen in one hole in about 50. Only once have I seen a snapping shrimp antenna running over the back a goby and I wonder if the relationship between shrimp and goby is as tight as the relationship is for reef living species.

Goby and shrimp obtained from tunnels in a mangrove creek bank.
There is much more to this discovery that I can report and many of the details remain shrouded in mystery. There is much more work to be done