A reef walk in Boat Bay

All photos by Jeff Larson

By Dr Helen K. Larson - Wongaling Beach

On 29 August 2011, a small group of us went for a spring tide (0.5 m low) walk in Boat Bay. “We” being myself, Jeff Larson, Tony O’Malley, Liz Gallie, Maurie Franklin, Peter Rowles, Attie Willy and David Tofler. It was a walk that I had been promising myself since we moved here nearly two years ago. Because I had not walked here before, I did not know if the amount of mud we observed was usual for the time of year or whether the bay had accumulated more sediment since TC Yasi. Close to the shore the mud was occasionally thick between the rocks.

Helen (with net) explaining what fun mud is, with Tony (with bucket) trying not to get his shoes dirty.

              Further out from the mangrove shore was less muddy, although a film of it covered most organisms, except for those such as the corals, which use their clear mucus to slough off sediments.

             Faviid corals like these exude mucus while they are exposed, to keep themselves from drying out and to protect themselves from the sun.

             Soft corals like this Sarcophyton don’t have a stony skeleton to keep them upright, so they collapse like leathery cushions. Soft corals also produce copious mucus to keep themselves damp and which include substances to protect themselves from the sun - their own sunscreen.

         We turned over rocks and turned them back the way they were, we poked with our fingers and dipped with small nets.

               And what did we find? Some creatures were rather beautiful, like this elegant nudibranch. These shell-less molluscs eat soft corals and other sessile animals.

   We found a young cowry, alive under its rock. These have the most beautiful shining shells and the thin fleshy mantle that covers the shell (when it isn’t alarmed and sitting in somebody’s hand) is very beautiful too. Like all the creatures we uncovered, this one was put back in its spot.

            Some of the things we found would also be called beautiful if you were an ichthyologist like me, but others didn’t seem to think so, such as this very well-disguised and very venomous Estuarine Stonefish (spotted by Liz).

The stonefish sat quietly with its tail curled up while it got moved about and its venomous spines erected by a stout pair of forceps, convinced that it was invisible in its coat of mud and algae, even though I had moved it onto my scoopnet so it could be seen more easily.

A young Milkspot Toadfish was very relaxed – we handled it gently so that it did not puff up in self-defence, though it kept a wary golden eye on us. These puffers are estuarine specialists, they like mud and mangroves. It will be interesting to see if this species still remains on the Boat Bay reef a year later – or if it has moved closer to the shore-hugging mangroves.

            It was very pleasing to see young staghorn corals growing among the muddy rocks; there may be whole beds of these just further offshore, we will have to go snorkelling in the bay next time.

These staghorns are classic corals. There were many very old chunks of large staghorn fragments all through the substrate, so Boat Bay clearly once had large beds of these corals. Many fish and invertebrates live among and within their branches.

This Chelonia mydas, Green Sea Turtle, Cheloniidae was very thin and unwell. Attie and David took it and another found later to the Cairns turtle rehabilitation centre. This one shown recovered completely and has been released!

We were walking in shallow, rather turbid water so could not see if any seagrass beds were present. Various algae (seaweeds) were regrowing after TC Yasi, or had survived being knocked around anyway. In this photo you can see two species of the green calcareous Halimeda, as well as various kinds of fine coralline red algae and fleshy brown algae.

Here is a list of the live plants and animals that we saw, with their scientific and common names as far as I can determine and the families to which they belong. I have forgotten too much marine botany! We would have missed seeing many animals as they were hiding in burrows and crevices awaiting the return of the tide.

Plants

Bryopsis sp., a feathery green alga, Bryopsidaceae
Dictyosphaeria cavernosa, a green alga, Siphonocladaceae
Padina sp., a fan-shaped brown alga, Dictyotaceae
Halimeda cylindrica, a fine-branched calcified green alga, Halimedaceae
Halimeda spp., other species of calcified green algae, Halimedaceae
Sargassum sp., sargassum (a brown alga), Sargassaceae
Neomeris van-bosseae, a calcified green alga, Dasycladaceae
Caulerpa racemosa, a “bunch of grapes” green alga, Caulerpaceae
Amphiroa probably , a fine-branched coralline red alga, Corallinaceae
Trichodesmium erythraeum, “sea sawdust”, a marine blue-green alga, Oscillatoriaceae
Many unidentified red and brown algae

Invertebrates

Acropora sp., staghorn coral, Acroporidae
Favites sp., faviid coral, Faviidae
Porites sp., porites coral, Poritidae (this is the ‘micro-atoll’ or bommie coral)
Palythoa sp., colonial zooanthid, Zooanthidae (look like soft corals but they aren’t)
Sarcophyton sp., leather soft coral, Alcyoniidae
Nassarius dorsatus, Dog whelk, Nassariidae (super-scavengers)
Alpheus sp., Snapping shrimp, Alpheidae
Unidentified hermit crab, Diogeniidae
Palaemon sp., Rock-pool shrimp, Palaemonidae
Portunus sp., juvenile swimmer crab, Portunidae
Pinna bicolor, Pen shell, Pinnidae
Cypraea gracilis, Graceful cowry, Cypraeidae
Glossodoris atromarginata, Black-margined glossodoris (a nudibranch mollusc; has a small shell), Chromodorididae
Unidentified shy octopus
Holothuria atra, Black seaslug, Holothuridae
Several unidentified small seaslugs

Fish

Periophthalmus argentilineatus, Silver-lined Mudskipper,Gobiidae
Pseudogobius sp., Mangrove fatnose goby, Gobiidae
Favonigobius melanobranchus, Blackthroat Goby, Gobiidae
Sillago spp., juvenile and post-larval whitings, Sillaginidae
Gobiopterus sp. Glass-goby, Gobiidae
Pelates sexlineatus, Eastern Striped Grunter, Terapontidae
Trachinocephalus myops, juvenile Painted Grinner, Synodontidae
Himatura granulata, Mangrove Whipray, Dasyatidae
Neopomacentrus taeniurus, Freshwater Demoiselle, Pomacentridae
Synanceia horrida, Estuarine Stonefish, Synanceidae
Unidentified post-larval clupeioids (just settled-out baby sardines and/or anchovies)

Reptiles

Chelonia mydas, Green Sea Turtle, Cheloniidae

Birds

Fregata ariel, Lesser Frigate, Fregatidae
Hirundo neoxena, Welcome Swallow, Hirudinidae
Todiramphus sanctus, Sacred Kingfisher, Halcyonidae
Haliaeetus leucogaster, White-bellied Sea-eagle, Accipitridae
Pandion cristatus, Eastern Osprey, Accipitridae
Thalasseus bergii, Crested Tern, Laridae