ABSTRACT
Two populations of Sphaerechinus granulans (Lamarck) from two different habitats in the Bay of Brest (Brittany, France) showed variations in life-history and morphological characteristics. The first population settled at about 5 m depth in a site of low tidal current. It inhabited a coralline algae bank with a large cover of seaweed. The second population occurred at a depth of 0 to 20 m in a site exposed to high tidal currents and characterized by coarse sand and sparse seaweed. The first population showed a rapid growth rate with an asymptotic diameter of 107 mm, a maximal observed longevity of 16 years and a periodic recruitment. The morphological characteristics revealed an isometric relationship of weight-diameter, a low dome body form and a low relative weight of the Aristote lantern. The feeding rate of this population was higher than the feeding rate of the second population. The last population showed a slower growth rate with an asymptotic diameter of 100 mm, a maximal observed longevity of 9 years and a sporadic recruitment. The relationship of weight-diameter revealed an allometric growth (slope < 3), the body form showed a high dome shape and the relative weight of the Aristotle lantern was heavier. Hydrodynamism and the quantity of available food seem to be the main environmental factors controlling these variabilities.
