Experimental in situ feeding of the sea urchin Paracentrotus lividus with invasive algae Caulerpa racemosa var. cylindracea and Caulerpa taxifolia in the Adriatic sea

An in situ experiment was conducted to determine whether one of the main herbivore species in the Adriatic Sea, the sea urchin Paracentrotus lividus, could feed exclusively on invasive green algae Caulerpa racemosa var. cylindracea or Caulerpa taxifolia. The food and the sea urchins were placed in experiment cages on the sea bottom, alongside with the controls for the duration of eight days. Sea urchins were offered C. racemosa var. cylindracea, C. taxifolia or seagrass Posidonia oceanica (common food) as the only available food in experiment cages. A difference between wet mass of offered food at the end and the beginning of the experiment was calculated. The results showed that P. lividus could feed on C. racemosa var. cylindracea in the summer period, even in greater quantities than with seagrass P. oceanica. Also, sea urchin "barrens" were observed inside dense C. racemosa var. cylindracea colonies. Paracentrotus lividus consumed minimal quantity of C. taxifolia during this short term feeding experiment.