Intertidal Ecology on a Broad ScaleA Study of Certain Aspects of the Ecology of the Intertidal Zone of the New South WalesCoast by W. J. Dakin; Isobel Bennett; Elizabeth PopeReview by: T. A. StephensonJournal of Animal Ecology, Vol. 18, No. 2 (Nov., 1949), pp. 230-231Published by: British Ecological SocietyStable URL: http://www.jstor.org/stable/1601 .

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REVIEWS INTERTIDAL ECOLOGY

ON A BROAD SCALE

W. J. Dakin, Isobel Bennett & Elizabeth Pope (1948). A study of certain aspects of the ecology of the intertidal zone of the New South Wales coast. Australian Journal of Scientific Research, Series B, I: 176-230, 9 photographic plates.

This study is a very welcome one, as it gives us for the first time a clear picture of the intertidal ecology of a long stretch of the Australian coast in a region outside the tropics. It is being increasingly realized at the present time, that in the past intertidal studies have been in- tensive examinations of small areas much more commonly than broad-scale investigations which bring out the bio- geographical aspects of life between tidemarks as well as the local interrelations of limited communities. For some time the main broad-scale studies available have been those of Fischer-Piette on the English Channel, E. F. Ricketts and Torsten Gislen on the Pacific coast of North America and Stephenson and his collaborators in South Africa. Recently, lacunae in our knowledge have also been filled, for instance, by the work of R. G. Evans on the British coast, and by the series of papers entitled 'Contribution 'a l'etude de la repartition actuelle et passee des organismes dans la zone neritique' published by the Soci6t,6 de Biogeographie (Paris, I940). Temper- ate Australia has hitherto been little known ecologically, though a few accounts exist, notably that of Hedley (I9I5) on the Sydney beaches.

The work leading to the present paper was pursued for several years and covered the whole coast of New South Wales, a stretch of about iooo miles. While this coastline offers estuaries, sandy bays, mangrove areas and so on, it was found that the rocky ocean shore presents a clear sequence of zones which is almost the same over more than the length of the stretch studied; consequently attention was restricted to the rocky ocean coast. It is a rather straight coast running almost north and south, between latitudes 28 and 38' S., and presents a series of rocky headlands alternating with sandy beaches, many of the headlands having intertidal platforms at their feet. Annual temperature-curves for a station 4 miles off the land in the latitude of Sydney (near 340 S.) show an average surface-temperature range from about I6 to 23? C., and other data suggest a higher winter minimum (perhaps 2o? C.) at the northern end of the area examined. The tidal range is in the neighbourhood of 6-7 ft. Of the common animal species between tidemarks the majority extend throughout the coast in question, which seems to represent a fairly distinct biogeographical area (Peronian province of certain systematists). There is, of course, some north to south change, and the appearance of the large Bull Kelp (Sarcophycus potatorium) near the southern end of the stretch is an example of this. The authors distinguish three principal zones, from below upwards, as follows:

(i) The littoral-sublittoral fringe. This has two sub- divisions: (a) a- kelp zone characterized by large brown algae, Ecklonia radiata and Phyllospora comosa, often re- placed by the red Pterocladia capillacea in situations too exposed to favour the brown weeds; and (b) a zone typic- ally densely populated by the large ascidian Pyura praeputialis.

(ii) The mid- and upper littoral. Here again we have two subdivisions: (a) the Galeolaria zone, characterized by a dense growth of the polychaete Galeolaria caespitosa, which forms masses and sheets of limy tubes resembling coral; and (b) a zone in which barnacles are abundant, several species being present and forming a sequence.

(iii) The supralittoral. The highest zone, extending well above tidal levels, has a population of littorinid snails, Melaraphe unifasciata and Nodilittorina tuberculata.

Following the account of the typical zonation is a dis- cussion of the geographical range of the 'basic associa- tions'. Nine ecologically important species are listed which disappear or become reduced in numbers either northward or southward on the coast; five of them being southern forms which fall off to northward, three warm- water species falling off to southward. The ninth appears to be limited to the New South Wales coast, and wanes both north and south.

The next section describes the common animals associated with the zones recognized; and throughout the paper variations in the zonation connected with differ- ences in degree of shelter from or exposure to wave- action, and other environmental factors, are recognized. At the end is a short discussion comparing some of the features of the New South Wales coast with similar features in other parts of the world.

In his monograph on the animal geography of the sea (I935), which rather surprisingly is not mentioned in the bibliography to this paper, Ekman says that the littoral fauna of Australia is divisible zoogeographically into two regions, a tropical-subtropical and a temperate; the boundary between the two, on the east coast, lying about 350 S. in the Sydney region. He classifies the southem fauna as a warm-temperate one. From the account given by Dakin and his associates, the whole New South Wales coast has the appearance, ecologically, of a warm- temperate region, though this appearance has yet to be substantiated by a fuller analysis. Should it prove to be warm-temperate rather than subtropical, the transition from tropical to temperate must actually lie farther north than Ekman supposes, nearer 28 than 350 S. The next step will be to discover whether, as we suspect, there follows a cold-temperate region to southward of the one here described; it seems doubtful whether the whole of the temperate part of the Australian coast is warm-temperate.

One of the most interesting features of this stretch of Australian coast is that in some ways it presents very close ecological parallels to the South African coast, and the memoir is written in such a way as to make the results presented comparable with those of Stephenson and his associates in South Africa. The authors point out some of

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Reviews 23 I

the similarities, for instance the amazing low-level de- velopment in both countries of a community of leathery ascidians (Pyura). The comparison could actually be carried a good deal further than the authors take it, how- ever, and they seem to have missed, for instance, the fact that their Galeolaria association is paralleled so exactly in South Africa by that of another polychaete, Pomatoleios crosslandi, that when the South African survey started the Pomatoleios was at first thought to be Galeolaria. The similarity is readily seen in some of the illustrations to the South African series, e.g. T. A. and A. Stephenson and Bright, Ann. Natal Mus. 9: P1. I; T. A. Stephenson, Ann. Natal Mus. IO: 303 (text-fig. 8), Pls. XII and XIII. Another interesting resemblance lies in the fact that one of the characteristic low-level kelps of the New South Wales sublittoral fringe is Ecklonia radiata, whereas on part of the South African coast a closely similar plant, E. biruncinata, occupies the same ecological position, and was earlier identified with E. radiata.

There is an epic misquotation on p. 195. Referring to the Pyura community in South Africa, the authors quote Stephenson as follows: 'this leathery ascidian conceals the rock in incredible numbers, closely packed; it must cover, altogether, many inches of rock'. For 'inches', read 'miles'!

The authors have not worked out the biogeographical implications of their work in any detail, and one feels that it might have been carried considerably further in this direction. They introduce a new term 'littoral-sublittoral fringe', which is quite unnecessary, as it is the same thing as the 'sublittoral fringe' of Stephenson, a term which is beginning to come into general use. The paper, however, is an excellent contribution and represents a very decided step forward in the attempt to produce a world-wide picture of plant and animal life between tidemarks.

T. A. STEPHENSON

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