20 



PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



ASSOCIATION AND DISTRIBUTION OF CORALS. 



In order to carry out a statistical study of the associations and abun- 

 dance of the various species of corals growing upon the great reef-flat of the 

 southeast side of Maer Island, a line (Line No. I, see map of Maer Island, 

 plate 2) was surveyed across the reef. The shore end of this line was 1,496 

 feet in a northeasterly direction from the mouth of Haddon Brook, this posi- 

 tion being just beyond the third stone fish-trap to the northeastward of 

 Haddon Brook. (See map of Maer Island, plate 2 and plate 6 b.) Line 

 No. I was run in a direction S. 39° E. and marked at intervals of 200 feet 

 by stakes driven into the rocky floor of the reef-flat. The depth of water 

 at low spring tides and the character of the bottom are shown in tables 

 I and 2. Table i gives a brief summary, while table 2 presents the results 

 of observations more in detail; and these tables may serve to give a general 

 idea of the changing character of the coral-growth and of the bottom as one 

 proceeds outward from the shore. 



Table i. — Depth of water at extreme low spring tides during September and October 191 J, over 

 Line No. I across the southeast reef of Maer Island, Murray Islands, Great Barrier Reef 

 of Queensland. [This line is 1,689 feet long and extends S. 39° E. across the reef.] 



Distance from 

 shore measured 

 from mean high- 

 tide hne. 



fut. 

 200 



400 



[ ,600 



1,780 

 1,869 



Depth of water. 



inches. 

 4 



4-5 



9 S 



About 8 inches 

 above low- 

 tide level. 



About 14 inches 

 deep. 



Remarks. 



Bottom of firm limestone mud about 4 inches deep, overlying volcanic 

 rock and thickly covered with sea-grass Posidonia australis. No corals 

 here. 



Bottom same as before. A few living corals on erratic limestone boulders 

 which have been driven shoreward by storms. Many sponges, Holo- 

 thuria, and blue star-fishes (Linckia lavigata). 



Clean sandy bottom, overlying limestone rock, without Posidonia. Pot- 

 ites and small stocks o( Pocillopora bulbosa are conspicuous. 



Seriatopora hystrix is here the most conspicuous coral. Bottom rocky, 

 covered thinly in places with limestone sand. 



Siriatopora is here at its acme and covers about a third of this area. It 

 forms masses 4 to 7 feet in diameter, the upper surface being flat and 

 killed at the level of low tide. Bottom of limestone rock. 



Seriatopora is still the dominant coral, but the stocks are all small, evi- 

 dently being broken in time of storms. 



Species of .-Icropora, especially .icropora pulchra, htbes, etc., are here the 

 most conspicuous corals. Bottom rocky and broken. Coral growth 

 is here most vigorous. This is about 200 feet inward beyond the usual 

 surge of the breakers. 



The rigid stems of Jcropora palifera constitute the most conspicuous 

 coral, but the nodular forms of Porites are much more numerous; but 

 due to the strong wash of the breakers, only the stouter and more mas- 

 sive forms of corals can thrive well in this region, and fragile, slender- 

 stemmed forms (such as Seriatopora) are found only in protected 

 crevices. Although most of the coral heads suffer here by rough 

 treatment from the surges, yet this is the region where one finds 

 the greatest number of species of corals, and this despite the fact that 

 coral stocks are not so numerous here as they are 200 feet nearer shore, 

 where the water is less agitated. Thus more kinds of corals live in the 

 region of the breakers than at any other part of the reef-flat. 



This is about the middle of the so-called lithothamnion ridge, a smooth, 

 flat, wave-worn rocky plateau with many small, shallow, crevice-like 

 tide pools, very few of which are more than 6 inches deep. 



This is on the edge of the submarine precipice which forms the seaward 

 front of the reef and which falls ofl^ rapidly into about 25 fathoms. 



