Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage . ecologicalanimal00hess Year: 1937 GEOGRAPHIC DIVISIONS OF THE PELAGIAL 271 17° (Fig. 75). Ortmann1 sets somewhat different boundaries on the basis of the distribution of the fairly constant high temperatures in which the warmth-limited, stenothermal tropical life can exist. His boundary lines therefore bend far toward the equator along the west coast of South America and of Africa on account of the cold Antarctic currents and the upwelling of water from the cold ocean depths. As
Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage . ecologicalanimal00hess Year: 1937 GEOGRAPHIC DIVISIONS OF THE PELAGIAL 271 17° (Fig. 75). Ortmann1 sets somewhat different boundaries on the basis of the distribution of the fairly constant high temperatures in which the warmth-limited, stenothermal tropical life can exist. His boundary lines therefore bend far toward the equator along the west coast of South America and of Africa on account of the cold Antarctic currents and the upwelling of water from the cold ocean depths. As shown in Fig. 75, the boundary lines of these two investigators differ essentially in that according to Meisenheimer the tropical animal com- Fig. 75.—Limits of the warm water region: heavily dotted line according to Ortmann, heavy broken line according to Meisenheimer; polar limits of the transition zone, lightly dotted line after Ortmann, light broken line after Meisenheimer. Distribution of reef corals vertically ruled, after Joubin. Up- welling cold bottom water, heavy coast line. munities of the Atlantic and Indian oceans are united around South Africa, whereas, according to Ortmann, they are entirely separated. Both the warm and the cold belts of the sea can be subdivided. Marine animals appear to recognize an equatorial belt of water with a temperature above 25° as distinct from cooler tropical waters lying on either side with temperatures from 20 to 25°. Similarly there are recognizably different animal communities in the cold-water areas around the poles with temperatures below 10° as distinguished from those of the less cold waters with temperatures between 10 and 15°. Indeed, in the best-studied region, the north Atlantic, other subdivisions can be made; for example, the animal communities of the cold waters
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