Food Preference and Chemotaxis in the Sea Urchin Arbacia Yunctulata

Abstiact: When offered single species of seaweeds in excess amounts, the sea urchin Arbuciapunctulata (Lamarck) Philippi consumed significantly more Gracilana folijr,a (Forsskal) Borgrsen and Codium z3thmocladium Vickers than Sargassum filipendula C. Agardh, Padina vickersiae Hoyt, or Dictyota dichotomu (Hudson) Lamouroux. When all five species were offered to urchins simultaneously, patterns of palatability remained the same but absolute consumption of favored species decreased significantly while consumption of less palatable species remained unchanged. During daytime hours, Arbacia is significantly more chemotactic toward Grucilaria (a rapidly eaten species) and Sargassum (a slowly eaten species) than toward Codium, Padina, or Dictyota.. At night, Arbacia i attraction for Gradaria increases significantly and its attraction toward Sargassum declines significantly. We propose that the day-night changes in chemotaxis may minimize fish predation on Arbacia by tending to keep them hidden beneath Sargassum canopies during the day and allowing them to increase their foraging for favored foods at night when visual predators are less active.