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?