Tuesday, 26 July 2016

What Beach Vegetation was like 30 Years Ago

Back in the mid-1980’s when I first visited the beaches of the Barron River Delta near Cairns in tropical Australia, they had coastal vegetation consisting of open woodland with scattered large old trees, small thickets of saplings and wide open grassy areas.  As the beach was rapidly retreating due to sand mining in the Barron River, the face of the beach was completely covered in fallen woodland trees.  Today beach almond and casuarina trees dominate the foredune and these were planted by revegetation groups in the mid-1990’s.  What was once open and sunny is now heavily shaded forest with an understorey of mainly Singapore daisy.  Coconut palms, which were entirely absent along the uninhabited stretches of beach,  have been planted all over the place by people who think that all beaches need them.

Holloways Beach as it is in 2016 - a vista of Casuarinas and coconut palms
Much of the strand forest is beach almond, which create shady forests
Usually a blanket of Singapore Daisy covers the forest floor
There are some vestiges of old style coastline near Cardwell and along the coastline near Yarrabah, to the east of Cairns and these provide the photos in this post.  Small vestiges also occur on Taylor Point and inaccessible areas of the Cook Highway coastline on the way to Port Douglas.

Holloways and Machans had scattered trees in tall grass (this is Edmund Kennedy NP)
Tall paperbarks occurred in the swales between dunes and made up many of the fallen trees when the beach retreated
Dry rainforest trees occurred in pockets on the edges of the dunes.
Savanna was present on the sandy flats bordering mangroves (Redden Island)
I suspect that I arrived at a particular time when indigenous burning had been suppressed and the vegetation was in the process of change.  Without fire or attempts to graze the land, the vegetation rapidly thickened.  Vegetation thickening is when too many tree saplings become established and they fill up all the space between the larger trees forming what looks a bit like dry rainforest. 

Before thickening the forest had large trees with an understorey of shrubs and blady grass
After thickening, spindly saplings form most of the forest and the understorey plants are virtually eliminated
Since 1994, non-eucalypt bushland trees have replaced the previously grassy understorey and the tall trees have since died
To someone who has seen the bush before thickening, today’s thickened bushland is painful to look at.  When I first saw the north Queensland woodlands they were full of well-formed trees and shrubs that were very healthy and which had attractive dense foliage.  I now suspect this was the first generation of trees growing up in the reduced fire regime and was transitional to the thickened forest that we see today.  Younger people probably think that the forest remnants they see are representative of what once existed, however this is not the case.

South of Yarrabah had seaside eucalypt woodlands in 2016
The tip of Taylor Point has a tall and thriving sward of giant spear grass
For wildlife, I think that the beach vegetation of eucalypt/paperbark woodland with pockets of dry rainforest was more productive for animals other than black cockatoos which eat beach almonds.  In thickened vegetation the bulk of the saplings struggle to survive and barely fruit or flower.  In contrast the understorey shrubs in the grassy woodlands have more space and can thrive and produce much more food for animals.  Finches and wrens love the grass.  On the beach with the blady grass, every metre of beach had wildlife footprints, including water rat, bandicoots, wallabies, goannas, and even crocodile.  It is amazing how much wildlife these area can support in there natural state.

Wallaby and joey footprints on the beach

Sunday, 17 July 2016

Karumba - Queensland's Gulf Coast

Last week, I described the coastline near Innisfail which lies at the heart of the wet tropics on the east coast and in this post I will visit Karumba which is at exactly the same latitude and 580 km to the west in the Gulf of Carpentaria. Latitude is possibly the main driver of biodiversity around the world so comparisons of places that are at the same latitude are informative.  

My time in Karumba was limited and I can only offer first impressions.  The bushland near the coast has trees in a variety of faded hues giving the landscape a pallid appearance that suggests it is lingering rather than alive.  The town itself is bustling mainly with tourists but has an industrial character that comes with being a port which has a fishing fleet and mineral export facilities in a part of the world where few people would choose to live.  However for tourists, the town is an oasis and I went to the tavern for some of the best seafood available to await the legendary green flash which reported to occur when the setting sun kisses the horizon goodbye. 

A road train arrives at the depot in the industrial part of the town
Waiting for the green flash
The moment of truth, sadly it was not a green flash day
Behind the town’s airport was a beach with slabs of beach rock and armies of hermit crabs and further along, a mangrove swamp full of locusts.  The edge of the sea was clear and sandy bottomed and I could only find a few dull grey sea anemones clinging to submerged rocks although aerial imagery suggest seagrass meadows further out.  Near the airport the foreshore has clearly been exploited in years past, probably by mining of beach rock and shell grit which would have been used for construction.  The foredune has developed a sparse scrub of unwanted toxic garden plants that are now considered environmental pests.

All the plants in this view are exotic pests
Hawks, kites and every other kind of raptor are abundant and circling or settled on the low vegetation or the ground.  Kangaroos and wallabies hit by cars probably feed many of the birds however the vast numbers of grasshoppers probably form part of their staple diet as well.  Locusts in mangroves are not unheard of.  Usually they are found in Avicennia mangroves and are large, fast and clever enough to evade my best efforts at catching them.  I have to resort to grabbing them in the fading half-light on the cusp of night when I can see them just that little bit better than they see me.  I used to sell them to researchers who study insect flight.   Yet here in Karumba were so many locusts that birds of prey were ignoring them. 

A kite eating a roo that was pulled out of a bull bar at a truck stop
A locust on a mangrove
The coastal mangroves consisted only of a single species, Avicennia marina.    Nearly all of them were standing on a small arch of stilt roots, a feature not usually associated with this species.  The pneumatophores or pencil roots coming up from the surface were unusually long and thin.  Most of them supported dense colonies of tiny oysters.  I failed to find any fiddler crabs or other wildlife of note.  That suggests that this type of fauna is not abundant but one has to observe a favourable tidal cycle before making such a statement.  Mangrove fauna does not come out when the tides fail to replenish the fertility of the forest floor. 

The swamp had no defined edge with scattered individual trees taking on the sea
Tiny oysters completely covered many of the mangrove breathing roots
Tall and very dense breathing roots
Most of the mangroves had stilt roots at their base
Closer to town, the beach carries a heavy armour of beach rock. Tidal range seems to be comparable to the east coast with a range of approximately 3 m and the stone beach is both high and wide.  Deep fissures separate the stone into tessellating slabs.  A shell grit beach lies in the curve of the bay, possibly were beach rock has been removed and every square inch of this beach has been trampled by terrestrial hermit crabs.  During the day they hide under the slabs of beach rock, in the moist sand. 

Slabs of beach rock
The dimples in the beach are from hermit crab feet
Hermit crabs hiding in a fissure in the beach rock
A large hermit crab, Coenbita variabilis
Karumba no doubt has more to see than I could manage in half a day and I am keen to go back.  In this flattest of landscapes, tidal influence extends at least 40 km inland creating a mosaic of woodlands, grasslands, freshwater wetlands and marine plains.  In stark contrast to similar habitats on Cape York Peninsula, wildlife is abundant.  Time to get off the main road is essential and access to boat to investigate the Norman River or clear shallows of the Gulf would open a range of potentially fascinating places.

Marine plain with river mangroves, 40 km inland

Unfortunately, the only conclusion that I can reach regarding a comparison of the Innisfail coast and Karumba is that possibly rivers are very important in both locations as both beaches were at the mouths of massive river systems and would experience freshwater plumes.  The Gulf can also be more saline than the ocean average, particularly when tides recede from the extensive salt pans, and this would stress mangroves and select for types that can stand high salinities.  In large parts of the Gulf there is almost a total absence of stone so there is very little habitat for animals that need surfaces to attach to or hide under.  If there was one question I would like to work on it would be why were the mangrove ecosystems near Karumba so different from the mangroves of dry places on the east coast such as near Townsville or Princess Charlotte Bay?  

Sunday, 10 July 2016

Where the Sea is not Salty Enough - Mouth of the Johnstone River

When it comes to mangroves, the less salty the environment, the taller and more diverse are the mangrove forests.  The most magnificent of all mangroves are found in the tidal reaches of large freshwater rivers.  Unfortunately the same cannot be said for fauna as diversity drops off quite dramatically as soon as the salinity drops.  In fact with fish, only about 2% of fish species can survive in brackish zone and I am sure that even fewer invertebrates would thrive in this environment.   However to my surprise this effect can even affect biodiversity levels in the sea near the mouths of large rivers.

Aerial view of sand flats in 2013, with river mouth at top of photo
For many years I had been itching to investigate the wide sand flats on the southern side of the Johnstone River mouth in Far North Queensland (Australia).  The Johnstone River flows from the wettest part of Australia, a place which has 4 m per year of rain on the coastal plain and up to 8 m per year in the mountainous headwaters of the river.  Furthermore, the river does not have a large mangrove estuary and pretty much flows straight into the sea.  At the mouth is a sand flat approximately 1.5 km long and 0.5 km wide.  Inspecting the sand flats with GoogleEarth shows several parallel sandbars with darker troughs between.  At Yule Point, the darker areas were fossil coral reef and in the mouth of theBarron River, the darker areas were shallow pools that often contained something whether seasnakes or sponges. 

Large, soft sand ripples and shallow pools
Getting to the sand flats is tidally restricted as one has to cross a small mangrove creek to get there. A few things stand out immediately.  There is grass on the lower creek banks between the mangroves and the channel, an arrangement that I have never seen before and something that is no doubt only possible were the tides pump mainly freshwater.  On the face of the beach is a broad swath of black mineral sand.  Heading out onto the sand flats, the surface had oversize sand ripples which were strangely soft underfoot.  The much hoped for intertidal biodiversity was absent and the sand flats were almost sterile save for saltwater yabby burrows.

Black mineral sand on the beach
Eventually some hundreds of metres from the river mouth, I began to find a few common sand flat creatures but even then, only in low numbers and small patches.  Even on the extreme low tide it seemed that the sand flats were struggling to shed water and emerge into the air.  There was nothing exciting.  Only small fish seemed to inhabit the deeper pools as on account of their mobility they could avoid the factors that were diminishing the intertidal fauna. 

The simplest explanation for the lack of intertidal organisms is that floods and high river flow regularly turn the sea fresh in this location.  The poor drainage of the sand flats would also mean that during a low tide deluge, any sea creatures present would be subject to a torrent of freshwater.  Such exposure to freshwater would kill most sea life.

Persistent sheet of water on flats at low tide well away from the beach
Freshwater seepage pours out of the base of the beach making the beach very flat

The dark troughs between the sand bars turned out to be deposits of dead rainforest tree leaves.  Many of the leaves were still recognisable to species level.  Despite the gift of abundant organic material, there was nothing that I could find that fed on this material, although hermit crabs did appreciate these deposits of flood detritus.  Teredos or ship worms are a marine animal that depends on logs washed into the sea to survive so the concept of marine animals feeding on terrestrial material is possible.  In places compacted deposits of leaf and stem material formed low ‘reefs’ across the sand flats.  I also suspect that these bars and layers of silt were buried under much of the sand flat and accounted for the strange softness underfoot.  It is often said that a particular fossil was formed when a river covered some animal or plant with sediment and here it is possible to see the process in action.

'Reef' of compacted flood debris
Close-up of reef of flood debris
In some places blankets of fresh rainforest leaf litter cover the ground
Moving to the rocks at the southern end of the beach revealed a rocky landscape with a community of algal turf, oysters and a low diversity of marine gastropods.   Some of the marine algae seemed to depend on terrestrial seepage.   Bedrock formed a large part of the coast and every few metres it changed texture and colour as it was probably a contact zone with hot intruding volcanic material.  Between the rock outcrops was a pavement of uniformly sized boulders, all tessellated into position by fierce storms.  In the corner of the bay was more recent evidence for such storms in the way of trees fallen into the sea and root systems exposed by erosion. 

Rocky shore with tessellated boulders and outcrops of bedrock
Mangroves in this area have dayglo green trunks when wet
Strange moss-like algal colonies occurred in seepage areas
The protected corner of the beach was covered with piled up remains of trees due to beach retreat during major cyclones.
In summing up, this location has lush vegetation overhanging the sea and a modicum of scenery but it is not a delightful place to visit.