ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 



21 



Table 2.— Depths of water and character of bottom along Line No. I of the southeast reef of 

 Maer Island, Murray Islands, Queensland, Australia. The depths are those of the "water 

 at extreme low spring tides during September and October 1913. 



Distance from 

 shore measured 

 from mean high- 

 tide line. 



feel. 

 200 



400 



600 



675 



800 



Depth of water 

 at low tide. 



inches. 

 4 



4 5 



6.S 



10,5 



16.25 



Character of bottom. 



Thin layer of limestone mud overlying a firm hard bottom of lava rock, 

 covered quite thickly with Posidonia. There are no corals here. The 

 tide goes out almost to this point and even 70 feet beyond it in places. 

 The bottom consists largely of finely broken shells of mollusca and 

 minute fragments of coral. There are no coral heads of any sort here, 

 not even dead and corroded coral blocks. 



Bottom of firm limestone mud, consisting of broken and dead fragments of 

 shells, corals, etc., and thickly covered with Posidonia. Loose corroded 

 blocks of dead coral evidently driven inward from the outer parts of the 

 reef-flat are found here, and the only living corals growing here are 

 attached to these blocks. These blocks of dead coral do not commonly 

 occur within 350 feet of the shore and evidently the waves (even in time 

 of storm) have not sufficient force to drive them ashore. Holothuria atra, 

 sponges, and blue-star fishes {Linckia Iwvigata) are common here. The 

 Posidonia extends about 460 feet out from the shore, beyond which the 

 sandy bottom is barren of green seaweeds save for a few Nullipore algae. 



Bottom barren of green sea-weeds, firm and sandy, and composed of 

 finely broken shells and fragments of other limestone-bearing organ- 

 isms. Most of the corals are growing upon eroded fiat blocks of lime- 

 stone which the waves in time of storm have evidently driven inward 

 from the outer parts of the reef. Pocillopora bulbosa is a dominant 

 coral, but the species of Pontes are even more abundant. At about 500 

 feet from shore Porites andrewsi is one of the commonest corals, but it 

 declines in numbers as one goes outward over the reef, and practically 

 disappears about 1,100 feet out from shore. 



The corals here are chiefly attached to the bare limestone floor of the reef, 

 although there is still much coral sand and many flat, unattached cor- 

 roded coral blocks. Branching Acropora appear here, and small stocks 

 of Seriatopora hystrix are rather common. 



Seriatopora is now the dominant coral, forming clusters which often 

 become conjoined and may be 5 to 7 feet in diameter. They are all 

 killed at low-tide level, and are thus flat-topped and dead above, only 

 the outer margin being alive and growing. Several nodular forms of 

 Porites, branching Acropora, Goniopora, and Pocillopora are represented 

 in the order named, the commonest being first named. The bottom 

 here is hard limestone with but little coral sand. 



The Seriatopora is here at its acme and covers about three to four tenths 

 of the area of the reef in this region. Nearly all other forms of coral are 

 relatively rare in this region, although they may be common both nearer 

 shore and near the outer parts of the reef-flat. Next to Seriatopora, 

 the most abundant corals are Porites, Acropora, Goniopora, and Euphyl- 

 lia. The bottom is hard and rocky wirh almost no coral sand. The 

 living coral here is growing vigorously, very little dead coral being 

 seen. The Euphyllia grows in crevices where it is protected from the 

 waves. 



Bottom hard and covered with broken stems of Acropora. The Seria- 

 topora is still the dominant coral, but there are no large stocks and the 

 coral is evidently broken by surges in time of storm, thus scattering 

 small, detached, loose-lying stocks over the broken limestone bottom, 

 which affords them a good lodgment, so that they continue to grow. 

 There is very little sand upon the bottom here. The commonest corals 

 are (in the order of their frequency) Seriatopora, Porites, Pocillo- 

 pora, and Acropora — Acropora and Seriatopora being the most con- 

 spicuous; the nodular forms of Porites consist of numerous small heads. 



