A Model of Marine Fish Herbivory in Cold Waters Dietary Choice, Growth, Food Processing and Metabolism of Temperate-Zone Seaweed-Eating Fishes

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The research proposed by Dr. Horn will comprise experiments designed to further our understanding of why there are so few species of herbivorous fishes in temperate and high latitudes of the ocean as compared to much larger numbers in tropical waters. The experiments will focus on the 1) role of seaweed toughness in dietary choice of temperate-zone herbivorous fish, 2) growth of these fish on diets of varying protein content and 3) the effect of temperature on food processing efficiencies and metabolic requirements of these cold-water herbivores. These experiments will test hypotheses that form the essential elements of a model of temperate-zone fish herbivory. This model predicts that 1) only relatively inactive fish can meet their energy demands at low environmental temperatures on an all-seaweed diet and therefore that 2) a seaweed diet is energetically feasible for more active fish only during the warmer periods of the year. The fishes to be studied are two abundant inshore California species--a sluggish year-round herbivore (Cebidichthys violaceus) from the rocky intertidal zone and an active, seasonal herbivore (Sebastes mystinus) from the adjacent kelp bed community.