Tuesday, 23 February 2016

Around the Rocks at Island Point – Port Douglas

Sometimes you can't get to the Great Barrier Reef because there is not enough time, the sea is too rough or you can't afford it. It is always good to know a few areas that are easy to get to and that can provide a little adventure.  Today, I walked around the sea coast of Island Point which is at the end of the famous Four Mile Beach at Port Douglas.
View from near near Port Dickson (click photos to enlarge)
View from near Four Mile Beach
This time instead of clambering over the cliffs at the Four Mile Beach side of the headland, I walked in from the Dickson Inlet side, which proved far easier.  On rounding the first corner, all of the bustle of the busy tourist port was left behind and it was like being on a deserted tropical island.  It is the kind of place Bear Grylls uses to challenge modern humans.  It was 37 degrees Celsius, and despite a sea breeze in the Port, the rocky coast was almost airless and 100% humid, right in the danger zone for the unacclimatised.  Visiting this area requires the crossing of almost a kilometre of large round boulders.  These boulders have a layer of ancient blue green bacteria (Nostoc) which is natures first attempt at a non-stick coating.  Finally, with the mangroves being close there is a low but credible risk of crocodiles, there are nasty oyster reefs and the rocky coast is where the toxic jellyfish breed so swimming around the headland is not recommended.  If you are are fit and take care then you will be rewarded with a rugged coastline featuring dozens of rock pools full of darting fish.
A rock pool with a black sea sausage
Juvenile diamond-scale mullet and two sergeant majors
Most of the fish present are specialised for living in rock pools and include a variety of gobies, pipefish, dart fish and juvenile reef fish which use rocky coasts as a nursery.  If it is high tide or if our seasonal 15-20 knot trade wind is pumping large waves onto the coast, very little of this marine life will be visible.

Higher up are smaller pools in the black rock.  These have grazing snails and sometimes even have live coral! It seems that under the right conditions, coral is even tougher than algae.  The rocks were so hot that the limpets were almost being cooked alive.

Most of the bottom of this tiny pool is covered by colony of hard coral.  It has a touch of bleaching on one edge.
Nerita costata snails feed on the thin layer of algae
Heat-stressed limpets were holding their shells as high as they could to cool down
The sub-tidal zone is dominated by brown macro-algae and black sea urchins (Diadema).  I do not know if this community is a recent community that has developed due to climate change and loss of coral.  Until recently it was incredibly hard to make an environmental record, there were no GPS, no cheap underwater cameras and each photo cost a dollar which is probably 1000 times the cost of a digital photo.  I only have fading memories of what places used to be like twenty years ago and these often do not include vital information such as which season it was.

The coast that I observed a few days ago is not that different to temperate coasts where algae dominate the swash zone.  Under the water, algae cover the rocks and a few metres further out the rocks give way to sand flats.  In this underwater rock garden, sea urchins are the gardeners.

Boulders quickly give way to a sandy seabed 
Diadema sea urchin
Close to then end of the headland, rainforest gives way to patches of natural grassland with pandanus trees due to the constant blasting of wind and salt spray. Up the top, parts of the hill belong to very rich people so avoid the temptation of bush bashing up the slope.  To get to the top, find the path at the end of the headland.

As with any posts on this blog, original photos and data are available to anyone doing biodiversity studies.

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