Tuesday, 8 November 2016

Coral Cay Island Birds – Great Barrier Reef - Part 1 Background

In late October and early November 2016 we were very fortunate to join my brother and his partner on their 46 ft. catamaran Alchemy 1 for two weeks sailing along part of the Queensland coast and the adjoining offshore Great Barrier Reef (GBR).

Alchemy 1

We joined the yacht at Yeppoon Marina and over a two week period sailed south past the Keppel Islands, through the Narrows between the mainland and Curtis Island, through a very busy Gladstone Harbour and on to Pancake Creek at Bustard Head. Then we went about 60kms out to Fitzroy Reef, a typical platform coral reef with lagoon, at the northern end of the Bunker Group. Next we went south east through the Bunker Group to its southern most island, Lady Musgrave, where we anchored in the lagoon for a few days. After that we sailed south again to Lady Elliot Island and then across to the Burnett River near Bundaberg. Finally, we headed south to Hervey Bay at the top end of Fraser Island and then on to the marina at Urangan where we left the yacht.

Along the coastal sections of our journey some highlight birds included White-bellied Sea-Eagles, Brahminy Kites and Eastern Ospreys, with Eastern Curlews and Whimbrels on the mangrove mud flats and a range of other shore and sea birds including cormorants, darter, gulls and terns. However, the real birding highlight for me was the coral key island birds we saw at Lady Musgrave Island.

Lady Musgrave Island (courtesy of Google Earth).

This photo taken from space of Lady Musgrave looks a little like a sectioned kidney. The coral cay island is located on the lee or NW side of the coral reef platform, the white fringe on the SE side is breaking surf on the outer reef edge, the inner lagoon is dark and light blue (deep and shallow water respectively) and an entry channel can be seen as a dark blue line above the Lady Musgrave Reef label. The grey/brown colour is coral reef.

We had many snorkelling sessions on the reef, both at Lady Musgrave and at Fitzroy Reef (which has a lagoon but no island). To explore the large number of colourful coral species and the associated marine life including a dazzling array of colourful fish species is truly a great experience.

Lady Elliot Island which lies about 37km SE of Lady Musgrave, is the southern most coral island on the Great Barrier Reef. The GBR is about 2,000km long and extends all the way to the top of Cape York. The GBR is only about 5,000 years old, about the age of the Great Pyramids, and was built by a multitude of tiny coral polyp species – a truly phenomenal World Heritage listed structure.

Lady Musgrave Island is unique on the GRB as it is the only Coral Cay Island with a lagoon that has a navigable channel, allowing access by boats into the lagoon. We were able to live on the yacht in the lagoon for 4 days, go snorkelling on the reef and visit the island in the yacht’s dingy and observe birds and other marine life passing over the lagoon or swimming by – a unique experience in a unique environment.

Setting off for a snorkelling session on the Lady Musgrave reef.

Lady Musgrave Island is part of the Capricornia Cays National Park which covers the Capricorn Group and the Bunker Group. The two groups straddle the Tropic of Capricorn (Latitude 23026’05”). The coral cay islands are important breeding sites for a number of sea bird species and also Green Turtles. While we were there Black Noddies, Wedge-tailed Shearwaters, Bridled Terns and Green Turtles were breeding. Brown Boobies were breeding on nearby Fairfax Island.

Lady Musgrave Island is an end stage in the coral cay island building process. The island is built from pulverised coral and marine mollusc shells which form graded materials ranging from cemented limestone rock and un-cemented rubble through to fine sand. Wind, tides, waves and currents work the materials into sand cays (islands) which are colonised at first by hardy grasses followed by a succession of shrubs and eventually trees. Birds and turtles soon use these islands for resting and breeding. The birds in turn bring nutrients from the sea and, together with their dead bodies, over time help form soils rich enough to support large trees such as the unique Pisonia Tree (Pisonia grandis). A perched fresh water table below the sand island which sits atop the denser salt water layer is also an important component of the island structure as this fresh water supports the larger tree species.

The following photos taken on Lady Musgrave Island and accompanying captions show the physical structure and small number of typical coral cay island plants which are so important for breeding sea birds.

Typical section of Lady Musgrave Island shoreline - photo taken from the dingy.

Cemented limestone rock which fringes the SE and N sides of Lady Musgrave Island. This rock allowed sand to accumulate and provides ongoing protection again wave erosion.

Coral and shell rubble coated in brown algae on the way to becoming sand.

Finer coral and shell fragments including the pulverised end product, sand.

Sandy beach above reef rock with Casuarina equisetifolia and Pandanus tectorius, both occupying the edge of the beach in the most exposed locations and then a Pisonia tree to the right. The Pisonia trees form a jungle that dominates the island.

Tournefortia argentea (tree heliotrope) in front of Pandanus Palms was the other common small tree/shrub that fringed the beach.

The Pisonia jungle dominates the island. Thousands of Black Noddies were building nests in the pisonia as well as the casuarina and pandanus.

Some of the pisonia trees are old and large.

Coral cay islands are fascinating ecological systems located well out to sea away from mainland predators. Breeding birds are relatively safe here and often allow close approach compared with much warier mainland bird species.

We did not see or hear any land birds on Lady Musgrave Island though an information board indicated Silvereyes may be present and no doubt a variety of vagrant land bird species turn up on the island from time to time.

We saw many pairs of Green Turtles mating in Lady Musgrave lagoon.

Green Turtles mating.

Tracks made by female Green Turtles hauling themselves up the beach at night to suitable sandy locations where they laboriously dig holes to lay their eggs.

The next post (Part 2) will cover Black Noddies, which we saw both out at sea in small to large feeding flocks and in the thousands on Lady Musgrave where they were breeding.

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