22 



PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



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

 Ma'er Island, Murray Islands, Queensland, Australia. The depths are those of the water 

 at extreme low spring tides during September and October 191J — Continued. 



Distance from 

 shore measured 

 from mean high- 

 tide line. 



feet. 

 1 ,400 



1 ,600 



1,72s 



1,780 



1,869 



Depth of water, 

 at low tide. 



inches. 

 '4 5 



9 5 



Awash. 



inches above 

 low - tide 

 level. 



About 14 inches 

 below low- 

 tide level. 



Character of bottom. 



Bottom hard and jagged with dead fragments of Acropora. The living 

 stems of .-Icropora hebes, etc., project about 2 inches above low-tide 

 level, but are all healthy and vigorous. Although Acropora is most 

 conspicuous, it is not the commonest coral; the order of frequency 

 is nodular Porites, Seriatopora, Pocillopora, and branching forms of 

 Acropora. Euphyllia grows in protected crevices among the fronds 

 of the Acropora. 



The conspicuous corals are all rigid and thick-stemmed, thus enabling 

 them to withstand the surge of the breakers which reaches them in 

 time of storm. Acropora palifera is the most conspicuous coral, and 

 Acropora hebes is next, but small heads of nodular Poriies are much 

 more numerous, although (being usually only i to 6 inches in diameter) 

 they are not so conspicuous. The bottom is thickly covered with 

 broken, wave-washed Acropora, and the heads of Poriies and other 

 solid forms are much cavernated. A few small stocks of Seriatopora 

 grow in well-protected crevices among the Acropora. The corals in 

 the order of their commonness are Poriies, .icropora, Pocillopora, and 

 Goniastrea. There is very little sand, and dead parts of all corals are 

 cavernated. 



This is the region of broken, detached blocks of dead coral which have 

 been torn from the Lithothamnion ridge and washed inward. These 

 coral blocks are all small, not over I or 2 feet wide, the coral upon them 

 being usually dead and the blocks covered with a green Spirogyra-like 

 seaweed. These blocks project a few inches above low-tide level and 

 are blackened like miniature "negroheads," which, indeed, they are. 

 Corals do not thrive, being broken and disturbed by the wash of 

 breakers and interfered with by seaweed which overgrows them. 



This is about the middle of the elevated "Lithothamnion ridge," a rela- 

 tively smooth, flat, wave-washed platform elevated about 6 to 8 inches 

 above the level of the low spring tides. This so-called " Lithothamnion 

 ridge" is composed of dead, compact coral covered with a veneer of 

 NuUipore alga, Lithothamnion, and Bryozoa. There are many living 

 coral heads, even on the highest part of the ridge, all in small tide-pools 

 and crevices, rarely more than 4 to 6 inches in depth and subjected to the 

 almost constant wash of the breakers. All these corals are rigid, or 

 massive forms clinging tenaciously to the bottom and sides of crevices 

 and growing only on their sides, their upper parts being killed by expo- 

 sure to the air at low tide, so they must spread out laterally. All dead 

 parts of the coral are incrusted by Nullipore algae and Bryozoa. The 

 corals of these shallow tide-pools are thicker, stouter, and with stronger 

 stems than are the stocks of the same species growing within 1,000 

 feet of the shore in calm regions of the reef-flat. This thickening is 

 especially noticeable in Pocillopora and to a lesser degree in Acropora; 

 and in these forms the branches tend to bend inward toward the shore, 

 thus recalling the condition of trees upon a storm-swept coast. Corals 

 which become dome-like heads on the inner parts of the reef-flat grow 

 only into thin incrusting forms in these shallow tide-pools of the litho- 

 thamnion ridge. This so-called "lithothamnion ridge" is a solid mass 

 of dead coral merely incrusted by lithothamnion, bryozoa, etc. Gonias- 

 trea is the commonest coral, with Porites and Favia next in the order 

 named. 



This is the outer edge of the reef which here falls oflT precipitously into 

 water about 25 fathoms deep. From a depth of about a fathom and 

 downward the steep outer wall of the reef is thickly covered with deli- 

 cate foliated corals, such as certain forms of Montipora, but the con- 

 stant breakers prevented a collection being taken in this region. 



