Feeding biology of the sea-starLuidia sarsiDüben & Koren

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Abstract
A population of the sea-star Luidia sarsi Düben & Koren, which probably metamorphosed in the spring of 1963 and which was first found in the fall of 1963, was followed in the Øresund during a two-year period. The irregular appearance of Luidia sarsi in the Øresund is discussed and it is concluded that it is due to -1. That larval invasions do not occur every year, -2. That larvae of an already existing population in the Øresund will be killed in the brackish water of the Baltic Sea. -3. That low salinity may reduce or eradicate the populations especially in winters, and -4. That the life length probably does not exceed 4–5 years. The stomach contents of 42 specimens were examined; it was found that L. sarsi feeds exclusively on the brittlest ars Ophiura albida and Amphiura filiform is and the sea-urchin Echinocardium cordatum, the first mentioned being by far the most important. These results were verified experimentally. Starved Luidia will also eat certain other species of brittlestars but at a reduced rate and it will not feed on any other uninjured bottom invertebrates (asterids, lamellibranchs, polychaetes). It will, however, accept pieces of meat of these animals. The feeding behaviour is described. Luidia sarsi was found to be among the fastest moving asterids described. It was demonstrated that L. sarsi, at least in the laboratory exhibits diurnal rhythmic activity which is controlled by light and that it seeks its food actively. The growth was studied over a two year period after settling. During this period they attained an arm length of up to 100 mm and a weight of up to 40 grams. Growth in relation to amount of food eaten was found experimentally (a growth efficiency of about 33 %) and a crude estimate of the food consumption in nature could be made.

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