14 
THE SEAWEEDS 
and provide fresh supplies of oxygen. Destroy all the seaweeds and the 
harbours will inevitably be polluted. 
The grasses and other forage plants constitute the foundation of all 
terrestrial animal life. “All flesh is as grass,” may be truthfully rendered 
“All flesh is assimilated grass.” For the herbivorous animals tins is true 
directly, and for the carnivorous intermediately. All animal material 
and energy is derived ultimately from the plants. 
In the same way all marine animal life depends upon, and has its basis 
in the marine plants. The algae, unicellular green plants and diatoms, 
floating in the plankton, manufacture their substance from inorganic 
matter and utilise directly the light energy of the sun. Smaller animals 
(crustacea, &c.) feed on them. Surface feeding fishes and the great whales 
themselves’ feed on this small fry. The surface-feeding fishes descend and 
some of them fall a prey to the inhabitants of the zone below. These again 
descend to further depths and serve as the food supply to a lower zone of 
life- and so, proceeding downwards, ultimately the abysmal fish and squids 
obtain their source of life from food derived from plants of the ocean 
surface. 
In similar fashion life spreads outward from the fringe of fixed plants 
which grow around the unending shores of the oceans. The algae are 
mainly confined to a depth of water not exceeding 25 fathoms. Inverte- 
brates of all classes, and some fish, feed on the seaweeds, and the dugong 
on the sea-wrack. These are preyed on by other forms— crabs, crayfish, 
cephalopods, and other fish— and the dugong by man himself; so the cycle 
extends to the sharks and dolphins (we have no true porpoises) and 
kil lers. 
A striking instance is given by Sir Douglas Mawson in his paper on 
“South Australian Algal Limestones in Process of Formation (Q.J.G.S.). 
Lake Robe, in the South-East of the State mentioned, is 1£ square miles 
in area, and is constantly inhabited by several thousand black swans. It 
has puzzled the local inhabitants of Robe to determine what so attracts 
and maintains the swans on this sheet of water. It has been found that 
growing in the water are species of algae which are fed on by abundant 
crustaceans, both algae and crustaceans forming the attraction and food 
supply of the swans. 
We have seen that certain of the algae secrete or excrete carbonate of 
lime which forms a skeletal structure. Coral reefs abound m such 
calcareous algae, the green Halimeda and the red Galax, aura, Liagora, 
AmpUroa, Corallina, &c. When they die the skeletons survive and, being 
brittle, break up into fragments which fill up nooks and corners between 
the coral blocks. They thus serve as a sort of mortar in the reef building. 
They arc of more importance than is usually realised. W. Stanley Gardiner 
in writing of the coral reefs of Funafuti, Rotumah and Fiji, says, “The 
chief organisms, so far as I have seen, engaged in building up coral reefs 
