Canaria Island (Spain). Arquipélago. Life and Marine Sciences. Supplement 2

(Part B): 77-81. Ponta Delgada. ISSN 0873-4704. Dunng the last decades the populations of the sea urchin Diadema antillarum Philippi, 1845 have experienced a great increase in density and distribution along the Canarian coasts. Diverse aspects of its biology have been reported elsewhere; however, no data are available on the reproductive effort of this sea urchin species at Canary Islands. The objective of this study is to evaluate the monthly evolution of the gonadal index of D. antillarum during an annual cycle comparing two different methods in order to determine which is more suitable. Samples were collected monthly in Gran Canaria Island from January 1997 to March 1998 at two locations (Puerto Sardina and Puerto Rico). with different oceanographic conditions. The gonadal index was calculated monthly by two methods previously tested in sea urchins by other authors: (a) the ratio of gonadal volume to dry body weight and (b) the ratio of gonadal volume to body volume. Both gonadal indexes showed the same trend with a maximum in April-May and minimum in September-October