Elements of ecology (1954) Elements of ecology elementsofecolog00clar Year: 1954 Influence of the Aquatic Substrata 67 will characteristically support a rich growth of brown, green, and red algae attached by 'holdfasts' and a wide variety of snails, mussels, sea anemones, starfish, and many other invertebrates secured by suck- ing or cementing devices. Some of these animals indirectly derive nourishment as well as attachment from the rock substratum. The snails, for example, scrape off and eat the slime that forms on all underwater surfaces as well as the bacteria and algae contained in the s
Elements of ecology (1954) Elements of ecology elementsofecolog00clar Year: 1954 Influence of the Aquatic Substrata 67 will characteristically support a rich growth of brown, green, and red algae attached by 'holdfasts' and a wide variety of snails, mussels, sea anemones, starfish, and many other invertebrates secured by suck- ing or cementing devices. Some of these animals indirectly derive nourishment as well as attachment from the rock substratum. The snails, for example, scrape off and eat the slime that forms on all underwater surfaces as well as the bacteria and algae contained in the slime. In shifting sand or gravel few species except rapidly burrow- ing animals can maintain themselves; but on and in firm sand, espe- cially when mixed with mud, a distinctive and rich population of mollusks, worms, and crustaceans will be found, provided that other environmental factors are favorable. On a mud bottom where the water is quieter, rooted plants like the eel grass often grow in abun- dance, and sea cucumbers, brittle stars, sea urchins, and a different selection of worms are among the common inhabitants. However, if oxygen has been depleted and hydrogen sulphide is formed in the mud habitat, the benthic population will be greatly reduced. Further Photo made with Ezving undersea camera by D. M. Owen, Woods Hole Oceanographic Institution Fig. Ripples on the sea floor at a depth of about 100 m on Georges Bank ofl^ Massachusetts. The numerous brittle stars and sand dollars visible in the 10 ni' area shown are able to maintain themselves on the shifting surface.
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