Factors Limiting Distribution and Size in the Starfish

Abstract

In shallow water of Malpeque bay, P.E.I., the distribution of the starfish Asterias vulgaris, Verrill, is limited by temperatures over 25 °C. in the summer and salinities less than 14 per mille in the winter. Small starfish have a higher temperature tolerance than large starfish. The population on denuded areas is replaced by the immigration of adults and the settlement of larvae. The maximum distance travelled by a marked starfish was 200 metres and the average about 20 metres, in four months. Starfish move directly towards food a distance of 12 metres at 6 metres per day. The maximum population density found was 60,000 per acre (15 per sq. metre) and the greater the population density, the smaller the modal size. Rate of growth varies with the kind and abundance of food and inversely with the size of the starfish. Spawning takes place in late May and early June and the larval life is about three weeks.