Temporal patterns of larval settlement of Diadema antillarum (Echinodermata: Echinoidea) in the Canary Islands using an experimental larval collector

Settlement of Diadema antillarum Philippi was measured at two barren ground sites, Abades and Masca (Tenerife), between April 2002 and April 2003, in order to assess the suitability of settlement collectors and to obtain settlement patterns of this keystone herbivore in the subtidal rocky bottoms of the Canary islands. Three samplers containing small plastic balls (experimental collectors) with a very high exposed surface area (0.04 m(2) ball(-1)) were deployed monthly over 1 yr. Post-larvae and early juvenile sea urchins (newly settled urchins) were recovered from the samplers by washing individual collectors. Bimodal peaks in settlement were observed at both locations, with a primary peak in late summer/fall (Aug-Oct) and a secondary increase in late winter (Jan-Feb). Samplers collected a monthly maximum of 24-26 (+/- 2-16) newly settled urchins/sampler. The primary settlement pulse corresponded roughly to the annual pattern of reproductive periodicity (gonad index-GI) of D. antillarum at Boca Cangrejo (Tenerife). GI peaked during spring (Apr-May-Jun) with a secondary peak in December. The secondary increase in settlement may be due to higher larval survival during favorable planktonic conditions.