I have not mentioned, so far in this blog account, the complexities that we have faced working this part of the coast from the boat's perspective. Starke river flows out onto a shallow extensive flat which meant that we can only bring the boat near shore with the right tide heights. We were fortunate the wind direction stayed fairly constant, as if it had shifted a bit too much to the East we would not be able to work at all. This did happen, just on one day, and we could fortunately shift our activities to the smaller turtle boats and do water quality studies in the river as a fall back. As it was, the wind stayed in the south-east, blowing us day and night but not too hard to make our work impossible.
Above is a view of the Starke River and connected waterways meandering to the sea. (Pic- Chris Roberts). You can make out the shallow bay beyond. You can also see the dunes system, the flecks of white on the horizon, that makes up part of the coastal geography of the region.
Hugging coast and river systems and ringing all the small islands or cays in the upper half of the intertidal zone of coastal areas worldwide are complex networks of mangroves. Mangroves are masters in dealing with the intertidal world of shifting waters, sediment and salinities. Turtle island group, which we visited again with another group from the camp, has three main species working their mangrove magic. But first the journey out...
As we were travelling Chris gave a short talk about coral (staghorn coral-pictured) and showed some living coral as we had only been looking at all the skeletal remains of coral on the shoreline. You can see in the second photo the living polyp emerging from the coral form.
Landing on the island we headed off to explore the edges and familiarise ourselves with the mangroves. 'Cape York has one of the highest speciies diversity of marine vegetation in the world. It contains 36 mangrove species compared to nine in south-east Queensland and one in Victoria (Duke 1992)' (From NATURAL RESOURCES ANAYLISIS PROGRAM (NRAP) MARINE VEGETION OF CAPE YORK PENINSULA. Karen F. Danaher Queensland DPI 1995)
The stunted bonzai mangroves were Avicennia marina or Grey mangrove. They are the only species that extend as far south as Victoria (in fact the only species as we only have Grey mangroves there.) They are characterised by pen like pneumatophores or aerial roots, which in the case of the Turtle group are also bonzaied daily by chunks of coral and calcareous debris, scarifying the upper reef flat. Chris was saying that he would not be surprised if 100 year old trees are barely a meter tall in that environment.
Above the rubble zone Ceriops tagal var. australis or Spurred mangroves occur. They have small strong buttresses to hold themselves upright in more extreme weather and tend to prefer a little more leeward and protected areas.The large stilt rooted mangroves occur where sediment begins to be able to drop out of the water column and to some degree produce their own environment as the stilt or prop roots of these Red mangroves (Rhizophora stylosa) slow the water enough to allow sediments to drop. These trees are found in the front line where their seeds can take root. Behind them we find Brugiera gymnorrhiza (Orange mangrove) which has tell tail "knee roots".
Much information was shared over the project about the importance of mangroves systems to the health and ecology of the coast. '75% of the total seafood landed in Queensland comes from mangrove esturine related species.' (From The Great Barrier Reef - Biology, Environment and Management-Pat Hutchings, Mike Kingsford and Ove Hoegh -Guldberg)
They are literally the architecture for a host of marine and intertidal species who shelter and feed in their dense forests and complex roots. Researching this I also discovered that the Green turtle is known to eat mangrove propagules during high tide. The relationship of the health of the mangroves to healthy populations of sea turtle and dugong is of deep interest to the Bama. ('The word ‘Bama’ (pronounced Bumma) is widely used throughout Cape York to mean an Aboriginal person, but in both Kuku Yalanji and Guugu Yimithirr the word simply means ‘person’ regardless of nationality or race.')
A recent study has found that tropical mangroves store more carbon dioxide than most other forests. Which is another reason to both understand and protect these ecosystems. Unfortunately these systems are under threat. In the Great Barrier reef region this is not only due to global warming and coral bleaching but due to a century of large scale land clearing and the conversion of 'GBR catchments into agricultural, port, urban and industrial developments.' (From The Great Barrier Reef- Springer)
Below is a photo of a Bristle worm reaching tentacles into the rising tidal waters of the island.
Other inhabitants of the island foreshore. I should title this picture. Rubbish and Irony!
Chris making his way back to the boat after another day's teaching on the island, carrying some interesting found objects. In his left hand is an example of the shell of an extremely large sea snail and the largest Recent shelled gastropod (Syrinx aruanus- Australian or false trumpet) -which he used as a teaching tool before dropping it back on the island. An interesting fact about molluscs in the GBR is that there are no non-native or introduced species among them.
Pelican readying for the journey back to the mainland.
Portraits of some of the Hope Vale participants of the days events. Trisha Gordon, Tellisa Pearson, Shaunica Lee Cheu, Teresa Thompson, Shaunica again and Ronan Bally with Austin Bally.
Thank you to Chris Roberts for all the mangrove knowledge!