Saturday, 10 March 2018

Fish spawning in the big wet

The day after the 2018 March deluge stopped, the local stormwater drain was full of fish. Not just any fish but strikingly colourful fish. These fish had come to spawn. They are all native fish that are usually brown, but on this day they were dressed up to impress. Two species were putting on a show, snakehead gudgeons and empire gudgeons. Snakehead gudgeons, not to be confused with Asian snakeheads or fishzilla, are a native Australian fish of mangrove estuaries.

Giurus margaritacea
The females were fat with eggs and males where brightly coloured (click to zoom)
Giurus margaritacea
A pale snakehead with bright ventral fins
The snakeheads gudgeons slowly circled in the main pool with males showing their colour to the females. There were two males and each time one made a move toward the girls, the other would approach and swim beside the first male to make sure that the girls knew he was there too. I did not see any fighting and the boys sometimes followed the girls and vice-versa. It was speed dating in slow motion and eventually the girls decided who was best.

Giurus margaritacea, courting
Two males trying to entice a female to their corner of the pond
Around the edges of the pool were bright red male empire gudgeons. At about 8 cm long, they were so full of confidence, that they were even approaching the 25 cm long snakehead gudgeons, which annoyingly had large patches of red. By the afternoon the empire gudgeons were gone, probably having expended themselves, they had ceased displaying. Their colours would have back to mostly brown although the keep their red head.

Hypseleotris compressa, male in breeding colours
Male empire gudgeon displaying on wall of drain
Surprisingly, the drain was almost empty before the deluge. Only a few rainbow fish (Melanotaenia splendida) had colonised since the wet reestablished a persistent pool at the outlet of the drain. In dry years, the drain can be dry for most of the year. During the wettest years, it can flow for most of the year and can support a diverse freshwater fish community of a dozen species. Being above normal tidal limits, the water within the drain is completely fresh, unless an extreme tide pushes in. Paperbarks and beach hibiscus line the drain and the beach hibiscus have grown long trailing roots into the flowing water, which now form a thick mat that the migrating fish have to negotiate.

Hibiscus tiliaceus creates deep root mats in flowing freshwater
Giurus margaritacea  close-up of head
Female snakehead gudgeon resting in the root mat
The drain is somewhat special. It is near the mouth of a river, so when the juveniles of freshwater fish are flushed out by floods, they often attempt to swim up the drain. Originally, before development, there was supposed to have been a drainage line in much the same position. Small creeks and drainage lines would once have been common but now have been replaced by farm drains and urban drains. There are not many small intact waterways which flow during the wet but dry out and prevent common freshwater fish such as guppies, tilapia and even native jungle perch from dominating the ecosystem. Perhaps this explains the desire for the gudgeons to breed in this waterway. 

Pool where water leaves concrete drain
stilt mangroves
25 metres below where the drain emerges,the freshwater flow fans out in a mangrove swamp
In the late afternoon, I decided to put my underwater compact camera on a pole and push it below the surface to see if I could get some close up photos. As I can’t clearly see what the camera is shooting, I use video, then create stills from the video. It was almost unbelievable, what the camera recorded. The fish were in the process of spawning when videoed.

The next day, I went back to try and get some new shots and the fish were largely gone. Only two or three snakehead gudgeon were present and they were much more wary of people and darted for cover. Males of both species were loitering and hoping for late females, but had lost most of their colour and enthusiasm. They only consolation was that I was able to photograph the very tiny eggs (white specs) that had been glued on dead wood the day before. The video clip shows these very eggs being deposited.  Firstly the female glues them to something with the pink appendage and then the male fertilises them (not visible in this clip) using a similar pink appendage.

Giurus margaritacea
Tiny white eggs deposited on a stick
Whilst I have called the fish snakehead gudgeons, I am not totally sure as they were identified using photos from the net. Usually, spangled gudgeons (Ophiocara porocephala) are the main local species and are of similar size and shape. So few photos of the fish in their breeding colours are on the net, that positive identification is difficult. Usually, it is best to review several sources, particularly authoritative sources before labeling species.

Spangled gudgeon usually hunt around this area.

Monday, 26 February 2018

When the Great Barrier Reef was a land of hills and trees

There is a great deal of academic research being conducted into how and when Aboriginal people arrived in Australia. The one be assumption is that people arrived when sea levels were at their lowest, to as much as 130 m below present levels during glacial periods. Lower sea levels reduced the gaps between land masses and are thought to have made island hopping much easier. At these times, all of the coral reefs we know today would have been on land. The Great Barrier Reef was a chain of limestone hills. All of this was only 10000 years ago. This transformation between terrestrial ecosystem into marine fires the imagination. What would it have been like to wander in a landscape where coral reefs were hills? There places on earth where it is possible to do so today. One of those places is the coast of Papua New Guinea. 

Diagram from Sceptical Sciences
On the southern coast of PNG, at a place called Bluff, which is in Gulf Province near Kerema there are a few uplifted coral reefs which are morphologically similar to the reefs of the present day Great Barrier Reef.  The headland of Bluff is one such old coral reef. It is formed of dense coral rock where the detail of the polyps has been lost. Caverns run through the headland.

This headland has a legend about a battle between a hunter and boar.
One of the caverns which face the sea and are partially filled at high tide

Not much detail in the rock, mainly live embedded sea anemones

To the north of Bluff is a low linear plateau with coral reef and rubble slopes on its southern end. Gulf Province is a land of large rivers that pump out stupendous quantities of sand and mud and looking now, I think the plateau is formed mainly from mud stone or argillite with a veneer of coral.

Waterfall from top of plateau, which is only about 20 m high.
Gulf Province has about 9 m of rain each year and the land is sparsely settled area of swamps and heavy jungle. The plateau is the only raised land for several kilometres. No-one lived there although springs on the side of the hill did provide drinking water for local villagers. 

Waterfront at Kerema 2012, plateau visible in background
The southern end of the plateau has sides covered with coral rubble which often has well preserved polyps. 

Coral colonies are clear visible
Coral rubble from beside drinking water spring
Ancient coral colonies become boulders on the beach.
On the western face of the plateau are some small caves and grottos. After squeezing into one grotto, I found that I was less than a metre from a rather deadly looking snake. I later identified it as a viper boa and not a viper. Viper boas are a type of boa, like a python but as they have live young are a boa and not a python. 

Entrance to a grotto which opens up inside
A viper boa was inside (Candoia aspera)

Also in caves were enormous cave crickets. They were lined up on the ledges and scurried around when I got close.

The limestone nature of the hills was clear from the cave features such as shawls that were developing in larger caverns.

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 frontalis)
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.