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Wave-swept rocky shores are among the most dynamic and beautiful areas on earth. They are also among the most physically stressful. As ocean waves crash on the shore, water can move at speeds greater than 30 m/s, and can change speeds at greater than 500 m/s². These extreme water motions impose large hydrodynamic forces on the plants and animals of the shore.

Physical stress is not limited to water motion, however. When the tide recedes, organisms that were previously bathed in cool seawater are exposed to the comparatively harsh terrestrial environment. In central California, it is common for the body temperature of intertidal animals to climb as high as 40°C during a midday low tide, only to rapidly chill to 10°C or less as the tide comes in. While exposed to air, the plants and animals of the shore can rapidly dry out. Some algae lose more than 70% of their bodies’ water in the course of a single low tide.

Algae hanging off rock

Despite the physical adversity of the wave-swept shore, this environment is highhly productive, and is home to an exceptional diversity of life. With the possible exceptions of tropical rain forests and coral reefs, rocky shores exhibit the greatest species richness of any area on earth.

The Denny lab is exploring the reasons behind this unique blend of adversity and diversity. Using the tools of physics and engineering, we examine the size and shape of wave-swept organisms – and the materials from which they are constructed – in an attempt to explain how individuals cope with the physical stress of the wave-swept shore. Physiological approaches help us to understand how organisms’ metabolism, growth, and reproduction adjust to changes in temperature and hydrodynamics. Information about individuals can then be combined to provide insight into the ecological interactions of the rocky shore wave-swept community. This interface between biomechanics and community ecology is of particular interest because the intertidal zone of wave-swept rocky shores has been (and will continue to be) a model system for the development and testing of ecological theories. The utility of this system therefore provides a link between our ability to predict the physical survivorship of intertidal plants and animals and the mainstream of ecological research.

At the heart of all of our studies is the theme of evolution. By understanding the mechanical and physiological design of nearshore organisms, we hope eventually to reveal how they evolved to thrive amidst the severe stresses of the shore. The principles that have guided evolution in this harsh environment may provide valuable insight into the design of all plants and animals.

3 snails on top of rock